HEART RATE–BASED TRAINING INTENSITY AND ITS
IMPACT ON INJURY INCIDENCE AMONG ELITE-LEVEL
PROFESSIONAL SOCCER PLAYERS
ADAM L. OWEN,1,2 JACKY J. FORSYTH,3 DEL P. WONG,4 ALEXANDRE DELLAL,5 SEAN P. CONNELLY,1
6
AND KARIM CHAMARI
1
Servette Football Club, Center for Football Research, Geneva, Switzerland; 2Center of Sports Research and Innovation, Claude
Bernard University Lyon.1, Lyon, France; 3Center for Sport Health and Exercise Research, Staffordshire University, Stafford,
United Kingdom; 4Human Performance Laboratory, Technological and Higher Education Institute of Hong Kong, Hong Kong,
China; 5Medical Center Excellence FIFA, Santy Orthopedicae Clinical, Lyon, France; and 6Athlete Health and Performance
Research Center, ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Doha, Qatar
ABSTRACT
Owen, AL, Forsyth, JJ, Wong, DP, Dellal, A, Connelly, SP, and
Chamari, K. Heart rate–based training intensity and its impact
on injury incidence among elite-level professional soccer players. J Strength Cond Res 29(6): 1705–1712, 2015—Elite-level
professional soccer players are suggested to have increased
physical, technical, tactical, and psychological capabilities
when compared with their subelite counterparts. Ensuring
these players remain at the elite level generally involves training
many different bodily systems to a high intensity or level within
a short duration. This study aimed to examine whether an
increase in training volume at high-intensity levels was related
to injury incidence, or increased the odds of sustaining an
injury. Training intensity was monitored through time spent in
high-intensity (T-HI) and very high-intensity (T-VHI) zones of
85–,90% and $90% of maximal heart rate (HRmax), and all
injuries were recorded over 2 consecutive seasons. Twentythree, elite professional male soccer players (mean 6 SD
age, 25.6 6 4.6 years; stature, 181.8 6 6.8 cm; and body
mass, 79.3 6 8.1 kg) were studied throughout the 2-years
span of the investigation. The results showed a mean total
injury incidence of 18.8 (95% confidence interval [CI], 14.7–
22.9) injuries per 1,000 hours of exposure. Significant correlations were found between training volume at T-HI and injury
incidence (r = 0.57, p = 0.005). Further analysis revealed how
players achieving more time in the T-VHI zone during training
increased the odds of sustaining a match injury (odds ratio =
1.87; 95% CI, 1.12–3.12, p = 0.02) but did not increase the
odds of sustaining a training injury. Reducing the number of
Address correspondence to Dr. Adam L. Owen, adamowen@
outlook.com.
29(6)/1705–1712
Journal of Strength and Conditioning Research
Ó 2015 National Strength and Conditioning Association
competitive match injuries among elite-level professional players may be possible if greater focus is placed on the training
intensity and volume over a period of time ensuring the potential reduction of fatigue or overuse injuries. In addition, it is
important to understand the optimal training load at which
adaptation occurs without raising the risk of injury.
KEY WORDS soccer, injury, odds ratio, training, periodisation
INTRODUCTION
S
occer is a high-intensity intermittent contact sport
that exposes elite-level players to continual physical, technical, tactical, psychological, and
physiological demands (33,36). The stressors
encountered during actual match-play have been suggested to show no detrimental effect of consecutive games’
physical performance, but a greater injury risk (8,12). From
a training perspective, cardiovascular and neuromuscular
adaptations are suggested to be stimulated through a high
training load (TL), induced through manipulation of intensity, duration, and frequency of training (10). However, if
the intensity or volume is increased by an amount above
the level at which various physiological systems can adapt,
injury may result (26). Therefore, it is important to understand the optimal TL at which adaptation occurs without
raising the risk of injury.
The implications of a high number of training days and
matches lost because of injury is suggested to be to the
detriment of team success (2), especially for soccer teams
unable to replace players of similar abilities because of limited resources. Recently, Eirale et al. (16) even showed a clear
relationship between teams’ ranking and injury rate. Indeed,
in the Qatari Professional league, it resulted that lower injury
incidence rate was strongly correlated to team success over
an entire season.
In soccer, high-intensity training has increasingly been
advocated and used to elicit cardiovascular adaptations
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Training Load, Intensity, and Injury
(11,30,36). Often, this type of training is reported to require
players working at high to very high intensities, indicated
through high heart rate responses (.85% maximal heart rate
[HRmax]) (36). Within the literature, mean match HRs of
;85% HRmax have been reported; however, these are averaged values that include numerous, recovering low-intensity
bursts that follow extremely high-intensity efforts.
