Old Have Blunted Response to Power Training Despite Reduced Antagonist Co-activation

Abstract

PURPOSE: To test the ability of a combination high-velocity / high-resistance training program to enhance muscle strength, power, nervous activation of muscle, and muscle activation time, as well as compare the response to training between young and old. METHODS: The study used 49, inactive women, with young (18-33 yr, n=25) and old (65- 84 yr, n=24) evenly distributed to training and control groups. Maximal, electrically evoked muscle twitches were measured for the knee extensors, then maximal, voluntary, isometric knee extensions were performed in a visually cued reaction time (RT) task, followed by eight weeks of explosive resistance training. Fractionated RT measures were determined using the onset of the visual stimulus, the beginning of the EMG burst, and the initiation of force development. The rate and magnitude of neural stimulation were taken from surface EMG and measures of power and impulse were calculated from the force vs. time curve. RESULTS: Training elicited increases in Peak Torque (+12%, P=0.03) and reduced Antagonist Coactivation (-13%, P=0.02) similarly for both age groups. The young increased Rate of Torque Development by 34% which was greater than young controls (-7%), old training (-1%), and old controls (+8%) (P=0.002). Impulse increased in the young training group by 53% which was greater than young controls (-11%), old training (+12%), and old controls (+9%) (P=0.001). The resistance training did not elicit differences over time for the electrically evoked twitch, reaction time (Premotor Time, Motor Time, or Reaction Time), or nervous activation measures (onset EMG amplitude or Rate of EMG Rise). CONCLUSIONS: The explosive force training program employed was ineffective at enhancing muscle twitch characteristics, neural drive, or reaction time in either young or old. The program did elicit equivalent improvements in peak muscle force in both young and old modulated through a reduction in antagonist coactivation. Older participants showed less of an improvement in the rate of force development and contractile impulse than young suggesting that the best strategy for effective aging is to preserve muscle power rather than attempt to develop it late in life.