Neurophysiological Adaptations to Resistance Training and Repetitive Grasping

Perhaps the most prominent feature of the central nervous system is its ability to respond to experience and its environment. Understanding the processes and mechanisms that govern adaptive behavior provides insights into its plastic nature. Capitalizing on this plasticity is of critical importance in response to injury and recovery: 35, 106), and the importance of its promotion is increasingly recognized by rehabilitation scientists. Neurophysiological techniques permitting study of cortical function in vivo may play a significant role in validating exercise interventions and disease management approaches: 14). It may be possible that with these advances we may better understand the relationship between brain function and therapeutic approaches. For this purpose, we present data on both cumulative and acute effects of motor training to better understand adaptive processes. Neural adaptations accompany resistance training, but current evidence regarding the nature of these adaptations is best characterized as indirect, particularly with respect to adaptation within central or supraspinal centers: 56). To this end, we recorded movement-related cortical potentials: MRCP), i.e. electroencephalography: EEG)-derived event-related potentials, in healthy adults prior to and following a program of lower body resistance training. The cumulative effects of nine progressive training sessions resulted in attenuation of relative MRCP amplitudes. We interpreted these findings in terms of neural efficiency such that for the same pre-training load, central effort is diminished post-training. These data demonstrate the impact of cumulative motor training sessions in fostering a reduction in the level of cortical motor activation. Such a program may be of a particular utility for individuals with limited motor reserves such as those with Parkinson disease: PD). Although cumulative effects may foster a more efficient cortical network, the acute demands of a training session have received less attention. It is reasonable to assume that the reverse might be expected: i.e. augmented amplitude) during a motor training session, much like the muscular system is taxed during resistance training exercise. At the level of the cortex, neural activity was studied by recording the MRCP during 150 repetitive handgrip contractions at a high intensity. The goal of this work was to examine whether central adaptive processes used to maintain task performance vary as a function of age or PD. We found that for healthy young adults, augmented activation of motor cortical centers is responsible for maintaining performance. However, this was not observed for older adults with and without PD, where minimal changes in cortical activity were observed over the duration of the protocol. Our findings suggest that older adults and those with PD may rely on alternative mechanisms: i.e. mobilization of additional cortical and subcortical structures) to maintain task performance as compared to increasing activity locally as seen with younger adults. Taken together, our work further supports the adaptable nature of the central nervous system. We note in passing the utility of the MRCP paradigm for observing such effects