At the elite level, the accumulative high intensity nature of
soccer match-play combined with multiple high-intensity
sessions may cause excessive bodily strain (3,34). The continual strain over a prolonged period of time may lead to
performance decrements and increase the risk of injury
(5,35). Injury incidence in soccer is high with approximately
20–35 injuries occurring per 1,000 hours of match exposure
(14,17) and injuries during training sessions ranging between
5.8 and 7.6 per 1,000 hours (2,38). Some authors report that
a greater number of overuse injuries occur in the preseason
training period (28,29), because of a greater intensity and
volume of training causing a residual fatigue that may be
attributed with an increased injury risk. It may be important
to consider whether training intensity relates to injury incidence, to educate coaches or other sport professionals
involved within the physical development of players. Program or session design must ensure that TLs = volume 3
intensity are not significantly exceeded, eliciting accumulative
fatigue responses and predisposing players to overuse injuries.
Gabbett and Dumrow (25) found that TL increased the
odds of sustaining an injury; however, this particular study
involved rugby players, and injury exposure was estimated
based on average training duration rather than calculated per
player. Furthermore, ratings of perceived exertion (RPE)
scores were used as a measure of intensity (TL = RPE 3
training duration). Although popular owing to its ease of use
(1,6), this method depends on the personal perception of physical effort a period after (6,26). Therefore, although it does
provide a valid estimate of total session mean intensity, it does
not provide data about the periods spent at various training
intensities (31). Heart rate training zones have been used as an
alternative and objective measure of estimating training intensity (6,15,23,36), with HR being reported as a valid and reliable
indicator of exercise intensity within soccer training (30,36).
Currently, there are no studies investigating the relationship
between injury incidence and high intensity quantified through
HR within elite-level professional soccer.
Because of the limited amount of research within this area,
the purpose of the investigation was to examine whether
a relationship exists between training volume and intensity
on injury incidence and also the odds of sustaining an injury
in both training sessions, and competitive matches. Many
publications have highlighted specific audits of injury types
at many levels of the game; however, no literature exists
regarding the potential effect of TL on injury rates. It was
hypothesized that a greater time spent in the very highintensity HR zones would increase the odds of injury, and
therefore be associated with a higher injury incidence.
1706
the
METHODS
Experimental Approach to the Problem
This prospective, cohort surveillance study was carried out
over 2 competitive soccer seasons. To examine if a greater
time spent at 85–,90% (time spent in high-intensity zone
[T-HI]) and $90% (time spent in high-intensity zone
[T-VHI]) of HRmax is associated with a higher injury incidence, the relationship between training intensity and injury
incidence was determined. Secondary outcome measures of
the study included injury severity, type, and frequency. Furthermore, odds ratios (ORs) were determined to examine if
a higher individual TL would increase the odds of injury.
Injury incidence was presented as the number of injuries
per 1,000 hours of exposure, with exposure recorded for
each player rather than being estimated for the group (27).
Because relationships have been previously reported
between injury incidence and players’ age, body composition, maximal oxygen consumption (V_ O2max), and vertical
jump height (4,17,18) these variables were measured in this
study to examine their impact on injury.
Subjects
Twenty-three elite, male professional soccer players participated in this investigation. At the initiation of the study,
players involved had a mean 6 SD age of 26.8 6 4.6 (range:
18–38) years, stature of 181.8 6 6.8 (1.70–1.92) cm, and body
mass of 79.3 6 8.1 (62.5–93.6) kg. Percentage body fat for
the 23 players was 10.1 6 2.7 (5.1–16.3) %, and mean
V_ O2max was 53.7 6 4.3 (52.1–68.6) ml$kg21$min21. All participants had been playing soccer for 8 years or more, and all
but 3 of them were competing at the international level.
Participants were informed that they were free to withdraw
from the study at any time. Procedures followed were in
accordance with the Helsinki Declaration of 1975, approved
by the Ethical Committee of the collaborating University
and followed the standards of the Sport Science and Medical
Department of the researching soccer club.
