Changes In Postactivation Potentiation At The Onset Of Exercise Training In Older Adults

Abstract

INTRODUCTION Postactivation potentiation (PAP) of resting twitch force is known to decline with age (Vandervoort and McComas, 1986). The inability to utilize enhanced muscular output may contribute to impaired motor function in the elderly. In daily tasks, older adults seldom experience the high-force muscular contractions that elicit PAP. PURPOSE The purpose of this experiment was to determine the extent to which PAP is recoverable in older adults due to exercise training. For specific applications to frail elderly adults, a low-force, high movement velocity training intervention was tested. The goal of this training protocol was to elicit a high volume of neural activation, which might have a positive impact on PAP and other neuromuscular factors. METHODS Seventeen healthy older adults, (7 males, 10 females; mean ± standard deviation: age 76±6.3 yrs.), who were not actively participating in a strength-training program involving dorsi/plantar flexion exercises, participated in this study. Each subject was required to attend three sessions, each 48 hours apart. At the start of each session subjects were evaluated for PAP by applying supramaximal stimuli to the tibial nerve before and after a 10 second maximal voluntary isometric contraction. Stimuli were applied three times within each of two stimulus trains in which the stimuli were separated by 2 seconds and the trains by approximately 3 seconds. Thus PAP was the difference between the average peak torques of 6 twitches. The training was conducted after testing on both days one and two and consisted of 4 exercises; up-tempo cycling, two plantar flexion exercises, and active and passive ankle rotations. RESULTS Older adults exhibited an average of 24.5 ± 17.7 % PAP at baseline. This is similar to the results of Petrella et al. (1989). In response to the combined effects of training and test contractions, there was a significant increase in PAP (F2.32=3.850, p=0.032). There was an 18.5% increase in PAP from day 1 to day 2, and a 37.0% increase from day 1 to day 3 (D1=24.5±17.7; D2=29.1±16.6; D3=33.6±16.9) There were no significant changes in resting twitch torque, or maximal voluntary torque in this group. CONCLUSIONS These results indicate that PAP is trainable in older adults. It must be noted however, that due to requirements for other aspects of this experiment, training stimuli included maximal voluntary contractions. Thus, we cannot isolate the low-resistance exercises as the only candidate stimuli for increased PAP.