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Strength training is as effective as stretching for improving range of motion:
A systematic review and meta-analysis.
Preprint · January 2021
DOI: 10.31222/osf.io/2tdfm
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Strength training is as effective as stretching for improving range of motion: A systematic
2
review and meta-analysis.
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José Afonso, Ph.D. 1*, Rodrigo Ramirez-Campillo, Ph.D. 2,3, João Moscão4, Tiago Rocha,
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M.Sc. 5, Rodrigo Zacca, Ph.D. 1,6,7, Alexandre Martins, B.Sc. 1, André A. Milheiro, M.Sc.1,
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João Ferreira, B.Sc. 8, Hugo Sarmento, Ph.D. 9, Filipe Manuel Clemente, Ph.D. 10,11
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Rua Dr. Plácido Costa, 91, 4200-450 Porto, Portugal.
Centre for Research, Education, Innovation and Intervention in Sport, Faculty of Sport of the University of Porto.
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Department of Physical Activity Sciences. Universidad de Los Lagos. Lord Cochrane 1046, Osorno, Chile.
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3
Centro de Investigación en Fisiología del Ejercicio. Facultad de Ciencias. Universidad Mayor. San Pio X, 2422,
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Providencia, Santiago, Chile.
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4
REP Exercise Institute. Rua Manuel Francisco 75-A 2º C 2645-558 Alcabideche, Portugal.
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5
Polytechnic of Leiria, Rua General Norton de Matos, Apartado 4133, 2411-901 Leiria, Portugal.
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Porto Biomechanics Laboratory (LABIOMEP), University of Porto, Rua Dr. Plácido Costa, 91, 4200-450 Porto,
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Portugal.
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of Brazil, Brasília, Brazil.
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Almeida, 431, 4249-015 Porto, Portugal.
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de Nun’Álvares, 4900-347, Viana do Castelo, Portugal.
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Coordination for the Improvement of Higher Educational Personnel Foundation (CAPES), Ministry of Education
Superior Institute of Engineering of Porto, Polytechnic Institute of Porto. Rua Dr. António Bernardino de
Faculty of Sport Sciences and Physical Education, University of Coimbra, 3040-256, Coimbra, Portugal.
Escola Superior Desporto e Lazer, Instituto Politécnico de Viana do Castelo, Rua Escola Industrial e Comercial
Instituto de Telecomunicações, Department of Covilhã, 1049-001, Lisboa, Portugal.
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*Corresponding author: José Afonso | jneves@fade.up.pt.
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Summary box
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What is already known?
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•
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Stretching is effective for improving in range of motion (ROM), but promising findings
have suggested that strength training also generates ROM gains.
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35
What are the new findings?
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•
Strength training seems to be as effective as stretching in generating ROM gains.
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•
In contradiction with existing guidelines, stretching is not strictly necessary for improving
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39
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ROM, as strength may provide an equally valid alternative.
•
These findings were consistent across studies, regardless of the characteristics of the
population and of the specificities of strength training and stretching programs.
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ABSTRACT
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Background: Range of motion (ROM) is an important feature of sports performance and
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health. Stretching is usually prescribed to improve promote ROM gains, but evidence has
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suggested that strength training (ST) also improves ROM. However, it is unclear if its efficacy
48
is comparable to stretching. Objective: To perform a systematic review and meta-analysis of
49
randomized controlled trials (RCTs) assessing the effects of ST and stretching on ROM.
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Protocol: INPLASY: 10.37766/inplasy2020.9.0098. Data sources: Cochrane Library,
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EBSCO, PubMed, Scielo, Scopus, and Web of Science were consulted in early October 2020,
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followed by search within reference lists and consultation of four experts. No constraints on
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language or year. Eligibility criteria (PICOS): (P) humans of any sex, age, health or training
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status; (I) ST interventions; (C) stretching interventions (O) ROM; (S) supervised RCTs. Data
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extraction and synthesis: Independently conducted by multiple authors. Quality of evidence
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assessed using GRADE; risk-of-bias assessed with RoB 2. Results: Eleven articles (n = 452
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participants) were included. Pooled data showed no differences between ST and stretching on
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ROM (ES = -0×22; 95% CI = -0×55 to 0×12; p = 0×206). Sub-group analyses based on RoB,
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active vs. passive ROM, and specific movement-per-joint analyses for hip flexion and knee
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extension showed no between-protocol differences in ROM gains. Conclusion: ST and
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stretching were not different in improving ROM, regardless of the diversity of protocols and
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populations. Barring specific contra-indications, people who do not respond well or do not
63
adhere to stretching protocols can change to ST programs, and vice-versa.
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KEYWORDS: systematic review; meta-analysis; strength training; flexibility; stretching;
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range of motion.
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68
4
69
70
Introduction
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Improving range of motion (ROM) is a core goal for the general population,[1] as well
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as in clinical contexts,[2] such as when treating acute respiratory failure,[3] plexiform
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neurofibromas,[4] and total hip replacement.[5] Unsurprisingly, ROM gains are also relevant
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in different sports,[6] such as basketball, baseball and rowing,[7-9] among others. ROM is
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improved through increased stretch tolerance, augmented fascicle length and changes in
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pennation angle,[10] as well as reduced tonic reflex activity.[11] Stretching is usually
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prescribed to increase ROM in sports,[12, 13] clinical settings such as chronic low back
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pain,[14] rheumatoid arthritis,[15] and exercise performance in general.[16] Stretching
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techniques include static (active or passive), dynamic, or proprioceptive neuromuscular
80
facilitation (PNF), all of which can improve ROM.[1, 17-20]
81
However, reduced ROM and muscle weakness are deeply associated.[21-23] Therefore,
82
although strength training (ST) primarily addresses muscle weakness through methods such as
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resistance training or similar protocols, it has been shown to increase ROM in athletic
84
populations,[24, 25] as well as in healthy elderly people[26] and women with chronic
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nonspecific neck pain.[27] ST focused on concentric and eccentric contractions has been
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shown to increase fascicle length. [28-30] Better agonist-antagonist co-activation[31],
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reciprocal inhibition,[32] and adjusted stretch-shortening cycles[33] may also explain why ST
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is a suitable method for improving ROM.
89
Nevertheless, studies comparing the effects of ST and stretching in ROM have
90
presented conflicting evidence,[34, 35] and many have small sample sizes.[36, 37] Developing
91
a systematic review and meta-analysis (SRMA) may help summarize this conflicting evidence
92
and increase statistical power, thus providing clearer guidance for interventions.[38] Therefore,
5
93
the aim of this SRMA was to compare the effects of supervised and randomized ST versus
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stretching protocols on ROM in participants of any health and training status.
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96
97
METHODS
98
Protocol and registration
99
100
The methods and protocol registration were preregistered prior to conducting the
review: INPLASY, no.202090098, DOI: 10.37766/inplasy2020.9.0098.
101
102
Eligibility criteria
103
Articles were eligible for inclusion if published in peer-reviewed journals, with no
104
restrictions in language or publication date. The Preferred Reporting Items for Systematic
105
Reviews and Meta-Analyses (PRISMA) guidelines were adopted.[39] Participants,
106
interventions, comparators, outcomes, and study design (P.I.C.O.S.) were established as
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follows: (i) participants with no restriction regarding health, sex, age, or training status; (ii) ST
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interventions supervised by a certified professional, using resistance training or similar
109
protocols; (iii) comparators were supervised groups performing any form of stretching (iv)
110
outcomes were ROM assessed in any joint; (v) randomized controlled trials (RCTs). RCTs
111
reduce bias and better balance participant features between the groups,[38] and are important
112
for the advancement of sports science.[40] There were no limitations regarding intervention
113
length.
114
Reviews, letters to editors, trial registrations, proposals for protocols, editorials, book
115
chapters, and conference abstracts were excluded. Exclusion criteria based on P.I.C.O.S.: (i)
116
research with non-human animals; (ii) non-ST protocols or ST interventions combined with
117
other methods (e.g., endurance); unsupervised interventions; (iii) stretching or ST + stretching
6
118
interventions combined with other training methods (e.g., endurance); protocols without
119
stretching; unsupervised interventions; (iv) studies not reporting ROM; (v) non-randomized
120
interventions.
