The effects of physical activity (PA) on bone mass gained during growth in Japanese are not well understood. The purpose of this study was to examine whether changes in PA affected bone mass gained by Japanese schoolchildren, as measured by calcaneus quantitative ultrasound (QUS). Three hundred and seven children aged 9–13 years participated in the study and were followed for a 2-year period. The stiffness index (Stiffness) of the calcaneus was measured by QUS, and PA evaluated by a questionnaire. Participants were divided into two groups according to PA: high (≥ 7 hours/week, H) or low (< 7 hours/week, L). Participants were also divided into four groups according to their 2-year change in PA: consistently high (HH), consistently low (LL), changed from high to low (HL), and changed from low to high (LH). Analysis of covariance was used to compare adjusted Stiffness across all four groups. The adjusted 2-year changes in Stiffness ranked in decreasing order among girls: HH (20.8 %), HL (17.6 %), LH (14.3 %), and LL (12.2 %), respectively (trend test, P = 0.027). This trend was not observed among boys. These results suggest that changes in PA significantly affected bone mass gain among peripubertal girls, and that a continuing PA of more than 7 hours a week (approximately ≥ 60 min/day) from a young age is effective in increasing peak bone mass. However, given the limitations of this study, further robust studies which recruit representative samples and consistently employ validated measurement instruments are needed.

The purpose of this study was to investigate the effect of attenuation of exercise-induced oxidative stress by antioxidant administration on brain-derived neurotrophic factor (BDNF) expression in the rat hippocampus. Wistar rats were assigned to four groups: non-exercise (Cont), exercise (Ex), or the combination of exercise with antioxidant administration (small dose: SP, large dose: LP) group. Exercise groups were subjected to treadmill running for 10 consecutive days. The exercise load increased gradually by 5 m/min per day for the first 5 days (10 m/min-30 m/min), and maintained at 30 m/min for the last 5 days. In addition, SP and LP were injected with N-tert butyl-a-phenyl nitrone (PBN) 1h prior to exercise. High-intensity exercise resulted in increased hippocampal 4-hydroxy-2-nonenal (4-HNE) contents compared with Cont. But this elevation was completely suppressed by a large dose of PBN. In Ex and SP, serum total antioxidative power were significantly decreased compared with Cont, whereas no changes were observed in LP. There was a significant negative correlation between hippocampal 4-HNE contents and serum total antioxidative power in SP and LP, suggesting the hypothesis that exercise-induced reduction in total antioxidant power might lead hippocampal 4-HNE accumulation. Furthermore, there was a significant increase of hippocampal BDNF level in LP compared with Cont and Ex. These findings indicate that an increase of oxidative stress might not have a beneficial effect on hippocampal BDNF expression. Our results of this study also suggest that attenuation of exercise-induced oxidative stress by some antioxidants contributes to BDNF expression in the hippocampus.