An investigation of dynamic human muscle function using a variable inertial loading system

This thesis has developed and utilised an inertial loading system to study human skeletal muscle power output. Specifically, the apparatus has been used to study the effects of different modes of exercise, muscle myosin isoform composition and the effects of ageing on the ability of the lower limb muscles to generate explosive power. A variable inertial loading system was designed and constructed which allowed for the sensitive detection of the rotational properties of a flywheel from which the contractile characteristics of muscle could be inferred. When housed in the Nottingham Power Rig (NPR) the peak power generated by young non-trained male subjects from a single lower limb thrust ranged from 608 - 965 Watts and was found to occur at inertial loads ranging from 0.09 - 0.22 kgm2. To investigate the low power outputs observed at the low inertial loads, where the contraction time was short, a pre release mechanism was incorporated into the flywheel assembly. Significant increases in power output of ~ 17% were achieved at the lowest inertial load (P = 0.02), if a prior build up of isometric torque was allowed prior to movement. This suggested that at the low inertial loads, without the pre release, insufficient time was allowed for the muscle to generate its maximum power output. The flywheel system was incorporated into a cycle ergometer to allow power - velocity characteristics to be examined during inertial sprint cycling. Peak power obtained in young subjects (n = 9) was significantly higher in the cycle exercise when compared with the NPR (1620 vs. 937 Watts). In contrast to the NPR where a parabolic relationship between power and inertial load was observed, during sprint cycling power plateaued above a 'critical' load. It was concluded that the repetitive acceleration of inertial loads, above this critical threshold, will always allow the expression of peak power during cycling as ultimately a velocity will be achieved which corresponds to that required for peak power generation. An analysis of the myosin ...