121
122
Information sources and search
123
Six databases were used to search and retrieve the articles in early October 2020:
124
Cochrane Library, EBSCO, PubMed (including MEDLINE), Scielo, Scopus, and Web of
125
Science (Core Collection). Boolean operators were applied to search the article title, abstract
126
and/or keywords: (“strength training” OR “resistance training” OR “weight training” OR
127
“plyometric*” OR “calisthenics”) AND (“flexibility” OR “stretching”) AND “range of
128
motion” AND “random*”. Specificities of each search engine: (i) in Cochrane Library, items
129
were limited to trials, including articles but excluding protocols, reviews, editorials and similar
130
publications; (ii) in EBSCO, the search was limited to articles in scientific, peer-reviewed
131
journals (iii) in PubMed, the search was limited to title or abstract; publications were limited
132
to RCTs and clinical trials, excluding books and documents, meta-analyses, reviews and
133
systematic reviews; (iv) in Scielo, Scopus and Web of Science, the publication type was limited
134
to article; and (v) in Web of Science, “topic” is the term used to refer to title, abstract and
135
keywords.
136
An additional search within the reference lists of the included records was conducted.
137
The list of articles and inclusion criteria were then sent to four experts to suggest additional
138
references. The search strategy and consulted databases were not provided in this process to
139
avoid biasing the experts’ searches. More detailed information is available as supplementary
140
material.
141
142
Search strategy
7
143
Here, we provide the specific example of search conducted in PubMed:
144
((("strength training"[Title/Abstract] OR "resistance training"[Title/Abstract] OR
145
"weight
146
"calisthenics"[Title/Abstract])
147
“stretching”[Title/Abstract])) AND (“range of motion”[Title/Abstract])) AND
148
(“random*”[Title/Abstract]).
149
After this search, the filters RCT and Clinical Trial were applied.
training"[Title/Abstract]
OR
"plyometric*"[Title/Abstract]
AND
(“flexibility”[Title/Abstract]
OR
OR
150
151
Study selection
152
J.A. and F.M.C. each conducted the initial search and selection stages independently,
153
and then compared result to ensure accuracy. J.F. and T.R. independently reviewed the process
154
to detect potential errors. When necessary, re-analysis was conducted until a consensus was
155
achieved.
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Data collection process
158
J.A., F.M.C., A.A.M. and J.F. extracted data, while J.M., T.R., R.Z. and A.M.
159
independently revised the process. Data for the meta-analysis was extracted by JA and
160
independently verified by A.A.M. and R.R.C. Data is available for sharing.
161
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Data items
163
Data items: (i) Population: subjects, health status, sex/gender, age, training status,
164
selection of subjects; (ii) Intervention and comparators: study length in weeks, weekly
165
frequency of the sessions, weekly training volume in minutes, session duration in minutes,
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number of exercises per session, number of sets and repetitions per exercise, load (e.g., %
167
1RM), full vs. partial ROM, supervision ratio; in the comparators, modality of stretching
168
applied was also considered; adherence rates were considered a posteriori; (iii) ROM testing:
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joints and actions, body positions (e.g., standing, supine), mode of testing (i.e., active, passive,
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both), pre-testing warm-up, timing (e.g., pre- and post-intervention, intermediate assessments),
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results considered for a given test (e.g., average of three measures), data reliability, number of
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testers and instructions provided during testing; (iv) Outcomes: changes in ROM for
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intervention and comparator groups; (vi) funding and conflicts of interest.
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Risk of bias in individual studies
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Risk of bias (RoB) in individual studies was assessed using the Cochrane risk-of-bias
177
tool for randomized trials (RoB 2).[41] J.A. and A.M. independently completed RoB analysis,
178
which was reviewed by F.M.C. Where inconsistencies emerged, the original articles were re-
179
analyzed until a consensus was achieved.
180
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Summary measures
182
Meta-analysis was conducted when ≥3 studies were available.[42] Pre- and post-
183
intervention means and standard deviations (SDs) for dependent variables were used after
184
being converted to Hedges’s g effect size (ES).[42] When means and SDs were not available,
185
they were calculated from 95% confidence intervals (CIs) or standard error of mean (SEM),
186
using Cochrane’s RevMan Calculator for Microsoft Excel.[43] When ROM data from different
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groups (e.g. men and women) or different joints (e.g. knee and ankle) was pooled, weighted
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formulas were applied.[38]
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Synthesis of results
191
The inverse variance random-effects model for meta-analyses was used to allocate a
192
proportionate weight to trials based on the size of their individual standard errors,[44] and
193
accounting for heterogeneity across studies.[45] The ESs were presented alongside 95% CIs
9
194
and interpreted using the following thresholds:[46] <0×2, trivial; 0×2–0×6, small; >0×6–1×2,
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moderate; >1×2–2×0, large; >2×0–4×0, very large; >4×0, extremely large. Heterogeneity was
196
assessed using the I2 statistic, with values of <25%, 25-75%, and >75% considered to represent
197
low, moderate, and high levels of heterogeneity, respectively.[47]
198
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Risk of bias across studies
200
Publication bias was explored using the extended Egger’s test,[48] with p<0×05
201
implying bias. To adjust for publication bias, a sensitivity analysis was conducted using the
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trim and fill method,[49] with L0 as the default estimator for the number of missing studies.[50]
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Moderator analyses
205
Using a random-effects model and independent computed single factor analysis,
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potential sources of heterogeneity likely to influence the effects of training interventions were
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selected, including i) ROM type (i.e., passive vs active), ii) studies RoB in randomization and
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iii) studies RoB in measurement of the outcome.[51] These analyses were decided post-
209
protocol registration.
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All analyses were carried out using the Comprehensive Meta-Analysis program
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(version 2; Biostat, Englewood, NJ, USA). Statistical significance was set at p≤0×05. Data for
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the meta-analysis was extracted by JA and independently verified by A.A.M. and R.R.C.
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Quality and confidence in findings
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Although not planned in the registered protocol, we decided to abide by the Grading of
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Recommendations Assessment, Development, and Evaluation (GRADE),[52] which addresses
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five dimensions that can downgrade studies when assessing the quality of evidence in RCTs.
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RoB, inconsistency (through heterogeneity measures), and publication bias were addressed
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above and were considered a priori. Directness was guaranteed by design, as no surrogates
221
were used for any of the pre-defined P.I.C.O. dimensions. Imprecision was assessed on the
222
basis of 95% CIs.
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RESULTS
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Study selection
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Initial search returned 194 results (52 in Cochrane Library, 11 in EBSCO, 11 in
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PubMed, 9 in Scielo, 88 in Scopus, and 23 in Web of Science). After removal of duplicates,
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121 records remained. Screening the titles and abstracts for eligibility criteria resulted in the
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exclusion of 106 articles: 26 were not original research articles (e.g., trial registrations,
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reviews), 24 were out of scope, 48 did not have the required intervention or comparators, five
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did not assess ROM, two were non-randomized and one was unsupervised. Fifteen articles
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were eligible for full-text analysis. One article did not have the required intervention,[53] and
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two did not have the needed comparators.[54, 55] In one article, the ST and stretching groups
235
performed a 20-30 minutes warm-up following an unspecified protocol.[56] In another, the
236
intervention and comparator were unsupervised[57], and in one the stretching group was
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unsupervised[58]. Finally, in one article, 75% of the training sessions were unsupervised.[59]
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Therefore, eight articles were included at this stage.[24, 34-37, 60-62]
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A manual search within the reference lists of the included articles revealed five
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additional potentially fitting articles. Two lacked the intervention group required[63, 64] and
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two were non-randomized.[65, 66] One article met the inclusion criteria.[67] Four experts
242
revised the inclusion criteria and the list of articles and suggested eight articles based on their
243
titles and abstracts. Six were excluded: interventions were multicomponent;[68, 69]
11
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comparators performed no exercise;[70, 71] out of scope;[72] and unsupervised stretching
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group.[73] Two articles were included,[74, 75] increasing the list to eleven articles,[24, 34-37,
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60-62, 67, 74, 75] with 452 participants eligible for meta-analysis (Figure 1).
