Resistive respiratory muscle training improves and maintains endurance swimming performance in divers.

Abstract

Respiratory work is increased during exercise under water and may lead to respiratory muscle fatigue, which in turn can compromise swimming endurance. Previous studies have shown that respiratory muscle training, conducted five days per week for four weeks, improved both respiratory and fin swimming endurance. This training (RRMT-5) consisted of intermittent vital capacity breaths (twice/minute) against spring loaded breathing valves imposing static and resistive loads generating average inspiratory pressures of approximately 40 cmH2O and expiratory pressures of approximately 47 cmH2O. The purpose of the present study (n = 20) was to determine if RRMT 3 days per week (RRMT-3) would give similar improvements, and if continuing RRMT 2 days per week (RRMT-M) would maintain the benefits of RRMT-3 in fit SCUBA divers. Pulmonary function, maximal inspiratory (P(insp)) and expiratory pressures (P(exp)), respiratory endurance (RET), and surface and underwater (4 fsw) fin swimming endurance were determined prior to and after RRMT, and monthly for 3 months. Pulmonary function did not significantly improve after either RRMT-3 or RMMT-5; while P(insp) (20 and 15%) and P(exp) (25 and 11%), RET (73 and 217%), surface (50 and 33%) and underwater (88 and 66%) swim times improved. VO2, VE and breathing frequency decreased during the underwater endurance swims after both RRMT-3 and RRMT-5. During RRMT-M P(insp) and P(exp) and RET and swimming times were maintained at post RRMT-3 levels. RRMT 3 or 5 days per week can be recommended to divers to improve both respiratory and fin swimming endurance, effects which can be maintained with RRMT twice weekly.

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Copyright © 2007 Undersea and Hyperbaric Medical Society, Inc 169
UHM 2007, Vol. 34, No.3 – Respiratory training improves diver performance.
Resistive respiratory muscle training
improves and maintains endurance
swimming performance in divers.
P. LINDHOLM1, J, WYLEGALA1,3, D. R. PENDERGAST1,2 , C.E.G. LUNDGREN1,2
Submitted 8-15-06; Accepted 12-9-06
1Center for Research and Education in Special Environments, and 2Departments of Physiology, 3Rehabilitation Sciences at the
University at Buffalo, Buffalo, NY 14214. Dr. Lindholm’s present address is: Department of Physiology, Karolinska Institute,
Sweden
Lindholm P, Wylegala J, Pendergast DR, Lundgren CEG. Resistive respiratory muscle training improves
and maintains endurance swimming performance in divers. Undersea Hyperb Med 2007; 34(3):169-180.
Respiratory work is increased during exercise under water and may lead to respiratory muscle fatigue, which
in turn can compromise swimming endurance. Previous studies have shown that respiratory muscle training,
conducted five days per week for four weeks, improved both respiratory and fin swimming endurance. This
training (RRMT-5) consisted of intermittent vital capacity breaths (twice/minute) against spring loaded
breathing valves imposing static and resistive loads generating average inspiratory pressures of ~ 40 cmH2O
and expiratory pressures of ~ 47 cmH2O. The purpose of the present study (n=20) was to determine if RRMT
3 days per week (RRMT-3) would give similar improvements, and if continuing RRMT 2 days per week
(RRMT-M) would maintain the benefits of RRMT-3 in fit SCUBA divers. Pulmonary function, maximal
inspiratory (Pinsp) and expiratory pressures (Pexp), respiratory endurance (RET), and surface and underwater
(4 fsw) fin swimming endurance were determined prior to and after RRMT, and monthly for 3 months.
Pulmonary function did not significantly improve after either RRMT-3 or RMMT-5; while Pinsp (20 and 15%)
and Pexp (25 and 11%), RET (73 and 217%), surface (50 and 33%) and underwater (88 and 66%) swim times
improved. V O2, ,V E and breathing frequency decreased during the underwater endurance swims after both
RRMT-3 and RRMT-5. During RRMT-M Pinsp and Pexp and RET and swimming times were maintained at
post RRMT-3 levels. RRMT 3 or 5 days per week can be recommended to divers to improve both respiratory
and fin swimming endurance, effects which can be maintained with RRMT twice weekly.
..
INTRODUCTION

respiratory work during underwater exercise
is increased due to the hydrostatic pressure
differences across the chest as well as increased
flow resistive respiratory work (1,2). Previous
studies have demonstrated an increased work of
breathing at rest and particularly during exercise
while utilizing self-contained underwater
breathing apparatus (scuba) at depth (2). The
increased work of breathing is principally
due to added airflow resistance from both the
apparatus and increased gas density (1,3,4).
This is likely to require augmented oxygen
delivery via increased blood flow to respiratory
muscles. It has recently been shown in
healthy individuals that ventilatory limitations

