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BRIEF REPORT
Effects of Respiratory Muscle Endurance Training on
Wheelchair Racing Performance in Athletes With
Paraplegia: A Pilot Study
Gabi Mueller, MSc,* Claudio Perret, PhD,† and Maria T. E. Hopman, MD, PhD‡
Objective: Respiratory muscle endurance training (RMET) has
been shown to improve both respiratory muscle and cycling exercise
endurance in able-bodied subjects. Since effects of RMET on upper
extremity exercise performance have not yet been investigated, we
evaluated the effects of RMET on 10-km time-trial performance in
wheelchair racing athletes.
Design: Pilot study, controlled before and after trial.
Setting: Spinal cord injury research center.
Participants: 12 competitive wheelchair racing athletes.
Interventions: The training group performed 30 sessions of RMET
for 30 min each. The control group did no respiratory muscle
training.
Main Outcome Measurements: Differences in 10-km time-trial
performance pre- versus postintervention.
Results: In the training group, the time of the 10-km time-trial
decreased significantly from before versus after intervention (27.1 6
9.0 vs. 24.1 6 6.6 min); this did not occur in the control group (23.3 6
2.8 vs. 23.2 6 2.4 min). No between groups difference was present
(P = 0.150). Respiratory muscle endurance increased significantly
within the training group (9.1 6 7.2 vs. 39.9 6 17.8 min) and between
groups, but not within the control group (4.3 6 2.9 vs. 6.6 6 7.0 min)
before versus after intervention.
Conclusion: There was a strong trend, with a large observed effect
size of d = 0.87, towards improved performance in the 10-km timetrial after 6 weeks of RMET.
Key Words: respiratory muscle training, exercise test, breathing
exercises, spinal cord injuries
(Clin J Sport Med 2008;18:85–88)
Submitted for publication April 26, 2007; accepted October 27, 2007.
From the *Swiss Paraplegic Research, Nottwil, Switzerland; †Swiss Paraplegic Centre, Institute of Sports Medicine, Nottwil, Switzerland; and
‡Medical Centre, Radboud University, Nijmegen, The Netherlands.
Reprints: Gabi Mueller, MSc, Swiss Paraplegic Research, CH-6207 Nottwil,
Switzerland (e-mail: [email protected]).
Copyright Ó 2008 by Lippincott Williams & Wilkins
Clin J Sport Med Volume 18, Number 1, January 2008
T
his study reveals that respiratory muscle endurance can be
increased in competitive athletes with paraplegia by isolated respiratory muscle endurance training. Our results show
preliminary indices, which may be interesting for the rehabilitation of patients with spinal cord injury.
Thirty minutes of respiratory muscle endurance training
(RMET), 5 times a week for 4 consecutive weeks, increased
respiratory muscle endurance more than 450% and leg cycling
exercise time at the anaerobic threshold by 38% in trained
able-bodied subjects.1 The effects of RMET on upper body
exercise performance have not yet been evaluated. Wheelchair
racing athletes with paraplegia, using muscles of the upper
extremities for breathing and locomotion concurrently, seem to
be an ideal group to study the effects of RMET on upper body
endurance exercise performance. We hypothesized that RMET
would improve ventilatory muscle endurance and upper body
exercise performance on a 10-km time-trial in athletes with
paraplegia.
METHODS
Twelve competitive wheelchair racing athletes with
paraplegia participated in the study. Subjects were divided as
matched pairs with respect to their lesion level and allocated
randomly either to the training group or to the control group by
toss of a coin (Table 1). The local ethics committee approved
the study and subjects provided written informed consent.
At the study’s inception, all subjects reported to the
laboratory on four separate occasions for baseline testing,
which included lung function measurements, a VO2peak test,
a 10-km time trial, and a respiratory muscle endurance test.