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248
12
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Records identified through
database search
(n = 194)
Records after duplicates removed
(n = 121)
Records excluded
(n = 106)
Records screened
(n = 121)
Full-text articles assessed for
eligibility
(n = 15)
Full-text articles excluded, with reasons
(n = 7)
• 3 articles did not have the required intervention
and/or comparators.
• 3 had at least one group of interest performing the
intervention unsupervised.
• 1 had an undisclosed warm-up protocol that was
longer than the intervention.
Additional records fitting inclusion criteria
identified after search within the reference
lists of the included articles
(n = 1)
Studies included in qualitative synthesis
(n = 8+1+2 = 11)
Additional records fitting inclusion criteria
recommended by four external experts from
two countries and three different institutions
(n = 2)
Studies included in quantitative synthesis
(n = 11)
250
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Figure 1. Flowchart describing the study selection process.
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253
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Study characteristics and results
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The data items can be found in Table 1. The study of Wyon, Smith [62] required
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consultation of a previous paper[76] to provide essential information. Samples ranged from
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27[37] to 124 subjects,[34] including: trained participants,[24, 36, 61, 62] healthy sedentary
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participants,[35, 60, 67] sedentary and trained participants,[75] workers with chronic neck
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pain,[37] participants with fibromyalgia,[74] and elderly participants with difficulties in at least
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one of four tasks: transferring, bathing, toileting, and walking.[34] Seven articles included only
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women[36, 62, 67, 74] or predominantly women,[34, 35, 37] three investigated only men[24,
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75] or predominantly men,[60] and one article had a balanced mixture of men and women.[61]
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Interventions lasted between five[60] and 16 weeks[67]. Minimum weekly training frequency
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was two sessions[37, 74] and maximum was five.[62] Six articles provided insufficient
266
information concerning session duration.[35, 36, 61, 62, 67, 75] Ten articles vaguely defined
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training load for the ST and stretching groups,[24, 34, 37, 60, 61, 74, 75] or for stretching
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groups.[35, 36, 67] Six articles did not report on using partial or full ROM during ST
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exercises.[24, 34, 36, 37, 61, 67] Different stretching modalities were implemented: static
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active,[35, 37, 60, 67, 74, 75] dynamic,[34, 36] dynamic with a 10-second hold,[24] static
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active in one group and static passive in another,[62] and a combination of dynamic, static
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active, and PNF.[61]
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Hip joint ROM was assessed in seven articles,[24, 34, 36, 60-62, 67] knee ROM in
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five,[34-36, 60, 75] shoulder ROM in four,[34, 36, 60, 74] elbow and trunk ROM in two,[34,
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36] and cervical spine[37] and the ankle joint ROM in one article.[34] In one article, active
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ROM (AROM) was tested for the trunk, while passive ROM (PROM) was tested for the other
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joints.[34] In one article, PROM was tested for goniometric assessments and AROM for hip
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flexion.[36] In another, AROM was assessed for the shoulder and PROM for the hip and
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knee.[60] Three articles only assessed PROM[35, 61, 75] and four AROM,[24, 37, 67, 74]
280
while one assessed both for the same joint.[62]
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282
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Table 1. Characteristics of included randomized trials.
Article
Population and common
Strength training group
program features
Task-Specific
Subjects: 161.
n = 81 (60 completed).
Resistance
Health status: Elderly people Weekly volume (minutes):
Training to
dependent on help for
180.
Improve the
performing at least one of four
Session duration in
Ability of
tasks: transferring,
minutes: 60.
Activities of
bathing, toileting and walking. No. exercises per session:
Daily Living–
Gender: ST: 84% women;
16.
Impaired Older
STRE: 88% women.
No. sets and repetitions:
Adults to Rise
Age: ST: 82·0±6·4; STRE:
1*7-8 based on maximum
from a Bed and
82·4±6·3.
target of 9 (bed-rise
from a Chair.[34]
Training status: Not
tasks). 1*5 based on
participating in regular
maximum target of 6
strenuous exercise.
(chair-rise tasks).
Selection of subjects: Seven
Load: Unclear. Loads
congregate housing facilities.
were incremented if
Length (weeks): 12.
subjects were not feeling
Weekly sessions: 3.
challenged enough.
Adherence: average 81% of
Full or partial ROM:
the sessions.
N/A.
Funding: National Institute on
Supervision ratio: 1:1.
Aging (NIA) Claude Pepper
Older Adults Independence
Center (Grant AG0 8808 and
NIA Grant AG10542), the
Department of Veterans
Affairs Rehabilitation
Research and Development,
and the AARP-Andrus
Foundation.
Conflicts of interest: N/A.
Stretching versus
Subjects: 45 undergraduate
n = 15.
strength training
students.
Weekly volume (minutes):
in lengthened
Health status: 30º knee
N/A.
position in
extension deficit with the hip
Session duration in
subjects with
at 90º when in supine
minutes: N/A.
tight hamstring
position. No injuries in the
Comparator group(s)*
ROM testing
STRE n = 80 (64 completed).
Weekly volume (minutes): 180.
Session duration in minutes: 60.
No. exercises per session: N/A.
No. sets and repetitions: N/A.
Stretching modality: Dynamic.
Load: Low-intensity, but without a
specified criterion.
Full or partial ROM: N/A.
Supervision ratio: One supervisor
per group, but group size was N/A.
Joints and actions: Elbow
(extension), shoulder
(abduction), hip (flexion and
abduction), knee (flexion and
extension), ankle
(dorsiflexion) and trunk
(flexion, extension, lateral
flexion).
Positions: Supine (elbow,
shoulder, hip, knee and
ankle); standing (lumbar
spine).
Mode: Active for trunk,
passive for the other joints.
Warm-up: N/A.
Timing: Baseline, 6 weeks,
12 weeks.
Results considered in the
tests: N/A.
Data reliability: ICCs of 0·65
to 0·86 for trunk measures.
Unreported for other
measures.
No. testers: N/A.
Instructions during testing:
N/A.
STRE n = 15.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: 1.
No. sets and repetitions: 4*30’’.
Stretching modality: Static.
Joints and actions: Knee
(extension).
Positions: Sitting.
Mode: Passive.
Warm-up: Yes, but unclear
with regard to specifications.
16
Qualitative
results for ROM
The ST group had
significant
improvements in
all ROM
measures, except
hip flexion and
abduction.
The STRE group
had no significant
change in any of
the ROM values.
None of the
groups
experienced
significant
improvements in
ROM.
muscles: A
randomized
controlled
trial.[35]
Group-based
exercise at
workplace: shortterm effects of
neck and
shoulder
resistance
training in video
display unit
workers with
work-related
chronic neck
pain – a pilot
randomized
trial.[37]
lower limbs and no lower
back pain.
Gender: 39 women, 6 men.
Age: 21·33±1·76 years (ST);
22·60±1·84 years (STRE).
Training status: No
participation in ST or STRE
programs in the previous year.
Selection of subjects:
announcements posted at the
University.
Length (weeks): 8.
Weekly sessions: 3.
Adherence: N/A.
Funding: N/A.
Conflicts of interest: N/A.
Subjects: 35 video display
unit workers, 27 completed
the program.
Health status: chronic neck
pain.
Gender: 27 women, 8 men.
Age: 43 (41-45) in ST; 42
(38·5-44) in STRE.
Training status: N/A.
Selection of subjects: intranet
form.
Length (weeks): 7.
Weekly sessions: 2.
Adherence: average 85% of
the sessions in ST and 86% in
STRE.
