Zafeiridis, A., Sarivasiliou, H., Dipla, K., & Vrabas, I. (2009). The effects of interval vs. heavy continuous exercise programs on oxygen consumption, heart rate, and lactate responses in adolescents. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

"Short and long high-intensity intermittent exercise, as well as continuous exercise have been consistently used to improve aerobic performance. Studies in adults have reported that short high-intensity exercise elicits greater VO2 responses compared to moderate intensity (50-75% VO2max) continuous exercise. However, when continuous exercise is performed at heavy intensity (above lactate thresholds for ~25 minutes) a slow component that is developed drives the metabolic rate closer to VO2max. No study has compared VO2 responses among short and long high-intensity intermittent exercise and heavy continuous exercise. The study of VO2 response during different aerobic regimens is essential since it characterizes the exercise stimulus and thereby aerobic adaptations. The VO2 responses to exercise depend also on VO2 kinetics that are likely to be different during growth from those of adults."

This study compared the physiological responses of short high-intensity intermittent exercise, long high-intensity intermittent exercise, and heavy continuous exercise all matched for exhaustion, in young adolescents (N = 9). Ss performed a treadmill test to assess VO2max, vVO2max, and HRmax. Ss performed a short high-intensity intermittent exercise (30 seconds at 110% vVO2max with 30 seconds recovery at 50% vVO2max), a long high-intensity intermittent exercise (3 minutes at 95% vVO2max with 3 minutes recovery at 35% vVO2max), and a heavy continuous exercise (at 83% vVO2max). The end-point for all protocols was a heart rate of 5 bpm below HRmax. VO2 and heart rate were continuously measured and blood samples were obtained before and after protocols to determine lactate.

When matched for total work and exhaustion heavy continuous exercise (at 83% vVO2max) required performance above the anaerobic threshold for ~25 minutes and elicited mean VO2, heart rate, lactate responses, and time spent above 90 and 95% VO2max similar to those in short high-intensity intermittent exercise. Long high-intensity intermittent exercise appears to generate a greater aerobic stimulus compared to short high-intensity intermittent exercise.

Implication. Various forms of high-intensity exercise stimulate adaptation in various aspects of the aerobic response. In adolescents, the differences between short-intermittent, long-intermittent, and continuous exercise would eventually seem to evaporate once each method was allowed to achieve its maximum effect. It would seem that the form of high-intensity exercise is of minor concern. The intensity of the stimulus is what stimulates the greatest adaptation. [Essentially, this study shows that hard training produces greater responses in adolescent athletes. However, one must ask "at what cost?" It would be reasonable to assume that high-intensity training stimuli produce an early onset of overreaching and if continued, overtraining.]

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