JEPonline
Journal
of
Exercise
Physiologyonline
Official
Journal of the American
Society
of Exercise Physiologists (ASEP)
ISSN
1097-9751
An
International Electronic Journal
Volume
3 Number 2 April 2000
Fitness
and Training
The Effect Of
Training While Breathing Oxygen-Enriched Air On Time-To-Exhauston And Aerobic
Capacity
W.
JEFFREY ARMSTRONG, DEAN E. JACKS, JAMES SOWASH, and FREDRICK F. ANDRES
Department of Health
Promotion and Human Performance, Exercise Physiology Laboratory, University
of Toledo, Toledo, OH 43606
W. JEFFREY ARMSTRONG,
DEAN E. JACKS, JAMES SOWASH, and FREDRICK F. ANDRES. The
effect of training while breathing oxygen-enriched air on time-to-exhaustion
and aerobic capacity. JEPonline,
Vol 3, No 2, 2000. Seventeen moderately-trained subjects (21±4
yr; 176.81±12.84 cm; and 74.04±12.31 kg, mean±SD)
completed a familiarization trial, a graded cycle ergometer test (VO2peak),
and a time-to-exhaustion cycling test at ~80% VO2peak
(TTE). Subjects were then match paired and randomly assigned (single
blind) to train for 40 min, 3 d/wk for 5 wk while breathing room air or
~80% O2. Each
was asked to pedal the cycle ergometer as fast as possible at the resistance
estimated to be 60% VO2peak
at 75 rpm and remain between 70-90% of age-predicted HRmax. The workload
was increased 0.25 kp at the beginning of weeks 2, 4, and 5. Following
training, VO2peak
and TTE were repeated. Doubly MANOVA repeated measures revealed a
significant improvement in VO2peak
and TTE (3.20±0.88 L/min to 3.55±0.90 L/min and 899.46±506.49
s to 2925.02±2044.76 s, respectively, (p = 0.002) and no significant
difference between the treatments across time for VO2peak
and TTE combined (p = 0.662). Student’s t-test for group differences
on total work output was not significant (p = 0.328). Thus, cycle
training with oxygen-enriched air did not significantly enhance endurance
performance and muscle function relative to exercise training when breathing
room air in moderately-trained subjects at sea level.
Key Words: Cycle
ergometer, Ergogenic aids, Exercise, Endurance, Hyperoxia, Performance
INTRODUCTION
The physiological benefits of breathing
oxygen-enriched air during an acute bout of exercise are well-documented
(3-12,15). Recently, Knight
et al. (2) and Moore et al. (3) proposed
the use of supplemental oxygen during daily exercise training to improve
the physical conditioning of patients with chronic heart failure (CHF).
Supplemental oxygen has been hypothesized to enable patients to exercise
with reduced symptoms, thereby improving compliance since the activity
is no longer intolerable. Furthermore, the oxygen enables the patient
to train vigorously and, thereby, improve the metabolic function of skeletal
muscles. The improvements in skeletal muscle function require exercising
at a higher intensity and for longer duration than would be possible without
the use of supplemental oxygen.
Endurance performance may be limited
by the ability to maintain a high percentage of oxygen saturation in the
blood. In studies of exercise-induced hypoxemia, Babcock et al. (13),
Dempsey et al. (14) and Moore et al. (3)
found that mild hyperoxia decreased the severity of the hypoxemia.
Exercising under conditions of higher than normal inspired oxygen would,
thus, be expected to enable the individual to exercise at a higher intensity
than usual, providing the potential for enhanced training adaptations and
improved exercise performance.
Supplemental oxygen may have potential
beneficial effects to athletes training at altitude. Chick and co-workers
(16) observed increased maximal cycle time (p = 0.015)
and increased endurance time at 85% maximal workload (p = 0.012) following
six weeks of hyperoxic (>70% O2 training
in trained subjects at an altitude of 1600 m. Conversely, Favier
and co-workers (17) concluded that, in high-altitude
natives, increasing oxygen availability to normoxic levels while training
at altitude has no advantage over training at sea level.
To date, few studies have been conducted
at lower altitudes to determine if supplemental oxygen can be used during
exercise training to enhance endurance performance by improving muscle
function. Kleiner and Snyder (5) observed an ergogenic
affect of hyperoxia that seems to aid only the aerobic aspect of resistance
exercise. Moore and co-workers (3) reported improvements
in exercise performance and a reduced ventilatory response in patients
with chronic heart failure during submaximal exercise while breathing oxygen-enriched
air. Significant increases were also reported for oxygen saturation
of arterial blood and cardiac output, with significantly reduced minute
ventilation. In addition, patients reported less fatigue and feelings
of breathlessness. Knight and co-workers (2) observed
a trend toward improved maximal oxygen consumption (VO2max)
after 10 wk of exercising three times a week at 70-90% of maximal heart
rates for 40 min on a stationary cycle ergometer while breathing 60% O2.
