Abstract
Low-intensity training involving high repetitions is recommended to enhance muscular endurance. Hyperoxic conditions could increase the number of repetitions until exhaustion and thereby improve the results of muscular endurance training. This study aimed to investigate the acute effects of hyperoxia on dynamic muscular endurance, and determine individual factors that may be related to these effects. A single-blinded, counterbalanced crossover design was used. Twenty-five young men performed repetitions of the one-arm preacher curl at 30% of their 1-repetition maximum until exhaustion under hyperoxic and normoxic conditions. The maximum number of repetitions was recorded as an index of muscular endurance. Electromyogram (EMG) and near-infrared spectroscopy parameters were measured in the biceps brachii. The maximum number of repetitions was greater (P < 0.001) under hyperoxic conditions (132 ± 59 repetitions) than under normoxic conditions (114 ± 40 repetitions). The root mean square amplitude of EMG and oxygenated hemoglobin concentration for the last five repetitions under normoxic conditions were greater than those under hyperoxic conditions (P = 0.015 and P = 0.003, respectively). The percent change in the maximum number of repetitions between hyperoxic and normoxic conditions had significant positive correlations with individual maximal oxygen uptake measured using an incremental cycle ergometer test (r = 0.562, 95% confidence intervals [CI] = 0.213–0.783, P = 0.003), but not with muscle strength (τ = −0.124, 95% CI = −0.424–0.170, P = 0.387). The 95% CI for the correlation coefficient between the percent change in the maximum number of repetitions and muscular endurance included 0 (τ = 0.284, 95% CI = −0.003–0.565, P = 0.047); this indicated no significant correlation between the two parameters. The results suggest that hyperoxia can acutely enhance dynamic muscular endurance, with delayed elevation of EMG amplitude due to fatigue, and the effects are associated with individual whole-body endurance capacity.
Highlights
Muscular endurance is defined as the ability of a muscle group to execute repeated contractions over a period of time sufficient to cause muscular fatigue, or to maintain a specific percentage of maximum voluntary contraction for a prolonged period of time [1]
Only a few studies have evaluated the effects of hyperoxia on local muscular endurance, and these studies reported that the mean value of peak torque during 60 maximal knee extensions was higher under hyperoxic conditions than normoxic conditions [15,16], suggesting positive effects of hyperoxia on muscular endurance
Multiple comparison testing showed that there was no significant difference between hyperoxic conditions (HOX) and normoxic conditions (NOX) values at 0% NOXmax (P = 0.058, d = 0.437) and 50% NOXmax (P = 0.026, d = 0.508); the HOX value was significantly lower than the NOX value at 100% NOXmax (P = 0.015, d = 0.569)
Summary
Muscular endurance is defined as the ability of a muscle group to execute repeated contractions over a period of time sufficient to cause muscular fatigue, or to maintain a specific percentage of maximum voluntary contraction for a prolonged period of time [1]. Many previous studies have reported positive effects of hyperoxia during whole-body aerobic and anaerobic exercise These advantages of hyperoxic conditions are provided mainly by higher oxygen delivery to muscles [4,12,13] and changes in muscle metabolism [10,14] compared to normoxic conditions. Only a few studies have evaluated the effects of hyperoxia on local muscular endurance, and these studies reported that the mean value of peak torque during 60 maximal knee extensions was higher under hyperoxic conditions than normoxic conditions [15,16], suggesting positive effects of hyperoxia on muscular endurance These previous studies used maximum voluntary contractions as the muscular endurance exercise, low-intensity repetitive exercise is recommended for appropriate muscular endurance training [1]. To the best of our knowledge, no reports have investigated the effects of hyperoxia on low-intensity repetitive muscle contractions
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