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Show COLLEGE OF IEALTH UNDERGRADUATE RESEARCH ABSTRACTS Jennifer Hillam James C. Martin 32 THE ROLE OF PEDAL RATE ON FATIGUE DURNIG MAXIMUM SPRINT CYCLING Jennifer Hillam (James C. Martin) Department of Exercise and Sport Science University of Utah Many previous investigators have reported fatigue during high intensity exercise to be related to anaerobic work [1,2,3]. Anaerobic work relies heavily on glycolytic ATP production and produces lactic acid and other metabolic byproducts. These byproducts can produce a metabolic milieu that reduces muscle contractility and thus produces fatigue[2]. However, recent findings indicate that each maximal contraction cycle may elicit a fixed amount of fatigue.. Our purpose was to examine the role of the contraction cycles on the development of fatigue during maximal cycling exercise. A maximal power pedaling rate relationship was determined for ten trained elite level cyclists. This was then used to determine their optimal pedaling rate, their power at 160 rpms, and a low rate at which the power matched the 160 rpm power (Figure 1). Subjects then performed three 20-s isokinetic cycling trials on three separate occasions. Linear regression showed a relationship between decrease in power and number of revolutions (R2=0.99), power and time (R2=0.66) and power and accumulated work (R2=0.48). Number of revolutions was shown to be the single best predictor in power loss (p<0.00001) (Figure 2). A multiple regression of accumulated work and revolutions with power showed a combined effort of both as significant contributors to predicting linear decreases in power (R2=0.99, p<0.0001). These results support a new idea that pedal rate, and not mechanical work, is the primary predictor of fatigue during maximal sprint exercise. While the present data do not provide a definitive mechanism, w e can speculate that the mechanism of fatigue is most likely associated with excitation and/or relaxation. Specifically, each maximal contraction/relaxation cycle requires release and uptake of calcium. Fatigue of the calcium pumping action, as reported by several authors, would reduce relaxation and could act progressively with each contraction [1,2,3]. Further investigations within the mechanism of this relationship could bring great strides in understanding fatigue. 1300 g 1200 R2 = 0.9706 • • •• • • a. 1000 | 900 SO 150 Figure 1: Power pedaling rate relationship of representative subject l~ l-a"* J - """* ^^SS?: ^==~ 5 10 mud) ======: ""^i^^». -^**|^^: "'""6 S 10 --OMi.1.00 ""•"J* Figure 2: Power graphed against accumulated word, time, and revolutions for the normalized average for 10 subjects. R1 reflects level of correlation between the loss of power and the respective variable. Power normalized to the max power of each subject. [1 ] Allen DG, L a m b GD, Westerblad H. Skeletal muscle fatigue: cellular mechanisms. Physiol Rev. 2008;88(1 ):287-332. [2] Byrd SK, McCutcheon LJ, Hodgson DR, Gollnick PD. Altered sarcoplasmic reticulum function after high-intensity exercise. J Appl Physiol. 1989;67(5):2072-7. [3] Williams JH, Klug GA. Calcium exchange hypothesis of skeletal muscle fatigue: a brief review. Muscle Nerve. 1995;18(4): 421-34. |