Ploutz-Snyder and associates (4) trained 19 male subjects
5 d/wk for 5 wk on a cycle ergometer at 70% of hyperoxic or normoxic maximal
heart rate while breathing 70% oxygen or room air. Throughout the
training period, the hyperoxic group was reported to have trained at an
intensity approximately 20 W higher than the normoxic group, however, improvements
in VO2max for the hyperoxic group did not
differ significantly from the normoxic group. In addition, maximal
lactate concentrations, heart rate, stroke volume, and cardiac output were
unchanged in both groups. Significant increases in the percentage of type
IIa muscle fibers were reported, with no significant differences between
groups. The hyperoxic group, however, retained a larger percentage
of type IIb fibers. Ploutz-Snyder and co-workers (4)
also reported no changes in creatine kinase, phosphofructokinase, and glyceraldehyde
phosphate dehydrogenase; increases in cytochrome c-oxidase and citrate
synthase for both groups; and 3-hydroxyacyl coenzyme-A dehydrogenase activity
increased in the normoxic group, but not in the hyperoxic group.
These researchers suggested that there were intramuscular differences between
hyperoxic and normoxic training, and that the muscle utilizes additional
oxygen, if available.
The effectiveness of breathing enriched
air may be dependent upon the oxygen concentration. Yet, there is
no consensus as to the optimal oxygen fraction to be used (2,4,5,7,12,18,19,20).
One explanation for these discrepancies may be the different exercise intensities
used in the studies (12,20).
Among the studies of hyperoxic exercise training, Knight and co-workers
(2) observed a trend toward increased maximal oxygen
consumption using 60% O2. Ploutz-Snyder
and co-workers (4) found no significant difference in
improvements in maximum oxygen consumption between training with 70% O2
and room air. The concentration of O2
used in these training studies, however, may not have been sufficient to
significantly increase the exercise capacity. There are no published
studies in which the researcher examined the effect of training while breathing
concentrations greater than 70% O2.
In the present study, it was proposed that a concentration of 80% O2
would increase the training intensity and be sufficient to observe an effect
on maximal oxygen consumption and time-to-exhaustion.
METHODS
Subjects
Eighteen subjects (12 males and 6 females)
were recruited from the student population at the University of Toledo
and surrounding community by word of mouth and flyers posted on campus.
One female subject, however, had to be dropped from the study during the
post-training testing due to illness. Subjects were apparently
healthy and free of contraindications to exercise as determined from a
self-reported medical history. All subjects were regularly active,
at least 3 d/wk, in endurance exercise for six months prior to the study.
Based on age, gender, height, weight, pre-training data, and self-reported
activity level, the subjects were matched and randomly assigned to receive
either hyperoxic training (HT, N = 9) or normoxic training (NT, N = 8).
Informed consent was obtained before participation and all procedures were
approved by the University of Toledo Human Subjects Review Committee.
Exercise Tests
Subjects reported to the exercise physiology
laboratory on three separate days for a familiarization trial and preliminary
testing. The first day involved a familiarization trial during which
each subject was fitted for seat height and completed a 13 to 15 min exercise
bout on a cycle ergometer (818E, Monark, Stockholm, Sweden). The
familiarization trial was designed to allow the subject to be accustomed
to the ergometer and to breathing through a mouthpiece and with a nose
clip during graded exercise. On the second day subjects performed
a graded exercise test on the cycle ergometer to determine peak oxygen
consumption (VO2peak). During this
test, the subject pedaled at 75 rpm and work was progressively increased
until no further increase in workload was tolerable. Stages I-III
were of 3 min duration at 1, 2, and 3 kp. Stages IV-VI were of 2
min duration and weight dependent. Subjects who weighed more than
70 kg increased in 1 kp increments, and subjects who weighed less than
or equal to 70 kg increased in 0.5 kg increments. Expired gases were
analyzed for O2 using a S-3A oxygen analyzer
and for CO2 by a CD-3A carbon dioxide analyzer
(Ametek, Thermomax Instruments Division, Pittsburgh, PA). Oxygen
consumption measurements were made using an open circuit spirometry system
(Rayfield Equipment, VT), and VO2peak was
determined as the average of the highest two 15 s data points. On
the third day subjects completed a time-to-exhaustion test (TTE).
