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Critical power as an endurance index
J F Vautier1, H Vandewalle, H Arabi
1Laboratoire de Physiologie du Travail, Université de Paris 6, 91 bd de l'Hôpital, 75013 Paris, France.
Applied Ergonomics
|April 1, 1995
Summary
Critical power, a measure of long-term exercise capacity, is best determined using specific work durations. This study found that slope b3, calculated from longer exercise bouts, is a more accurate critical power than slope b1 from shorter, maximal efforts.
Area of Science:
- Exercise Physiology
- Sports Science
- Human Performance
Background:
- The relationship between exhaustion time and work performed in constant-power exercises is often described by the critical power model (Wlim = a + b t(lim)).
- The slope 'b' in this model, known as critical power, is a proposed index for sustained work capacity.
- Previous research has used varying protocols to determine critical power, leading to potential inconsistencies.
Purpose of the Study:
- To compare critical power values derived from short-duration, maximal/supramaximal cycling exercises (slope b1) versus longer-duration exercises (slope b3, 3.5-35 min).
- To investigate the physiological significance of the critical power derived from whole-body cycling work (slope b3).
Main Methods:
- Ten subjects performed five cycling exhaustive exercises at 60, 73, 86, 100, and 120% of maximal aerobic power (MAP).
- Slope b1 was calculated from maximal and supramaximal efforts; slope b3 was calculated from efforts lasting between 3.5 and 35 minutes.
- Physiological markers including lactate levels, heart rate, and oxygen uptake were monitored.
Main Results:
- Slope b1 was significantly higher than slope b3.
- Exhaustion times at power outputs equivalent to b1 and b3 were 29.0 ± 19.1 min and 48.6 ± 9.8 min, respectively.
- Exhaustion times at 60% and 73% MAP correlated significantly with slope b3, but not with slope b1.
- The workload corresponding to lactate steady state was not significantly different from b3 (68.8 ± 6.0% vs 68.7 ± 6.3% MAP).
- Slope b3 represented a workload with a slight but significant drift in heart rate and oxygen uptake.
Conclusions:
- Slope b3, calculated from longer exercise durations, should be considered the critical power for whole-body cycling, rather than slope b1 derived from shorter, maximal efforts.
- Critical power (slope b3) represents a sustainable workload for approximately one hour, beyond which physiological drift becomes significant.
- The findings support the use of slope b3 as a more accurate index of long-term exercise capacity in cycling.