Thereafter, training group subjects performed RMET by
means of normocapnic hyperpnoea for 30 training sessions of
30 min each (5 sessions per week for 6 consecutive weeks),
while control group subjects performed no respiratory muscle
training. Otherwise, both groups followed their usual wheelchair training throughout the study. After 6 weeks, the 4 baseline testing sessions were repeated in the same order.
All athletes completed the VO2peak test and the 10-km
time-trial using their own racing wheelchair. They performed
the VO2peak test on a treadmill (Saturn HP Cosmos, Munich,
Germany) and started at a speed of 10 km/hour and an
inclination of 0.7%. Every 3 minutes, speed increased by 2
km/hour until volitional exhaustion.
The athletes performed the 10-km time trial on a nearly
frictionless training roller (Spinner, New Hall’s Wheels,
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Mueller et al
TABLE 1. Anthropometric and Training Data
Group
Sex
Training
M
W
M
W
M
M
Mean (SD)
Control
Mean (SD)
M
M
M
W
M
M
Height
(cm)
Weight
(kg)
Age
(years)
Lesion
Level/ASIA
Race
Class
Lesion Duration
(years)
Training Volume
(hours/week)
Training Duration
(years)
178
150
188
170
165
173
170 (13)
173
165
170
165
168
155
166 (6)
60
40
67
46
50
60
54 (10)
60
65
58
50
69
57
60 (7)
46
34
29
18
31
18
29 (10)
40
40
19
20
24
27
28 (10)
T4/B
T6/A
T6/A
L1/C
L1/C
L3/C
T53
T52
T53
T54
T54
T54
T5/A
T6/A
T8/C
T12/B
L1/C
L3/C
T53
T53
T53
T54
T54
T54
26
24
1.5
4
10
18
14 (10)
18
13
9
11
24
27
17 (7)
14
5
5
6
7.5
8.5
7.5 (3.6)
8.5
8
6
6
2.5
6.5
6.3 (2.1)
24
12
1
2
7
6
9 (9)
16
10
3
5
8
13
9 (5)
There were no significant differences between groups.
L, lumbar lesion; T, thoracic lesion; ASIA, American Spinal Injury Association.
Cambridge, MA). No information was given to the athletes
during the test other than notification of each accomplished
kilometer. Subjects simply had to complete 10 km as fast as
possible.
Subjects performed the respiratory muscle endurance
test with the RMET device (SpiroTiger Medical, Idiag AG,
Fehraltorf, Switzerland). Breathing frequency was adjusted to
reach target minute ventilation (VE), which could be maintained for 5 to 10 minutes during pretests, corresponding to an
intensity of 65% to 75% of the individual maximal voluntary
ventilation value. Either the experimenter aborted the test
if target VE could not be maintained for more than 30 s after
indication or the athlete himself stopped the test due to
exhaustion.
We used Wilcoxon’s rank-sum tests to evaluate within
groups differences between pre- and postintervention values
and Mann-Whitney-U tests to calculate between-group
differences on the pre-post change scores. Significance was
set at P , 0.05. Statistical analyses were performed with
a computer software package (Version 10.2; Systat Software;
Point Richmond, CA).
RESULTS
Respiratory muscle endurance increased significantly by
332% in the training group (P = 0.028) after RMET, while the
control group did not show any change in muscle endurance.
A significant difference existed between groups (P = 0.016;
Table 2).
Lung function values and Pimax did not change between
pre- and posttests within or between groups. Pemax increased
significantly by 25% within the training group (P = 0.028) but
showed no significant differences within the control group nor
between groups (Table 3).
The 10-km time-trial performance showed significant
within-group differences for the training group (P = 0.046) but
not for the control group (Table 4). Even if between groups
comparisons were not significantly different (P = 0.150), the
effect size of 10-km time-trial performance was high (d = 0.87).