The subject was required to pedal the cycle ergometer at a workload of
approximately 80% of VO2peak until unable
to maintain a cadence of ~75 rpm. All testing was performed while
breathing room air. Following training, VO2peak
and TTE were repeated under the same conditions as pre-testing.
Training Protocol
Following completion of the preliminary
testing, subjects were matched according to the pre-training data and randomly
assigned to either 5 wk of cycling while breathing room air (NT) or 5 wk
of cycling while breathing approximately 80% O2
(HT). Training was conducted 3 d/wk. Each subject wore a facemask
or mouthpiece during administration of the appropriate gas mixture, as
described below. Heart rate was monitored continuously during training
using telemetry (Polar Electro, Port Washington, NY). The subject
was asked to pedal the cycle ergometer at a predetermined workload for
40 min, maintain a cadence that was as fast as possible for the duration,
and remain between 70-90% of age-predicted maximum heart rate. During
the first week of training, this workload was the resistance estimated
to elicit a work output of 60% VO2peak
if pedaling at a cadence of 75 rpm. The workload was increased 0.25
kp at the beginning of weeks 2, 4 and 5. After 20 min of training,
the subject was permitted to remove the facemask or mouthpiece for 3 min,
and the pedal cadence was reduced while the subject was permitted to drink
water. Following this relief period, the facemask or mouthpiece was
re-positioned and exercise was resumed for an additional 20 min.
Throughout training, the subjects were permitted to watch commercial video
recordings or listen to radio. Ergometers were calibrated periodically
and samples of the mixed inspired gas were analyzed to maintain a consistent
oxygen concentration.
The system used to administer gas to
both groups is depicted schematically in Figure 1.
The inspired hyperoxic gas was mixed from tanks of compressed 100% O2
and 100% N2 by a Air-Oxygen Blender (Bird
Products Corporation #03800A) and passed through a nebulizer to humidify
the gas and into a series of six 100-200 L Douglas bags. Gas from
the reservoir bags was fed by two hoses into PVC pipe regulated by three
3-way valves. These valves permitted gas flow to be switched from
room air to hyperoxic air and back without the subjects’ knowledge.
This also permitted the training of up to three subjects simultaneously.
This system permitted hyperoxic gas samples to be taken from the nebulizer
or from any available outflow regulator. By periodic analysis of
the mixed air, the average gas concentration was found to be
82.49 ± 3.52% O2.
Figure 1. The system
used to administer gas to both groups.
Data Analysis
The SPSS 7.5 for Windows statistical
package was used for all statistical analyses. Doubly MANOVA repeated
measures was used to determine whether there were significant effects for
time and treatment by time for the linear combination of the dependent
variables (VO2peak and TTE). The
data are reported as mean±SD and Student’s t-tests were used to
compare initial group differences for age, height, weight, pre-training
VO2peak and TTE, and group differences
for total work output (WO) and average daily work outputs for each training
week. In addition, effect size and power were calculated. Significance
was accepted at an alpha-level of 0.05 for all analyses.
RESULTS
Pre-training Data
The age, height, and weight of the
participants were 21±4 yr, 176.81±12.84 cm, and 74.04±12.31
kg, respectively. The two treatment groups were successfully matched.
Although NT was slightly higher than HT for mean VO2peak
(3.44 L/min vs. 2.98 L/min) and TTE (1075.65 s vs. 742.84 s), the groups
did not differ for age, height, weight, VO2peak,
and TTE at the start of training (p = 0.683, 0.892, 0.837, 0.288, and 0.184,
respectively). There were no significant differences between groups
in age, height, weight, and the pre-training testing using Student’s t-tests
(Table 1).
Table 1. Physical characteristics of subjects (mean±SD).
Group |
Height
(cm) |
Weight
(kg) |
Age (yr) |
NT (N=8) |
177.28 ±
11.20 |
74.73 ±
13.08 |
21.75 ±
4.95 |
HT (N=9) |
176.39 ±
14.82 |
73.44 ±
12.35 |
21.00 ±
2.12 |
Training Work Output
A plot of the group means for the average
daily training power output for each week of the training is provided in
Figure
2. Although mean average daily power output for NT was slightly
higher than that for HT, except for Week 2, there was no significant difference
between groups for each week.
Figure 2 -- Plot of group
means for average daily work output during 5 wk of exercise training while
breathing room air (NT) or a hyperoxic gas mixture (HT)
[* p < 0.05].
