Baan, Guus C.

Huijing, Peter A.

Maas, Huub

English

University of Twente Research Information

Force transmission via myofascial pathways between EDL muscle and other muscles of the rat anterior compartmentHuub Maas1, Guus C. Baan1, Peter A. Huijing1, 21Instituut voor Fundamentele en Klinische Bewegingswetenschappen, Faculteit Bewegingswetenschappen,Vrije Universiteit, Amsterdam, The Netherlands2Integrated Biomedical Engineering for Restoration of Human Function, Instituut voor BiomedischeTechnologie, Faculteit Werktuigbouwkunde, Universiteit Twente, Enschede, The NetherlandsIntroductionAnatomical studies have revealed intermuscular connections in human (Vleeming et al., 1995) and rat (Vander Wal, 1988). Indications for mechanical interactions between muscles have also been found (Gregor et al.,1988; Riewald & Delp, 1997). It has been suggested that force is transmitted out of muscle onto structures inits direct environment or to neighboring muscles without passing its tendons (Huijing, 1999a). This wasnamed extra- and intermuscular myofascial force transmission. Unequal forces between proximally anddistally measured EDL force, which is direct evidence for the proposed hypothesis, have been reported(Huijing, 1999b; Huijing, 2000).The aim of the present study was to investigate mechanical interactions between muscles in theanterior crural compartment of rat, containing tibialis anterior (TA), extensor hallucis longus (EHL) andextensor digitorum longus (EDL) muscles. Specifically, length effects of the TA+EHL complex on proximaland distal EDL forces are studied.MethodsThe tendons of the muscles of the anterior crural compartment were exposed but connective tissue at themuscle bellies of TA, EHL and EDL was left intact. Isometric force was measured simultaneously atproximal and distal tendons of EDL muscle as well as at the tied distal tendons of TA and EHL (theTA+EHL complex). Effects of TA+EHL complex length and force on proximally and distally measuredforces of EDL muscle kept at constant muscle−tendon complex length were assessed. Supramaximalstimulation of the peroneal nerve excited all muscles maximally and simultaneously.Results & DiscussionIsometricChanges of TA+EHL active force, obtained by lengthening the distal tendons, affected proximal as well asdistal EDL active force, despite the fact that EDL muscle−tendon complex length was left unchanged (Fig.1). Distal EDL forces were significantly higher than proximal EDL forces at low TA+EHL forces. DistalTA+EHL lengthening decreased the proximo−distal difference in EDL active force (from ≈ −18% to 0% ofproximally determined optimum active EDL force). This is brought about by differential effects of increasingTA+EHL length on proximally and distally measured EDL force: diminishing distal force but increasingproximal force significantly.Fig. 1 Proximally and distally measured active force (Fma) of EDL kept at constant muscle-tendon complex length as a function of TA+EHL active force. Forces are normalized withrespect to optimal active force (Fmao) of proximal EDL (2.60 ± 0.40 N, mean ± SD) or theTA+EHL complex (8.55 ± 1.01 N, mean ± SD). Values are shown as mean either + or – SD(n=7).DynamicDuring one experimental trial, the connection of the TA+EHL complex to the force transducer was severed(Fig. 2). First, TA+EHL force decreased from approximately 9 N to just below 6 N. Simultaneously,proximal EDL force declined and distal EDL force increased. Temporary, the force bearing capacity of theconnection between TA+EHL and its force transducer was restored. The definite release of the TA+EHLcomplex, the rapid drop from about 6 N to zero, resulted in more pronounced changes of proximal as well asdistal EDL force. It should be noted that the signal of the force transducer did no longer represent TA+EHLforce after release. Vibration of the force signal of the TA+EHL complex, and likely also of proximallymeasured EDL, is brought about by vibration of the force transducer. These results are compatible with theresults shown in Fig. 1: a small or no difference between proximal and distal EDL active force at highTA+EHL forces, and an increasing difference at low TA+EHL forces.The interaction between properties of the TA+EHL complex and EDL muscle, in isometric (Fig. 1) as well asdynamic (Fig. 2) conditions, indicates intermuscular myofascial force transmission. Such transmission mustbe mediated by the intra-, inter and extramuscular connective tissues. The TA+EHL complex length effectscan be understood on the basis of changes in the configuration, and consequently the stiffness, of thecompartmental connective tissue network. The anterior tibial compartment should therefore be viewed as onefunctional unit consisting of a connective tissue tunnel−like network and muscle fibers that are able toshorten. It is concluded that the concept of morphologically defined muscles acting as independentcomponents is not appropriate to describe force transmission from muscle to bone. These phenomena mayplay an important role under in vivo muscle functioning and, therefore, should be incorporated into models ofhuman movement, which up to now have predominantly been based on properties of "isolated" in situmuscle.Fma EDL (% Fmao EDLprox)0%10%20%30%40%0% 20% 40% 60% 80% 100%Fma (TA+EHL) dist (% Fmao TA+EHL)ProximalDistalFig. 2 Distally force time signals of the TA+EHL complex(upper panel) as well as proximally and distally force timesignals of EDL muscle (lower panel). During isometriccontraction, the connection between the TA+EHL complex andthe force transducer was severed. TA+EHL force dropped tozero, proximal EDL force decreased and distal EDL forceincreased at the same time. The TA+EHL force recoveryindicates that the force bearing capacity of the fixation wasrestored temporary before the TA+EHL complex was definitelydisconnected from its force transducer.ReferencesGregor, R. J. et al.. J. Biomech. 21, 721-32, 1988.Huijing, P. A. J. Biomech. 32, 329-45, 1999a.Huijing, P.A. Arch. Physiol. Biochem. 107, 292-311, 1999b.Huijing, P.A. Proc. of the 5th annual congress of the ECSS. Jyväskylä, Finland, 2000.Riewald, S.A. and Delp, S.L. Develop. Med. & Child. Neurol. 39, 99-105, 1997.Van der Wal, J.C. The organisation of the substrate of proprioception in the elbow region of the rat. PhD.Rijksuniversiteit Limburg, Maastricht. 1988Vleeming, A. et al. Spine, 20, 753-8, 1995.Fm EDL (N)0 100 200 300 400 500 600 70000.40.81.21.62.0Time (ms)ProximalDistal0 100 200 300 400 500 600 700-20246810Time (ms)Fm TA+EHL (N)Fm EDL (N)Fm TA+EHL (N)

Force transmission via myofascial pathways between EDL muscle and other muscles of the rat anterior compartment

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Force transmission via myofascial pathways between EDL muscle and other muscles of the rat anterior compartment

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