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Changes in geometry of activily shortening unipennate rat gastrocnemius muscle
Author(s) -
Zuurbier C. J.,
Huijing P. A.
Publication year - 1993
Publication title -
journal of morphology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.652
H-Index - 74
eISSN - 1097-4687
pISSN - 0362-2525
DOI - 10.1002/jmor.1052180206
Subject(s) - sarcomere , aponeurosis , isometric exercise , anatomy , contraction (grammar) , parallelogram , muscle contraction , muscle fibre , gastrocnemius muscle , fiber , geometry , biology , materials science , mathematics , myocyte , physics , skeletal muscle , physiology , hinge , classical mechanics , composite material , endocrinology
Abstract Muscle geometry of the unipennate medial gastrocnemius (GM) muscle of the rat was examined with photographic techniques during isometric contractions at different muscle lengths. It was found that the length of fibers in different regions of GM differs significantly, and proximal aponeurosis length varies significantly from distal aponeurosis length; the angle of the aponeurosis with the muscular action differs significantly among regions at short muscle lengths (full contraction). These data support the idea that the unipennate GM cannot be represented by a parallelogram in a two‐dimensional analysis. As the muscle shortens, the area of the mid‐longitudinal plane of the GM decreases by 24%, a decrease that may be explained by assuming fiber diameter to increase in all directions. The angle between fiber and aponeurosis is determined by more than fiber length. Hence, such important assumptions as a parallelogram with constant area and fiber angle γ changes determined by fiber length changes, freqently used in the theoretical analysis of the morphological mechanism of unipennate muscle contraction, do not hold for the unipennate GM of the rat. Length of the sarcomere within the mid‐longitudinal plane of GM varies from 1.92 to 2.14 μm among the different muscle regions at muscle optimum length (length at which force production is highest), whereas shortening to 6 mm less than optimum length produces a range of sarcomere lengths from 0.89 to 1.52 μm. These data suggest that fibers located in different regions of the GM reach their optimum and slack lengths at various muscle lengths. © 1993 Wiley‐Liss, Inc.