Measure of Injury
The injury definitions and method used for analysis of each
injury followed the guidelines recommended by the International Soccer Injury Consensus Group (22,27). In this regard, an injury was defined as any physical complaint sustained
by the soccer player either in training or in competition, which
prevented the injured player from participating in competition or
normal training for at least 1 day, but not including the day of the
injury (22). This type of injury has been referred to as a timeloss injury (22). Injury incidence was categorized according
to incidence per match (i.e., the number of match injuries in
relation to the time spent in matches), and incidence per
training (the number of injuries during time spent in training), and total injury incidence (sum of training and match
injuries in relation to overall training and match exposure)
(22,27). The severity of each injury was defined by the time
lost from usual training or competition and was categorized
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uptake (V_ O2max) and HRmax
to determine individual HR
TABLE 1. Site of injury.
training zones. Players followed the V_ O2 max running
Match injuries
Training injuries
Site of injury
N (%)
N (%)
protocol of Hoff et al. (30),
and a precalibrated breath-byCalf/lower leg
18 (20.7)
4 (12.5)
breath metabolic system was
Ankle and foot
18 (20.7)
9 (28.1)
used (Medical Graphics CarKnee
15 (17.2)
4 (12.5)
diopulmonary Exercise System,
Hamstring
14 (16.1)
4 (12.5)
Thigh
12 (13.8)
5 (15.6)
CPX/D; Medgraphics Corp.,
Groin
4 (4.6)
1 (3.1)
St. Paul, MN, USA). Individual
Head
3 (3.4)
0 (0.0)
HRmax and V_ O2max were
Chest and abdomen
2 (2.3)
1 (3.1)
derived by using the mean of
Spine
1 (1.1)
26.3
the 2 highest 15-second averShoulder
0 (0.0)
2 (6.3)
Total
87
32
ages achieved during the final
stage of the V_ O2max test. A
true HRmax and V_ O2max were
considered to have been
achieved, if both variables
in the following way: slight as 1–3 days, minor as 4–7 days,
failed to increase despite an increase in exercise intensity
moderate as 8–21 days, and major as .21 days (28). Injuries
(37). The protocol is commonly used for testing endurance
were classified according to whether they were overuse or
performance in professional football players (26) and
traumatic (22). Other information recorded about the injury
involved participants running on a treadmill at a 38 incline
included the nature of the injury (sprain, fracture, etc.), the
with speed increases of 1 km$h21 every minute until exhauslocation (body part), the date, and whether or not the injury
tion. Before the protocol test, players performed a 3-minute
was a preceded by a previous one (recurrent), the latter
warm-up eliciting an intensity of around 70% HRmax in
being defined as an injury that had occurred previously at
addition to self-selected stretching exercises.
the same location and of the same nature (22). All injuries
Heart rate was recorded and assessed at 5-second intervals
were diagnosed and recorded by the club’s medical staff.
by portable HR monitors (Polar Team System 2; Polar Electro
Injuries were recorded throughout both seasons. Illness
OY, Kempele, Finland) throughout the training sessions for
was not taken into account within this study.
the duration of the investigation (36). Goalkeepers were not
included within the data group. After each testing session, HR
data was downloaded to a computer using dedicated software
Training Load
(Polar Precision S-Series Software SW 3.0; Polar Electro OY)
A laboratory-based, maximal incremental running treadmill
and stored for analysis. The mean and %HRmax achieved
test (Run 500 model; Technogym, Cesena, Italy) was
during each game was calculated for each player, with each
conducted once during preseason before the commenceplayer’s total time spent in specific HR zones following
ment of the training period to determine maximal oxygen
methods used in previous studies (25,36): #50%; 50–,60%;
60–,70%;
70–,85%; 85–
,90% HRmax (T-HI) and
TABLE 2. Type of injury.
$90%HRmax (T-VHI). However, for the purpose of this parMatch
Training
ticular study, the time spent
injuries
injuries
Type of injury
N (%)
N (%)
within the higher intensity
zones, T-HI and T-VHI, has
Muscle and tendon (muscle rupture/tear/strain;
42 (48.3)
13 (40.6)
been assessed and reported to
tendinopathy)
differentiate between “training
Contusions (hematoma, contusion, effusion, bruise)
28 (32.2)
9 (28.1)
Sprain/ligament injury
15 (17.2)
9 (28.1)
intensity” (11). These 2 HR
Dislocation
0 (0.0)
1 (3.1)
zones were chosen because preLaceration
1 (1.1)
0 (0.0)
vious and current research
Concussion
1 (1.1)
0 (0.0)
investigating elite-level soccer
Total
87
32
has reported how HR .85% is
key when discussing training
adaptations (36).
