Author(s): MAAS, H., GEUSEBROEK, G., TIJS, C., VAN DIEËN, J.H., Institution: VRIJE UNIVERSITEIT AMSTERDAM, Country: NETHERLANDS, Abstract-ID: 833

INTRODUCTION:
Muscle stretching is frequently applied in sports practice, but also in the treatment of joint contractures. The goal of stretching is to lengthen the muscle fibers, but the actual distribution of the imposed strain among the different structures is unknown. Previously, differences in length of in-series sarcomeres within muscle fibers of rat and mouse tibialis anterior (TA) muscle have been reported (Moo et al., 2016; Tijs et al., 2015). The aim of the present study is to investigate how muscle-tendon strain is distributed within the muscle belly of medial gastrocnemius (MG) muscle.
METHODS:
The hindlimbs of 24 adult male Wistar rats (body mass = 316±5g) were positioned in predefined ankle and knee angles (included angles 55°, 90°, 125°, 160° for both joints) and fixed in a formaldehyde solution. MG muscle was removed and whole muscle fibers were dissected from three regions: proximal, intermediate and distal. Muscle belly and mean sarcomere length were assessed.
RESULTS:
Increasing knee angle (i.e. extension) and decreasing ankle angle (i.e. dorsiflexion) caused lengthening of MG muscle belly and mean sarcomere length. Length changes were higher in response to changes in ankle angle than to changes in knee angle, in accordance with joint moment arms (Ettema, 1997). Mean sarcomere length did not differ between regions. Also, changes in sarcomere length in response to muscle-tendon lengthening were not different between regions.
CONCLUSION:
These results indicate that muscle-tendon strain caused by ankle and knee joint rotations was distributed homogeneously within the MG muscle belly. The difference with previous results in a different muscle (TA) suggests that the distribution of muscle-tendon strain is muscle specific.

REFERENCES:
Ettema, G.J.C., 1997. Gastrocnemius muscle length in relation to knee and ankle joint angles: verification of a geometric model and some applications. The Anatomical Record 247, 1-8.
Moo, E.K., Fortuna, R., Sibole, S.C., Abusara, Z., Herzog, W., 2016. In vivo Sarcomere Lengths and Sarcomere Elongations Are Not Uniform across an Intact Muscle. Front Physiol 7, 187.
Tijs, C., van Dieen, J.H., Maas, H., 2015. Effects of epimuscular myofascial force transmission on sarcomere length of passive muscles in the rat hindlimb. Physiol Rep 3.