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.

本研究は,システム生理学的研究手法を用いて週一回の高強度インターバルトレーニングが呼吸化学調節系のフィードバック制御機能や心形態・心機能に及ぼす影響を明らかにすることを目的とした.対象は健常男性7名.トレーニング前後で最大酸素摂取量(VO2max)及び心形態の測定評価を行った.また安静時,低強度,高強度運動時の各々の条件下にて,呼吸化学調節フィードバック系をコントローラ(制御部)とプラント(制御対象部)の2つのサブシステムに分離した後,定量化し,それぞれの機能特性をトレーニング前後で比較検討した.高強度インターバルトレーニング後のVO2max(+9.5±7.5%)及び左室後壁厚(+17.9±8.6%)はトレーニング前と比較して有意に増加した(p<0.01).また,トレーニングによって高強度運動時のコントローラ特性曲線のリセッティングが生じ,プラント特性(双曲線)の比例定数の増加及びx軸漸近線の値の減少が認められた(p<0.05).本研究から,週一回の高強度インターバルトレーニングは最大呼吸循環機能を向上させるだけでなく,高強度運動時における呼吸化学調節系の機能特性を特異的に変化させること,制御部特性の機能的変化が,高強度運動時の換気抑制の主たるメカニズムとして動作していることが判明した.(著者抄録)