Measurement of work and power output using friction-loaded cycle ergometers

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Abstract
Friction-loaded cycle ergometers are widely used to measure the work done in short-duration high-intensity exercise. This work is calculated from the product of the average values of flywheel speed and resistive load. This method assumes the flywheel to be revolving at a constant speed and does not take into account the work required to accelerate it. This study examines the possible error resulting from such an assumption. Ten subjects (five males and five females) each performed a single bout of 30 s maximal exercise on a cycle ergometer, from a rolling start, against a resistive loading of 75 g/kg bodyweight. High frequency logging of the flywheel speed was performed by a microcomputer. Two sets of instantaneous and average values of power and work were calculated by the computer at the conclusion of the exercise. The first used the standard method of calculation and did not take into account the acceleration of the flywheel, whereas the second corrected for it. Statistical comparisons of the two sets of results showed: (1) That when no correction is made for flywheel acceleration peak power is greatly underestimated (mean 35·8 ±9·3%). (2) The time taken to reach peak power is shorter when corrected values are used. (3) The instantaneous values of power throughout the 30 s, and the work done calculated for 5 s time intervals, were also different. (4) The total work done during the 30 s was, however, the same irrespective of the method of calculation.

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