Myofascial force transmission: muscle relative position and length determine agonist and synergist muscle force

• Published in: Journal of applied physiology (1985) 2003-03, Vol.94 (3), p.1092-1107
• Main Authors: Huijing, Peter A, Baan, Guus C
• Format: Article
• Language: English
• Subjects: Algorithms; Anatomy & physiology; Animals; Biological and medical sciences; Calibration; Connective Tissue - physiology; Electrodes, Implanted; Fundamental and applied biological sciences. Psychology; Hindlimb - physiology; Male; Muscle Contraction - physiology; Muscle, Skeletal - anatomy & histology; Muscle, Skeletal - physiology; Muscular system; Rats; Striated muscle. Tendons; Tendons; Tendons - physiology; Vertebrates: osteoarticular system, musculoskeletal system
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00173.2002

1  Instituut voor Fundamentele en Klinische Bewegingswetenschappen, Faculteit Bewegingswetenschappen, Vrije Universiteit, 1081 BT Amsterdam; and 2  Integrated Biomedical Engineering for Restoration of Human Function, Instituut voor Biomedische Technologie, Faculteit Construerende Technische Wetenschappen, Universiteit Twente, 7522 NB Enschede, The Netherlands Equal proximal and distal lengthening of rat extensor digitorum longus (EDL) were studied. Tibialis anterior, extensor hallucis longus, and EDL were active maximally. The connective tissues around these muscle bellies were left intact. Proximal EDL forces differed from distal forces, indicating myofascial force transmission to structures other than the tendons. Higher EDL distal force was exerted (ratio 118%) after distal than after equal proximal lengthening. For proximal force, the reverse occurred (ratio 157%). Passive EDL force exerted at the lengthened end was 7-10 times the force exerted at the nonlengthened end. While kept at constant length, synergists (tibialis anterior + extensor hallucis longus: active muscle force difference    10%) significantly decreased in force by distal EDL lengthening, but not by proximal EDL lengthening. We conclude that force exerted at the tendon at the lengthened end of a muscle is higher because of the extra load imposed by myofascial force transmission on parts of the muscle belly. This is mediated by changes of the relative position of most parts of the lengthened muscle with respect to neighboring muscles and to compartment connective tissues. As a consequence, muscle relative position is a major codeterminant of muscle force for muscle with connectivity of its belly close to in vivo conditions. anterior crural compartment; connective tissue; length-force characteristics; muscle proximo-distal force difference