Kang, J., Chaloupka, E. C., Mastrangelo, M. A., Hoffman, J. R., Ratamess, N. A., & O'Connor, E. (2004). Comparisons between exercise of constant and variable intensity: Physiological and perceptual responses. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 1899.

"An exercise regimen in which intensity varies has become popular within recent years. However, whether it is more demanding than an equivalent exercise of constant intensity remains unknown" (p. S278).

This investigation compared physiological and perceptual responses between exercise of constant and variable intensity. Ss (M = 7; F = 8) underwent two experimental trials. During each trial, Ss performed a 30-minute cycle exercise that was followed by a 30-minute recovery period. In the constant exercise condition, exercise was performed at 65% of maximal heart rate. In the variable exercise condition, the similar intensity was also achieved, although the protocol entailed alternating phases of both higher (~80% VO2max) and lower (~50% VO2max) intensity arranged similarly to what is designed for a typical Spinning™ workout. Oxygen uptake (VO2) and heart rate (HR) were measured throughout both exercise and recovery, whereas ratings of perceived exertion (RPE) were recorded during exercise only. Plasma lactate concentrations were determined at the end of exercise and recovery.

No differences in average VO2, HR, and RPE were found during exercise between the constant exercise condition and the variable exercise condition. During recovery, however, both VO2 and HR exhibited a slower decline in the variable exercise condition and average VO2and HR were higher in the variable exercise condition than the constant exercise condition. Plasma lactate was higher at the end of exercise in the variable exercise condition than the constant exercise condition, but became similar at the end of recovery.

An exercise regimen in which intensity varies exerts no added effect upon physiological and perceptual responses during exercise so long as overall intensity is kept the same. However, this exercise arrangement provokes more persistent elevations in oxygen uptake and heart rate following exercise and this augmented post-exercise metabolism may be mediated in part by elevated plasma lactate.

Implication. Constant and variable workload exercises yield similar physiological effects if the average workload is similar to that of the constant workload. Variable workloads that include higher intensity work levels provoke high oxygen uptake and heart rates suggesting harder work.

Return to Table of Contents for this issue.