Oxygen uptake as related to work rate increment during cycle ergometer exercise.

Area of Science:

• Exercise Physiology
• Human Metabolism
• Sports Science

Background:

• The linear relationship between oxygen consumption (VO2) and work rate during incremental cycle ergometry is commonly observed.
• This relationship is often assumed to reflect a constant cost of external work.

Purpose of the Study:

• To investigate whether the relationship between VO2 and work rate is truly linear and constant.
• To determine if varying the rate of work incrementation affects the VO2/work rate relationship.

Main Methods:

• 10 healthy men performed cycle ergometry to exhaustion with varying work rate increments (15, 30, 60 W/min).
• VO2 was measured continuously.
• The relationship between VO2 and work rate (delta VO2/delta wr) was analyzed using linear regression, excluding initial and final exercise phases.

Main Results:

• The overall delta VO2/delta wr varied significantly with the rate of work incrementation (11.2, 10.2, and 8.8 ml.min-1.W-1 for 15, 30, and 60 W/min tests, respectively).
• The lower halves of 15 and 30 W/min tests showed values (9.9 ml.min-1.W-1) similar to aerobic work costs.
• The upper halves of the tests showed significant differences in delta VO2/delta wr (12.4, 10.5, and 8.7 ml.min-1.W-1 for 15, 30, and 60 W/min tests, respectively).

Conclusions:

• The observed linear VO2-work rate relationship is likely fortuitous.
• The energy cost of exercise varies with work rate and test duration.
• Factors influencing these variations include the contribution of anaerobic energy sources and the increased metabolic demand at higher work rates.