Discussion
The mechanical relevance of the extramuscular connective tissue (i.e. the deep fascia) represents one of the main topics of fascia researchAgainst this background, the present study is the first demonstrating caudal-cranial in-vivo interactions of serially connected muscles in a randomized, controlled design. Our results show that the knee angle can have a relevant impact on soft tissue displacement following non-local movement. As expected, there was significantly less soft tissue displacement of the SM with the knee flexed (3.81 ± 2.36 mm) when compared to the extended knee (4.83 ± 2.04 mm). The results observed in the extended knee condition are basically consistent with the findings of Wilke et al.Our findings have significant implications for clinical practice. As indicated, the here presented data strengthen the evidence that local stretching has a mechanical impact on neighboring body parts. While this had already been demonstratedBesides investigating the influence of the knee position on force transmission, our study also showed that the displacement of the GM aponeurosis is a better predictor of SM displacement than ankle ROM. This is plausible because ROM does not only depend on structural (e.g., stiffness) but also on neural (e.g., stretch tolerance) factorsSome methodological considerations should be made when interpreting the results of our study. First, measurements of soft tissue displacement represent a highly plausible surrogate of force transmission, but not a direct measurement of force. Furthermore, we defined maximum ankle dorsal extension as the subjective maximum tolerated by the participants, which caused ROM to vary in the two starting positions (26.02° ± 6.15° with the knee extended; 28.22° ± 7.41° with the knee flexed). Also, with the knee flexed, the participants tended not to report a maximum stretch sensation of the calf muscles but rather a blocking sensation in the ankle joint. Again, this can be explained by the biarticularity of the gastrocnemius muscle: when the knee is flexed, the muscle does not reach a fully stretched position