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Training Load, Intensity, and Injury
Odds ratios were used to
examine whether the TL
increased or decreased the
odds of injury. Odds ratios
were derived by tallying the
frequency
of
injury
on
a monthly basis, because training was organized into mesocycles (4 weeks). Training load
per mesocyle was categorized
according to whether it was
considered to be a “high TL”
or a “low TL,” by using
a median split of the data.
Odds of TL increasing the frequency of match injuries, training injuries, traumatic and
Figure 1. Individual training intensity (time spent in HR zone) and frequency of training injuries on a monthly basis.
overuse injuries, and total injuT-HI = mean time spent in the 85–89% heart rate training zone; T-VHI = mean time spent at or above 90%
maximum heart rate.
ries, and of increasing the frequencies of injury severity,
were examined.
Statistical Analyses
A x2 test was used to determine whether the observed
Before analysis, injury incidence and HR data were explored
injury frequency differed from the expected injury frequency.
(and confirmed) for normality and for equality of variances.
Expected injuries were calculated as the same proportion of
Data are expressed as mean 6 SD, percentages, and 95%
the total injuries as the mesocycle TL score was of the total
confidence intervals (CIs), where relevant. Statistical signifiTL score, following the method of Gabbett (23).
cance was set at p # 0.05.
The TL within the previous mesocycle before the injury
Pearson’s correlations were used to examine the relationbeing sustained was determined and assessed to provide an
ships between TL and injury (incidence, severity, type, and
accurate picture of the relationship between TL and injury.
frequency), as well as between injury incidence and physioThis was due to anticipation that TLs would be lower in the
logical/anthropometrical data. The magnitude of the corremonth when an injury was sustained because of reduced
lations was determined using the modified scale by Hopkins
training availability. An independent samples t-test was then
(2000): trivial: r , 0.1; low: 0.1–,0.3; moderate: 0.3–,0.5;
used to examine whether TL, training exposure, and match
high: 0.5–,0.7; very high: 0.7–,0.9; nearly perfect $0.9;
exposure differed significantly in the mesocycle before injury,
and perfect: 1.
compared with the mesocycles when injury did not occur.
A stepwise, multiple linear regression analysis was used to
RESULTS
predict injury incidence; variables having a higher correlation coefficient than r = 0.50 (and a significant relationship)
Over the 2 seasons, the players were exposed to a total of
were included in the analysis. The adjusted R2 was used to
1,704.4 hours of match-play, and 5350.0 hours of training,
assess the proportion of the variance explained by the indewhich equated to an average of 4.8 6 3.8 hours of training
pendent variables.
time per match hour. The team played 116 matches, 54 in
TABLE 3. Odds ratios (95% CI) of sustaining a match or training injury because of training load.*†
Training injury
T-HI
T-VHI
Match injury
Odds ratios
p
Odds ratios
p
0.60 (0.28–1.28)
0.52 (0.24–1.12)
0.20
0.10
1.87 (1.12–3.12)
1.28 (0.78–2.10)
0.02
0.38
*CI = confidence interval; T-HI = mean time spent in the 85–89% maximum heart rate training zone; T-VHI = mean time spent at or
above 90% maximum heart rate training zone.
†p denotes significance using Fisher’s exact probability test using a 2-tailed analysis.
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and 48 (55.2%) were traumatic.
Seventeen of the 32 training
injuries (53.1%) were overuse,
and 15 (46.8%) were traumatic.
Total injury incidence was 18.8
(95% CI, 14.7–22.9) injuries per
1,000 hours of exposure. Training injury incidence was 6.7 injuries per 1,000 hours of
training exposure (95% CI,
3.7–9.6), and match injury incidence was of 54.1 (95% CI,
39.7–68.6). Of the match injuries, 9.2% (n = 8) were slight,
35.6% (n = 31) were minor,
33.3% (n = 29) were moderate,
and 21.8% (n = 19) were major.
Of the training injuries, 28.1%
(n = 9) were slight, 21.9%
Figure 2. Mean differences (including SD represented by error bars) in time spent in each heart rate zone (T-HI
and T-VHI) in the month preceding an injury, and in the month when an injury did not occur. T-HI = mean time spent
(n = 7) were minor, 28.1% (n =
in the 85–89% heart rate training zone; T-VHI = mean time spent at or above 90% maximum heart rate.
9) were moderate, and 21.9%
(n = 7) were major.