Funding: Under
“disclosures”, the authors
stated “none”.
Conflicts of interest: Under
“disclosures”, the authors
stated “none”.
No. exercises per session:
1.
No. sets and repetitions:
3*12.
Load: 60% of 1RM.
Full or partial ROM:
Partial.
Supervision ratio: N/A.
Load: Unclear.
Full or partial ROM: Full.
Supervision ratio: N/A.
Timing: Baseline, 1-week
post-protocol.
Results considered in the
tests: mean of three
measures.
Data reliability: High.
No. testers: 1 (blinded).
Instructions during testing:
N/A.
n = 14.
Weekly volume (minutes):
90.
Session duration in
minutes: 45.
No. exercises per session:
10.
No. sets and repetitions:
2-3*8-20. Isometric
contractions up to 30’’.
Load: free-weights with a
maximum of 75% MVC
and elastic bands of
unspecified load.
Full or partial ROM:
N/A.
Supervision ratio: ~1:8.
STRE n = 13.
Weekly volume (minutes): 90.
Session duration in minutes: 45.
No. exercises per session: 11.
No. sets and repetitions: 10*10’’.
Stretching modality: Static.
Load: N/A.
Full or partial ROM: N/A.
Supervision ratio: ~1:8.
Joints and actions: Cervical
spine (flexion, extension,
lateral flexion, rotation).
Positions: Sitting (flexion,
extension, lateral flexion) and
supine position (rotation).
Mode: Active.
Warm-up: N/A.
Timing: Baseline, 1-week
post-protocol.
Results considered in the
tests: N/A.
Data reliability: N/A.
No. testers: 1 (blinded).
Instructions during testing:
N/A.
17
Significant
improvements in
both groups for
all ROM
measurements.
No differences
between the two
groups.
A randomized
controlled trial of
muscle
strengthening
versus flexibility
training in
fibromyalgia.[74]
Influence of
Strength and
Flexibility
Training,
Combined or
Isolated, on
Strength and
Subjects: 68; 56 completed
the program.
Health status: Diagnosed with
fibromyalgia (FM).
Gender: Women.
Age: 49·2±6·36 years in ST,
46·4±8·56 in STRE.
Training status: 87% were
sedentary. Not engaged in
regular strength training
programs.
Selection of subjects: FM
patients referred to
rheumatology practice at a
teaching university.
Length (weeks): 12.
Weekly sessions: 2.
Adherence: 85% of the initial
participants attended ≥13 of
24 classes. N/A for the 46
women that completed the
interventions.
Funding: Individual National
Research Service Award
(#1F31NR07337-01A1) from
the National Institutes of
Health, a doctoral dissertation
grant (#2324938) from the
Arthritis Foundation, and
funds from the Oregon
Fibromyalgia Foundation.
Conflicts of interest: N/A.
Subjects:28 women.
Health status: Presumably
healthy.
Gender: Women.
Age: 46±6·5.
Training status: Trained in
strength and stretching.
n = 28.
Weekly volume (minutes):
120.
Session duration in
minutes: 60.
No. exercises per session:
Presumably 12.
No. sets and repetitions:
1*4-5, progressing to
1*12.
Load: Low intensity.
Slower concentric
contractions with a 4’’
isometric hold in the end,
and a faster eccentric
contraction.
Full or partial ROM:
Full.
Supervision ratio:
Presumably 1:28.
STRE n = 28.
Weekly volume (minutes): 120.
Session duration in minutes: 60.
No. exercises per session:
Presumably 12.
No. sets and repetitions: N/A.
Stretching modality: Static.
Load: Low intensity.
Full or partial ROM: N/A.
Supervision ratio: Presumably
1:28.
Joints and actions: Shoulder
(the authors report on internal
and external rotation, but the
movements used actually
required a combination of
motions).
Positions: Presumably
standing.
Mode: Active.
Warm-up: N/A.
Timing: Baseline, 12 weeks.
Results considered in the
tests: N/A.
Data reliability: referral to a
previous study, but no values
for these data.
No. testers: 1.
Instructions during testing:
Reach as far as possible.
Both groups had
significant
improvements in
ROM.
No differences
between groups.
n = 7.
Weekly volume (minutes):
N/A.
Session duration in
minutes: N/A.
No. exercises per session:
8.
STRE n = 7.
Weekly volume (minutes): 240.
Session duration in minutes: 60.
No. exercises per session: N/A.
No. sets and repetitions: 3*30.
Stretching modality: Dynamic.
Load: Stretch to mild discomfort.
Joints and actions: Shoulder
(flexion, extension, abduction
and horizontal adduction)
elbow (flexion), hip (flexion
and extension), knee
(flexion), and trunk (flexion
and extension).
None of the
groups
experienced
significant
improvements in
ROM.
18
Flexibility
Gains.[36]
Effects of
Flexibility and
Strength
Interventions on
Optimal Lengths
of Hamstring
Muscle-Tendon
Units.[61]
Selection of subjects:
Volunteers that would refrain
from exercise outside the
intervention.
Length (weeks):12.
Weekly sessions: 4. Not
explicit; 48 sessions over 12
weeks.
Adherence: Minimum was 44
of the 48 sessions.
Funding: N/A.
Conflicts of interest: N/A.
No. sets and repetitions:
3*8-12 during the 1st
month; 3*6-10RM in the
2nd month; 3*10-15RM in
the 3rd month.
Load: 6-15RM,
depending on the month.
Full or partial ROM:
N/A.
Supervision ratio: N/A.
Subjects: 40 college students.
Health status: No history of
lower extremity injury in the 2
years prior to the study.
Gender: 20 men, 20
women.
Age: 18–24 years.
Training status: participating
in exercise 2–3 times per
week.
Selection of subjects: college
students.
Length (weeks): 8.
Weekly sessions: 3.
Adherence: N/A.
n = 20.
Weekly volume (minutes):
N/A.
Session duration in
minutes: N/A
No. exercises per session:
4.
No. sets and repetitions:
2-4*8-15. For one
exercise, 2*50-60’’.
Load: N/A.
Full or partial ROM:
N/A.
Supervision ratio: N/A.
Full or partial ROM: Full.
Supervision ratio: N/A.
STRE + ST n = 7.
Completion of both protocols.
Unknown duration.
ST + STRE n = 7.
Completion of both protocols in
reverse order. Unknown duration.
STRE n = 20.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: 4.
No. sets and repetitions: 2*15 for
dynamic stretching, 2*40-60’’ for
static stretching, 3*50’’ for PNF
and 3*40-50’’ for foam roll.
Stretching modality: active static,
dynamic and PNF.
Load: N/A.
Full or partial ROM: N/A.
Supervision ratio: N/A.
19
Positions: Supine (shoulder
flexion, abduction, horizontal
adduction, elbow and hip
flexion), prone (shoulder and
hip extension, and knee
flexion) and upright (trunk
flexion and extension) for
goniometric evaluations.
Sitting for sit-and-reach.
Mode: Passive for
goniometry. Active for sitand-reach.
Warm-up: 5- minute walking
on treadmill at mild to
moderate intensity and four
stretching exercises.
Timing: Baseline, 12 weeks.
Results considered in the
tests: Best of 3 trials.
Data reliability: Very high.
No. testers: 1.
Instructions during testing:
N/A.
Joints and actions: Hip
(flexion).
Positions: Supine.
Mode: Passive.
Warm-up: Six-minute warmup including jogging and
jumping.
Timing: Baseline, 8 weeks.
Results considered in the
tests: Mean of three trials.
Data reliability: Very high.
No. testers: N/A.
Instructions during testing:
N/A.
Men and women
in both groups
significantly
improved ROM.
No differences
between groups.
Resistance
training vs. static
stretching:
Effects on
flexibility and
strength.[60]
Eccentric
training and
static stretching
improve
hamstring
flexibility of high
school men.[75]
Funding: Partially supported
by the National Natural
Science Foundation of China
(Grant No.: 81572212) and
the Fundamental Research
Fund for the Central
Universities, Beijing Sport
University (Grant No.:
2017XS017).
