Wave Summation o The degree to which a muscle contracts is dependent upon several factor – including the number of motor units recruited by the brain o The number recruited, will determine the FORCE that can be generated within the muscle. o The greater the strength required – the greater the number of motor units (and therefore muscle fibres) that contract. o The frequency with which impulses arrive at the muscle fibres o The motor unit will respond to a stimulus (impulse) by giving a ‘twitch’ – a brief period of contraction followed by relaxation When a second impulse is applied to the Motor Unit before it completely relaxes from the previous stimuli, the sum of both stimuli occurs – increasing the total contraction o THIS IS MULTIPLE WAVE SUMMATION

Wave Summation When rapid firing of stimuli occurs, giving muscles little or no time for relaxation – Tetanus/tetanic contractions take place An increase in total contraction can be explained by the release of calcium ions which causes greater cross bridge attachment of myosin onto actin. Prac: High degree of force to be generated over a relatively short period of time – such as a shot putter. Multiple Wave summation – muscle fatigue will soon kick in.

Spatial Summation Athletes requiring muscular forces over an extended period of time, will recruit motor units slightly out of synchronisation. Therefore they will not all contract at the same time. Whole muscle shares the workload – so when some motor units contract, others will be recovering. This spreads fatigue throughout the muscle, therefore delaying the ‘fatiguing effects’ throughout the muscle. M.U 1+3 contracting simultaneously, while MU 2+4 are recovering (see diagram) `