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Human Skeletal Muscle Possesses an Epigenetic Memory of Hypertrophy | Scientific Reports

Analysis of lower limb lean mass via DEXA, identified a significant increase of 6.5% (1.0%; P=0.013) in lean mass after 7-wks of chronic loading compared to baseline (20.741.11kg loading vs. 19.471.01kg baseline). Following 7-wks of unloading, lean mass significantly reduced by 4.6%0.6% (P=0.02) vs. the 7 weeks loading, back towards baseline levels (unloading, 19.831.06kg), confirmed by no significant difference between unloading and baseline. Subsequently, a significant increase in lean mass of the lower limbs was accrued after the reloading phase of 12.41.3%, compared to baseline (reloading, 21.852.78kg, P=0.001, Fig. 1Ci ), resulting in an increase of 5.91.0% compared to the earlier period of loading (P=0.005). Pairwise t-test analysis that corrected for any lean mass that was maintained during unloading demonstrated a significant increase in lean muscle mass in the reloading phase (unloading to reloading), compared to the loading phase (baseline to loading) (P=0.022; Fig. 1Cii ). Analysis of muscle strength suggested a similar trend. Isometric peak torque increased by 9.33.5% from 296.222.1Nm at baseline to 324.527.3Nm after 7-wks of loading, this difference was not statistically significant (Supplementary Figure 2 ). Upon 7-wks of unloading, peak torque reduced by 8.32.8% vs. loading, back towards baseline levels. Upon subsequent reloading, a significant 183.6% increase in isometric peak torque production (349.627.7Nm) was observed compared to baseline (P=0.015; Supplementary Figure 2A ).