Conflicts of interest: N/A.
Subjects: 37 college students.
Health status: Healthy.
Gender: 30 men, 12 women;
ratio is unclear in the final
sample.
Age: 21·91±3·64 years.
Training status: Untrained.
Selection of subjects:
Recruited from Physical
Education or Exercise Science
Classes.
Length (weeks): 5.
Weekly sessions: 3.
Adherence: N/A.
Funding: N/A.
Conflicts of interest: N/A.
Subjects: 69 high-schoolers.
Health status: Healthy, but
with a 30º loss of knee
extension.
Gender: Men.
Age: 16·45±0·96 years.
Training status: Some
sedentary, others involved in
exercise programs.
n = 12.
Weekly volume (minutes):
135-180.
Session duration in
minutes: 45-60.
No. exercises per session:
eight in days 1 and 2, four
in day 3.
No. sets and repetitions: 4
sets of unspecified
repetitions.
Load: N/A.
Full or partial ROM:
Full.
Supervision ratio: 1:12.
STRE n = 12.
Weekly volume (minutes): 75-90.
Session duration in minutes: 2535.
No. exercises per session: 13.
No. sets and repetitions: 1*30’’ for
most stretches. 3*30’’ for one
exercise and 3*20’’ for two.
Stretching modality: Static.
Load: N/A.
Full or partial ROM: Full.
Supervision ratio: 1:12.
n= 24.
Weekly volume (minutes):
N/A.
Session duration in
minutes: N/A.
No. exercises per session:
1.
No. sets and repetitions: 6
repetitions with 5’’
STRE n= 21.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: 1.
No. sets and repetitions: Unknown
number of repetitions, each lasting
30’’.
Stretching modality: Static.
20
Joints and actions: Hip
(flexion, extension), knee
(extension) and shoulder
(extension).
Positions: Supine (knee and
hip). Prone (shoulder).
Mode: Passive for hip and
knee, active for shoulder.
Warm-up: 5 minutes of
stationary bicycle with
minimal resistance.
Timing: Baseline, 1-week
post-protocol.
Results considered in the
tests: N/A.
Data reliability: N/A.
No. testers: 1.
Instructions during testing:
Technical instructions
specific to each test.
Joints and actions: Knee
(extension).
Positions: Supine.
Mode: Passive.
Warm-up: No warm-up.
Timing: Baseline, 6 weeks.
Results considered in the
tests: Two measures for
previous reliability
Both groups had
significant
improvements in
knee extension,
hip flexion and
hip extension, but
not shoulder
extension.
No differences
between the
interventions.
Both groups
improved ROM.
No differences
between the
interventions.
Effects of
flexibility
combined with
plyometric
exercises vs.
isolated
plyometric or
flexibility mode
in adolescent
men
hurdlers.[24]
Selection of subjects:
Volunteers with tight
hamstrings.
Length (weeks): 6.
Weekly sessions: 3 for STRE.
N/A for ST.
Adherence: N/A for ST.
STRE: subjects missing >4
sessions were excluded.
Funding: N/A.
Conflicts of interest: N/A.
Subjects: 34 trained hurdlers.
Health status: No lower
extremity injury in the
previous 30 days.
Gender: Men.
Age: 15±0·7 years.
Training status: ≥3 years of
experience in hurdle racing.
Selection of subjects:
Recruited from three athletic
teams.
Length (weeks): 12.
Weekly sessions: 4.
Adherence: N/A.
Funding: No funding.
Conflicts of interest: No
conflicts of interest.
isometric hold between
each.
Load: N/A.
Full or partial ROM:
Full.
Supervision ratio:
Description suggests a
1:1 ratio.
Load: Stretch until a gentle stretch
was felt on the posterior thigh.
Full or partial ROM: Full.
Supervision ratio: Description
suggests a 1:1 ratio.
calculations, but unclear for
the groups’ evaluation.
Data reliability: Very high.
No. testers: 2 (1 blinded).
Instructions during testing:
N/A.
n= 9.
Weekly volume (minutes):
320.
Session duration in
minutes: 80.
No. exercises per session:
4.
No. sets and repetitions:
3*30’’.
Load: Evolved from low
to hard intensity, but no
criteria were provided.
Full or partial ROM:
N/A. Supervision ratio:
N/A.
STRE n = 8.
Weekly volume (minutes): 320.
Session duration in minutes: 80.
No. exercises per session: 7.
No. sets and repetitions: 5*10’’.
Stretching modality: Dynamic with
10’’ static hold.
Load: Evolved from low to hard
intensity, but no criteria were
provided.
Full or partial ROM: N/A.
Supervision ratio: N/A.
Joints and actions: Hip
(flexion and extension).
Positions: Supine.
Mode: Active.
Warm-up: N/A.
Timing: Baseline, 12 weeks.
Results considered in the
tests: Best of 3 attempts.
Data reliability: Referral to a
previous study, but no values
for these data.
No. testers: 2.
Instructions during testing:
N/A.
STRE+ ST n = 9.
Weekly volume (minutes): 320.
Session duration in minutes: 80.
No. exercises per session: 11 (4
plyometric; 7 flexibility).
No. sets and repetitions: 3*30’’ for
plyometrics, 5*10’’ for stretching.
Stretching modality: Dynamic with
10’’ static hold.
Load: Evolved from low to hard
intensity, but no criteria were
provided.
Full or partial ROM: N/A.
Supervision ratio: N/A.
21
All interventions
had significant
improvements in
ROM.
No differences
between the
interventions.
The influence of
strength,
flexibility, and
simultaneous
training on
flexibility and
strength
gains.[67]
A comparison of
strength and
stretch
interventions on
active and
passive ranges of
movement in
dancers: a
randomized
control trial.[62]
Subjects: 80 women.
Health status: Healthy.
Gender: Women.
Age: 35±2·0 (ST), 34±1·2
(STRE), 35±1·8 (ST +
STRE), 34±2·1 (nonexercise).
Training status: Sedentary.
Selection of subjects:
Volunteers that were
sedentary ≥12 months.
Length (weeks): 16.
Weekly sessions: 3.
Adherence: Minimum was 46
of the 48 sessions.
Funding: N/A.
Conflicts of interest: N/A.
Subjects: 39 dance students,
35 completed.
Health status: N/A.
Gender: Women (39).
Age: 17±0·49 years (ST
group); 17±0·56 years (lowintensity STRE); 17±0·56
years (moderate to high
intensity STRE).
Training status: Moderately
trained dance students.
Selection of subjects:
Recruited from dance college.
Length (weeks): 6.
Weekly sessions: 5.
Adherence: N/A.
Funding: N/A.
Conflicts of interest: N/A.
n = 20.
Weekly volume (minutes):
N/A.
Session duration in
minutes: N/A.
No. exercises per session:
8.
No. sets and repetitions:
3*8-12 in the 1st and 4th
months; 3*6-10 in 2nd
month; 3*10-15 in 3rd
month.
Load: 8-12RM (1st and
4th months); 6-10RM (2nd
month); 10-15RM (3rd
month).
Full or partial ROM:
N/A.
Supervision ratio: N/A.
n = 11.
Weekly volume (minutes):
N/A.
Session duration in
minutes: N/A.
No. exercises per session:
1.
No. sets and repetitions:
3*5, increasing to 3*10
during the program. Each
repetition included a 3’’
isometric hold.
Load: Unclear, but using
body weight.
Full or partial ROM:
Partial (final 10º).
Supervision ratio: N/A.
STRE n = 20.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: N/A.
No. sets and repetitions: 4*1560’’. Duration of each set started at
15’’ and progressed to 60’’ during
the intervention.
Stretching modality: Static.
Load: Performed at the point of
mild discomfort.
Full or partial ROM: N/A.
Supervision ratio: N/A.
ST + STRE n = 20.
STRE protocol followed by the ST
protocol.
