It is well known that daily exercise has health benefits, and physical inactivity is unhealthy. Inactivity, typically characterized by daily sitting time, needs to be interrupted periodically with physical activity. However, the most effective amount and type of activity have not been fully elucidated. The American College of Sports Medicine recommends approximately 30 minutes per day of moderate-intensity physical activity. Nevertheless, if a person performs this recommendation, yet also sits for several hours per day, the inactivity appears to override the potential benefits of physical activity in terms of fat metabolism and general health. This study determined if a very small amount of high intensity cycling (known as high-intensity interval training or sprint interval training) could counteract prolonged sitting. Participants completed two trials of sitting for eight hours. In only one of these trials, at the end of each hour, they cycled as fast as possible for four seconds against the resistance of an exercise bike with a heavy flywheel and then rested 45 seconds. Five of these four-second sprints were performed every hour, amounting to only 160 seconds per day of exercise. When compared to sitting only, the sprint cycling trial resulted in significant improvements in fat breakdown and blood triglyceride concentration. Cycling at the highest intensity possible (five to 10 times higher than that of a typical spin class) likely activated a maximal amount of muscle fibers (cells), especially the hard to activate fast-twitch fibers. However, the exercise was rated as neither hard nor fatiguing by the participants. This raises the question as to what is the least amount and type of exercise that can acutely improve fat metabolism and other aspects of health.
