What kind of exercise is effective even when performed for a short time? A research group led by Professor Yasuo Kawakami of the Faculty of Sport Sciences at Waseda University and Researcher Takaki Yamagishi of the Japan Institute of Sports Sciences sought to answer this question, and found that a brief, high-intensity intermittent exercise for only 40 seconds significantly increased whole-body oxygen consumption and activity of the major muscles in the femoral region. They also found that the increase in oxygen consumption was not necessarily proportional to the number of iterations of high-intensity exercise. The work was published in Medicine & Science in Sports & Exercise.
Recently, the "minimum amount" (of exercise) that exerts training effects has been a theme of active research. The latest findings have shown that high-intensity intermittent exercise for as short as 40 seconds (two iterations of 20-second maximum-intensity exercise with a rest period in between) can improve maximal oxygen consumption as much as or more than moderate-intensity aerobic exercise for 30 minutes or more. In contrast to this, it has been observed that intermittent exercise for a reduced duration (two iterations of 10-second exercise or one set of 20-second exercise) does not produce the same effect; however, the reason behind this remains unclear.
Most studies on high-intensity intermittent exercise have focused primarily on energy metabolism, and the effects on muscle have been unknown. In this study, they examined whole-body and local energy metabolism and muscle activity in the femoral region during different high-intensity intermittent exercises from multiple perspectives, with the aim of elucidating the "minimum amount" that produces training effects. The two exercise tasks used were "four 10-second maximum-intensity sprints with an 80-second rest period in between" and "two 20-second maximum-intensity sprints with a 160-second rest period in between." Both exercise tasks were performed using a bicycle ergometer, and the total exercise duration (40 seconds) and the sprint-to-rest duration ratio (1:8) were standardized across exercise tasks.
The results showed that the increase in whole-body and muscle oxygen consumption plateaued after the second sprint when the 10-second or longer sprints were repeated, that 20-second sprints increased muscle oxygen consumption compared to 10-second sprints, and that both exercise tasks significantly increased the activity of the eight muscles in the femoral region. Furthermore, these results revealed that for 10-second or longer maximum-intensity sprints, two iterations were sufficient to increase whole-body and muscle aerobic energy metabolism, and that when the total exercise duration (40 seconds) was fixed among exercise tasks, reducing the number of sprints to increase the duration per sprint was effective to maximize muscle oxygen consumption. High-intensity intermittent exercise for only 40 seconds increased the activity of the major muscles in the femoral region.
The findings obtained in this study will contribute to improving the prevalence rates of exercise in Japan and other countries around the world. The latest WHO guidelines on physical activity recommend aerobic exercise for at least 150 minutes per week and strength training at least twice a week. While these are ideal, it is not easy to follow recommendations in a busy modern society. The study showed that two 20-second maximum-intensity sprints sufficiently increased aerobic energy metabolism and muscle activity in the femoral region. Therefore, regularly performing this exercise once or twice a week is expected to improve maximal oxygen consumption (a measure of whole-body endurance) and muscle mass and strength in the femoral region.
Kawakami said, "High-intensity intermittent exercise is a type of exercise that is gaining increasing attention worldwide. The method includes repeating short-duration, high-intensity exercise in a concentrated manner, but the specific 'optimal solutions' for the intensity, duration, and number of iterations were not clear. The results of this study are expected to facilitate more efficient training of athletes and help the general public incorporate exercise into their daily lives."
Yamagishi said, "The search for the 'minimum amount' that produces training effects is my main research theme. With this study, we are going to further develop exercise modalities with high levels of feasibility and time efficiency. We would be pleased if you are interested in this study and try to incorporate high-intensity intermittent exercise as part of your training, starting with what you can, for example, shortening the exercise duration slightly (10−15 seconds) or reducing sprint intensity slightly from maximum intensity."
Journal Information
Publication: Medicine & Science in Sports & Exercise
Title: Physiological and Metabolic Responses to Low-Volume Sprint Interval Exercises: Influence of Sprint Duration and Repetitions
DOI: 10.1249/MSS.0000000000003420
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.