Chapter Summary

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Chapter 4 Summary

• Skeletal muscle structure, function and metabolism is a key area in our understanding of sport and exercise science, with this dispersed ‘organ’ accounting for around 50% of the body mass of most individuals.
• Muscle and nerve meet at the neuromuscular junction, a chemical synapse that allows action potentials to cross the synaptic cleft, the endplate potential depolarises adjacent areas of muscle membrane, and the action potential initiates muscle excitation-contraction (EC) coupling.
• Sarcomeres are the basic functional units of the muscle fibre and contain structural and contractile proteins which maintain integrity of the functional unit and allow for the molecular mechanism that is the basis of the sliding filament model of muscle action.
• ATP production is maintained as a result of ADP rephosphorylation (using PCr), through glycolysis, and by oxidative phosphorylation, and the relative contribution of these routes is dependent on the physiological state of the body (e.g. rest, light exercise, high-intensity exercise).
• Key pathways of energy metabolism are glycolysis, the TCA cycle, and the electron transport chain/oxidative phosphorylation.
• The body has a number of mechanisms to control acid-base balance, and these are challenged severely as a result of high-intensity exercise which results in a decline in muscle pH.
• There are two principal muscle cell or fibre types, type I and type II, with different contractile, histochemical and metabolic properties.
• Muscle fibre type proportions have been compared with exercise performance capability to indicate a dominance of type I muscle fibres in endurance trained humans, and a dominance of type II fibres in sprint trained individuals.
• Tension (Force) is generated by muscle and there are distinct relationships between the length of muscle and tension, and, between force and velocity.