TABLE 2. Values During Respiratory Muscle Endurance Tests
Training Group (n = 6)
Pre
Time of RMET (min)
Mean HR (bpm)
Mean VE (L/min)
Mean tidal volume (L)
Mean breathing frequency (per min)
Mean end tidal CO2 (kPa)
9.1
124
91
2.52
37
3.9
(7.2)
(13)
(28)
(0.90)
(4)
(0.7)
Post
39.9
122
91
2.58
36
3.7
(17.8)*†
(11)
(28)
(0.90)
(5)
(1.3)
Control Group (n = 6)
Pre
4.3
130
107
2.82
38
3.2
(2.9)
(17)
(18)
(0.63)
(3)
(1.0)
Post
6.6
128
107
2.83
38
3.4
(7.0)
(19)
(17)
(0.60)
(3)
(1.0)
Data are means (SD). Note that mean values are calculated over the whole test duration.
HR, heart rate; VE, minute ventilation.
*Significant between-group difference.
†Significant within-group difference.
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Respiratory Muscle Training in Wheelchair Athletes
TABLE 3. Lung Function Measurements by Body Plethysmography
Training Group (n = 6)
Pre
TLC (%)
RV (%)
FVC (%)
FEV1 (%)
FEV1/FVC (%)
PEF (%)
MVV (%)
Pimax (%)
Pemax (%)
89.2
171.6
85.3
84.5
102.1
76.8
124.8
90.8
46.4
Control Group (n = 6)
Post
(14.9)*
(31.0)
(29.0)
(26.6)
(10.8)*
(20.6)*
(61.9)
(29.3)
(11.3)
90.7
176.5
88.5
87.4
102.7
83.3
134.4
102.3
59.8
Pre
(21.8)
(35.7)
(31.3)
(28.4)
(11.2)
(28.1)
(66.7)
(17.7)
(11.2)†
69.2
144.1
94.6
101.7
114.2
104.8
118.8
104.2
52.4
Post
(8.0)
(29.6)
(30.9)
(27.5)
(10.8)
(13.3)
(12.6)
(16.7)
(16.2)
74.3
138.6
95.8
103.2
113.6
112.9
126.3
104.5
56.3
(17.1)
(38.0)
(26.0)
(23.1)
(8.8)
(19.2)
(15.3)
(17.7)
(15.4)
Data are mean percents of able-bodied predicted (SD). Note that there were no significant differences in changes from pre to post between groups.
TLC, total lung capacity; RV, residual volume; FVC, forced vital capacity; FEV1, forced expiratory volume in 1 s; PEF, peak expiratory flow;
MVV, maximal voluntary ventilation; Pimax, maximal inspiratory muscle strength; Pemax, maximal expiratory muscle strength.
*Significant between-group difference (baseline testing).
†Significant within-group difference.
Peak oxygen consumption (Table 5) showed no significant
differences before versus after intervention for within- or
between-group comparisons.
DISCUSSION
This study shows that RMET has a positive effect on
respiratory muscle endurance, while there is no effect of RMET
on maximal exercise performance (VO2peak) in wheelchair
racing athletes. Our results provide first evidence that RMET
increases upper extremity exercise performance, showing significant within training group decreases in exercise time on
a 10-km wheelchair racing time trial. Results of the 10-km time
trial should be considered with care because between-group
difference was not statistically significant due to large interindividual differences and the small size of the groups tested.
A spinal cord injury (SCI) causes lesion dependent
functional loss of respiratory muscles.2,3 Nevertheless, lung
function in our SCI subjects was normal, but Pemax was severely
decreased (Table 3). Interestingly, Pemax significantly increased
within training group after RMET. Thus, RMET seems to offer
an interesting option for the rehabilitation of subjects with SCI
to improve expiratory muscle strength. Our results further
show that RMET improves respiratory muscle endurance in
athletes with paraplegia to a similar extent as in able-bodied
individuals.1,4
Training group subjects showed a significant withingroup difference of an 11% mean decrease in time over a
10-km time trial. This result is of high practical relevance for
wheelchair racing competitions.
