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First published online December 15, 2004
Journal of Experimental Biology 208, 129-140 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01360
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Extramuscular myofascial force transmission for in situ rat medial gastrocnemius and plantaris muscles in progressive stages of dissection

J. M. Rijkelijkhuizen1,*, G. C. Baan1, A. de Haan1,2, C. J. de Ruiter1 and P. A. Huijing1,3

1 Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands
2 Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Crewe and Alsager Faculty, Cheshire ST7 2HL, UK
3 Integrated Biomedical Engineering for Restoration of Human Function, Instituut voor Biomedische Technologie, Faculteit Construerende Wetenschappen, Universiteit Twente, Postbus 217, 7500 AE Enschede, The Netherlands



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  		Fig. 1. Representation of the experimental set-up. (A) Medial view of the GM and PL in the experimental set-up after biceps femoris muscle, semitendinosus and gracilis posticus muscles were removed. The GM and GL were separated by cutting fibres in such a way that the GM was not damaged. The GM is made transparant in the image to show the position of the PL. The soleus, deep flexors, peroneal muscles and muscles in the anterior crural compartment were left intact, but for clarity are not shown. Only extramuscular tissues around the GM were left intact (see B-D). Image A also shows the sciatic nerve (SN) and the femoral artery (FA) approaching GM laterally and medially respectively and entering GM proximally as a neuro-vascular tract (i.e. nerve, bloodvessel and surrounding connective tissue). Proximally, the dissected origin of the GM was attached to a force transducer using a metal rod (represented by an arrow). In the initial condition, the distal tendons of the GM and PL, the epitendinous tissues and a piece of the calcaneal bone were connected to a force transducer with a metal rod (represented by an arrow). The femur was clamped in such a way that the knee could be fixed at an angle of approximately 120°, with the lower leg horizontally. (B) Extramuscular tissues around the distal GM and PL tendons, i.e. remnants of the general fascia, epimysium, neuro-vascular tract and compartmental fascia (referred to as epitendinous tissues and indicated by an arrow). Medial view. Note that these tissues are exposed only for clarity by lifting the piece of the calcaneal bone. (C) Extramuscular tissues around the GM and PL muscle bellies, i.e. remnants of the general fascia and epimysium. Dorsomedial view. This image does not provide a representation of the position of the muscles in the experiment. For clarity, the GM and PL are pulled apart to expose the extramuscular tissues (indicated by an arrow and broken lines). (D) Medial view of the dissected origin of GM. The origin of GM was dissected with a piece of the femur. The image also shows a part of the neuro-vascular tract embedding the femoral artery approaching and entering GM proximally (indicated by an arrow). The sciatic nerve approaches the GM from the lateral side and is therefore not visible.

 


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  		Fig. 2. Overview of the experimental conditions in progressive stages of dissection. Note that images do not show the position of the rat hind limb in the experimental set-up. (A) Initial condition. Dorsal view of the lower hind limb of the rat after the GM and GL have been separated. Below the GM and GL, the PL is visible. The distal tendons of the GM and PL were the only tendons connected to the calcaneal bone. The tip of a pair of tweezers is shown in the image, pointing at the GM and PL tendons. The cut calcaneal bone was connected to a force transducer (not shown). The dissected proximal origin of GM is not visible in this image. SN indicates the sciatic nerve. (B) Post PL-tenotomy. Dorsolateral view. A very small area of the connective tissue (barely visible but indicated by an arrow) was dissected to perform the PL-tenotomy. (C) Connective tissues around the GM muscle belly. Medial view. After dissection of the epitendinous tissues, the GM muscle belly is still connected to extramuscular tissue (i.e. remnants of the general fascia and epimysium). These tissues, holding the muscle belly, are indicated by an arrow. (D) Full dissection of the GM muscle. Ventral view. The GM muscle belly has been dissected free from its extramuscular tissues except for the neuro-vascular tract (i.e. nerves, blood vessels and the connective tissue). The arrow indicates the femoral artery entering the GM proximally and medially; the nerve is entering GM proximally and laterally and is therefore not visible in this image. In this view, the dissected GM origin, with a piece of the femur, is visible.

 


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  		Fig. 3. Forces exerted at the proximal and distal transducers by rat medial gastrocnemius (GM) and plantaris (PL) muscles connected to extramuscular connective tissue at the level of the tendons and the muscle bellies (initial condition), within a dissected compartment. (A,B) Proximal active and passive force exerted at the GM tendon. (C,D) Distal active and passive force exerted at the calcaneal bone. Proximal force (closed symbols) represents force exerted predominantly by the GM muscle. Distal force (open symbols) represents predominantly the summed force exerted by the GM and PL muscles. Note that, at short lengths, the summed distal active force was lower than the proximal active force. Muscle-tendon complex length (Lm+t) is expressed as deviation from optimum length (L0). Force is shown as mean ± S.E.M.

