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The central nervous system structures involved in the genesis of oscillatory activity within the motor system and their functional role were investigated in humans. Assessment of the common modulation of motor unit firing patterns in various muscle groups reveals that the pattern of descending oscillatory drives to distal hand and axial muscles differs in healthy subjects. Such oscillatory drives can be affected by neurological disease. In rotational torticollis oscillatory drives to the affected muscles are of lower frequency compared to controls and tend to synchronise the firing of motor units between the affected muscles possibly contributing to the symptoms of dystonia. In Parkinson's disease, whilst off dopaminergic medication, there is a decrease in high frequency (15-30 Hz) coherence between distal upper limb muscles. Following clinically effective stimulation of the subthalamic nucleus or the administration of dopaminergic medication the 15-30 Hz coherence is increased. Direct recordings of local field potentials from a macroelectrode inserted into the subthalamic nucleus simultaneously with muscle and electroencephalography over the sensorimotor cortex demonstrate that the subthalamic nucleus is part of a circuit that is entrained in oscillations extending between 7-45 Hz. Significant coherence between signals recorded from the ventralis intermedius nucleus of the thalamus, sensorimotor cortex and contralateral muscle has also been detected in patients surgically treated for the alleviation of tremor. The coherence, which extends up to 28 Hz, may be decreased in the presence of a cerebellar lesion. Recording contralateral muscle and electrocorticographic activity from sites whose functional properties had previously been defined by electrical stimulation further revealed that spatially disparate cortical sites could be coherent and synchronised with each other and with contralateral muscle. This supports the hypothesis that oscillatory activity may have a role in binding together neural activity in functionally related neuronal pools.

Running injuries have been linked to morphology and lower limb function, and changes in foot and ankle biomechanics and function within a run may contribute to the predisposition to injury. This thesis investigates the effects of prolonged running on the foot and ankle, and potential mechanisms underlying changes in foot posture. Methods: A series of studies were undertaken from field to laboratory, measuring foot posture changes after prolonged running of different durations. Further measures of ankle invertor strength and medial ankle stiffness were taken in the laboratory studies as well as kinematic and plantar pressure data captured every ten minutes to enable repeated measures analysis of pedal movement to be conducted. Reliability across the foot posture, strength and stiffness measures was also determined. The latter studies involved the development and mechanical testing of a novel foot orthosis component which was compared to a standard open cell orthotic foam. A double blind randomised controlled trial then compared how the novel and standard foam components affected foot posture, ankle invertor strength and medial and plantar soft tissue stiffness after a 30-minute run. Results: A mean drop in NH and increase in FPI-6 following the half marathon, hour long and 30-minute treadmill runs was seen, with changes decreasing as running duration reduced. Ankle invertor strength and medial ankle stiffness reduced but did not correlate to the change in foot posture. Changes in foot and ankle kinematics were seen within 30 minutes of running. Mechanical testing of the novel orthotic component and standard foam revealed characteristic differences in response to loading, and changes in foot posture measures after 30 minutes of running in the randomised controlled trial were almost identical across both conditions. Further comparison of invertor strength and medial foot and ankle stiffness revealed no significant differences, but a large difference between exertion measures was seen. Conclusion: There was an overall effect of duration of running on changes in foot posture in this thesis, and the foot posture change was moderated by two different foot orthosis conditions although the mechanism remains unclear.

Hypertonia is seen in 85% of people with Multiple Sclerosis (pwMS) resulting in disability and functional restrictions. Hypertonia can be caused by increases in passive stiffness and enhanced stretch reflexes (spasticity) and is frequently managed clinically using passive stretches. However, the optimal parameters of stretching such as the applied torque and stretch duration remain unclear. During commonly prescribed ankle plantarflexor stretches pwMS produced higher torques when standing in a weight bearing position compared to stretches applied using the upper limbs. Stretches could be held for 120 seconds on average and stretch duration was mainly limited by fatigue. People with higher disability tended to favour more supported stretching positions. The effects of stretching for either 30 or 10 minutes using a customised motor at three torque levels covering the range that MS participants could produce was investigated. Compared to the 10 minute stretch, greater reductions in passive stiffness and greater increases in range of movement (ROM) were seen immediately following the 30 minute stretch with the effects being sustained for the 30 minute post stretch period. Higher levels of applied torque resulted in a greater change in ROM however; there was no effect of applied torque on passive stiffness. Stretch reflex mediated stiffness was unaffected by the stretching intervention and showed transient post stretch increases. Ultrasonography was used to investigate changes in muscle–tendon length and strain in pwMS and controls and following stretching. PwMS showed evidence of stiffer muscles and increased tendon length at baseline compared to controls. Following a 10 minute stretch overall muscle length did not increase in pwMS, although increases in strain in the musculotendinous junction region were observed suggesting that more proximal regions of the muscle was likely to have contributed significantly to overall stiffness. This work highlights that stretch duration and levels of applied torque are critical factors in determining the effectiveness of stretches. The pathological mechanisms underlying hypertonia at a molecular and structural level and the effects of stretching on components of the musculo-tendinous structure and on functional ability should be ascertained.