In comparison to exercise on land,
may cause a reduction of maximal exercise
performance on land (5,6,7,8). The weakened
exercise capacity has been attributed to
a reduction in locomotor muscle oxygen
transport secondary to diminished locomotor
muscle blood flow (6,9,10). In several studies
on land, respiratory muscle fatigue has been
reported as a contributing factor to reduced
maximal and endurance exercise performance
(5,6,7,8,11,12,13). These same factors may
also limit exercise performance in divers.

Leith and Bradley (14) were the first to
demonstrate that respiratory muscle strength
and endurance can be improved through specific
respiratory muscle training (RMT). More
recently, significant improvements in whole-
body exercise endurance on land following
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UHM 2007, Vol. 34, No.3 – Respiratory training improves diver performance.
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METHODS
The study protocol was approved by the
Human Subjects Institutional Review Board of
the University at Buffalo. Informed consent was
obtained from the subjects prior to enrollment
in the study. This study compared the effects
resistance respiratory muscle training (RRMT)
performed 3 days per week with RRMT five
days per week, for 4 weeks, on respiratory and
fin swimming performance in trained scuba
divers. In addition, the potential usefulness of a
two day per week RRMT (maintenance RRMT-
M), after RRMT-3, was evaluated over a three
month period.
Subjects
Twenty experienced and practicing
SCUBA divers were recruited from the local
diving community. The physical characteristics
of the subjects in the RRMT-3 and RRMT-M
were: age 22.9 ± 5.0 (SD) years, height 179.8
± 28.0 cm, and weight 81.7 ± 12.7 kg, and for
RRMT-5: age 25.0 ± 5.0 (SD) years, height
179.2 ± 5.1 cm, and weight 81.9 ± 7.7 kg.
The subjects were divided into two
groups, one doing RRMT three days per week
(RRMT-3) and one five days per week (RRMT-
5). Both performed 4 weeks of fin swimming
training followed by RRMT for 4 weeks. The
RRMT-3 group also did RRMT-M.

