Initial neuromuscular performance in older women influences response to explosive resistance training

The purpose of the study was to identify both demographic and neuromuscular traits that characterize successful or unsuccessful adaptation to resistance training in older women. Twelve, older women underwent electrically evoked muscle twitches for the knee extensors; and performed maximal, voluntary, isometric knee extensions, followed by eight weeks of resistance training. Prior to training nonresponders had 67% higher twitch peak torque than responders (0.29 ± 0.05 vs. 0.18 ± 0.06 Nm·kg(-1) respectively), 64% higher twitch rate of torque development (RTD) (3.96 ± 0.47 vs. 2.42 ± 0.62 Nm·s(-1)·kg(-1)), 51% higher voluntary peak torque (1.86 ± 0.40 vs. 1.23 ± 0.33 Nm·kg(-1)), 101% greater RTD (9.43 ± 1.52 vs. 4.70 ± 2.40 Nm·s(-1)·kg(-1)), 86% greater impulse (0.13 ± 0.01 vs. 0.07 ± 0.03 Nm·s·kg(-1)) and 27% faster motor time (80 ± 13 vs. 109 ± 34 ms), (all P < 0.05). Following training, responders showed an 11% increase in twitch peak torque over baseline (0.18 ± 0.06 to 0.20 ± 0.05 Nm·kg(-1)), 15% increase in voluntary peak torque (1.23 ± 0.33 to 1.41 ± 0.36 Nm·kg(-1)), 47% increase in RTD (4.70 ± 2.40 to 6.93 ± 2.02 Nm·s(-1)·kg(-1)), 43% increase in impulse (0.07 ± 0.03 to 0.10 ± 0.04 Nm·s·kg(-1)), and 26% increase in rate of EMG rise (886 ± 214 to 1116 ± 102 % pEMG·s(-1)) (all P < 0.05). Initially higher muscle mass and contractility, coupled with greater neural drive, likely explains why older women with good muscle performance seem to have a lower capacity for improvement than women with low initial levels of performance.