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In vivo measurement of human wrist extensor muscle sarcomere length changes.

Authors
Type
Published Article
Journal
Journal of neurophysiology
Publication Date
Volume
71
Issue
3
Pages
874–881
Identifiers
PMID: 8201427
Source
Medline

Abstract

1. Human extensor carpi radialis brevis (ECRB) sarcomere length was measured intraoperatively in five subjects using laser diffraction. 2. In a separate cadaveric study, ECRB tendons were loaded to the muscle's predicted maximum tetanic tension, and tendon strain was measured to estimate active sarcomere shortening at the expense of tendon lengthening. 3. As the wrist joint was passively flexed from full extension to full flexion, ECRB sarcomere length increased from 2.6 to 3.4 microns at a rate of 7.6 nm/deg joint angle rotation. Correcting for tendon elongation during muscle activation yielded an active sarcomere length range of 2.44 to 3.33 microns. Maximal predicted sarcomere shortening accompanying muscle activation was dependent on initial sarcomere length and was always < 0.15 microns, suggesting a minimal effect of tendon compliance. 4. Thin filament lengths measured from electron micrographs of muscle biopsies obtained from the same region of the ECRB muscles were 1.30 +/- .027 (SE) microns whereas thick filaments were 1.66 +/- .027 microns long, suggesting an optimal sarcomere length of 2.80 microns and a maximum sarcomere length for active force generation of 4.26 microns. 5. These experiments demonstrate that human skeletal muscles can function on the descending limb of their sarcomere length-tension relationship under physiological conditions. Thus, muscle force changes during joint rotation are an important component of the motor control system.

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