Fin Training
To ensure that all subjects had uniform
fitness for fin swimming, and that fitness would
not influence the data collected pre- or post-
RRMT, all subjects underwent fin training for
four weeks (3 days/week) prior to participation
in the RRMT. Fin training was conducted in
an annular pool (60 m circumference) with
the subjects’ speed paced by a computerized
underwater pace-light system using a training
program previously shown to optimally
improve V O2max and fitness in swimmers (24).
The same model of fins was worn by all
subjects (US Divers-Blades, Aqua-Lung Corp,
.
specific respiratory muscle training have been
documented in elite athletes (8,15,16,17,18,19).
It has recently been shown in our laboratory that
resistive RMT (RRMT) which is performed by
vital capacity maneuvers against spring loaded
breathing valves imposing about 50 cmH20
inspiratory and expiratory opening pressures
(which is 25 -50% of max pressures) five days
per week for four weeks significantly improved
swimming endurance at the surface and at 1.22
m under water (referenced to the membrane
of a back-mounted breathing regulator) (20).
These improvements were greater than those
achieved by voluntary isocapnic hyperpnea
which has been employed in many other land
based studies (8,15,16,17,18,19). Training five
days per week may be too intense to maximize
improvements in respiratory and fin swimming
muscles. We reasoned that reducing the number
of training days to three may result in greater
improvements in swimming performance as
has recently been shown for locomotor muscles
(21,22,23). On the other hand, three days per
week for 4 weeks of RRMT may not provide
a sufficient stimulus for adaptation and thus
performance improvement may not occur, or
be less that of RRMT-5.
The purpose of this study therefore, was
to evaluate whether resistive respiratory muscle
training three days per week for four weeks
could improve respiratory function and surface
swimming (with snorkel) and underwater
swimming performance while utilizing scuba
to the same degree as previously shown for
a training schedule of five days per week for
four weeks (20). In addition, we hypothesized
that the improvements after RRMT-3 could be
sustained over three months by RRMT twice
per week (RRMT-M).
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Vista, CA) for all swimming. Three 10-minute
fin swimming periods, interspersed with 10-
minute rest intervals were performed during
each training session. The pace of each 10-
minute swimming interval was established to
require an effort of approximately 80%, 90%,
and >95% of maximum heart rate, respectively.
Heart rates were monitored with Polar heart rate
monitors (Polar Electro Inc., Lake Success, New
York). After the fin training period and during
the 4 weeks of RRMT and during the three
months of RRMT-M, all subjects participated
in a maintenance swim program twice per
week (three 10-minute swim periods, paced at
60-65% maximum heart rate, interspersed with
10 minute rest periods).
Pre- and Post-RMT Testing
Pulmonary function testing
A Morgan Spiroflow Spirometer Model
#131 (PK Morgan Ltd., Rainham, Gillingham,
Kent, UK) was used to obtain maximal voluntary
ventilation in 15 seconds (MVV), slow vital
capacity (SVC), forced vital capacity (FVC),
and forced expiratory volume in one second
(FEV1). All of these variables were recorded
in accordance with ATS standards and are
reported at BTPS. Respiratory muscle strength
was estimated from measurements of maximal
inspiratory pressure (PImax) at residual volume
(RV) and expiratory pressure (PEmax) exerted
at total lung capacity (TLC). These pressures
were measured with a manometer connected to
the mouthpiece. A small hole in the manometer
system generated a leak that prevented the use
of buccal muscles to generate false pressure
readings. A timed, isocapnic respiratory muscle
endurance test (RET) was also performed.
Using a tidal volume of approximately 50%
SVC and a frequency determined by dividing
60% of the MVV value by the tidal volume,
subjects breathed into a mouthpiece and
rebreathing bag (to maintain normocapnia)
until they were unable to maintain the target
ventilation presented to each subject on the
computer display (20).
Maximal V
Surface Swimming
Paced surface V
prior to and after RRMT. Using fins, subjects
swam at the surface following a monitoring
platform that paced swimming speed and on
which data were collected. The velocity was
increased from 0.4 m/s in 0.1 m/sec increments
every three minutes until the diver could no
longer maintain the speed. Via a two-hose
mouth piece expired gases were collected in
“Douglas” bags during the last minute of each
speed segment for determination of V
venous blood sample was taken 5-7 min post-
swim for lactate (anaerobic metabolism).
Expired gas volume was measured with a dry
gas meter (Harvard Model#AH-50-6164) and
CO2 and O2 concentrations were analyzed with
the previously calibrated mass spectrometer
(MGA1100, Perkin-Elmer, Pomona, CA).
Standard equations were used to calculate V
and V CO2 and values were expressed at standard
temperature, pressure dry gas (STPD).
.
O2 determined during
.
O2max tests were conducted


