[Truncated abstract] Previously, it was postulated that the phenomenon of post-exercise corticomotor depression reflected fatigue of the central nervous system following demanding exercises. However, peripheral fatigue is implicated with maximally demanding exercises, which makes it difficult to ascertain the mechanisms underlying post-exercise corticomotor depression. Recently, Rodrigues et al. (2009) reported a novel index finger flexion-extension task performed at maximal voluntary rate that breaks down rapidly in the absence of peripheral fatigue. They suggested that a loss in central motor command was the most likely cause due to the lack of peripheral changes. To determine the extent in which central change are involved in the breakdown of movement following the index finger flexion-extension task, the aims were to, firstly, investigate the dynamics of post-exercise corticomotor depression and short-interval intra-cortical inhibition following a 10-sec flexion-extension task at maximal and submaximal voluntary rates in both the dominant and non-dominant hand. Secondly, determine if motor practice and neuro-modulation will attenuate movement breakdown during the maximal voluntary rate task. Finally, the thesis will compare the relevance of the flexion-extension task against the finger-tapping task) in Parkinson's disease patients, and to determine the dynamics of post-exercise corticomotor depression following the flexion-extension task in Parkinson's disease patients during OFF and ON levodopa medication. The kinematic findings showed that healthy subjects were not able to sustain both movement rate and movement amplitude throughout a 10-sec index finger flexionextension task at maximal voluntary rate. No change in pre- and post-task ballistic finger flexion/extension speed and M-wave amplitude was observed. A period of post-exercise corticomotor depression and increased short-interval cortical inhibition lasting up to 6 minutes was also observed. Paradoxically, the results also showed that postexercise corticomotor depression and short-interval cortical inhibition were more profound following the flexion-extension task performed at a moderate sustainable rate. Between-hand comparisons also showed an increase in post-exercise corticomotor depression and short-interval cortical inhibition following tasks performed by the dominant hand. The effects of motor practice and neuro-modulation (using a repetitive TMS paradigm at I-wave frequency [ITMS]) on motor performance and learning of the flexion-extension task at maximal voluntary rate were then investigated. Subjects were randomised into a 15-min sham- or real-ITMS that was delivered prior to 6 practice sets of 10-sec flexion-extension task at maximal voluntary rate. Immediately after sham- ITMS, no change in corticomotor excitability was observed compared to baseline. However, motor practice lead to improved task sustainability as demonstrated by a reduction in the decline in movement rate. Corticomotor excitability increased steadily after each training bout, and was maintained up to 20 min after the last practice bout. Following real-ITMS, an increase in corticomotor excitability was immediately observed...