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This thesis sought to: 1) examine the effect of a number of organism and task constraints on the control of two forms of physiological tremor, namely postural and finger-pinch force tremor; and 2) determine if the expected constraint-related changes in tremor output were associated with alterations in the control strategy utilised by the performer. The organism constraints were age and resistance-training (for both forms of tremor), while the task constraints were visual feedback, target size and limb preference (postural tremor) and mean force, target shape and limb preference (force tremor). The postural (index finger) tremor amplitude of young adults was significantly greater in the augmented vision (AV) than normal vision (NV) conditions and when using the non-preferred than preferred limb. Even greater differences/changes in postural tremor amplitude were observed as a function of aging and training. Older adults had significantly more index finger tremor amplitude than young adults. Regardless, the older adults who completed a six weeks program of unilateral strength- or coordination-training were able to significantly reduce their tremor amplitude. Although the training-related reductions in tremor amplitude were of a greater magnitude for the trained than untrained limb, a significant reduction in the tremor amplitude of the untrained limb was also observed for the coordination-training group. All of these significant differences/changes in tremor amplitude were associated with significant changes in a number of other dependent variables. For example, the task- and age-related increases in tremor amplitude were primarily a result of greater 8-12 Hz tremor power and were associated with increased EMG activity/co-activation of the extensor digitorum (ED) and flexor digitorum superficialis (FDS) muscles and a significant reduction in intra-limb (index finger-hand and forearm-upper arm) coupling. The significant reductions in tremor amplitude observed for the resistance-trained older adults was a result of a significant decline in 8-12 Hz power and were associated with a significant reduction in ED and FDS co-activation. However, no significant change in intra-limb coupling was observed. The overall trends observed in the results for the finger-pinch force tremor experiments were similar to those for postural tremor. Older adults had significantly more finger-pinch force tremor (i.e. force variability and targeting error) than young adults, although older adults who performed six weeks of unilateral strength-training were able to significantly reduce the force variability and targeting error of the trained limb. No significant training-related reduction in force tremor was however observed for the untrained limb. The significant age-related increase in force tremor was a result of greater low frequency (less than 2 Hz) power and was associated with a significant loss of inter-digit force sharing and coupling as well as tactile sensitivity. Interestingly, the training-related decreases in force tremor were not associated with significant changes in any of the frequency, sharing or coupling measures. Collectively, the results of the five experiments contained in this thesis add much to our understanding of postural and force tremor. Results indicated that numerous task and organism constraints can have a substantial effect on the resulting tremor output. Furthermore, the task- and age-related differences in the power spectral, muscle activity and coupling measures suggested that the changes in tremor output were the result of the use of an altered (sub-optimal) control strategy. The age-related increase in postural and force tremor amplitude may therefore reflect not only an overall decline in neuromuscular system function, but also the relative inability of older adults to effectively coordinate the output of numerous degrees of freedom (limb segments). The effect of the aging process on tremor output was somewhat reversible, with the older adults who performed resistance-training significantly improving their control of both postural and force tremor. There was some evidence that resistance-training could produce cross-education effects in older adults, although these were only statistically significant for postural tremor amplitude in the coordination-training group and for wrist flexion strength in the strength-training group. The relative brevity of the training program (6 weeks) and the observable cross-education effects suggest that the reduction in tremor amplitude and increases in strength were primarily a result of neural adaptations. Such findings further support the prescription of resistance-training for improving physical function in older individuals.

The contemporary training practices of powerlifters are presently being adopted by athletes from a variety of sports seeking to improve their performance. The aims of this PhD were to: 1) identify the contemporary training practices of powerlifters; 2) investigate the biomechanical stimulus the training practices create; and 3) assess whether the training practices have the potential to improve the athletic performance of general athletes The aims were achieved through the completion of five related studies. The first study employed questionnaires and interviews to indentify the contemporary training practices used by elite powerlifters. The results demonstrated that elite powerlifters used a wide variety of training practices, many of which would not have been attributed to the group based on previous literature. The practices were categorised based on their underlying mechanical principles so that the essential features could be investigated in the subsequent studies. A regression-based approach was used in the second study to identify the biomechanical variables associated with performance of common sporting tasks. Maximum force production, power, velocity and rate of force development (RFD) were shown to explain a large percentage of variation in performance of tasks such as sprinting, jumping and changing direction (adjusted R2 ranged from 0.43 to 0.86). These mechanical variables were then measured in a series of experimental studies to assess the potential of the contemporary powerlifting practices to improve athletes‟ physical performance. Assessments were based on a central paradigm in strength and conditioning that asserts that improvements in the ability to express biomechanical variables (e.g. force and power) are best obtained with training practices that maximise acute production of the same variable. Based on the categorisation of the mechanical principles underlying the assessed training practices, three experimental studies were conducted that investigated: 1) the practice of performing traditional resistance exercises at maximum velocity; 2) the effects of manipulating the external resistance through the use of variable resistance material (chain resistance) and an unconventional barbell (the hexagonal barbell); and 3) the effects of altering the movement strategy used to perform the squat. The results of the studies clearly demonstrated that each of the practices investigated could be used to substantially alter and in most cases enhance the biomechanical stimulus created. The practice of performing traditional resistance exercises at maximum velocity revealed that all key mechanical variables were significantly increased (p<0.05) compared with the standard practice of performing repetitions with a sub-maximum velocity. In addition, the results demonstrated that when performing a traditional resistance exercise such as the deadlift at maximum velocity, experienced resistance trained athletes could accelerate the load for the majority (75% to 90%+) of the movement. The second experimental study featuring the separate use of chain resistance and the hexagonal barbell to alter the characteristics of the external resistance demonstrated contrasting effects. The change in position of the external resistance when using the hexagonal barbell significantly (p<0.05) increased the participants' ability to produce high force, power, velocity and RFD values across a range of loads in comparison with the same movement performed with a traditional straight barbell. In contrast, the results from the study evaluating the effects of adding chain resistance showed that whilst force values were increased with the addition of chains, velocity, power and RFD values substantially decreased compared to standard repetitions performed with barbell resistance only. The results also demonstrated that the effects of the chain resistance were more noticeable with heavier chain and barbell loads. The final experimental investigated the effects of altering the movement strategy used to perform the back squat exercise. The results confirmed that changes to the movement strategy had a significant effect on a range of kinematic and kinetic variables. In particular, the contemporary techniques promoted by powerlifters resulted in substantial kinematic and kinetic changes at the hip and reduced kinetic output at the ankle joint. Collectively, the work from this PhD supports the selective use of contemporary powerlifting training practices for the development of athletic potential. Future research should build on the framework created in this thesis, progressing to longitudinal and ultimately implementation studies to increase the likelihood of transferring the results to practice.