The effects of length and stimulus rate on tension in the isometric cat soleus muscle

We have developed a method of stimulating different groups of motor units in rotation to obtain a smooth contraction of the whole muscle with stimulus rates that would otherwise have given an unfused tetanus

P. M. H. Rack

2014

Scholarcy highlights

  • Attempts to study the control of posture and movement in animals have often been impeded by a lack of knowledge of the behaviour of skeletal muscles under physiological conditions
  • We have developed a method of stimulating different groups of motor units in rotation to obtain a smooth contraction of the whole muscle with stimulus rates that would otherwise have given an unfused tetanus
  • The stimulus rate-tension plot, and the fusion frequency for synchronous stimulation differed at different muscle lengths, but whenever in these experiments a change from synchronous to distributed stimulation was associated with a large decrease in the tension fluctuation, this smoothing was accompanied by an increase in the mean tension
  • The tension fell steeply when the fibre was shortened to sarcomere lengths less than 1-6,t, at which lengths the ends of the thick filaments could be expected to be compressed against the Z lines
  • The isometric tension falls steeply when the muscle is shortened to sarcomere lengths less than about 2-2 It, though the thick filaments in this muscle are 1-5-1-6 Mu in length (Sally G
  • We believe that at low stimulus rates this muscle is best able to generate tension when the fibres are quite still. This property of muscle fibres would explain the gain in tension that occurred whenever, at low stimulus rates, the muscle contraction was made smoother by distribution of the stimulating pulses
  • Mean sarcomere lengths in soleus could be related to the angle at the ankle

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