| Describe the neural factors that contribute to changes in muscle force | Neural factors involve the ability of the nervous system to modulate muscle force by varying the number of activate motor units (recruitment) and the rate at which they discharge action potential (rate coding). Recruitment - number of muscle fibres contracting within a muscle Rate of modulation - twitch summation of each contracting fibre by increasing rate of action potentials (rate modulation) |
| Differentiate between the different types of rates of modulation | Single twitch – muscle fibre is restimulated after it has completely relaxed (the second twitch is the same magnitude as the first) Twitch summation – muscle fibre is restimulated before it has completely relaxed (the second twitch is added on to the first twitch, resulting in summation) Tetanus – muscle fibre is stimulated so rapidly that it does not have an opportunity to relax at all between stimuli (maximal sustained contraction) |
| Describe the muscular factors that contribute to changes in muscle force | Muscular factors involve differences in muscle size, muscle fibre type, muscle fibre length and the velocity of shortening. The maximum force that a muscle can exert depends on the Physiological cross-sectional area (PCSA). (PCSA) – measure of the number of cross-bridge that are in parallel. Muscles with large PCSA produce large forces but have short muscle fibres and lower contractile velocity. |
| Describe the mechanical factors that contribute to changes in muscle force | Mechanical factors are determined by the origin and insertion of muscle on bones to generate torque (Formula: Torque = Force x Length of power arm) |
| How does muscle size/muscle fibre type (mechanical factor) contribute to changes in muscle force | Fast-twitch – high force and fast fatigue Fast-twitch – moderate force and fatigue resistant Slow-twitch – low force and fatigue |
| How does muscle fibre length (mechanical factor) contribute to changes in muscle force | The length-tension relationship shows that the force that a muscle fibre can exert varies with the degree of overlap between the thick and thin filaments. |
| How does the velocity of shortening (mechanical factor) contribute to changes in muscle force | The force that a muscle fibre can exert varies with the velocity of the contraction. The variation in force is mainly due to the time it takes for cross-bridges to produce force (concentric) and detachment of cross-bridges (lengthening). |
| How does muscle torque (mechanical factor) contribute to changes in muscle force | The action of a muscle about a joint depends on the torque that it exerts Formula: Torque (Nm) = Force (N) x power or load arm (m) |
