Issues of fractionization of exercise (short vs long bouts).

PURPOSE: To evaluate evidence comparing the influence on health outcomes of different patterns and intensities of exercise with equivalent total energy expenditure.
METHODS: A computerized literature search, with searches of the reference lists of papers identified.
RESULTS: Studies fell into two categories: 1) comparisons of one continuous session of exercise with several short (> or = 10-min) sessions of the same total duration; and 2) comparisons of a session of moderate/hard exercise with a session of lower intensity but equivalent energy expenditure. Within each category, studies were found for training effects and for acute effects. Category 1: Several small, randomized controlled trials showed that improvements in measures of cardiorespiratory fitness did not differ significantly between training regimens based on long or short sessions. Acute effects of two short sessions on excess postexercise oxygen consumption were reported to be greater than those of one longer session. By contrast, short-term decreases in postprandial triglyceride concentrations were found to be similar with three short or one long session. Category 2: Higher-intensity training was consistently found to elicit greater increases in VO(2max) than lower-intensity training of longer duration. No conclusion could be drawn for any other outcome. A session of hard/moderate exercise may be more likely than to induce short-term negative energy balance than light exercise. Findings on the comparability of sessions of different intensities on blood lipids and glucose/insulin dynamics are conflicting.
CONCLUSION: Further research is required before the principle of fractionization can be endorsed with confidence.