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A Journal on Internal Medicine and Pharmacology

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Gazzetta Medica Italiana Archivio per le Scienze Mediche 2008 February;167(1):1-7

language: English

Exercise intensity and substrate utilization

Birnbaum L. 1, Ritsche K. 2, Boone T. 1

1 Deparment of Exercise Physiology College of St. Scholastica, Duluth, MN, USA
2 Department of Human Performance and Sports Science Winston-Salem State University Winston-Salem, NC, USA


Aim. This study compared the effects of low-intensity (30% .VO2max) and high-intensity (70% .VO2max) exercise on substrate utilization in order to help determine an exercise prescription for weight loss.
Methods. Ten college-aged males exercised at two different intensities on a treadmill for 30 min each. Heart rate (HR), oxygen consumption ( .VO2), expired carbon dioxide ( .VCO2), respiratory exchange ratio (RER), and total caloric expenditure were measured during both exercise sessions. Total fat and carbohydrate calories burned were determined from each subject’s average RER during each exercise bout.
Results. Significant differences were found between .VO2, .VCO2, and RER, and thus substrate utilization at the two exercise intensities. During exercise at 30% .VO2max, the average percent of calories derived from fat oxidation was 39.5% (71 calories) and the remaining 60.5% (108 calories) was derived from carbohydrate oxidation. During the 70% .VO2max session, 90.1% (374) of the calories were derived from carbohydrate oxidation compared to 9.9% (41 calories) derived from fat oxidation.
Conclusion. The results of this study indicate that low-intensity exercise is better than high-intensity exercise for maximizing the loss of fat calories provided the duration is sufficient to burn a significant number of calories. A brisk walk at 5 or 6 km·HR-1 is the appropriate exercise intensity to safely decrease body fat among persons who are overweight and obese. Overweight persons are also more likely to maintain a low-intensity rather than a high-intensity exercise program, thus increasing the probability of long-term success.

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