Seiler, K. S., & Sjursen, J. E. (2002). Effect of work bout duration on physiological and perceptual response to interval training in runners. Medicine and Science in Sports and Exercise, 34(5), Supplement abstract 1535.

Interval training theory is based on fixed-intensity work. However, in practical situations, work levels range extensively. This investigation measured physiological responses to varied intensity interval training. Runners (M = 9; F = 3), after initial testing, performed four interval training conditions of 24 x 1, 12 x 2, 6 x 4, or 4 x 6 minute bouts with equal work and rest durations, resulting in a total of 48 minutes of involvement for each condition.

Average running velocity decreased with increase in interval duration. Peak VO2 was significantly higher for 2, 4, and 6 minute intervals (~92% VO2max) than for 1 minute intervals (~82% VO2max). Blood lactates and RPE were similar across all conditions, both increasing as each exercise bout progressed. The greatest physiological load was experienced in the 4-min intervals.

Implication. Physiological loading in interval training is greatest when work intervals are four minutes. The shorter the interval, the less demanding is the work, but the greater is the potential volume of a particular work quality.

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