VO2peak
and TTE
The pre- and post-training VO2peak
and TTE data for both groups are shown in Figures 3
and 4. Despite the short duration, the training
period was sufficient to elicit a significant improvement in VO2peak
and TTE (p = 0.002). VO2peak increased
7.3% and 14.6% for NT and HT, respectively, and TTE increased 156.4% and
313.8% for NT and HT, respectively. However, these increases for
each of VO2peak and TTE were not significantly
different.
Statistical Power
Effect size for the treatment and time-by-treatment
effects (0.054 and 0.057, respectively) were very small, and consequently
observed power for the present study was quite low (0.10 and 0.11, for
VO2peak and TTE, respectively). For
an acceptable power of 0.8, we would have only been able to detect a mean
difference of 1.29 L/min and 1306 s for VO2peak
and TTE, respectively. For more physiologically meaningful differences
of 250 mL/min and 250 s for VO2peak and
TTE, respectively, the number of subjects required would have been greater
than 200 per group. Clearly, the small improvements seen with hyperoxic
training compared to normoxic training, using our methodology, requires
a large number of subjects to attain potential significance. This
is an unrealistic requirement in human subjects research. Nevertheless,
based on poor statistical power our non-significant findings need to be
interpreted with caution.
DISCUSSION
The present study was initiated to ascertain
whether the acute effects of exercise while breathing oxygen-enriched air
(~80%) would enable one to train at a higher intensity and, thereby, enhance
post-training performance. If intensity of training is the most important
factor in improving performance, as Mujika and co-workers (1)
have indicated, then one could hypothesize that training while breathing
oxygen-enriched air will improve performance. These data fail to
support any beneficial effect of hyperoxic training at sea level.
Nevertheless, the subjects who trained while breathing a hyperoxic gas
mixture did show a trend for greater mean improvements in VO2peak
and TTE (14.6% vs. 7.3% and 313.81% vs. 156.4%, respectively).
Although the subjects who participated
were regularly active, they were not highly-trained. This may have
dampened the ability to see the added results from hyperoxic training.
For example, had the subjects been highly-trained, a larger difference
in the training effects may have been expected as the availability of oxygen
might then have been a potential limiting factor to further training improvements.
In a recent study by Ploutz-Snyder et
al. (4), subjects breathing a 70% O2
gas mixture were able to train at an intensity of 20 W higher than subjects
breathing room air. This was not the case in the present study.
Subjects breathing ~82.5% O2 produced a
mean accumulated power output of 101061.1±24253.1 W compared to
116568.3±38224.0 W for the normoxic group. Although NT trained
at a slightly higher intensity than HT, this may be attributable to the
slightly higher average fitness level rather than an effect of breathing
oxygen-enriched air. The groups were matched as closely as possible,
however, the loss of one subject from this group resulted in a positive
shift in the mean. The difference in pre VO2peak
was insignificant (Figure 3), and statistically,
there was no difference in mean total power output between groups.
Thus, the hypothesized increase in power output for the subjects breathing
hyperoxic gas was not observed.
During training, the resistance on the
cycle ergometer was set at a level that was estimated to elicit an oxygen
consumption of 60% VO2peak if pedaling
at 75 rpm. Subjects were asked to pedal as fast as they could at
this resistance, when considering the exercise duration, while maintaining
a heart rate of 70-90% age-predicted maximum heart rate. While other
training protocols may have been selected, the authors anticipated that
the hyperoxic gas mixture (~80%) would permit an increased maximal rate
of work rate during exercise (4,5,9).
Thus, if two subjects were matched and asked to exercise with the same
resistance setting on the cycle ergometer, a subject breathing a hyperoxic
gas mixture would pedal at a higher cadence and average power output than
his/her normoxic counterpart. This, however, was not the case.
One consideration that was omitted, though, was motivation. It is
certainly possible that some subjects would be more driven to push themselves
than others. This would, nonetheless, only be possible within the
permitted heart rate range, and random assignment was intended to minimize
group differences for which there were no controls. No distinct disparity
in motivation was observed, but any difference, albeit slight, may have
affected the power output.
