Which is better for reducing fat: long bouts of exercise, or breaking physical activity into smaller sessions with an added rest period? According to a study in Journal of Applied Physiology (2007; 102, 2158–64), taking a break in the middle of a workout may metabolize more fat than exercising without stopping.
Seven healthy men (average age 25) participated in the study. The subjects were physically active and familiar with exercise. Researchers put them through the following trials:
- one 60-minute bout of exercise followed by a 60-minute recovery period (single)
- two 30-minute bouts of exercise with a 20-minute rest after the first bout and a 60-minute recovery period at the end (repeat)
- one 60-minute rest period (control)
The men performed each of the three trials at the same time of day, after fasting overnight. They exercised on a single ergometer at 60% of maximum oxygen intake and
sat in chairs for their recovery and rest periods. Researchers took blood samples every 15 minutes during the exercise and every 30 minutes during the recovery period. Respiratory gas and heart rates were continuously monitored.
The “repeat” trial showed a greater amount of lipolysis (fat breakdown) than the “single” trial. The repeat trial also led to a pronounced increase in concentrations of free fatty acids and glycerol (chemical compounds released when stored fat is used) in the final 15 minutes of exercise. These concentrations increased only progressively throughout the single trial.
“Many people believe prolonged exercise will be optimal in order to reduce body fat, but our study has shown that repetitions of shorter exercise may cause enhancements of fat mobilization and utilization during and after the exercise,” said lead researcher Kazushige Goto, PhD, in a press release.