Shingo Otsuki

According to prior research, high-intensity endurance training (HIT) conducted more than twice a week significantly improves the maximum oxygen uptake (V_O2max), a marker of cardiorespiratory fitness, compared to low or moderate-intensity training. This training modality not only benefits athletes but also aids individuals with metabolic syndrome and circulatory and respiratory conditions, enhancing their quality of life. Despite these potentials, exploratory studies of exercise regimens with shorter durations, lower frequencies, and fewer sets remain insufficient; thus minimalistic HIT protocols remain under-investigated. In this research, our objective was to investigate the impact of an even less frequent, once-weekly, maximum effort high-intensity training (HIT) on cardiorespiratory function and exercise performance across various age groups. We enrolled 11 healthy participants (4 males and 7 females;age 36.9±16.7 years;height 163.4±11.7cm;weight 58.4±10.6kg) to participate in exhaustive training sessions for 8 weeks. The intensity was set at 80%of their maximum load reached in an initial ramp test (80%WR_max) . Before and after the training, participants underwent ramp test and head-up tilt (orthostatic load) test to assess adaptations in cardiorespiratory function during maximum exercise and circulatory adjustment to postural changes. Exercise performance was evaluated by maximum exercise duration until exhaustion (Exhaustion Time) . Post-training results indicated significant improvements in V_O2max (＋12%, p=0.02), ＋7.5% (p=0.026) WR_max＋12.7%, and Exhaustion Time. Furthermore, in the head-up tilt test, a significant increase in end-tidal CO₂ partial pressure (P_ETCO2) (＋17.5%, p=0.04) was observed in the supine position, and P_ETCO2 increased by ＋11.9% (p=0.03) while tidal volume decreased by -19.9% (p=0.02) in the tilt position. Although no interaction was found in ANOVA, significant Primary effects of training and condition were observed for P_ETCO2. Our findings suggest that once-weekly HIT to maximum exertion enhances cardiorespiratory function and exercise performance. No changes in parameters maintaining blood pressure were observed during the head-up tilt test. These findings may be valuable for future development of efficient exercise training programs for wider age groups.

本学の健常学生16名を被験者とし、下半身陰圧負荷装置を用いて-45mmHgの起立性ストレスを10分間加える実験を行い、起立性ストレスに対する呼吸・脳循環調節系および心血管系の相互作用について検討した。結果、起立性ストレスによって中心循環血液量が減少したが、動脈圧受容器反射によって血圧と脳血流反応性は維持されていたことから、呼吸調節系と循環調節系が協調して脳内のCO2ホメオスタシスを維持する機構が効果的に機能している可能性が示唆された。