Clara Mitchinson, Lance Bollinger. University of Kentucky, Lexington, KY.

BACKGROUND: Spaceflight induces rapid loss of muscle mass and aerobic capacity. Flywheel-based inertial training (FIT) - a gravity-independent form of exercise - provides external resistance through the moment of inertia (I = ½ mr2) of a rotating disk in a velocity-dependent manner. FIT preserves muscle mass during prolonged unloading and increases aerobic capacity in ambulatory subjects. Optimizing FIT exercise protocols for muscle recruitment and cardiorespiratory responses may improve exercise efficiency and reduce exercise hardware needs. PURPOSE: To determine cardiorespiratory and muscle recruitment responses to FIT with varying workloads. METHODS: We will recruit 40 healthy participants (20M, 20F) between the ages of 18 and 50 y who regularly engage in aerobic and resistance training. Each participant will visit the lab four times. The first session will consist of screening and body composition testing (Bioelectrical Impedance Analysis, BIA). The second session will consist of a maximal intensity graded exercise test using a bicycle ergometer and familiarization with the FIT exercise device (Exxentric Kbox 4Pro). At least 3 d after the familiarization visit subjects will complete session 3 and will then complete session 4 at least 7 d later. During testing each participant will complete unloaded quarter-squats at 30 and 50 repetitions per minute. Squat depth (60⁰ knee flexion ) will be monitored by wireless electrogoniometer of the knee in real-time. This procedure will be repeated with increasing moments of inertia increments of 0.005 kg∙m2. Cardiorespiratory (heart rate, gas exchange) and muscle recruitment (electromyography of the gluteus maximus, vastus lateralis, biceps femoris, and soleus) data will be collected during FIT exercise. Reliability of cardiorespiratory and electromyography (EMG) data will be compared by Cronbach’s alpha. Responses to speed and inertial load will be compared by 2x2 repeated measures ANOVA with α = 0.05. ANTICIPATED RESULTS : We hypothesize that O2consumption and EMG activity will increase with increasing repetition speed and inertial load. We further hypothesize that there will be a speed x load interaction on O2 consumption and EMG activity. Future work will aim to identify a FIT workload which concurrently elicits sufficient cardiorespiratory and EMG stimulus to prevent systemic deconditioning during prolonged unloading.

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