UBC Theses and Dissertations
The effect of cadence on aerobic and anaerobic contributions to the total energy requirements of cycling at constant power output Reimer, Brad W.
Steady-state cycling at constant power output can be achieved at any one of a number of cadences. Data have been published (Coast and Welch, 1985) that suggest riding at a particular cadence which minimizes oxygen uptake (VO₂) aids in achieving optimal performance. This cadence has been referred to as optimal. However, optimal cadences based solely on an indicator of aerobic metabolism (e.g. VO₂) fail to recognize any contributions made by anaerobic metabolism to the total energy costs of performing the work. The anaerobic contribution becomes particularly important at power outputs greater than a rider's anaerobic threshold. This study was designed to evaluate the effect of cadence on a) the contributions of the aerobic and anaerobic energy pools to the total energy cost of cycling and b) the EMG activity of five major leg muscles at constant power outputs below and above the anaerobic threshold. Male cyclists (n=4) completed progressive, incremental maximal exercise tests at cadences of 60 and 120 rpm to determine the ventilatory threshold (Tvent) for each cadence. Six minute steady-state rides at power outputs 20% below and 20% above Tvent were subsequently performed at both experimental cadences on separate days. VO₂ and excess CO₂ data were collected throughout the steady-state rides and presented as the mean value over the final three minutes of each ride. EMG data were collected during the final 10 seconds of each six minute ride and averaged to represent one mean cycle of normalized EMG activity. Both VO₂ and excess CO₂ were found to be significantly greater (p < 0.05) at 120 rpm than at 60 rpm. However, when these data were corrected to account for the zero-load costs of cycling at each cadence, no significant differences were found in either variable. Only one of the five muscles studied (rectus femoris) exhibited significantly greater (p < 0.05) integrated activity at 60 rpm. Based on the results of this study, it was concluded that cadence does play a significant role in the aerobic and anaerobic contributions to the total energy cost of performing work at constant power output. It was found that simply moving the legs at a higher cadence significantly (p < 0.05) elevated the ventilatory response thereby resulting in significant (p < 0.05) increases in the responses at sub-Tvent and supra-Tvent power outputs. Cadence was also found to have a significant effect on the amount of activity in the rectus femoris, but not on any other muscle studied suggesting that there may be a shift in the metabolic profile of the active muscle fibers that cannot be measured by the EMG quantification methods used in this study. It was concluded that the increases in steady-state VO₂ and excess CO₂ observed with increases in cadence were primarily due to the increase in the energy requirements of the lower limb which is moving at a higher rate. The effect of load at each cadence was not a significant factor. The absolute amount of muscular activity did not significantly change between the two cadences suggesting that the mechanisms underlying muscle activation at different cadences may be more complicated and require measures more sensitive than surface EMG.
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