Data for injury frequency
season 1 and 62 in season 2, with the higher number in
and training intensity are given in Figure 1. There was a sigseason 2 because of UEFA Champions League fixtures.
nificant correlation between total injury incidence and trainThere were a total of 130 injuries recorded over the 2 seaing intensity (T-HI: r = 0.57, p = 0.005; T-VHI: r = 0.568, p =
sons. Type and site of injuries (for both match-play and
0.005). There was also a significant correlation between
training) are given in Tables 1 and 2, respectively.
training injury incidence and training intensity, but only for
Injuries and illnesses sustained outside of soccer hours
T-HI (r = 0.48, p = 0.02). Correlations were low between
were excluded from further analysis regarding injury incimatch injury incidence and training intensity (T-HI: r = 0.09,
dence, injury type, cause, site, and severity, leaving a total of
p = 0.69; T-VHI: r = 0.19, p = 0.38). Correlations were
119 soccer-related injuries. Recurrent injuries were also
significant for number of days off because of injury (an indiexcluded when describing injury type, cause, and severity,
cation of injury severity) and training intensity (r = 0.51, p =
so as not to falsely elevate these values. Of the remaining 119
0.01 for T-HI, and r = 0.47, p = 0.02 for T-VHI). There was
injuries, 87 were match injuries and 32 were training injuries.
a significant correlation between training intensity and total
Thirty-nine of the 87 match injuries (44.8%) were overuse,
number of traumatic injuries (r = 0.42, p = 0.04 for T-HI, and
r = 0.44, p = 0.03 for T-VHI).
A significant negative correlation was observed between
injury incidence and percentage
body fat (r = 20.43, p = 0.04),
but correlations between injury
incidence and all other anthropometrical/physiological variables were low and nonsignificant.
A forward, stepwise linear
regression, with T-HI and
T-VHI in the model, gave an
adjusted R2 of 0.28, p = 0.014 for
injury incidence; hence, training
intensity explained 28% of the
variance in injury incidence.
The ORs of sustaining an
injury because of training
Figure 3. Number of training injuries and monthly hours of training over the 2 seasons.
intensity are given in Table 3.
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Training Load, Intensity, and Injury
Only one of these values was significant, with a greater time
spent in T-HI resulting in a greater odds of sustaining
a match injury (x2 = 7.22, p = 0.059).
There was a significant difference between the observed
total injury frequency and the expected injury, as determined
as a proportion of training intensity (mean T-HI, x2 = 33.2,
p = 0.04; mean T-VHI, x2 = 33.5, p = 0.04). Differences were
also significant when separately analyzing training injuries
(for T-HI, x2 = 38.0, p = 0.01; and T-VHI, x2 = 36.7, p =
0.02) and match injuries (for T85, x2 = 48.4, p , 0.001; and
T90, x2 = 48.3, p = 0.001).
Mean differences (including significance) in time spent in
each intensity zone in the month preceding an injury and in the
mesocycle when an injury did not occur are given in Figure 2.
DISCUSSION
The main purpose of this study was to examine whether
training intensity, as assessed using T-HI and T-VHI,
increased the odds of sustaining an injury. Findings from
this study have revealed that individual training intensity and
load were highly related to total injury incidence (r = 0.57,
p = 0.005). Training intensity (T-HI and T-VHI) explained
28% of the variance in injury incidence. Odds ratios for
training intensity and injury incidence were negligible with
no discernible pattern apparent. For instance, an increased
proportion of time spent at 85–,90% HRmax significantly
increased the odds of sustaining a match injury but did not
increase the odds of sustaining a training injury (Table 2).
Accumulative fatigue derived from high intensity training
and competitive match-play may have played a fundamental
role because of its residual effect in explaining the higher
ORs for match injury incidence. In addition, the significant
increase in match contusion injuries (n = 28) vs. training
contusion injuries (n = 9) as a result of contact with competitors during match-play should be highlighted as a key
factor of increased odds. Using x2 analysis, the observed total
injury frequency and the observed training injury frequency
were significantly different (p # 0.05) from the number of
injuries that were expected to occur based on training intensity, which suggests that training intensity and injury frequency were not associated. It seems, therefore, that TL
approach, assessed using specific HR zones, has only a moderate effect on injury incidence and does not increase the
odds of injury. This finding is contrary to what was reported
by Gabbett and Dumrow (25), who found that high TL
increased the odds of injury in rugby players. The discrepancy in relation to this study may be explained by how
Gabbett and Dumrow (25) estimated training intensity
through RPE as opposed to HR zones used in this study.
It should also be noted that the previous study (25) defined
exposure as the number of players multiplied by session
duration to give an average exposure, as opposed to individual exposure data used in this study. Similar to this study,
Killen et al. (32) found no relationship between TL (as assessed using RPE) and training injury incidence in rugby
1710
the
players. Their suggestion was that the high-caliber nature
of the athletes was protective against injury, which may also
account for the current findings. However, significant relationships have been found between individual session–RPE
and HR-based TL, therefore strengthening the use of HR as
a valid method of assessing TL in sports.
It may be suggested that injury results from an accumulation of TL. For these reasons, an attempt was made to
analyze whether differences in TL occurred before the injury
being sustained, through consideration of the TL in the
preceding period. On the occurrence of injuries, duration
sustained within T-VHI was significantly greater in the
preceding mesocycle when compared with the duration
accumulated in T-VHI if an injury had not occurred
(Figure 2). Although training intensity was related to injury
incidence but not increased odds of training injuries, the
accumulation of training at high intensity combined with
match-play may affect injury incidence; however, further
research is needed to confirm this. When analyzing injuries,
both training intensity and volume over time should be considered, and coaches should try to ensure that excessive
durations’ training at these high levels are avoided through
appropriate periodization.
On a month-by-month basis, using x2-analysis, the
frequency of training injuries reflected training exposure
(Figure 3); to note, months when training duration was
greater, such as in the preseason period, injury frequency
was high. The frequency of training injuries did not, however,
reflect the training intensity. Therefore, it could be suggested
that when training intensity is $85% HRmax, injury does not
necessarily result, but when exposure to training is prolonged,
more injuries maybe more prevalent. In agreement with the
present findings, other researchers have found a similar relationship between exposure and injury frequency (14,17,18). In
this study, the players did not train for long periods of time in
comparison to that reported by others (13). Indeed, training
was often of a high intensity but short duration, using a predominance of soccer-specific intermittent training. This
approach to training might explain the high relationship
found between injury incidence and training intensity but further specific investigations are warranted.
The low injury incidence for training (6.7 injuries per
1,000 hours of training exposure) was comparable with that
previously reported (13), although match injury incidence
(54.1 injuries per 1,000 hours of match exposure) was higher
(13), although this could be a direct link to the increased
number of games played. Match injury incidence has been
found to be higher in certain circumstances. For instance,
Dupont et al. (12) reported a match injury incidence of
97.7 per 1,000 hours of match exposure when players played
2 matches a week. Dvorak et al. (14) reported a match injury
incidence of 81 per 1,000 hours of match exposure in the
2002 FIFA World Cup.
The site, type, and severity of injuries reported within this
investigation were within the ranges reported previously
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among other professional soccer players. Previous literature
purports how a greater proportion of injuries occurred to the
lower extremities (Table 1) (20,27–29,36). Results from this
study concur with previous findings as a greater number of
injuries, both during training and match-play, consisted of
muscle strains, contusions, and ligament sprains (Table 2)
(17,36). Therefore, the present sample of injuries in the studied team is representative of usual soccer injuries, and the
conclusions of the study are more likely to be interpreted as
providing knowledge on actual soccer.
Relationships between injury incidence and anthropometrical and physiological variables were weak in this study, as
also reported by others (18,24,35), possibly explained by the
homogenous nature of the players. Considering that training
intensity did seem to affect injury incidence, interestingly
anthropometrical and physiological variables did not relate
to injury incidence, other intrinsic risk factors, such as joint
instability, functional skill, psychology (34) and other extrinsic
factors such as playing surface and foul play (34,35) may have
contributed to injury. Based on this information, it can be
confirmed that the cause of injury is multifactorial, with this
study highlighting training intensity being a significant factor.
Participants within the study were elite-level footballers,
and unique with respect to comparisons of previous research
in the area of injury incidence and training intensity (19,25).
Killen et al. (32) described that it is difficult to compare
results obtained from semiprofessional/amateur players with
those from professional players, therefore suggested research
on professional players was required. Amateur players generally have lower cardiovascular endurance capability,
strength, and skill base, which may predispose them to
a greater injury risk (25). To date, this study is the only
one having investigated the relationship between HR intensity and injury incidence in professional soccer players. As
a result, the practical implication that injury incidence is
highly related to high-intensity training is important considering the professional nature of the players, and the individual auditing. Continual bodily strain eliciting greater training
durations at T-VHI levels during training may increase the
odds of sustaining a match injury, but not the odds of sustaining a training injury.
