Results from a small exploratory study suggest that short bouts of intermittent exercise may stimulate fat metabolism more effectively than longer continuous exercise sessions.
Physical activity is routinely recommended to help prevent weight gain in adults, but recent research indicates that, once diet has been accounted for, weight increases cannot be consistently explained simply by lower levels of physical activity or decreased exercise over time.
Shigeho Tanaka (National Institute of Health and Nutrition, Tokyo, Japan) and colleagues recruited nine healthy young men, aged 22.2 years on average, to test whether the frequency and duration of exercise performed influences the degree of fat utilization by the body.
The volunteers took part in two 39-hour sessions (2 nights, 3 days) during which they stayed in a respiratory chamber that allows carbon dioxide and oxygen measurement. During both sessions the participants completed 85 minutes of exercise on a cycling ergometer at a workload of 5.5 metabolic equivalents on day 2 of their stay. They also consumed four high-fat meals during, after eating a high carbohydrate calorie-controlled diet for 3 days before entering the chamber.
In one session the volunteers performed the exercise continuously. This involved 10 minutes of warm up and 45 minutes of exercise, followed by a 10-minute break then a further 40 minutes of exercise and a 15-minute cool down period. In the other session, the same type and difficulty of exercise was performed for 5 minutes every 30 minutes a total of 17 times.
As reported in Medicine and Science in Sport and Exercise, the intermittent physical activity session resulted in greater fat utilization than the continuous session.
The researchers used the 23-hour respiratory exchange ratio (RER) - the ratio between carbon dioxide exhaled and oxygen inhaled - to assess fat metabolism. They found that the 23-hour RER measures for the intermittent trial were significantly lower than those collected for the continuous trial, at 0.837 versus 0.843, indicating that a greater percentage of fat rather than carbohydrate was being utilized by the body as fuel.
Tanaka and team concede that "because these results were obtained from only a few subjects during a short-term laboratory experiment, additional longitudinal studies and intervention studies are needed to confirm whether intermittent physical activity rather than continuous physical activity is effective for preventing obesity."
However, they conclude that "the present study specifically suggests that the intervals between dynamic body movements should be as short as possible for more efficient utilization of ingested fat."
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