Figure 2 contains
a comparison of average daily power outputs. From week 2 to 3, NT
declined slightly, while HT maintained a steady power output. Resistance
was increased for all subjects during weeks 2, 4 and 5. During week
3, power output might have been expected to increase, if pedal cadence
increased, or stay the same, if pedal cadence was maintained. That
pedal cadence was maintained by HT may indicate that the subjects found
a more or less comfortable cadence that they maintained throughout the
training despite increases in resistance. Interestingly, the decline
in work output for NT between week 2 and week 3 may be attributable to
the fact that television and video entertainment was introduced for most
of the subjects at this time. This is, however, speculative since
there were no steps taken to quantify the effect of such entertainment
on the subjects’ attention to the exercise activity at hand. It may
be that the introduction of the videos initially distracted the subjects,
but after a brief time progression resumed. However, this interpretation
is not supported in the literature (21,22).
Brownley et al. (23), suggested that listening to upbeat
music may be beneficial for untrained runners, but counterproductive for
runners who are trained. It may also be that NT had a heightened
enthusiasm during the first two weeks of training that motivated them to
train harder during the early weeks and waned after a time.
Practical Importance of Hyperoxic
Exercise
With the small effect sizes we reported
for the variables VO2peak and TTE, it was
a practical impossibility to study a sufficient number of subjects to attain
statistical significance. One must consider the time, cost and convenience
of training individuals under hyperoxic conditions. Given that only
small training improvements are important to the performance of elite level
athletes, the within and between subjects variability in the physiological
responses to hyperoxic training may cause experimental research to never
be able to document a statistically significant benefit of hyperoxic training.
In this case, physiological significance becomes a secondary, but important
assessment of this procedure.
Hyperoxic exercise training has previously
been found to be beneficial in patients with CHF (2)
and trained individuals at moderate altitude (16).
The ergogenic effects of such training may be limited to conditions of
impairment, and the small effect of such training for healthy individuals
training at sea level may be of little practical benefit. CHF patients
generally have impaired exercise capacity because of muscle fatigue or
other symptoms, including dyspnea (3). Moore et
al. (3) indicated that improved skeletal muscle conditioning
may play a role in increasing aerobic capacity in CHF. Knight et
al. (2) found only a non-significant trend toward improved
VO2peak for CHF patients after 10 weeks
of hyperoxic exercise training, and this benefit was not long-lasting.
This may indicate a skeletal muscle adaptation that produces a short-term
performance enhancement in poorly-conditioned individuals.
The research done at altitude is interesting.
It appears that hyperoxic exercise training at altitude permits athletes
to train at higher intensities despite the effects of lowered oxygen pressures
(16). Thus, it may be possible that athletes living
high may simulate training low without leaving altitude. It appears,
however, that this notion does not carry over to the prospect of living
low/training lower, as was tested in the present study.
Ploutz-Snyder et al. (4)
also concluded that there was no significant effect of hyperoxic exercise
in healthy young adults at sea level. Thus, hyperoxic exercise training
may be most beneficial when performance is impaired rather than in situations
where it is desirable to push normal exercise performance to a higher level.
However, it may be concluded that cycle training while breathing oxygen-enriched
air (82.5% O2) did not enhance endurance
performance and muscle function of moderately-trained subjects living at
sea level.
Suggestions for Future Research
This study and that of Ploutz-Snyder
et al. (4) were of short duration (five weeks).
Knight et al. (2) trained CHF patients for 10 weeks.
A longer training study with non-diseased subjects may be warranted. A
comparison of the response of high fitness subjects and low fitness subjects
to exercise training while breathing oxygen-enriched air also merits consideration.
It would also be worthwhile to consider the ergogenic benefit of hyperoxic
exercise training at altitude. The intensity for TTE may have been
too low to elicit a significant difference between HT and NT. Ideally,
the intensity should be such that the subjects fatigue between 5 and 10
min in the pre-training trial. In addition, it would be interesting
to examine whether breathing oxygen-enriched air affects work output, controlling
for motivational factors. This could be accomplished using a 2x2
factorial design (gas concentration x work output) in which subjects are
matched and randomly assigned to one of four treatments: hyperoxic-high,
normoxic-high, hyperoxic-low, and normoxic-low. Hyperoxic-high and
normoxic low would train as described in the present study. Normoxic-high
would then be matched to the work output of hyperoxic-high and hyperoxic-low
to that of normoxic-low. Such design might control the effects of
motivation and examine whether it is the gas mixture or work output that
facilitated any improvement in training adaptations.
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Address for Correspondence:Dr.
W. Jeffrey Armstrong, Department of HPERD, Eastern Michigan University,
Ypsilanti, MI 48197. E-mail: Jeff.Armstrong@emich.edu.
Copyright
©1997-1999
American Society of Exercise Physiologists. All rights reserved.
ASEP
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