The relationship between strength, power and ballistic performance.

The purpose of this investigation was to answer the question, "Does Stronger Mean Faster?". After a screening for elbow strength and speed, four groups of 8 subjects were selected for further investigation that fell into the extreme quartiles of the strength and speed continuums. The main investigation employed an apparatus that could freely rotate in the sagittal plane. Three isometric trials were performed at 60 degrees , 90 degrees and 120 degrees of elbow extension. Dynamic trials were performed with relative resistances (0, 20, 40, 60 and 80%), determined from the lowest maximum isometric torque produced from the three joint angles mentioned above, and absolute resistances of 1.1 kg and 2.2 kg. A 1:1 relationship between strength and speed was not established (r=0.498). Normalized peak power proved to be the best kinetic variable for predicting peak velocity (r ranging between 0.793 and 0.918). Individuals with similar peak torques were compared and the patterns of torque development, whether torques peaked early or late during the movement, physiologically agreed with known theoretically established mechanical responses. Similar velocities were also achieved with different peak torques demonstrating a timing issue. Estimated fibre-typing could not account for the performance differences.

An investigation into the deformable characteristics of the human foot using fluoroscopic imaging.

BACKGROUND: To determine the behaviour of the human foot during in vivo loading and unloading. METHODS: Fluoroscopic imaging was used to investigate the movement of the bones and 13 skin markers during loading and unloading for the medial aspect of the left foot. A foot-pressure measuring system was compared with a force plate used to gather kinetic information, simultaneously. Four male and two female subjects performed three tasks that mimicked jumping, walking, and sprinting. Two-dimensional vector displacements were calculated between bone landmarks over time. Foot rigidity was assessed by a 5 mm length variability threshold determined as the difference between the third and first quartiles of the data set. FINDINGS: The displacement between the first metatarso-phalangeal joint and distal aspect of the calcaneous varied more than the 5 mm threshold. A new foot model was developed which included three rigid segments joined together by hinge joints located at the first metatarso-phalangeal joint and between the anterior talus and navicular. The comparison between skin mounted markers and bone landmarks yielded a range of correlation slopes close to 1.00 for both the x- and y-directions. Foot pressure and force plate comparisons were promising (%RMS(error) approximately 10%) for the vertical ground reaction forces but not so for the centres of pressure (%RMS(error) up to 50%). INTERPRETATION: A multi-segment foot model is required to better represent the behaviour of a human foot. No consistent skin marker movement was determined. Better pressure distribution devices need to be developed to determine more accurate foot kinetics. Precise foot kinematics are required in order that accurate ankle moments and reaction forces be determined for the purpose of assessing foot and ankle function.

Ballistic muscle mechanisms determined using an EMG-driven model.

The purpose of this study was to determine the mechanisms responsible for improving ballistic elbow extension. In doing so, an electromyography (EMG)-driven model was developed to predict the actual triceps torque so that the model parameters between subjects could be compared. Thirty-two subjects performed maximum isometric trials at 60 degrees , 90 degrees and 120 degrees of elbow extension to determine torque-angle relations. Dynamic elbow extension trials were then performed against relative loads of 0%, 20%, 40%, 60% and 80% and absolute loads of 1.1 and 2.2 kg. These trials were used to determine the torque-angular velocity relation for each subject. The model predicted the triceps torque during the unloaded, 1.1 and 2.2 kg trials with an average r = 0.964 and an average root mean square error of 4.34 Nm. As a result of the good predictions, a forward dynamics approach was used to substitute different neuro-muscular mechanisms of a poor performance with those from an individual that displayed a superior performance. Performance was shown to improve when these modifications were made. Therefore, the EMG-driven model was capable of modeling the actual muscle torque which allowed for the identification of areas of weakness of a poor performance. A prescription for improvement was identified, albeit artificially, on an individual basis. The next stage is to determine which specific interventions can accomplish those theoretically proposed.