Lower Extremity Electromyography During Submaximal Squats with Varying Moments of Inertia

INTRODUCTION: S paceflight impairs muscle size, strength, recruitment, and aerobic capacity. Flywheel-based inertial training (FIT) has been used as a countermeasure to preserve muscle strength and size. The objective of this study was to determine how submaximal FIT squats with varying moments of inertia (MOI) affects lower extremity muscle recruitment. METHODS: S ubjects (7 men, 7 women) completed FIT squats with various MOI: 0.000, 0.005, 0.010, 0.015, and 0.020 kg · m−2 (stages 1–5, respectively) at a pace of 50 squats/min for 3 min each. Electromyography (EMG) of the vastus lateralis, gluteus maximus (GM), biceps femoris, and soleus (SOL) were measured and normalized to maximal effort. Data were analyzed by repeated measures analysis of variance. RESULTS: Peak EMG amplitude [effect size (ES): 0.75–1.43] and integrated EMG activity (ES: 0.73–1.24) for all muscles increased linearly across MOI. Mean eccentric EMG amplitude was greater than concentric for the vastus lateralis (19–63% greater; ES: 1.58). A significant phase × MOI interaction was noted for the GM and SOL (ES: 1.27 and 2.08, respectively) where greater MOI preferentially increased eccentric EMG amplitude. DISCUSSION: I ncreasing MOI increases EMG amplitude of hip extensors, knee extensors, and plantarflexors during submaximal FIT squats in the concentric and eccentric phases. At higher MOI, EMG amplitude is preferentially increased in GM and SOL, especially in the eccentric phase. Submaximal FIT squats can be performed for up to 3 min continuously with active concentric and eccentric phases. This training modality may concomitantly preserve muscle and cardiorespiratory fitness during unloading but this remains to be tested.