Low-intensity STRE n = 13.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: 5.
No. sets and repetitions: N/A, but
1’ for each stretch.
Stretching modality: Active static.
Load: 3/10 perceived exertion.
Full or partial ROM: N/A.
Supervision ratio: N/A.
Moderate-intensity or highintensity STRE n = 11.
Weekly volume (minutes): N/A.
Session duration in minutes: N/A.
No. exercises per session: 5.
No. sets and repetitions: N/A.
Stretching modality: Passive.
Load: 8/10 perceived exertion.
Full or partial ROM: N/A.
22
Joints and actions: Hip
(flexion) and knee
(extension) combined.
Positions: Sitting.
Mode: Active.
Warm-up: 4 stretching
exercises (2*10’’).
Timing: Baseline, 16 weeks.
Results considered in the
tests: Maximum of 3
attempts.
Data reliability: Very high.
No. testers: 1.
Instructions during testing:
N/A.
The interventions
significantly
improved ROM.
Joints and actions: Hip
(flexion).
Positions: Standing.
Mode: Active and passive.
Warm-up: 10 minutes of
cardiovascular exercise and
lower limb stretches.
Timing: Baseline, 6 weeks.
Results considered in the
tests: N/A.
Data reliability: N/A.
No. testers: N/A.
Instructions during testing:
Positioning cues for ensuring
proper posture.
The three groups
significantly
improved passive
ROM, without
differences
between the
groups.
No differences
between the
interventions.
The moderate-tohigh intensity
STRE group did
not improve in
active ROM. The
two other
interventions did.
284
285
286
Supervision ratio: N/A.
Legend: N/A – Information not available. ST – Strength training. STRE - Stretching. ROM – Range of motion. MVC – Maximum voluntary contraction. PNF –
Proprioceptive neuromuscular facilitation. * Non-exercise groups are not considered in this column.
287
23
288
289
290
In seven articles,[24, 37, 60, 61, 67, 74] ST and stretching groups significantly
291
improved ROM, and the differences between the groups were non-significant. In one article,
292
the ST group had significant improvements in 8 of 10 ROM measures, while dynamic
293
stretching did not lead to improvement in any of the groups.[34] In another article, the three
294
groups significantly improved PROM, without between-group differences; the ST and the
295
static active stretching groups also significantly improved AROM.[62] In two articles, none of
296
the groups improved ROM.[35, 36]
297
298
Risk of bias within studies
299
Table 2 presents assessments of RoB. Bias arising from the randomization process was
300
low in four articles,[34, 36, 62, 74] moderate in one,[37] and high in six.[24, 35, 60, 61, 67,
301
75] Bias due to deviations from intended interventions, missing outcome data, and selection of
302
the reported results was low. Bias in measurement of the outcome was low in six articles,[35-
303
37, 67, 74, 75] but high in five.[24, 34, 60-62]
304
305
24
306
307
Table 2. Assessments of risk of bias.
Cochrane’s
RoB 2
1.1.Was the
allocation
sequence
random?
1.2.Was the
allocation
sequence
concealed
until
participants
were enrolled
and assigned
to
interventions
?
1.3.Did
baseline
differences
between
groups
suggest a
problem with
the
randomizatio
n process?
1.4.RoB
judgement
Leite, De
Morton,
Souza
Li, Garrett
Nelson and
Whitehead
Teixeira
[61]
Bandy [75]
[60]
[36]
1.Bias arising from the randomization process
Alexander
, Galecki
[34]
Aquino,
Fonseca
[35]
Caputo,
Di Bari
[37]
Jones,
Burckhard
t [74]
Racil, Jlid
[24]
Simão,
Lemos [67]
Wyon,
Smith
[62]
Yes.
No
information
.
Yes.
Yes.
No
information
.
No
information
.
No
information
.
No
information.
No
information
.
No
information
.
Yes.
Yes.
Probably
no.
Yes.
Yes.
Yes.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Yes.
No.
No
information
.
Yes.
No.
No.
No.
Probably
no.
No.
No.
No.
No.
Low risk.
High risk.
Some
concerns
.
Low risk.
Low risk.
High risk.
High risk.
High risk.
High risk.
High risk.
Low
risk.
2.Bias due to deviations from intended interventions
25
(effect of assignment to intervention)
2.1.Were
participants
aware of their
assigned
intervention
during the
trial?
2.2.Were
carers and
people
delivering the
interventions
aware of
participants’
assigned
intervention
during the
trial?
2.3.If
Y/PY/NI to
2.1 or 2.2:
Were there
deviations
from the
intended
intervention
because of
the trial
context?
2.4.If Y/PY
to 2.3: Were
these
deviations
likely to have
affected the
outcome?
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probabl
y no.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
26
2.5.If
Y/PY/NI to
2.4: Were
these
deviations
from the
intended
intervention
balanced
between
groups?
2.6.Was an
appropriate
analysis used
to estimate
the effect of
assignment to
intervention?
2.7.If
N/PN/NI to
2.6: Was
there
potential for a
substantial
impact (on
the result) of
the failure to
analyze
participants
in the group
to which they
were
randomized)?
2.8.RoB
judgement
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
Probabl
y yes.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low
risk.
Yes.
Yes.
Yes.
Yes.
3.Bias due to missing outcome data
3.1.Were data
for this
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
27
Yes.
outcome
available for
all, or nearly
all,
participants
randomized?
3.2.If
N/PN/NI to
3.1.: Is there
evidence that
the result was
not biased by
missing
outcome
data?
3.3.If N/PN
to 3.2: Could
missingness
in the
outcome
depend on its
true value?
3.4.If
Y/PY/NI to
3.3: Is it
likely that
missingness
in the
outcome
depended on
its true value?
3.5.RoB
judgement
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
N/A.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low
risk.
No.
No.
No.
No.
4. Bias in measurement of the outcome
4.1.Was the
method of
measuring the
outcome
No.
No.
No.
No.
No.
No.
28
No.
inappropriate
?
4.2.Could
measurement
or
ascertainment
of the
outcome have
differed
between
intervention
groups?
4.3.If
N/PN/NI to
4.1. and 4.2:
Were
outcome
assessors
aware of the
intervention
received by
study
participants?
4.4.If
Y/PY/NI to
4.3: Could
assessment of
the outcome
have been
influenced by
knowledge of
intervention
received?
4.5.If
Y/PY/NI to
4.4: Is it
likely that
assessment of
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probabl
y no.
Probably
yes.
No.
No.
No.
No.
Probably
yes.
Probably
yes.
Probably
yes.
Probably
yes.
No.
Probabl
y yes.
Probably
yes.
Probably no
[blinded
goniometer]
.
Probably
yes.
N/A.
Probabl
y yes.
Probably
yes.
N/A.
Probably
yes.
N/A.
Probabl
y yes.
Probably
yes.
N/A.
N/A.
N/A.
N/A.
Probably
yes.
Probably
yes.
N/A.
N/A.
N/A.
N/A.
Probably
yes.
29
the outcome
was
influenced by
knowledge of
intervention
received?
4.6.RoB
judgement
High risk.
Low risk.
Low risk.
Low risk.
Low risk.
High risk.
High risk.
Low risk.
High risk.
Low risk.
High
risk.
5.Bias in selection of the reported results
5.1.Were the
data that
produced this
result
analyzed in
accordance
with a prespecified
analysis plan
that was
finalized
before
unblinded
outcome data
were
available for
analysis?
5.2.Is the
numerical
result being
assessed
likely to have
been selected,
on the basis
of the results,
from multiple
eligible
outcome
measurement
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Yes.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probabl
y no.
30
s (e.g., scales,
definitions,
time points)
within the
outcome
domain?
5.3.Is the
numerical
result being
assessed
likely to have
been selected,
on the basis
of the results,
from multiple
eligible
analyses of
the data?
RoB
judgement
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probably
no.
Probabl
y no.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low risk.
Low
risk.
