Effects of Weekly Interval Training at High Intensity interval training on Dynamic Cardiorespiratory Responses to Exercise

Purpose Previously we reported that high‐intensity interval training (HIIT) at 80% maximal work‐rate (WR max ), even when performed at a low frequency of once a week, markedly improves maximal cardiorespiratory function and maximal performance time (Med Sci Sports Exerc. 2015). However, it has not been determined whether more intense interval exercise training will have the similar effect on maximal oxygen uptake (VO 2max ) or alter the dynamics of the cardiorespiratory response during maximal exercise. The purpose of this study was to examine whether or not the same effect can be obtained, even with HIIT at 95%WR max for 8 weeks which further increased exercise intensity than the previous study. Methods Seventeen healthy male college students were randomly assigned to one of the two following groups; high‐intensity interval training group (HIT; n = 9) and control group (n = 8). HIT group performed the training on a cycle ergometer once a week for 8 weeks. The training was consisted of three bouts until volitional fatigue at 95%WR max . Cardiorespiratory function during maximal ramp and step (high‐intensity) exercise test was investigated before and after the intervention period. Results The training resulted in increased VO 2max (+9%, p = 0.037), maximal heart rate (+4%, p = 0.023) and maximal minute ventilation (+19%, p = 0.007) during maximal ramp test, respectively. Significant changes in the dynamic response of heart rate and blood pressure at the onset of high‐intensity exercise were observed after the training program compared with baseline, and improvement in exhaustion time was also observed (+ 93%, P < 0.001). In addition, increased left ventricular posterior wall thickness at rest was also observed after training (+12%, p = 0.004). Conclusion The present results indicate that more intense HIIT performed at a low frequency once a week not only increased maximal cardiorespiratory function and exercise performance, but also induced cardiovascular adaptation in the enhancement of heart rate and blood pressure response during step exercise, as well as induces cardiac morphological adaptations involving left ventricular hypertrophy, as we have already found in previous studies.