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Journal of Exercise Physiologyonline
June 2014
Volume 17 Number 3
Official Research Journal of
Editor-in-Chief
Tommy
the American
Boone, PhD,
Society
MBA
of
Exercise
Physiologists
Review
Board
Todd Astorino, PhD
ISSN 1097-9751
Julien Baker,
PhD
Steve Brock, PhD
Lance Dalleck, PhD
Eric Goulet, PhD
Robert Gotshall, PhD
Alexander Hutchison, PhD
M. Knight-Maloney, PhD
Len Kravitz, PhD
James Laskin, PhD
Yit Aun Lim, PhD
Lonnie Lowery, PhD
Derek Marks, PhD
Cristine Mermier, PhD
Robert Robergs, PhD
Chantal Vella, PhD
Dale Wagner, PhD
Frank Wyatt, PhD
Ben Zhou, PhD
Official Research Journal
of the American Society of
Exercise Physiologists
ISSN 1097-9751
JEPonline
Effect of Inspiratory Muscle Training and Core
Exercise Training on Core Functional Tests
Lorrie R. Brilla1, Teresa H. Kauffman2
1
Western Washington University, Bellingham, WA, 98225, 2Kent
School District Kent, WA, 98030
ABSTRACT
Brilla LB, Kauffman TH. Effect of Inspiratory Muscle Training and
Core Exercise Training on Core Functional Tests. JEPonline
2014;17(3):12-20. This study tested the effects of inspiratory
muscle training on core function compared to a typical core training
program. Subjects consisted of 32 healthy, recreationally active
individuals (18-25 yrs of age) who were randomly assigned to one
of three groups: Control (C), Inspiratory Muscle Training (IMT), and
Core Exercise Class (AbEx). IMT performed inspiratory muscle
training for 6 wks at 85% maximal inspiratory pressure (MIP), while
AbEx performed standard core training of the same duration. Core
function was assessed pre- and post-training using a side bridge,
prone extension and Stabilizer test of transversus abdominis (TrA)
function. MIP was also assessed before and after the treatment.
Significant interaction effect was observed for MIP (P≤0.05). IMT
MIP increased from 1.06 ± 0.37 to 1.71 ± 0.41 cm H2O (P≤0.05)
with no significant pre-post changes in C (1.09 ± 0.29 to 1.15 ±
0.36 cm H2O) or AbEx (0.78 ± 0.31 to 0.88 ± 0.33 cm H2O). A
significant interaction effect was noted in prone extension (P≤0.05).
Time increased in AbEx from 114.0 ± 53.0 to 154.0 ± 77.6 sec
(P≤0.05), with no significant changes in C (158.9 ± 75.5 to 152.1 ±
62.6 sec) or IMT (132.0 ± 39.2 to 132.8 ± 40.3 sec). A significant
interaction for the Stabilizer test of TrA function was found
(P≤0.05). The IMT group improved from -6.9 ± 12.6 to -10.0 ± 11.0
mmHg (P≤0.05), with no significant changes in the Control (-5.0 ±
12.1 to -4.8 ± 13.4 mmHg) or AbEx groups (-15.0 ± 5.8 to -9.7 ±
10.4 mmHg). There were no significant differences (P≥0.05) in the
side bridge test. Six weeks of core training and inspiratory muscle
training improve core function and target different muscles.
Key Words: Core Function, Inspiratory Muscle Training
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INTRODUCTION
Strength training for the abdominal and lower back muscles is used for many purposes, including
the improvement of athletic performance and relieving low back pain. Including core stability as
part of an overall conditioning program for athletes has been shown to improve athletic
performance (14). Core training alone, however, has not been shown to have an impact on athletic
performance (1). Core function also influences low back pain (8), and it has been shown that
recruitment of core muscles is altered in people with low back pain (11). The transversus
abdominis (TrA) muscles function as a key component of low back pain treatment and prevention
(8,11) and those without a history of low back pain activate the TrA before movement of the trunk
or extremities, while those with low back pain activate the TrA after the movement is initiated (11).
Training these recruitment patterns, especially the recruitment of the TrA, might help prevent low
back pain (11).
Yoga and Pilates are popular forms of exercise. Both incorporate breathing with movements.