.
O2, a
.
O2
.
Swimming Endurance at the Surface
Subjects swam with fins on the surface,
paced by the underwater lights at a rate requiring
an effort of approximately 70-75% of maximal
heart rate, until they could no longer maintain
the pace. Heart rates (HR) throughout and post-
swim plasma lactate levels were determined as
described above.
Swimming Endurance Underwater
Prior to the underwater endurance swim
test, all subjects underwent a familiarization
trial on the equipment. For the underwater
fin-swim endurance test at a depth of 1.22 m
(referenced to the membrane of a back-mounted
breathing regulator) the subject maintained a
prone position on a platform with shoulders
against a padded harness. The platform could
slide with very low friction on a frame fastened
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UHM 2007, Vol. 34, No.3 – Respiratory training improves diver performance.
172
to the pool wall. A pulley system incorporated
a weight which imposed a rearward pull on the
diver via the platform. The weight was kept off
the bottom of the pool as long as the subject’s
swimming effort generated enough forward
thrust on the platform; his inability to keep
the weight suspended marked the end of the
endurance swim. The weight the subject had to
keep suspended with his swimming effort was
set to require a V
O2 of 70-75 % (~ 2.0 l/min) of
the subject’s individual swimming V
mean weight used by all subjects was 5.62 ±
1.35 kg.
The subject breathed from a two-hose/
two-stage balanced regulator (Royal Aqua-
Master #747709, Aqua Lung Corp, Vista, CA)
supplied with breathing air from a standard
tank (80 cu ft, 3000 psi). The breathing gear
was adjusted to impose a breathing resistance
equal to the highest acceptable flow resistance
as recommended for scuba (10-15 cm negative
static lung load) (1,2). Expired gases were
collected by the two hoses of the regulator
being attached via PVC pipes and valves (2 ½
in diameter)to a pressurized “bag in the box”
containing a Douglas air bag. The box pressure
was automatically equilibrated to the water
pressure acting on the chest (2 psi) by a scuba
breathing regulator placed under water at the
proper depth relative to the subject’s chest.
Expired gas was directed either into the bag,
into the box, or back out through the exhaust
side of the regulator depending upon the stage
of gas collection or gas analysis. Expired
gas was collected for one min, every fourth
min, depressurized to one atmosphere, and
analyzed for volume with a calibrated dry gas
meter, temperature (Yellow Springs Instrument
Co.), and CO2 and O2 fractions by a calibrated
mass spectrometer (MGA1100, Perkin-Elmer,
Pomona, CA). Standard equations were used to
calculate V
O2 (STPD) and V
rates were monitored every 4 minutes. Five
minutes after the underwater endurance swim
the divers completed pulmonary function
testing as well as maximal Pexp and Pinsp.
.
.
O2max. The
..
E (BTPS). Heart
Resistive Respiratory Muscle
Training (RRMT)
After completing all base line testing,
subjects were randomly assigned to either
RRMT-3 or RRMT-5. Training for all
protocols was 30 min/day for 4 weeks. The
training devices consisted of a nose clip and
a mouthpiece with a pressure transducer, the
output of which was registered on a laptop
computer. The mouthpiece was fitted with
spring loaded expiration and inspiration valves
imposing opening pressures of 70.1 ± 16.1(SD)
and 61.0 ± 9.6 cmH2O and sustained pressures
of 46.6 ± 4.8 and 40.1 ± 3.3 cm H2O. Thus the
training device generated a combination static/
resistive load. The laptop computer was used
to pace the breathing frequency and to record
each RRMT session. A “timer” displayed on
the computer screen, along with an audible
tone, was used to prompt each training breath.
At time zero, the subject expired to RV, put the
mouth piece in the mouth and took a full vital
capacity inspiration followed by a complete
exhalation to RV. The subject then removed
the mouthpiece, breathed normally, and waited
for the next timed cycle. This procedure was
repeated every 30 sec for 30 min. Thus, the
subject performed 60 vital capacity breaths
against resistance during each training session.
Each subject performed one RRMT
session per week under the supervision of
the investigator. The subjects’ adherence to
prescribed RRMT schedules during training
at home was ascertained by weekly review of
the laptop recordings of the ventilatory pattern
used during each training session.


STATISTICAL ANALYSIS

3 and RRMT-5 data for surface endurance
swims, pulmonary function tests, underwater
endurance swim times and related variables
were analyzed by a one-way ANOVA with
Pre- and post-RMT data for RRMT-
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UHM 2007, Vol. 34, No.3 – Respiratory training improves diver performance.
173
repeated measures (P≤ 0.050). These variables
included pulmonary function data, swim time,
V
O2, V E (total ventilation), VT, fb, lactate and
heart rate (HR) and are shown in Tables 1 to 3
as the absolute mean and standard deviations
of the group data. Normalizing for differences
in pre-RRMT data the relative improvement
in swimming endurance for each subject was
also calculated in percent and the means and
standard deviations of those calculations are
shown in Fig. 1.
..
RESULTS
All subjects in both groups complied
with the protocol and all their data are included
in the analysis.
Pulmonary function
The data for pulmonary function and
respiratory endurance are shown in Table 1, and
Figure 2. There were no significant changes
in VC, FEV1, and FVC for either RRMT-3 or
-5, while MVV increased significantly only
after RRMT-3 (18%). After RRMT-3 and
RRMT-5, respectively, significant increases
were recorded in Pexp (20% and 15%) and in
Pinsp (25% and 11%). In addition, respiratory
endurance increased 73% after RRMT-3 and
217% after RRMT-5.

V
Comparing pre to post-RRMT for either
the 3 or 5 day RRMT during the progressive
velocity surface swim tests there were no
.
O2max swim
Fig. 1. The average percentage increases (±SD) Pre-
to Post-RRMT in surface (left panel) and underwater
swimming endurance (right panel) are plotted for
RRMT-5 (5 d/w) and RRMT-3 (3 d/w). The * indicates
a significant improvement from pre-RRMT. The %
improvements in individual subjects were not different
between RRMT-3 and RRMT-5.
Table 1. Comparison of respiratory performance pre-
and post- RRMT-3 and RRMT-5. Values are mean ± SD
for all variables. Significant differences between pre-
RMT recordings are shown by the * for each group.
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