 


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  		Fig. 4. Forces exerted at the proximal and distal transducers by rat GM and PL muscles connected to extramuscular connective tissue, within a dissected compartment after distal PL-tenotomy. Note that after distal PL-tenotomy, epitendinous tissues connected to the calcaneal bone were left intact. (A) A comparison of proximal active force exerted at the GM tendon (closed symbols) and distal active force exerted at the calcaneal bone (open symbols). (B) A comparison of proximal passive force exerted at the GM tendon (closed symbols) and distal active force exerted at the calcaneal bone (open symbols). Note that, despite PL-tenotomy, distal active force was higher at long muscle lengths and lower at short muscle lengths than proximal active force. Distal passive force was higher than proximal passive force. Muscle-tendon complex length (Lm+t) is expressed as deviation from optimum length (L0). Force is shown as mean ± S.E.M.

 


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  		Fig. 5. Effect of distal plantaris-tenotomy on proximo-distal force differences. (A) Proximo-distal active force differences. (B) Proximo-distal passive force differences. Closed symbols represent the data before tenotomy (i.e. both medial gastrocnemius (GM) and plantaris (PL) distal tendons connected to calcaneal bone). Open symbols represent post-tenotomy data. Note that a substantial fraction of PL force was still transmitted to the distal force transducer. Muscle tendon complex length (Lm+t) is expressed as deviation from optimum length (L0). Force is shown as mean ± S.E.M.

 


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  		Fig. 6. Force-length characteristics of partially dissected rat medial gastrocnemius (GM) muscle connected only at the level of the muscle belly by extramuscular connective tissue (i.e. remnants of the general fascia and epimysium). (A) Active forces exerted at the proximal tendon (closed symbols) and at the distal tendon (calcaneal bone) (open symbols). (B) Passive forces exerted at the proximal tendon (closed symbols) and at the distal tendon (calcaneal bone) (open symbols). Muscle-tendon complex length (Lm+t) is expressed as deviation from optimum GM muscle-tendon complex length (L0). Force is shown as mean ± S.E.M.

 


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  		Fig. 7. Force-length characteristics of fully dissected rat medial gastrocnemius (GM) muscle with only the neuro-vascular tract as extramuscular connective tissue. GM had been dissected free from extramuscular tissues except for its innervation, blood supply and associated connective tissues. (A) Active forces exerted at the proximal tendon (closed symbols) and at the distal tendon (calcaneal bone) (open symbols). (B) Passive forces exerted at the proximal tendon (closed symbols) and at the distal tendon (calcaneal bone) (open symbols). Muscle-tendon complex length (Lm+t) is expressed as deviation from optimum GM muscle-tendon complex length (L0). Force is shown as mean ± S.E.M.

 


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  		Fig. 8. Effects of muscle relative position of fully dissected in situ rat medial gastrocnemius (GM) muscle on force. Muscle relative position was manipulated by moving the origin 3 mm proximally or distally from the reference position (i.e. the position corresponding to a knee angle of 120°). (A) Active force-length characteristics after moving the origin in the proximal direction. (B) Passive force-length characteristics after moving the origin in the proximal direction. (C) Active force-length characteristics after moving the origin in the distal direction. (D) Passive force-length characteristics after moving the origin in the distal direction. Proximal and distal forces (mean ± S.E.M.) are represented by closed and open symbols, respectively. Muscle-tendon complex length (Lm+t) is expressed as deviation from optimum length (L0).

 


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  		Fig. 9. Representation of the orientation of the epitendinous tissues relative to GM- and PL-tendons, being dependent on muscle length. Proximally, GM is attached to a force transducer, whereas distally, GM and PL are both attached to one force transducer. Force transducers are indicated by black squares. Epitendinous tissues are represented by solid lines attached to the tendons. At short muscle lengths (upper panel), the epitendinous tissues are oriented in such a way that the force borne by these connections (indicated by arrows) is directed distally, but not to the force transducer. In contrast, at long muscle lengths (obtained by distal lengthening), the epitendinous tissues are oriented in an opposite direction, bearing force to a proximal direction (lower panel).

 

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© The Company of Biologists Ltd 2005