Parker, D. L., Peiffer, J., Faria, I. E., & Quintana, R. (2006). Heart rate and perceived effort do not regulate pacing during a cycling time trial. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1536.

This study determined if perceived effort or heart rate regulate pacing during a 576 kJ cycling time trial. Highly trained cyclists (N = 9) served as Ss. Prior to completing ergometer time trials, each S underwent a graded exercise test to determine VO2max and peak aerobic power (Wmax). Ergometer resistance was adjusted based on the S's Wmax to approximate 70% Wmax at 90 rpm. Ss then completed a 576 kJ time trial as fast as possible altering power output by altering cadence. 576 kJ was chosen as it closely approximates 20 Km. Heart rate, power output, and ratings of perceived exertion were measured every 28.8 kJ (~1 Km).

Power output during the time trial fell significantly at the fourth kilometer compared to that recorded in the first kilometer. After the fourth kilometer, power output did not change significantly. Rating of perceived exertion rose significantly at the fourth kilometer compared to that recorded in the first kilometer, then again rose significantly at the eighth kilometer, and rose still further at the nineteenth and twentieth kilometer. Heart rate rose significantly at the third kilometer compared to the first kilometer. It did not change significantly until the nineteenth and twentieth kilometer.

Implication. Significant changes in ratings of perceived exertion and heart rates without corresponding changes in power output suggest they do not regulate pacing strategy during a cycling time trial.

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