308
309
31
310
311
312
Synthesis of results
313
Comparisons were performed between ST and stretching groups, involving eleven
314
articles and 452 participants. Global effects on ROM were achieved pooling data from the
315
different joints. One article did not have the data required,[35] but the authors kindly supplied
316
it upon request. For another article,[36] we also requested data relative to the goniometric
317
evaluations, but obtained no response. Therefore, only data from the sit-and-reach test was
318
used. For one article,[37] means and SDs were obtained from 95% CIs, while in another SDs
319
were extracted from SEMs,[74] using Cochrane’s RevMan Calculator.
320
Of the five articles including both genders, four provided pooled data, with no
321
distinction between genders.[34, 35, 37, 60] One article presented data separated by gender,
322
without significant differences between men and women in response to interventions.[61]
323
Weighted formulas were applied sequentially for combining means and SDs of groups within
324
the same study.[38] Two studies presented the results separated by left and right lower limbs,
325
with both showing similar responses to the interventions;[24, 62] outcomes were combined
326
using the same weighted formulas for the means and SDs. Five articles only presented one
327
decimal place,[24, 34, 37, 61, 67] and so all values were rounded for uniformity.
328
Effects of ST versus stretching on ROM: no significant difference was noted between
329
ST and stretching (ES = -0×22; 95% CI = -0×55 to 0×12; p = 0×206; I2 = 65×4%; Egger’s test p =
330
0×563; Figure 2). The relative weight of each study in the analysis ranged from 6×4% to 12×7%
331
(the size of the plotted squares in Figure 2 reflects the statistical weight of each study).
332
333
32
334
Study name
Hedges's g and 95% CI
Stretching
(n)
Alexander et al. (2001)
Aquino et al. (2010)
Caputo et al. (2017)
Jones et al. (2002)
Leite et al. (2015)
Li et al. (2020)
Morton et al. (2011)
Nelson & Bandy (2004)
Racil et al. (2020)
Simão et al. (2011)
Wyon et al. (2013)
Strength
(n)
Hedges's
g
0.045
0.087
0.220
-0.282
-0.229
-0.616
0.123
-0.101
-0.000
-1.922
0.247
-0.215
-3.00
-1.50
Favours stretching
335
0.00
1.50
3.00
Favours strength
336
Figure 2. Forest plot of changes in ROM after participating in stretching-based compared to strength-based
337
training interventions. Values shown are effect sizes (Hedges’s g) with 95% confidence intervals (CI). The size
338
of the plotted squares reflects the statistical weight of the study.
339
340
Additional analysis
341
Effects of ST versus stretching on ROM, moderated by study RoB in randomization: No
342
significant sub-group differences in ROM changes (p = 0·256) was found when programs with
343
high RoB (6 studies; ES = -0·41; 95% CI = -1·02 to 0·20; within-group I2 = 77·5%) were
344
compared to programs with low RoB (4 studies; ES = -0·03; 95% CI = -0·29 to 0·23; within-
345
group I2 = 0·0%) (Supplementary figure 1).
346
Effects of ST versus stretching on ROM, moderated by study RoB in measurement of
347
the outcome: No significant sub-group difference in ROM changes (p = 0·320) was found
348
when programs with high RoB (5 studies; ES = -0·04; 95% CI = -0·31 to 0·24; within-group
349
I2 = 8·0%) were compared to programs with low RoB (6 studies; ES = -0·37; 95% CI = -0·95
350
to 0·22; within-group I2 = 77·3%) (Supplementary figure 2).
351
Effects of ST versus stretching on ROM, moderated by ROM type (active vs. passive):
352
No significant sub-group difference in ROM changes (p = 0·642) was found after training
33
353
programs that assessed active (8 groups; ES = -0·15; 95% CI = -0·65 to 0·36; within-group I2
354
= 78·7%) compared to passive ROM (6 groups; ES = -0·01; 95% CI = -0·27 to 0·24; within-
355
group I2 = 15·3%) (Supplementary figure 3).
356
Effects of ST versus stretching on hip flexion ROM: Seven studies provided data for hip
357
flexion ROM (pooled n = 294). There was no significant difference between ST and stretching
358
interventions (ES = -0·24; 95% CI = -0·82 to 0·34; p = 0·414; I2 = 80·5%; Egger’s test p =
359
0·626; Supplementary figure 4). The relative weight of each study in the analysis ranged from
360
12·0% to 17·4% (the size of the plotted squares in Figure 6 reflects the statistical weight of
361
each study).
362
Effects of ST versus stretching on hip flexion ROM, moderated by study RoB in
363
randomization: No significant sub-group difference in hip flexion ROM changes (p = 0·311)
364
was found when programs with high RoB in randomization (4 studies; ES = -0·46; 95% CI =
365
-1·51 to 0·58; within-group I2 = 86·9%) were compared to programs with low RoB in
366
randomization (3 studies; ES = 0·10; 95% CI = -0·20 to 0·40; within-group I2 = 0·0%)
367
(Supplementary figure 5).
368
Effects of ST versus stretching on hip flexion ROM, moderated by ROM type (active vs.
369
passive): No significant sub-group difference in hip flexion ROM changes (p = 0·466) was
370
found after the programs assessed active (4 groups; ES = -0·38; 95% CI = -1·53 to 0·76; within-
371
group I2 = 87·1%) compared to passive ROM (4 groups; ES = 0·08; 95% CI = -0·37 to 0·52;
372
within-group I2 = 56·5%) (Supplementary figure 6).
373
Effects of ST versus stretching on knee extension ROM: Four studies provided data for
374
knee extension ROM (pooled n = 223). There was no significant difference between ST and
375
stretching interventions (ES = 0·25; 95% CI = -0·02 to 0·51; p = 0·066; I2 = 0·0%; Egger’s test
376
p = 0·021; Supplementary figure 7). After the application of the trim and fill method, the
377
adjusted values changed to ES = 0·33 (95% CI = 0·10 to 0·57), favoring ST. The relative
34
378
weight of each study in the analysis ranged from 11·3% to 54·2% (the size of the plotted
379
squares in Supplementary figure 7 reflects the statistical weight of each study).
380
One article behaved as an outlier in all comparisons (favoring stretching),[67] but after
381
sensitivity analysis the results remained unchanged (p>0·05), with all ST vs. stretching
382
comparisons remaining non-significant.
383
384
Confidence in cumulative evidence
385
Table 3 presents GRADE assessments. ROM is a continuous variable, and so a high
386
degree of heterogeneity was expected.[77] Imprecision was moderate, likely reflecting the fact
387
that ROM is a continuous variable. Overall, both ST and stretching consistently promoted
388
ROM gains, but no recommendation could be made favoring one protocol.
389
390
35
391
392
Table 3. GRADE assessment for the certainty of evidence.
Outcome Study
RoB1
Publication
design
bias
ROM
393
394
11 RCTs,
452
participants
in metaanalysis.
Randomization – low in
four articles, moderate in
one, and high in six.
Deviations from intended
interventions – Low.
Missing outcome data –
Low.
Measurement of the
outcome – low in six
articles and high in five.
Selection of the reported
results – Low.
No
publication
bias.
Inconsistency
Indirectness
Imprecision
9 RCTs showed
improvements in ROM
in both groups.
2 RCTs showed no
changes in ROM in
either group.
11 RCTs
showed effects of equal
magnitude for ST and
stretching.2
No serious
indirectness.
Moderate.3
Quality
of
evidence
Moderate.
⨁⨁⨁
Recommendation
Strong
recommendation
for either strength
training or
stretching4.
No
recommendation
for choosing one
of the protocols
over the other, as
their efficacy in
ROM gains was
statistically not
different.
1 - Meta-analyses moderated by RoB showed no differences between studies with low and high risk.
2 - Because ROM is a continuous variable, high heterogeneity was expected. However, this heterogeneity is mostly between small and large beneficial effects. No adverse
effects were reported.
3 - Expected because ROM is a continuous variable. Furthermore, imprecision referred to small to large beneficial effects.
