Changes In Grip Strength During 5-day Metabolic Reduction

PURPOSE: Many animals reduce metabolic rate and core temperature to survive harsh environments and conserve resources while preserving skeletal muscle health. While humans do not do this naturally, inducing such changes could have practical applications. Lowering metabolism decreases use of finite resources (e.g. food and O2 consumption, CO2 scrubbing capabilities), which may be beneficial in scenarios where resources are limited (e.g. spaceflight, austere terrestrial environments). However, the effects of sustained metabolic reduction on muscle strength are unknown. We previously demonstrated a sublingual loading dose of dexmedetomidine followed by an 18-hour subcutaneous infusion (SQI) effectively reduces metabolism in healthy volunteers. In this study we examined changes in skeletal muscle strength over five days of sustained metabolic reduction, using grip strength as a proxy measurement of global strength. METHODS: Participants completed five-day, controlled laboratory studies. To induce metabolic suppression, participants received an oral loading bolus of dexmedetomidine (1 μg/kg) followed by an 18-hour SQI (1 μg/kg) each day. We assessed metabolic rate and reduction with indirect calorimetry and doubly labeled water. During the wake period of each 24-hours, we evaluated daily muscle strength with handgrip dynamometry prior to performing a whole-body isometric and flywheel resistance training protocol. RESULTS: We observed a mean decrease of 1.4 kg in grip strength over the 5-day protocol (Figure 1; p < 0.01). CONCLUSIONS: Our results suggest a significant decrease in muscle strength occurs during this metabolic reduction strategy. Future research should assess muscle strength using whole body measures instead of proxies and evaluate novel methods of muscle health preservation including nutritional strategies. Supported by: NASA Grant NNX16AO69A; NIH grant UL1TR001857