Discharge behaviour of single motor units during maximal voluntary contractions of a human toe extensor.

摘要: A sustained maximal voluntary contraction (MVC) ultimately results in loss of the force-generating capacity contracting muscle—fatigue sets in. Associated with this fall force output is a progressive slowing muscle's relaxation rate (Bigland-Ritchie et al. 1983b), and mean firing rates motoneurones supplying muscle (Grimby 1981; Bigland-Ritchie 1983a; Marsden 1983; Woods 1987; Gandevia 1990; Peters & Fuglevand, 1999). Using intramuscular tungsten microelectrodes to sample brief trains single motor unit action potentials at different times during MVCs, quantitative data on decline has been obtained for three human muscles—adductor pollicis 1983b) first dorsal interosseous (Gandevia 1990) hand, quadriceps femoris leg (Woods 1987). Such an approach allows assessment temporal change population as fatigue develops, but gives little information how discharge individual changes time. It important understand patterns because it argued that motoneurone would serve optimize by ‘matching’ frequency contractile units—the ‘muscular wisdom’ hypothesis (Marsden 1983). In present investigation we have specifically addressed issue ‘adapt’ using follow units over course contraction. We chose study posture locomotion—the primary extensor big toe (extensor hallucis longus)—for which not previously recorded, force-frequency relationships (assessed intraneural motor-axon microstimulation) are known (Macefield 1996). addition measuring peak frequencies, assessing whether fatiguing contraction, examined variability determine or parameter contraction—discharge also speculated play role optimizing (see Bevan 1992). Some work appeared abstract form (Fuglevand 1994).