The absence of neuromuscular transmission failure in sustained maximal voluntary contractions.

1. Muscle mass action potentials (M waves) were evoked by supramaximal single shocks to the ulnar nerve given at 5‐10 s intervals throughout sustained isometric maximal voluntary contractions (m.v.c.) of the adductor pollicis and first dorsal interosseous muscles. Both muscles were fatigued simultaneously. Recordings were made from the muscle surface and also intramuscularly. 2. During a maximal contraction lasting for 60 s there was 30‐50% loss of force. No decline was observed in intramuscularly recorded M wave amplitude, while the areas of the total and half M wave forms increased due to a slowing in conduction velocity. The area measured over a fixed time period declined. No evidence was obtained that these M wave potentials were contaminated by electrical activity arising in adjacent muscles. The size of the single unit potentials appeared to remain unaltered during maximal voluntary activity. 3. We conclude that neuromuscular block is not a cause of force loss during this type of fatiguing voluntary contraction.

[1]  R. Miledi,et al.  Failure of neuromuscular propagation in rats , 1958, The Journal of physiology.

[2]  B. Burns,et al.  Fatigue and neuromuscular block in mammalian skeletal muscle , 1949, Proceedings of the Royal Society of London. Series B - Biological Sciences.

[3]  O. Lippold,et al.  Altered synchronization of motor unit firing as a mechanism for long-lasting increases in the tremor of human hand muscles following brief, strong effort [proceedings]. , 1977, The Journal of physiology.

[4]  J. J. Woods,et al.  Excitation frequency and muscle fatigue: Electrical responses during human voluntary and stimulated contractions , 1979, Experimental Neurology.

[5]  P. Merton Voluntary strength and fatigue , 1954, The Journal of physiology.

[6]  J. Stephens,et al.  Fatigue of maintained voluntary muscle contraction in man , 1972, The Journal of physiology.

[7]  E. Godaux,et al.  Ballistic contractions in man: characteristic recruitment pattern of single motor units of the tibialis anterior muscle. , 1977, The Journal of physiology.

[8]  E Stalberg,et al.  Propagation velocity in human muscle fibers in situ. , 1966, Acta physiologica Scandinavica. Supplementum.

[9]  P A Merton,et al.  Fatigue of long duration in human skeletal muscle after exercise. , 1977, The Journal of physiology.

[10]  O. Lippold,et al.  Motor unit activity in the voluntary contraction of human muscle , 1954, The Journal of physiology.

[11]  S. Thesleff Motor end‐plate ‘desensitization’ by repetitive nerve stimuli , 1959, The Journal of physiology.

[12]  I Petersén,et al.  Dynamic spectrum analysis of myo-potentials and with special reference to muscle fatigue. , 1968, Electromyography.

[13]  A. Storm-Mathisen,et al.  Fatique of sustained tetanic contractions. , 1955, Acta physiologica Scandinavica.

[14]  R. Kadefors,et al.  An electromyographic index for localized muscle fatigue. , 1977, Journal of applied physiology: respiratory, environmental and exercise physiology.

[15]  O. Lippold,et al.  Changes in muscle activation during prolonged maximal voluntary contractions [proceedings]. , 1979, The Journal of physiology.

[16]  C D Marsden,et al.  Isolated single motor units in human muscle and their rate of discharge during maximal voluntary effort. , 1971, The Journal of physiology.

[17]  B Bigland-Ritchie,et al.  Central and peripheral fatigue in sustained maximum voluntary contractions of human quadriceps muscle. , 1978, Clinical science and molecular medicine.