Triceps surae muscles are mechanically connected by the shared Achilles tendon and by epimuscular myofascial connections. We aimed to assess effects of proximal lengthening of gastrocnemius (GA) and plantaris muscles, imposed by changes in knee angle, on (i) the magnitude and direction of the 3D ankle moment exerted by the soleus (SO) muscle, and on (ii) mechanical interaction between ankle plantar flexor muscles during co-activation of GA muscle, in the rat (n=9). Ankle angle was kept constant (90°), while knee angle was varied between 60° and 130°. At each knee angle, SO was excited individually as well as simultaneously with GA (SO&GA). The mathematical sum of individual SO and GA ankle moments was compared with the ankle moment exerted by SO&GA to assess nonlinear summation. Knee angle did not affect the magnitude of the SO ankle moment (p=0.695). Moment directions in the transverse (p=0.050) and frontal (p=0.008) planes were affected by knee angle, but dissection indicated that this was not caused by length changes of the two-joint synergistic muscles. Nonlinear summation was found in the magnitude (-1.4±1.9%, mean±s.d., p<0.001) and in the frontal plane vector direction of the ankle moment (0.13±0.23°, p=0.003), however, the extent did not change with knee angle. While SO&GA contraction increased Achilles tendon length compared to rest, this length was not knee angle dependent (p=0.649). Despite that intermuscular force transmission per se cannot be excluded, we conclude that in vivo the mechanical effects of epimuscular myofascial connections between rat ankle plantar flexors are not functionally relevant.
No functionally relevant mechanical effects of epimuscular myofascial connections between rat ankle plantar flexors
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Chris Tijs, Jaap H. van Dieën, Huub Maas; No functionally relevant mechanical effects of epimuscular myofascial connections between rat ankle plantar flexors. J Exp Biol 2015; jeb.122747. doi: https://doi.org/10.1242/jeb.122747
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