Strength and stability gains observed in these programs may be related to the focus on breathing
(7). A Pilates program improves a person’s ability to contract the TrA, which is an important skill for
core strength and stability (7). The deep breathing used during yoga can increase core muscle
activation and improve cardiorespiratory function (21).
Deep breathing exercises have been shown to require more abdominal muscle activity than
abdominal crunches (16), and it is suggested that breathing exercises can be incorporated into a
core training program in order to achieve maximum benefits. Inspiratory muscle training is one way
to train the muscles used during respiration (5). Research has consistently shown that inspiratory
muscle training improves respiratory muscle strength, but how this influences core stability is
unknown (4,13,15,19). Alternatively, abdominal exercises, such as sit ups and leg lifts, compress
the abdomen, leading to increased diaphragmatic work. The abdominal exercises yielded different
pressures, some greater than 50% of the pressures generated during a maximal inspiratory
maneuver (20). Some of these exercises generated high enough pressures to help strengthen the
diaphragm.
Thus, the purpose of this study was to investigate the influence of inspiratory muscle training on
core function compared to a typical core training program. It seeks to determine if increased
strength of the respiratory muscles shows similar improvements on tests of core function and
stability as a standard core exercise training program.
METHODS
Subjects
Thirty-two healthy, recreationally active subjects (18-25 yrs old) were randomly assigned to one of
three groups: Control (C), Inspiratory Muscle Training (IMT), and Core Exercise Class (AbEx). All
subjects were free of low back pain or injury. The IMT and Control subjects were not currently
participating in a core training program. Data are reported for 10 IMT subjects (5 males, 5
females), 12 AbEx subjects (all females), and 10 Control subjects (3 males, 7 females). The
subjects’ characteristics are presented in Table 1. All subjects read and signed an informed
consent prior to data collection. This study was approved by the Human Subjects Review
Committee.
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Table 1. Description of the Subjects.
Group
Age
Weight
Height
BMI
(yrs)
(kg)
(cm)
(kg·m-2)
IMT
21.8 ± 1.7
78.1 ± 8.5
178 ± 7.8
24.0 ± 2.1
AbEx (Core)
19.7 ± 1.5
61.5 ± 9.8
164 ± 4.8
22.9 ± 3.1
Control
22.7 ± 1.4
62.5 ± 7.7
167 ± 7.3
22.2 ± 1.9
Mean ± SD for: IMT = Inspiratory Muscle Training; AbEx = Core Exercise Class; BMI = Body Mass Index
Procedures
A three group repeated measures design was used to study core function. Supervised IMT was 5
d·wk-1 for 6 wks, 10 to 15 min totaling approximately 60 min·wk-1. Data were excluded from the
subjects who attended fewer than 90% of the training sessions. The subjects in the AbEx group
were required to attend a 30-min class 2x·wk-1 during the duration of the study. Less than 90%
attendance to the classes excluded the subjects’ data from the results. The Control group received
no training.
Data Collection
Tests of core function included a timed prone extension endurance test, side bridge endurance
test, and a test of transversus abdominis (TrA) function. During the prone back extension
endurance test, the subject’s lower extremities were supported and the subject held the upper
body in a position parallel to the floor while lying on an examining table. During the side bridge test,
each subject supported their body on one hand and the same side foot with the spine in a straight,
neutral position. Subjects chose their preferred side for this test. Maximal times for the endurance
tests were recorded in seconds. Breaking from the correct position ended the test.
The test of TrA function measured the change in pressure during TrA contraction. The subjects
began the test lying prone on a flat surface. The Stabilizer (Chattanooga Group, Hixson, TX), an
inflatable pad, was positioned under the abdomen and inflated to 70 mmHg. The subjects were
instructed to raise their abdomen away from the pad without appreciably moving the spine or pelvis
and hold that position for 5 sec. Change in pressure was recorded from the Stabilizer unit. A
negative change in pressure indicated contraction of the TrA. One practice test was performed,
which was followed by three trials. The highest negative pressure value or lowest positive value of
the three was used as the subject’s score.
Maximal inspiratory pressure (MIP) was measured using a device engineered at Western
Washington University by Scientific Technical Services. The MIP was conducted during pre- and
post-testing for the AbEx (core) training group and the Control group and weekly for the IMT group.
Subjects performed the maneuver while standing. They were instructed to perform a maximal
exhalation to residual volume, then, perform a maximal forced inhalation. The procedure was
repeated two times allowing at least a 30-sec rest between each measurement. The highest value
was recorded in cm H2O.
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The IMT subjects performed IMT under supervision. Five sets of 12 repetitions were performed
with a Powerbreathe (Southam, Warwickshire, UK) device. IMT was performed 5 d·wk-1 for 6 wks.
Intensity was set at 80% MIP, which was adjusted based on gains in MIP as training progressed.
MIP was tested at the beginning of each week to maintain training intensity at 80%.
The AbEx (core training) group participated in 30 min group fitness classes 2x·wk-1. The training
focused on abdominal muscles for 6 wks. Typical exercises consisted of various supine curl-ups,
crunches, and stability ball exercises. Although the Control group did not participate in any training,
the subjects were tested at the same time the IMT and AbEx (core) subjects were tested.
Statistical Analyses
A two-way mixed analysis of variance (ANOVA) was performed with the factors group and time
(SPSS version 16). Group had three levels (IMT, AbEx, and Control). Time had two levels (preand post-intervention). If a significant change was found, post hoc analysis was performed. The
alpha level was set at a probability of P≤0.05.
RESULTS
The data are reported for 10 IMT subjects (5 males, 5 females), 12 AbEx (core) subjects (all
female), and 10 Control subjects (3 males, 7 females) as shown in Table 1. There were no
differences in age, height, and body mass index between the three groups, but the IMT group had
a greater body weight. This was likely due to the greater number of male subjects.
The results for the AbEx (core) functional tests are presented in Table 2. On the side bridge test,
there was no significant interaction. All three groups showed a significant increase in time on the
side bridge test (P=0.002). The IMT group increased mean time by 17%, while the AbEx (core) and
the Control groups improved ~10%. Large standard deviations were observed in all three groups
Table 2. Core Functional Tests (Mean ± SD).
Side
Bridge
IMT
IMT
AbEx (Core)
AbEx (Core)
Control
Control
(Pre-Test)
(Post-Test)
(Pre-Test)
(Post-Test)
(Pre-Test)
(Post-Test)
71.0 ± 28.8
85.5 ± 41.2
66.9 ± 21.7
74.5 ± 21.5
77.7 ± 29.4
86.8 ± 26.1
132.0 ± 39.2
132.8 ± 40.3
114.0 ± 53.0
154.0 ± 77.6
158.9 ± 75.5
152.1 ± 62.6
-6.9 ± 12.6
-10.0 ± 11.0
-15.0 ± 5.8
-9.7 ± 10.4
-5.0 ± 12.1
-4.8 ± 13.4
(sec)
Prone
Extension
(sec)
Stabilizer
(mmHg)
A significant interaction was found for the prone extension test (P=0.014). The post hoc analysis
indicated that the AbEx (core) group improved significantly more than the IMT and Control groups
(P=0.034). Figure 1 shows the results for the prone extension endurance test. No significant
change was found in the IMT or Control group. Figure 2 shows there was a significant interaction
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for the Stabilizer test (P=0.038). The mean score for the IMT group decreased, which indicates
improved performance because contraction of the transversus abdominis lifts the abdomen up and
away from the Stabilizer pad causing a decrease in pressure. During exhalation, most people
perform a contraction of the transversus abdominis without the rectus abdominis (3). The AbEx
(core) group increased the mean score. The Control group showed no change in performance.
There were no significant differences between the three groups at baseline.
Figure 1. Prone Extension
Figure 2. Stabilizer
Maximal inspiratory pressure (MIP) data are
presented in Table 3. A significant interaction for
MIP was found (P=0.000), as shown in Figure 3.
There was a significant increase in the mean
score for the IMT group. The mean increase in
the AbEx (core) group and the Control group
were not significant. Pre-test scores showed a
significant difference between MIP for the AbEx
(core) group and the Control group (P=0.034).
No significant difference was found between the
IMT group and the AbEx (core) or IMT and the
Control group before training.
Figure 3. Maximal Inspiratory Pressure
Table 3. Maximal Inspiratory Pressure.
