Issues of fractionization of exercise (short vs long bouts)

Purpose: To evaluate evidence comparing the influence on hearth outcomes of different patterns and intensities of exercise with equivalent total energ y expenditure. Methods: A computerized literature search, with searches of the reference lists of papers identified. Results: Studies fell into two ca tegories: 1) comparisons of one continuous session of exercise with several short (greater than or equal to 10-min) sessions of the same total duratio n; 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 m easures of cardiorespiratory fitness did not differ significantly between t raining regimens based on long or short sessions. Acute effects of two shor t sessions on excess postexercise oxygen consumption were reported to be gr eater than those of one longer session. By contrast, short-term decreases i n postprandial triglyceride concentrations were found to be similar with th ree short or one long session. Category 2: Higher-intensity training was co nsistently found to elicit greater increases in VO2max than lower-intensity training of longer duration. No conclusion could be drawn for any other ou tcome. A session of hard/moderate exercise may be more likely than to induc e short-term negative energy balance than light exercise. Findings on the c omparability of sessions of different intensities on blood lipids and gluco se/insulin dynamics are conflicting. Conclusion: Further research is requir ed before the principle of fractionization can be endorsed with confidence.