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.

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Background: During menopause, bone density decreases, and low-density lipoprotein cholesterol (LDL-C) rapidly increases; a decrease in the estrogen level is a common factor in these phenomena. Methods: In this study, we focused on the fact that menopause is a spontaneous process, and aimed to derive the conditions that mitigate the decline in the osteo sono-assessment index (OSI), an index of bone mineral density (BMD), using a chemical equilibrium model. We attempted to establish the relationship between variables related to female hormone secretion (OSI, LDL-C) and a variable related to work capacity (physical work capacity [PWC] at 75% of maximal heart rate) by analogy, using the fact that Gibbs free energy, a thermodynamic variable related to spontaneous change, is related by three variables. Results: Consequently, if linearity is established between PWC and OSI when LDL-C is used as the standard, then the analogy of chemical equilibrium can be established between the deviation values of these three variables, with equilibrium constant K. Finally, the theoretically determined equilibrium model with constant K was applied to data obtained from the Sports Program Service (SPS) of the Yokohama Sports Medical Center. Conclusions: The present study suggests that the decrease in bone density could be alleviated by promoting an increase in LDL-C or by mitigating the decrease in PWC. In discussing personal health, mitigating bone density loss and maintaining a high work capacity are important components, which should also take into account the appropriate levels of LDL-C.