Group
Pre-Test (cm H2O)
Post-Test (cm H2O)
IMT
1.063 ± 0.372
1.718 ± 0.418
AbEx (Core)
0.782 ± 0.316
0.887 ± 0.332
Control
1.093 ± 0.290
1.157 ± 0.367
Mean ± SD for: IMT = Inspiratory Muscle Training; AbEx = Core Exercise Class; BMI = Body Mass Index
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DISCUSSION
Tests of core function showed that inspiratory muscle training (IMT) and core training (AbEx)
improved the function of the core muscles. All three groups showed a significant improvement on
the side bridge test. The greatest improvement was observed in the IMT group, which uses the
diaphragm to contribute to intra-abdominal pressure. The increase in strength of the diaphragm
may contribute to an improved stabilization of the spine that is required in the side bridge test (10).
Additionally, the abdominal draw-in maneuver activates contraction of the transversus abdominis
muscle (TrA). This action is similar to inspiring against a resistance. When the thickness of the TrA
was measured by ultrasound to find the activation ratio, the TrA was activated in the side bridge
test in both healthy and low back pain patients (9).
The AbEx (core) training group was the only group to significantly improve performance on the
prone extension test. The training for the AbEx (core) program targeted the extensor muscles in
addition to the other muscles of the trunk. Similar improvements have been seen in other research
on AbEx (core) training (1,8). Back extensor endurance can be improved by core training, while
IMT did not have an effect on back extensor endurance on the prone extension test.
Improvements were observed in the IMT group over the core training group in the Stabilizer test of
TrA contraction. An acceptable level of function is seen by a negative pressure difference of 6 or
greater (17). The mean score of the IMT group met this level at the post-test. Transversus
abdominis activity is increased with forced exhalation (17). Although IMT focuses on inspiratory
muscles, exhalation may also have been effected. A meta-analysis of respiratory muscle training
confirmed better muscle endurance in muscles other than those targeted (12).
The AbEx (core) training group showed a rise in mean pressure difference indicating that core
training had a detrimental effect on TrA contraction. Only one out of the 12 subjects improved after
the 6 wks of core training. A higher or more positive score may be a result of a contraction of other
abdominal muscles, especially the rectus abdominis (17). A correct contraction of the TrA may be
accompanied by the contraction of the internal oblique muscles. However, contraction of these
muscles would not impact the pressure change observed on the pressure biofeedback unit (17).
During the AbEx (core) training program, the subjects would have been contracting the rectus
abdominis while performing supine trunk flexion exercises (6). This training may have contributed
to the difference seen in the TrA contraction in the core training group. The results are consistent
with other research that examined the effects of abdominal curls and Pilates training on function of
the TrA (7). The control group was very consistent from baseline to post-test.
Inspiratory muscle training significantly improved maximum inspiratory pressure (MIP), which is
consistent with other research using similar training protocols (5,18,22). An improvement in fitness
may also have contributed to an improvement in MIP (2), but no change was observed in exercise
or physical activity during the 6 wks of training.
Specificity of training was an important projection of performance on the tests of core muscle
function. Six weeks of IMT showed an improvement in core muscle function by side bridge
improvement, as has been implicated in other studies on non-respiratory muscle activation and
influence on respiratory muscles such as the diaphragm (2,12). Function of the TrA improved in the
IMT group. Back extensor endurance was shown to improve with 6 wks of core training. Improved
performance on these core tests indicates it is possible that IMT can be used to improve some
aspects of core muscle function in healthy subjects. However, it is important to remember that IMT
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and AbEx (core) training impact the core muscles differently. Yoga and Pilates training include
exercise for the core muscles as well as breathing practice. There is likely a benefit to using a
combination of these training programs to maximize results and improve core function.
CONCLUSIONS
The results of this study may be used when designing core training programs. Inspiratory muscle
training can have a positive effect on core muscle function independent of specific core training.
Thus, it may be a beneficial supplement to a traditional core training program. IMT may also be
used to improve core function in subjects with physical limitations that prevent them from
performing traditional core exercises.
ACKNOWLEDGMENTS
Grateful acknowledgement to the Wade King Student Rec Center for providing a trained Ab Lab
instructor for the core training program.
Address for correspondence: Lorrie R. Brilla, PhD, PEHR Department, Western Washington
University, Bellingham, WA 98225-9067, Email: Lorrie.Brilla@wwu.edu
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