Neuromuscular and Body Composition Associations with Estradiol Throughout the Lifespan

Many studies have sought to understand estradiol withdrawal throughout the female lifecycle and its role in the brain and cognitive function, while little is known about its specific role at the neuromuscular junction and body composition. PURPOSE: The purpose of this study is to examine estradiol as a predictor of DXA- derived fat-free mass (FFM), lower body muscle quality (MQ), total fat mass (FM), and maximal muscle activation (EMGRMS). METHODS: This is a secondary analysis from an existing data set using a cross-sectional design of eleven untrained women (pre-menopausal, n=6; age=23.3±4.3 years; height=160.6±8.3 cm; weight=60.5±11.6 kg; post-menopausal n=5; age=61.0±3.3 years; height=164.2±8.0 cm; weight=77.1±9.3 kg). All participants underwent DXA sans to determine FM and FFM. Lower body muscle quality was calculated using a standardized equation relative strength divided by DXA-derived FFM. 1 repetition maximum (1RM) was determined using NSCA guidelines on a standard leg press machine. Surface EMG was collected from the VL and RF with standardized skin prep and landmark placement. All signals were analyzed via EMGRMS for peak activation. RESULTS: Estradiol concentrations were not significantly associated with estimates of FFM or MQ (P>0.10). Estradiol was significantly associated with FM (R2=0.51, p=0.014) and EMGRMS of the VL (R2=0.48, 95% CI[0.000071, 0.000596], p=0.018) and RF (R2=0.59, 95% CI[0.00015, 0.00066], p=0.006) during 1RM leg press. CONCLUSION: Estradiol was more strongly associated with neural activation than with DXA-derived estimates of muscle mass or muscle quality, suggesting that DXA-based measures may not fully reflect functional contractile area across estrogen decline.