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UBC Theses and Dissertations

The effect of steady rate exercise on the pattern of force production of the lower limbs in cycling Black, Alexander H.


The role of fatigue in the cessation of activity has been studied extensively and reported i n the physiology literature. Biomechanical compensations that occur as a result of fatigue, however, have had little focus in the scientific literature. Data have been published (Black et al. 1992 and Amoroso et al., 1993) that suggest there are biomechanical compensations that occur just prior to the cessation of activity as a result of the fatigue process in cycling. These compensations include increases in the index of effectiveness, earlier maximum force production in the pedal cycle, and increased dorsiflexion at the ankle. These changes suggest that there are compensations by the muscles in response to the onset of whole body fatigue. The purpose of the present investigation was to quantify the biomechanical changes that result from the progressive onset of fatigue in cycling. The criterion measurements included timings of maximum joint angle excursions, timings of maximum force production and timings of maximum joint moments at the ankle, knee and hip. Male cyclists (n=12) completed a progressive, incremental maximal exercise test at 90 RPM on a bicycle ergometer to determine maximum power outputs. Two steady rate, constant power output rides followed: one at 80% maximum power output (max P.O.) to exhaustion, and one at 30% max P.O., for the same length of time as the 80% max P.O. ride. Force data were collected from the right pedal of an instrumented bicycle for 3 pedal cycles at the end of each minute of the steady rate exercise tests. Kinematic data were recorded ongoing throughout the steady rate exercise test. Kinematic and kinetic data for the initial and final minutes of both steady state rides were then time matched and joint moments for the ankle, knee and hip were calculated using the inverse dynamics approach. There were significant differences between the initial and final minutes of the study. These changes included earlier maximum hip extensor moment, greater ankle plantarflexor moment, increased knee flexor moment and increased hip extensor moment (p<0.05). These increased joint moments summed to produce a significantly larger propulsive moment in the final minute of the exercise (p<0.05). These changes were results of changes in the kinematic data and the kinetic data that were the result of fatigue. Based on the results of this study, it was concluded that the increase in the propulsive moment was necessary to overcome a decrease in the index of effectiveness (p<0.05), which was a product of whole body fatigue. The increase i n the propulsive moment was a result of increases in the maximum joint moments at each of the lower limb joints. In summary, as the results of fatigue affect an athlete, the athlete is forced to change the strategy of muscle recruitment which is used to overcome the given power output in order postpone the cessation of exercise.

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