Lower Loading Schemes Show Higher Power Generation and Activation of Select Muscles During Exercise on a Gravity‐Independent Resistance Device

Abstract

Exposure to microgravity in space has resulted in reduced muscle size and strength. The YoYo™ inertial flywheel device presents a gravity‐independent method to counteract effects of deconditioning due to microgravity exposure. Previous studies utilizing flywheel devices have been shown to induce muscle size and strength during ambulation, unilateral lower limb suspension, and bed rest. Research examining optimal exercise prescription using flywheel devices is lacking. With the growing population of female astronauts, the purpose of this study was to explore the effects of squatting with various amounts of flywheel resistance on electromyography (EMG) of the leg musculature to more effectively guide the prescription of exercise regimens using flywheel devices. Eleven recreationally trained females who have exercised regularly for 6 months prior (20.2 ±1.6 yrs, 167 ±6.8 cm, 133.32 ±7.5 kg.) participated in the study. Participants conducted four randomized sets of seven repetitions of the squat exercise at different loading schemes. Loads were determined by interchanging and/or combining flywheel disks of two different moments of inertia: #1 disk (0.025 Kg*m2 moment of inertia) and #2 (0.050 Kg*m2) into four different loading schemes: #1 disk (0.025 Kg*m2), #2 disk (0.050 Kg*m2 m), #1, #2 disks (0.075 Kg*m2 m), and two #2 disks (0.100 Kg*m2 m). Average and peak power generation (W) and muscle electrical activity (uV) of the vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM) were measured utilizing Bluebrain software and a Noraxon DTS Desktop EMG system. A linear mixed‐effects model was used to determine the effects of load and repetition on the dependent variables with significance set at p ≤ 0.05. Analysis revealed a significant main effect for load (p < 0.001) and repetition (p < 0.001) with the #1 disk showing the highest power output and a general increase in power output as exercise sets progressed (repetitions increased). Load showed a trend (p = 0.052) for peak EMG activity of the RF with Disk #2 having the highest peak EMG and increasing EMG activity as sets progressed (rep main effect, p = 0.002). Mean EMG activity was affected by load only for the BF (p = 0.014) with a trend for the GM (p = 0.058) both showing highest mean activity during the #1 disk set. In conclusion, the YoYo™ flywheel may be more effective in targeting specific muscles at lower loading schemes due to higher activations of muscle. Power output was consistently higher at lower loading schemes, suggesting more effective usage at lower loading schemes with the unique eccentric overload that occurs with this device. Results suggest possibilities of prescribing exercise on the flywheel device utilizing lower inertial loads but also highlight a need to explore additional parameters such as number of sets and repetitions needed to optimize chronic adaptations to exercise on a flywheel device.Support or Funding InformationThis research was supported by the National Institutes of Health under Award Numbers; 5UL1GM118979; 5TL4GM118980; 5RL5GM118978.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.