Wave Summationo 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) `