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Effects of prolonged exercise at a similar percentage of maximal oxygen consumption in trained and untrained subjects

  • G. C. Gass
  • T. M. McLellan
  • E. M. Gass
Article

Summary

Six trained male cyclists and six untrained but physically active men participated in this study to test the hypothesis that the use of percentage maximal oxygen consumption (%\(\dot VO_{2max} \), as a normalising independent variable is valid despite significant differences in the absolute\(\dot VO_{2max} \) of trained and untrained subjects. The subjects underwent an exercise test to exhaustion on a cycle ergometer to determine\(\dot VO_{2max} \) and lactate threshold. The subjects were grouped as trained (T) if their\(\dot VO_{2max} \) exceeded 60 ml ·kg−1 ·min−1, and untrained (UT) if their\(\dot VO_{2max} \) was less than 50 ml · kg−1 · min-−1. The subjects were required to exercise on the ergometer for up to 40 min at power outputs that corresponded to approximately 50% and 70%\(\dot VO_{2max} \) The allocation of each exercise session (50% or 70%\(\dot VO_{2max} \) was random and each session was separated by at least 5 days. During these tests venous blood was taken 10 min before exercise (−10 min), just prior to the commencement of exercise (−10 min), after 20 min of exercise (20 min), at the end of exercise and 10 min postexercise (+ 10 min) and analysed for concentrations of cortisol, [Na+], [K+], [CI], glucose, free fatty acid, lactate [la-], [NH3], haemoglobin [Hb] and for packed cell volume. The oxygen consumption (\(\dot VO_2 \)) and related variables were measured at two time intervals (14–15 and 34–35 min) during the prolonged exercise tests. Rectal temperature was measured throughout both exercise sessions. There was a significant interaction effect between the level of training and exercise time at 50%\(\dot VO_{2max} \) for heart rate (ϕc:) and venous [la]. At 70%\(\dot VO_{2max} \) and ventilation (\(\dot V_E \)) for the T group and\(\dot VO_2 \)\(\dot V_E \) and carbon dioxide production for the UT group increased significantly with time and there was a significant interaction effect forfc, ]Ia−1], [Hb] and [NH3]. The change in body mass at 50% and 70%\(\dot VO_{2max} \) was significantly greater in the T group. The present study found that when two groups of male subjects with different absolute\(\dot VO_{2max} \) exercised at a similar percentage of\(\dot VO_{2max} \) some effector responses were significantly different, questioning the validity of selecting %\(\dot VO_{2max} \) as a normalising independent variable.

Key words

Lactate Ammonia Core temperature Effector response 

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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • G. C. Gass
    • 1
  • T. M. McLellan
    • 1
  • E. M. Gass
    • 1
  1. 1.Rehabilitation Research Centre and Department of Biological Sciences, Cumberland College of Health SciencesThe University of SydneyLidcombeAustralia

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