Effects of aging and life-long physical training on collagen in slow and fast skeletal muscle in rats

Summary Intramuscular collagen in a slow (m. soleus) and a fast (m. rectus femoris) skeletal muscle was studied by biochemical, morphometric, and immunohistochemical methods. Wistar white rats of 1, 4, 10, and 24 months were used as experimental animals. Our aim was to evaluate the effects of life-long physical training (treadmill running, 5 days a week for 1, 3, 9, and 23 months depending on the age attained). The biochemical concentration of collagen was higher in m. soleus than in m. rectus femoris and it increased in youth and in old age in m. soleus. The trained rats had higher concentrations of collagen than the untrained rats at 10 and 24 months. The morphometrically measured area-fractions of both the endomysium and perimysium were higher in m. soleus than in m. rectus femoris. The age-related increase in intramuscular connective tissue was of endomysial origin. The immunohistochemical staining of type-I, -III, and -IV collagens indicated the more collagenous nature of m. soleus as compared with m. rectus femoris for all major collagen types; this was most marked for type-IV collagen of basement membrane. The results indicate that both age and endurance-type physical training further distinguish the slow and fast muscles with respect to their connective tissue.     

Epimuscular myofascial force transmission between antagonistic and synergistic muscles can explain movement limitation in spastic paresis

Details and concepts of intramuscular, extramuscular and intermuscular myofascial force transmission are reviewed. Some new experimental data are added regarding myofascial force transmission between antagonistic muscles across the interosseal membrane of the lower hind limb of the rat. Combined with other result presented in this issue, it can be concluded that myofascial force transmission occurs between all muscles within a limb segment. This means that force generated within sarcomeres of an antagonistic muscle may be exerted at the tendon of target muscle or its synergists.

Some, in vivo, but initial indications for intersegmental myofascial force transmission are discussed. The concept of myofascial force transmission as an additional load on the muscle proved to be fruitful in the analysis of its muscular effects. In spastic paresis and for healthy muscles distal myofascial loads are often encountered, but cannot fully explain the movement limitations in spastic paresis. Therefore, the concept of simultaneous and opposing myofascial loads is analyzed and used to formulate a hypothesis for explaining the movement limitation: Myofascially transmitted antagonistic force is borne by the spastic muscle, but subsequently transmitted again to distal tendons of synergistic muscles.