4 – Both strength training and stretching presented benefits without reported adverse effects.
Legend: ROM – Range of motion. RCTs: randomized controlled trials. RoB: risk of bias.
395
36
396
397
DISCUSSION
398
Summary of evidence
399
The aim of this SRMA was to compare the effects of supervised and randomized ST
400
compared to stretching protocols on ROM, in participants of any health and training status.
401
Qualitative synthesis showed that ST and stretching interventions were not statistically
402
different in improving ROM, regardless of the nature of the interventions and moderator
403
variables such as gender, health, or training status. Meta-analysis including 11 articles and 452
404
participants showed that ST and stretching interventions were not statistically different in
405
active and passive ROM changes, regardless of RoB in the randomization process, or in
406
measurement of the outcome. RoB was low for deviations from intended interventions, missing
407
outcome data, and selection of the reported results. No publication bias was detected.
408
High heterogeneity is expected in continuous variables,[77] such as ROM. However,
409
more research should be conducted to afford sub-group analysis according to characteristics of
410
the analyzed population, as well as protocol features. For example, insufficient reporting of
411
training volume and intensity meant it was impossible to establish effective dose-response
412
relationships, although a minimum of 5 weeks of intervention,[60] and two weekly sessions
413
were sufficient to improve ROM.[37, 74] Studies were not always clear with regard to the
414
intensity used in ST and stretching protocols. Assessment of stretching intensity is complex,
415
but a practical solution may be to apply scales of perceived exertion,[62] or the Stretching
416
Intensity Scale.[78] ST intensity may also moderate effects on ROM,[79] and ST with full vs
417
partial ROM may have distinct neuromuscular effects[70] and changes in fascicle length.[28]
418
Again, information was insufficient to discuss these factors, which could potentially explain
419
part of the heterogeneity of results.
37
420
Most studies showed ROM gains in ST and stretching interventions, although in two
421
studies neither group showed improvements.[35, 36] Though adherence rates were unreported
422
by Aquino, Fonseca [35], they were above 91.7% in Leite, De Souza Teixeira [36], thus
423
providing an unlikely explanation for these results. In the study of Aquino, Fonseca [35], the
424
participants increased their stretch tolerance, and the ST group changed the peak torque angle,
425
despite no ROM gains. The authors acknowledged that there was high variability in
426
measurement conditions (e.g., room temperature), which could have interfered with
427
calculations. Leite, De Souza Teixeira [36] suggested that the use of dynamic instead of static
428
stretching could explain the lack of ROM gains in the stretching and stretching + ST groups.
429
However, other studies using dynamic stretching have shown ROM gains.[24, 34]
430
Furthermore, Leite, De Souza Teixeira [36] provided no interpretation for the lack of ROM
431
gains in the ST group.
432
Globally, however, both ST and stretching were effective to improve ROM. Why would
433
ST improve ROM in a manner that is not statistically distinguishable from stretching? ST with
434
an eccentric focus demands the muscles to produce force on elongated positions, and a meta-
435
analysis showed limited to moderate evidence that eccentric ST is associated with increases in
436
fascicle length.[80] Likewise, a recent study showed that 12 sessions of eccentric ST increased
437
fascicle length of the biceps femoris long head.[29] However, ST with an emphasis in
438
concentric training has been shown to increase fascicle length when full ROM was
439
required.[28] In a study with nine older adults, ST increased fascicle length in both the eccentric
440
and concentric groups, albeit more prominently in the former.[81] Conversely, changes in
441
pennation angle were superior in the concentric group (35% increase versus 5% increase).
442
Plyometric training can also increase plantar flexor tendon extensibility.[33]
443
One article showed significant reductions in pain associated with increases in
444
strength.[37] Thus, decreased pain sensitivity may be another mechanism through which ST
38
445
promotes ROM gains. An improved agonist-antagonist coactivation is another possible
446
mechanism promoting ROM gains, through better adjusted force ratios.[31, 62] Also, some
447
articles included in the meta-analysis assessed other outcomes in addition to ROM, and these
448
indicated that ST programs may have additional advantages when compared to stretching, such
449
as greater improvements in neck flexors endurance,[37] ten repetition maximum Bench Press
450
and Leg Press,[36, 67] and countermovement jump and 60-m sprint with hurdles,[24] which
451
may favor the choice of ST over stretching interventions.
452
453
454
Limitations
455
After protocol registration, we chose to improve upon the design, namely adding two
456
dimensions (directness and imprecision) that would provide a complete GRADE assessment.
457
Furthermore, subgroup analyses were not planned a priori. There is a risk of multiple subgroup
458
analyses generating a false statistical difference, merely to the number of analyses
459
conducted.[38] However, all analyses showed an absence of significant differences and
460
therefore provide a more complete understanding that the effects of ST or stretching on ROM
461
are consistent across conditions. Looking backwards, perhaps removing the filters used in the
462
initial searches could have provided a greater number of records. Notwithstanding, it would
463
also likely provide a huge number of non-relevant records, including opinion papers and
464
reviews. Moreover, consultation with four independent experts may hopefully have resolved
465
this shortcoming.
466
Due to the heterogeneity of populations analysed, sub-group analysis according to sex
467
or age group were not possible, and so it would be important to explore if these features interact
468
with the protocols in meaningful ways. And there was a predominance of studies with women,
469
meaning more research with men is advised. There was also a predominance of assessments of
39
470
hip joint ROM, followed by knee and shoulder, with the remaining joints receiving little to no
471
attention. In addition, dose-response relationships could not be addressed, mainly due to poor
472
reporting.
473
474
CONCLUSIONS
475
Overall, ST and stretching were not statistically different in ROM improvements, both
476
in short-term interventions[60] and in longer-term protocols,[67] suggesting that a combination
477
of neural and mechanical factors is at play. Therefore, if ROM gains are a desirable outcome,
478
both ST and stretching can be prescribed, in the absence of specific contraindications,
479
especially because studies did not report any adverse effects. People that do not respond well
480
or do not adhere to stretching protocols can change to ST programs, and vice-versa.
481
Furthermore, session duration may negatively impact adherence to an exercise program.[82]
482
Since ST generates ROM gains similar to those obtained with stretching, clinicians may
483
prescribe smaller, more time-effective programs when deemed convenient and appropriate,
484
thus eventually increasing patient adherence rates.
485
486
40
487
488
489
Declaration of interests: J.M. owns a company focused on Personal Trainer’s education but
490
made no attempt to bias the team in protocol design and search process and had no role in
491
extracting data for meta-analyses. The multiple cross-checks described in the methods
492
provided objectivity to data extraction and analysis. Additionally, J.M. had no financial
493
involvement in this manuscript. The other authors have no conflict of interest to declare.
494
495
Funding: No funding was used for conducting this meta-analysis.
496
497
41
498
499
Author’s contributions (following ICMJE recommendations)
Authors
José Afonso
Rodrigo RamirezCampillo
João Moscão
Tiago Rocha
Rodrigo Zacca
Alexandre Martins
André A. Milheiro
João Ferreira
Hugo Sarmento
Filipe Manuel
Clemente
Acknowledgements
Richard Inman
Pedro Morouço
Daniel MoreiraGonçalves, Fábio
Yuzo Nakamura plus
two experts who
wished to remain
anonymous.
Substantial
contributions to the
conceptualization
or design of the
study; OR the
acquisition,
analysis, or
interpretation of
data
√
√
Drafting the
manuscript; OR
revising the
manuscript
critically for
important
intellectual
content
Final
approval
of the
version to
be
published
√
√
√
√
Agreement to be
accountable for all
aspects of the work, and
to ensure that issues
related to the accuracy or
integrity of any part of
the work are
appropriately
investigated and resolved
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
Role
Language editing and proof reading.
Thorough pre-submission scientific review of the manuscript. Signed consent form
below.
Review of inclusion criteria and included articles, and proposal of additional articles
to be included in the systematic review and meta-analysis.
Signed consent forms below.
500
501
42
502
503
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