PRACTICAL APPLICATIONS
In professional soccer, training is generally comprised of
a variation of small-, medium-, and large-sided games
alongside high-intensity intermittent bouts used as a time
efficient and effective means of enhancing cardiovascular
fitness (9,30,36). Such training methods may impose more
stress on the body than more traditional training methods,
with heart rates of .85% often being elicited (9,36). This is
the first study to have examined the relationship between
HR-based assessment of training intensity and injury incidence in soccer. Based on the data collected in this study, it
is recommended that training intensity be considered as one
of the many factors in injury prevention. Reducing the
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number of competitive match injuries among elite-level professional players may be possible if greater focus is placed on
the training intensity and volume over a period of time,
ensuring the potential reduction of fatigue or overuse injuries. In addition, it is important to understand the optimal
TL at which adaptation occurs without raising the risk of
injury. Therefore, monitoring training to ensure that optimal
loading is not significantly exceeded, should be considered as
vitally important at the elite level of professional soccer with
respect to injury incidence.
ACKNOWLEDGMENTS
The authors thank Prof. Anthony Stewart, who advised on
statistical approaches, and critically reviewed the article for
statistical accuracy; Mr. Jordan White, who assisted with
initial data compilation; the soccer players for their participation in the study; and the sport science and medical staff.
REFERENCES
1. Alexiou, H and Coutts, AJ. A comparison of methods used for
quantifying internal training load in women soccer players. Int J
Sports Physiol Perform 3: 320–330, 2008.
2. Arnason, A, Andersen, TE, Holme, I, Engebretsen, L, and Bahr, R.
Prevention of hamstring strains in elite soccer: An intervention
study. Scand J Med Sci Sports 18: 40–48, 2008.
3. Arnason, A, Sigurdsson, SB, Gudmundsson, A, Holme, I,
Engebretsen, L, and Bahr, R. Physical fitness, injuries, and team
performance in soccer. Med Sci Sports Exerc 36: 278–285, 2004.
4. Bahr, R and Krosshaug, T. Understanding injury mechanisms: A key
component of preventing injuries in sport. Br J Sports Med 39: 324–
329, 2005.
5. Banister, EW. Modelling elite athletic performance. In: Physiological
Testing of the High-performance Athlete. J.D. MacDougall, H.A.
Wenger, and H.J. Green, eds. Champaign, IL: Human Kinetics,
1991. pp. 403–424.
6. Borresen, J and Lambert, MI. Quantifying training load: A
comparison of subjective and objective methods. Int J Sports Physiol
Perform 3: 16–30, 2008.
7. Carling, C, Le Gall, F, and Dupont, G. Are physical performance
and injury risk in a professional soccer team in match play affected
over a prolonged period of fixture congestion. Int J Sports Med 33:
36–42, 2012.
8. Chamari, K, Haddad, M, Wong del, P, Dellal, A, and Chaouachi, A.
Injury rates in professional soccer players during Ramadan. J Sports
Sci 30(Suppl 1): S93–S102, 2012.
9. Coutts, AJ, Rampinini, E, Marcora, SM, Castagna, C, and
Impellizzeri, FM. Heart rate and blood lactate correlates of
perceived exertion during small-sided soccer games. J Sci Med Sport
12: 79–84, 2009.
10. Coyle, EF. Physical activity as a metabolic stressor. Am J Clin Nutr
72: 512S–520S, 2000.
11. Dellal, A, Chamari, K, Pintus, A, Girard, O, Cotte, T, and Keller, D.
Heart rate responses during small-sided games and short
intermittent running training in elite soccer players: A comparative
study. J Strength Cond Res 22: 1449–1457, 2008.
12. Dupont, G, Nedelec, M, McCall, A, McCormack, D, Berthoin, S,
and Wisløff, U. Effect of 2 soccer matches in a week on physical
performance and injury rate. Am J Sports Med 38: 1752–1758,
2010.
13. Dvorak, J and Junge, A. Football injuries and physical symptoms. A
review of the literature. Am J Sports Med 28: S3–S9, 2000.
VOLUME 29 | NUMBER 6 | JUNE 2015 |
1711
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Training Load, Intensity, and Injury
14. Dvorak, J, Junge, A, Grimm, K, and Kirkendall, D. Medical report
from the 2006 FIFA world cup Germany. Br J Sports Med 41: 578–
581, 2007.
15. Edwards, S. The Heart Rate Monitor Book. Sacramento, CA: Fleet
Feet Press, 1993.
16. Eirale, C, Tol, JL, Farooq, A, Smiley, F, and Chalabi, H. Low injury
rate strongly correlates with team success in Qatari professional
football. Br J Sports Med 47: 807–808, 2013.
