Acta Physiol Scand, 1970; 79(4): 435-52, PMID: 5472111

Contraction times and fibre types in intact human muscle

Year: 1970

Buchthal F, Schmalbruch H.
Institute of Neurophysiology, University of Copenhagen, Denmark, On leave from the Institute of Biophysics and Electronmicroscopy, University of Düsseldorf, Germany, working under a fellowship from the Rask-Ørsted Foundation, Copenhagen and the Ernst Poen

Abstract

Twitches were recorded in situ in muscles of normal humans by small transducers connected to a needle in the tendon. The twitches were elicited by stimuli in the endplate zone, the force of the smallest twitches corresponding to the average of one or two motor units. The time to peak contraction was measured of 20–30 bundles of fibres in each muscle examined. The histograms of contraction times agreed with histochemical findings; contraction times longer than 60 msec corresponded to the proportion of fibres rich in mitochondria. Thus, long contraction times predominated in the soleus and gastrocnemius muscles, comprised half the times in the anterior tibia], a third in the brachial biceps (long head) and a few per cent in the brachial triceps muscle (lateral head). Bundles of fibres with short contraction times, those poor in mitochondria had a higher temperature coefficient of the time to peak than bundles with long contraction times. During hypoxia the contraction times shortened. The contraction time of motor units first activated voluntarily lay near the mean of bundles activated electrically. The contraction times of fasciculating fibres were in the range of electrically evoked twitches; the force was about three times that of voluntarily activated units.

Keywords: Contraction Time, muscle function
GID: 1995; Last update: 23.10.2009