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Show COLLEGE OF HEALTH UNDERGRADUATE RESEARCH ABSTRACTS Tony Church James C. Martin 30 INCREASING DUTY CYCLE DURING SINGLE-LEG CYCLING TO APPROACH IN VITRO POTENTIAL: CAN THE LEG DO WHATTHE MUSCLE CAN DO? Tony Church (James C. Martin) Department of Exercise and Sport Science University of Utah Muscles produce force and power when they actively shorten. Many locomotor tasks involving cycling action are composed of active shortening and passive lengthening phases. If the shortening and lengthening phases each occupy 5 0 % of the cycle, muscle can only produce power for half the time. Bicycling is a c o m m o n activity for sport, recreation, and rehabilitation, which involves cycling contractions. Many modifications have been made to the conventional bicycle crank arm and circular sprocket system to increase power, including oval and non-circular chain rings, with limited success. One approach to increasing power output is to increase the portion of a pedal cycle that the leg and hip are spent in extension (primarily quadriceps and gluteus maximus shortening), which may increase maximal power produced per pedal cycle. W e hypothesized that by utilizing a single-leg cycling mechanism with a duty cycle of 65/35% (extension/flexion), w e could achieve significant gains in power production per pedal cycle. In order to assist in coordinating the extremely rapid leg flexion phase, a spring and counterweight device was fitted to the non-drive side of the ergometer. Three male and two female cyclists each performed a 5-minute double-leg cycling warm-up, followed by six approximately 5-second maximal sprints on a cycle ergometer, with two minutes of recovery between sprints. Three sprints were at 50/50% duty cycle and three at 65/35% duty cycle. Maximum per cycle average power output at baseline (50/50%) was compared to maximum per cycle average power output at 65/35%. Results indicate significant variability in individual performance during the exaggerated duty cycle. Three of the five subjects increased power output, with a maximum individual increase of 7.31%. However, the results for the study population (N=5) were not statistically significant (p=0.73). While the increased time spent in muscle contraction may have produced instantaneous power gains during the leg extension phase, all participants encountered difficulty in coordinating the extremely rapid flexion phase. While the assistive mechanism provided some help, enough power was lost in this phase to essentially negate the benefits of the lengthened extension phase. |