27. Hägglund, M, Waldén, M, Barhr, R, and Ekstrand, J. Methods
for epidemiological study of injuries to professional football
players: Developing the UEFA model. Br J Sports Med 39:
340–346, 2005.
28. Hägglund, M, Waldén, M, and Ekstrand, J. UEFA injury study-an
injury audit of European Championships 2006 to 2008. Br J Sports
Med 43: 483–489, 2009.
17. Ekstrand, J, Hägglund, M, and Waldén, M. Injury incidence and
injury patterns in professional football: The UEFA injury study. Br J
Sports Med 45: 553–558, 2011.
29. Hawkins, RD, Hulse, MA, Wilkinson, C, Hodson, A, and
Gibson, M. The association football medical research programme:
An audit of injuries in professional football. Br J Sports Med 35: 43–
47, 2001.
18. Ekstrand, J, Waldén, M, and Hägglund, M. Risk for injury when
playing in a national football team. Scand J Med Sci Sports 14: 34–38,
2004.
30. Hoff, J, Wisløff, U, Engen, LC, Kemi, OJ, and Helgerud, J. Soccer
specific aerobic endurance training. Br J Sports Med 36: 218–221,
2002.
19. Eriksson, LI, Jorfeldt, L, and Ekstrand, J. Overuse and distortion
soccer injuries related to player’s estimated maximal aerobic work
capacity. Int J Sports Med 7: 214–216, 1986.
31. Impellizzeri, FM, Rampinini, E, Coutts, AJ, Sassi, A, and
Marcora, SM. Use of RPE-based training load in soccer. Med Sci
Sports Exerc 36: 1042–1047, 2004.
20. Faude, O, Jung, A, Kindermann, W, and Dvorak, J. Risk factors for
injuries in elite female soccer players. Br J Sports Med 40: 785–790,
2006.
32. Killen, NM, Gabbett, TJ, and Jenkins, DG. Training loads and
incidence of injury during the preseason in professional rugby
league players. J Strength Cond Res 24: 2079–2084, 2010.
21. Foster, C, Florhaug, JA, Franklin, J, Gottschall, L, Hrovatin, LA,
Parker, S, Doleshal, P, and Dodge, C. A new approach to
monitoring exercise training. J Strength Cond Res 15: 109–115, 2001.
33. Little, T and Williams, AG. Suitability of soccer training drills for
endurance training. J Strength Cond Res 20: 316–319, 2006.
22. Fuller, CW, Ekstrand, J, Junge, A, Andersen, TE, Bahr, R, Dvorak, J,
Hägglund, M, McCrory, P, and Meeuwisse, WH. Consensus
statement on injury definitions and data collection procedures in
studies of football (soccer) injuries. Br J Sports Med 40: 193–201, 2006.
23. Gabbett, TJ. Influence of training and match intensity on injuries in
rugby league. J Sports Sci 22: 409–417, 2004.
34. Mallo, J, González, P, Veiga, S, and Navarro, E. Injury incidence in
a Spanish sub-elite professional football team: A prospective study
during four consecutive seasons. J Sports Sci Med 10: 731–736, 2011.
35. Östenberg, A and Roos, H. Injury risk factors in female European
football. A prospective study of 123 players during one season.
Scand J Med Sci Sports 10: 279–285, 2000.
24. Gabbett, TJ. Changes in physiological and anthropometric
characteristics of rugby league players during a competitive season.
J Strength Cond Res 19: 400–408, 2005.
36. Owen, A, Wong del, P, McKenna, M, and Dellal, A. Heart rate
responses and technical comparison between small-vs. large-sided
games in elite professional soccer. J Strength Cond Res 25: 2104–
2110, 2011.
25. Gabbett, TJ and Dumrow, N. Relationships between training load,
injury, and fitness in sub-elite collision sport athletes. J Sports Sci 25:
1507–1519, 2007.
37. Rhea, MR, Lavinge, DM, Robbins, P, Esteve-Lanao, J, and
Hultgren, TL. Metabolic conditioning among soccer players. J
Strength Cond Res 23: 800–806, 2009.
26. Haddad, M, Chauochi, A, Castagna, C, Wong, DP, Behm, DG, and
Chamari, K. The construct validity of session RPE during an
intensive camp in young male taekwondo athletes. Int J Sports Phys
Perform 6: 252–263, 2011.
38. Schmikli, SL, de Vries, WR, Inklaar, H, and Backx, FJG. Injury
prevention target groups in soccer: Injury characterstics and
incidence rates in male junior and senior players. J Sci Med Sport 14:
199–203, 2011.
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