Non-random fluctuations in power output during self-paced exercise

Ross Tucker ¹, Andre Bester ¹, Vicki E Lambert ¹, Timothy D Noakes ¹, Christopher L Vaughan ¹ and Alan St Clair Gibson ^1*

¹ University of Cape Town, South Africa

^* To whom correspondence should be addressed. E-mail: agibson{at}sports.uct.ac.za.

Accepted 28 August 2006

Abstract

Objectives: The aim of this study was to analyze the power output measured during a self-paced 20 km cycling time trial, during which power output was free to vary, in order to assess the level and characteristics of the variability in power output which occurred during the exercise bout.

Methods: Eleven well-trained cyclists performed a 20 km cycling time-trial, during which power output was sampled every 200 m. Power spectrum analysis was performed on the power output data, and a fractal dimension was calculated for each trial using the Higuchi method.

Results: In all subjects, power output was maintained throughout the trial until the final kilometre, when it increased significantly, indicating the presence of a global pacing strategy. The power spectrum revealed the presence of 1/f-like scaling of power output and multiple frequency peaks during each trial, with the values of the frequency peaks changing over the course of the trial. The fractal dimension (D-score) was similar for all subjects over the 20 km trial and ranged between 1.5 and 1.9.

Conclusions: The presence of an endspurt in all subjects, 1/f-like scaling and multiple frequency peaks in the power output data, indicates that there may be both a global pacing strategy and multiple, simultaneously occurring system control strategies, and the shift of these frequency peaks during differing epochs of the trials suggests that there may be dynamic alterations in the underlying control strategies that regulate pacing strategy. The measured oscillations in power output during cycling exercise activity therefore may not be system noise, but may be associated with system control mechanisms.

Key Words: endspurt, fatigue, feedback, fractal, pacing

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