During upper body exercise, similar muscles are innervated for movement and breathing. Therefore, these muscles
are concurrently used. It has been shown that the ventilatory
pattern changes during upper-body exercise and exercise
endurance is decreased compared to leg exercise.5 Consequently, improvements in respiratory muscle endurance may
have a positive influence on upper-body exercise performance.
The lesion dependent differences in the amount of innervated upper-body muscle mass differ among athletes and
may therefore provide a source of variation in exercise
performance and in potential to increase upper-body endurance performance.
TABLE 4. 10-km Time-Trial Data
Training Group (n = 6)
Pre
Time of 10-km time-trial (min)
Mean VO2 as % of VO2peak
Mean heart rate (bpm)
Mean VE (L/min)
Mean tidal volume (L)
Respiratory equivalent for O2
Mean breathing frequency (per min)
Mean end tidal CO2 (kPa)
27.1
71.5
161
52.6
1.28
30.6
41.5
3.3
(9.0)
(9.9)
(13)
(18.6)
(0.33)
(2.3)*
(11.6)
(0.2)
Post
24.1
77.1
168
64.6
1.47
28.5
44.8
3.3
(6.6)†
(12.2)
(15)
(27.9)*
(0.51)†
(3.9)
(13.2)
(0.3)
Control Group (n = 6)
Pre
23.3
77.8
173
75.5
1.43
24.6
57.5
2.9
(2.8)
(4.6)
(11)
(24.3)
(0.69)
(2.0)
(17.9)
(0.4)
Post
23.2
74.6
172
68.3
1.40
25.8
52.5
3.0
(2.4)
(7.7)
(14)
(19.0)
(0.56)
(3.4)
(9.1)
(0.2)
Data are means (SD). Note that mean values are calculated over the whole test duration.
*Significant between-group difference (baseline testing).
†Significant within-group difference.
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TABLE 5. VO2peak Test Values
Training Group (n = 6)
Pre
VO2peak (mL/min/kg)
HRpeak (bpm)
VEpeak (L/min)
Tidal volumepeak (L)
Breathing frequencypeak (per min)
41.2
185
96
1.97
60
(10.6)
(16)
(31)
(0.61)
(13)
Post
40.3
184
94
1.96
62
(6.8)
(14)
(30)
(0.56)
(14)
Control Group (n = 6)
Pre
38.4
191
109
2.08
77
(7.7)
(7)
(22)
(0.69)
(20)
Post
37.4
190
114
2.03
76
(6.9)
(6)
(25)
(0.82)
(21)
Note that there were no significant differences in changes from pre to post between groups.
VO2, oxygen uptake; HR, heart rate; VE, minute ventilation.
CONCLUSION
REFERENCES
This study shows that 6 weeks of RMET increases
respiratory muscle endurance in wheelchair-racing athletes.
Because there was a large observed effect size in the 10-km
time trial of d = 0.87, there is evidence that 6 weeks of RMET
may also improve upper-body exercise performance.
1. Boutellier U, Buchel R, Kundert A, et al. The respiratory system as an
exercise limiting factor in normal trained subjects. Eur J Appl Physiol
Occup Physiol. 1992;65:347–353.
2. Haas A, Lowman EW, Bergofsky EH. Impairment of respiration after spinal
cord injury. Arch Phys Med Rehabil. 1965;46:399–405.
3. Ohry A, Molho M, Rozin R. Alterations of pulmonary function in spinal
cord injured patients. Paraplegia. 1975;13:101–108.
4. Boutellier U, Piwko P. The respiratory system as an exercise limiting factor
in normal sedentary subjects. Eur J Appl Physiol Occup Physiol. 1992;64:
145–152.
5. Celli B, Criner G, Rassulo J. Ventilatory muscle recruitment during
unsupported arm exercise in normal subjects. J Appl Physiol. 1988;64:
1936–1941.
ACKNOWLEDGMENTS
We thank Prof. Dr. Hans Folgering for critical reading
of the manuscript and all subjects for their enthusiastic
participation.
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