Fatigue responses in exercise under control of VO2

Area of Science:

• Exercise Physiology
• Sports Science
• Human Performance

Background:

• Understanding fatigue mechanisms during exhaustive exercise is crucial for optimizing training and performance.
• Previous research has explored steady-state exercise but less is known about fatigue responses under controlled oxygen uptake versus constant power output.

Purpose of the Study:

• To compare the physiological fatigue responses during exhaustive supra-lactate threshold exercise under two conditions: controlled oxygen uptake (SS@V.O2Delta50) and constant power output (SS@pDelta50).

Main Methods:

• Eleven trained males underwent an incremental test to determine VO2peak and lactate threshold.
• Subjects performed two exhaustive steady-state cycling exercises at an intensity between lactate threshold and VO2peak.
• Exercise conditions involved either controlled oxygen uptake (SS@V.O2Delta50) or constant power output (SS@pDelta50).

Main Results:

• Controlled oxygen uptake (SS@V.O2Delta50) led to lower average power output and eliminated the slow component of oxygen kinetics.
• Maximal cardiac output (CO) and heart rate (HR) were sustained significantly longer in SS@V.O2Delta50 compared to SS@pDelta50.
• SS@pDelta50 elicited peak oxygen uptake (VO2peak), whereas SS@V.O2Delta50 did not.
• Time spent at maximal CO and HR correlated with time to exhaustion in SS@V.O2Delta50.

Conclusions:

• Fatigue origins differ between controlled oxygen uptake and constant power output during exhaustive supra-lactate threshold exercise.
• Both exercise protocols elicit maximal heart rate and cardiac output, but the duration differs significantly.
• Sustained maximal cardiovascular output may be a key factor in prolonged exercise tolerance under controlled oxygen uptake conditions.