The aim of this thesis is to investigate the responses of the neuromuscular system to changes and constraints during explosive multi-segment movements of the lower limbs. The trunk segment was constrained into different positions during pendulum rebound exercises to observe how the neuromuscular system reorganises the movement. It was also aimed to examine how the neuromuscular system coordinates maximal countermovement jumps when the muscle forcegenerating properties of part and all muscles involved in these movements are reduced by the acute effects of fatigue or increased after training. The kinematic characteristics of pendulum rebound exercises were affected by constraining the trunk segment. Greater knee joint angular velocity was achieved when the movements were performed in the upright sitting posture (90) in comparison to the other sitting conditions (135° and 180°). The constraint applied on the trunk segment did not result in the emergence of a particular segmental movement between the hip, knee and ankle joints and variability was observed in the initiation of the joint extension of all rebound conditions. The absence of a fixed order for joint extension initiation showed that sequential and temporal variances can emerge during rebound jumps, where the hip joint, in most cases,e xtendedb efore the other joints. The biarticular musclesw ere suggestedto regulatet he distribution of forces between joints by transporting the large amounts of energy produced by monoarticular muscles, irrespective of the constraints imposed on the trunk segment. It was proposed the existence of a pre-programmed pattern that guides the execution of the movement irrespective of the constraints applied on the trunk segment. Fatiguing part and/or all muscle groups involved in maximal countermovemenjtu mps suggestedt he existence of a common drive that mediates and controls the activation timing between agonistantagonist muscle pairs. A similar muscle activation pattern found after fatigue indicated that the neuromuscular system does not reorganise the co-ordination strategy of explosive movements to compensate for the acute effects of muscular fatigue and acts without the knowledge of the muscle force-generating properties. The decline in the ability of the muscles to produce force was the major factor responsible for the decreases observed in jump height and changes in several kinematic and kinetic variables of the movement. The early occurrence of the peak joint angular velocity may have contributed to jump height decrease and indicated that an "optimal" solution (high countermovement jump performance) was not found under fatigue. It was suggested that training under fatigue should be avoided because the subjects may learn a muscle activation pattern that does not represent an optimal solution. Countermovement jump training (specific stimulus) was more effective than a weight lifting programme (non-specific stimulus) to improve jump height performance. This occurred despite the greater gains in isokinetic peak torque of the knee flexor and extensor muscles achieved after the nonspecific training programme in comparison to the specific training programme. It was observed that the training using non-specific stimulus did not cause the neuromuscular system to reorganise the controls. The neuromuscular system was able to reorganise the movement after the training programme that used a specific stimulus. It was concluded that the increased jump height performance observed after the countermovement jump programme can be attributed to a compounded effect, in which the increased ability of the extensor muscles to generate large amounts of energy around the hip joint was linked to the ability of the biarticular muscles to transfer part of this energy to the distal joints. It was noticed that movement co-ordination changes are sensitive to the order in which the training stimuli are introduced. Jump height performance was improved to a greater extent when the countermovement jumps programme followed the knee extensor and flexor muscles strengthening programme than when the training programmes were introduced in the opposite order.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:327157 |
| Date | January 2001 |
| Creators | Rodacki, Andre Luiz Felix |
| Publisher | Manchester Metropolitan University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0023 seconds