title: Effects of inter- and extramuscular myofascial force transmission on adjacent synergistic muscles: assessment by experiments and finite-element modeling.
abstract: The effects of inter- and extramuscular myofascial force transmission on muscle length force characteristics were studied in rat. Connective tissues at the bellies of the experimental synergistic muscles of the anterior crural compartment were left intact. Extensor digitorium longus (EDL) muscle was lengthened distally whereas tibialis anterior (TA) and extensor hallucis longus (EHL) were kept at constant muscle-tendon complex length. Substantial differences were found in EDL force measured at the proximal and distal tendons (maximally 46% of the proximal force). EDL with intact inter- as well as extramuscular connections had an increased length range between active slack and optimum length compared to EDL with extramuscular connections exclusively: optimum muscle length was shifted by more than 2 mm. Distal EDL lengthening caused the distal force exerted by TA+EHL complex to decrease (approximately 17% of the initial force). This indicates increased intermuscular myofascial force transmission from TA+EHL muscle complex to EDL muscle. Finite-element modeling showed that: (1) Inter- and extramuscular myofascial force transmission leads to a substantial distribution of the lengths of the sarcomeres arranged in series within muscle fibers. Distribution of stress within the muscle fibers showed that the muscle fiber cannot be considered as a unit exerting equal forces at both ends. (2) Increased heterogeneity of mean fiber sarcomere lengths (i.e., a "parallel" distribution of length of sarcomeres among different muscle fibers) is found, particularly at high muscle lengths. This also explains the shift in muscle optimum length to higher lengths. It is concluded that inter- and extramuscular myofascial force transmission has substantial effects on muscle length-force characteristics.
authors: Department of Biomechanical Engineering, Instituut voor Biomedische Technologie, Integrated Biomedical Engineering for Restoration of Human Function, University of Twente, Enschede 7500 AE, The Netherlands. c.a.yucesoy@wb.utwente.nl
authors: Can A
authors: CA
authors: Yucesoy
authors: Bart H F J M
authors: BH
authors: Koopman
authors: Guus C
authors: GC
authors: Baan
authors: Henk J
authors: HJ
authors: Grootenboer
authors: Peter A
authors: PA
authors: Huijing
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004548:Elasticity; D004558:Electric Stimulation; D005205:Fascia / Q000502:physiology*; D020342:Finite Element Analysis; D006614:Hindlimb / Q000502:physiology; D008297:Male; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012518:Sarcomeres / Q000502:physiology*; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical