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Ventilatory and gas exchange responses during heavy constant work-rate exercise
Marshall S Riley1, Christopher B Cooper
1Division of Respiratory & Critical Care Physiology & Medicine, Harbor-UCLA Medical Center, Torrance, CA, 90509, USA. marshall.riley@bch.n-i.nhs.uk
Medicine and Science in Sports and Exercise
|January 10, 2002
Summary
Heavy exercise triggers an excessive metabolic response, with oxygen uptake (VO2) exceeding predictions from lighter exercise. This excess VO2 aligns with the slow phase of the VO2 response during intense workouts.
Area of Science:
- Exercise Physiology
- Human Metabolism
- Cardiorespiratory Fitness
Background:
- Oxygen uptake (VO2) typically reaches a steady state within 3 minutes at work rates below the gas exchange threshold (VO2 theta).
- At work rates exceeding VO2 theta, VO2 may continue to rise, often described by a three-exponential model with a slow phase beginning 2-3 minutes into exercise.
Purpose of the Study:
- To precisely estimate the VO2, VCO2, VE, and fC required for exercise above VO2 theta.
- To compare these estimated values with actual measurements during heavy exercise.
Main Methods:
- Nine cyclists completed five 8-minute constant work rate tests, four below VO2 theta and one above.
- VO2, VCO2, VE, and fC were averaged from the final 2 minutes of below-VO2 theta tests and found to be linear with work rate (r2 > 0.95).
- Variables for above-VO2 theta work rates were predicted by extrapolation and compared to measured values.
Main Results:
- VO2 exceeded predicted values by 12.4%, VCO2 by 23.2%, VE by 51.0%, and fC by 8.8% during heavy exercise.
- The onset of excessive VO2 during above-VO2 theta exercise coincided with the start of the VO2 slow phase.
Conclusions:
- Heavy exercise elicits a greater metabolic response than predicted by extrapolation from lighter exercise.
- The excess VO2 observed during heavy exercise approximates the slow phase of the VO2 response.