Total muscle mass is thought of as one of the intrinsic limiting factors of aerobic power. But it is not yet clarified how the total muscle mass limits the magnitude of aerobic power. The purpose of this study was to clarify the relationship between total muscle mass and aerobic power and to make a further discussion conscerning its limiting factors. 17 sedentary students with a mean age of 19.3 (18-23) years, and 17 varsity footballers 19.9 (19-21) years old, were measured for lean body mass, which was an approximate indicator of the total muscle mass, by underwater-weighing method and VO₂ max by bicycle ergometer. The correlationship between lean body mass and VO₂max for sedentary students was found to be higher (r=0.821) than for footballers (r=0.595) . It was also shown that footballers had a significantly larger VO₂max per 1kg of lean body mass than sedentary students. Previous studies showed that the increment of VO₂max through endurance training was caused by the increment of such factors as mitochondria, maximum cardiac output and maximum stroke volume, and was not by lean body mass. So, it was concluded that lean body mass was a reasonable limiting factor for sedentary students, but was not a stable factor of VO₂max because of lower linearlity for footballers and the significant difference on VO₂max per 1kg of lean body mass between two groups.

Several studies have reported that molecular hydrogen (H₂) acts as a therapeutic medical gas owing to scavenging reactive oxygen species (ROS). However, little is known about effects of H₂ on exercise-induced oxidative stress. The purpose of this study was to investigate the effects of weekly hydrogen bathing on exercise-induced oxidative stress and delayed-onset muscle soreness (DOMS). Nine healthy and active young men participated in this study, and each subject performed hydrogen bathing trial and placebo bathing trial in a crossover design. The subjects performed downhill running (8 % decline) at 75 % peak oxygen uptake (VO₂peak) for 30 min, and each subjects conducted hydrogen or placebo bathing for 20 min, respectively, 1-6 days after downhill running. Before and after exercise, we measured visual analogue scale (VAS) and collected blood samples (Pre- and 5 min, 60 min after the end of bathing, 1day, 2days, 3days, 7days after downhill running). Blood sample analyses include creatine kinase (CK), myoglobin (Mb), malondialdehyde (MDA), reactive oxygen metabolites (d-ROMs), biological antioxidant potential (BAP), myeloperoxidase (MPO), interleukin-6 (IL-6), interleukin-17a (IL-17a) and lactate concentrations. Weekly hydrogen bathing had no effects of exercise-induced oxidative stress and muscle damage. On the other hand, hydrogen bathing significantly reduced DOMS (VAS) 1 and 2days after downhill running (p=0.033). These findings suggest that hydrogen bath after downhill exercise can be effective for reduction of DOMS.

Real-world data (RWD), such as a health insurance claim database and electronic medical record database, which records daily medical care information, is one of the most important data sources in pharmacoepidemiological studies. In Japan, a post-marketing database study has been added as a new category of post-marketing surveillance since April 2018. It is expected that the post-marketing database studies will be conducted in the actual risk management plan； however, at this point, few have reached the stage of publishing study results. On the other hand, overseas, many database research results using RWD have already been reported. Although it is necessary to keep in mind that there are differences in the characteristics of the databases (e.g., data contents, structures) and the differences in the medical environment between overseas and Japan, we think that critically reviewing these reports has a reference value for the planning, execution, and interpretation of the results in performing post-marketing database studies in Japan. The purpose of this report is to examine the characteristics and cautions of the database studies through a critical review of published articles of overseas RWD studies and to make recommendations that are useful for conducting post-marketing database studies in Japan. We hope this article will become a help in the planning and implementation of future post-marketing database studies.