Stretching does not only increase ankle range of motion, but also seems to induce adaptations in muscle tissue and nerve tissue, according to the authors. Directly after completing the intervention programme, the 20 students in the nervous stretching group, showed evidence of a more flexible ischiadic nerve at several anatomic locations: the shear wave velocity – a measure for connective tissue stiffness, determined by ultrasound – was significantly smaller than before the stretching programme, while in the other two conditions this remained unchanged. According to the authors, this increased flexibility might explain the increase in range of motion. Moreover, they argue that this would be the first study to demonstrate changes in nerve tissue after stretching exercises.
Muscle fibre length
In the 21 students in the muscle stretch group, the researchers found evidence that there were structural changes in the muscle tissue: the muscle fibre bundles of the medial head of the gastrocnemius were on average 0,4 centimetre longer directly after the stretching programme compared to the baseline measurement. No changes were demonstrated for muscle fascicles in the lateral head of the gastrocnemius and the soleus. In the other two groups, no changes in muscle fibre length were observed.
Both the muscle as well as the nerve stretching methods led to an improvement of the ankle dorsiflexion range of motion, but only in the specific stretching position. The students in the muscle stretch condition performed five repetitions of 45 seconds of stretching, five times a week: they stood with their forefeet on a platform and dropped their heels as far as they could. These repetitions were performed with both a slightly flexed knee as well as with the knee in full extension, to stretch the soleus and gastrocnemius muscles, respectively. Immediately after the intervention the dorsiflexion range of motion was increased with 7.5 degrees compared to the baseline measurement, but only for the measurement with a straight hip. For the second range of motion measurement, students sat down with a flexed hip (90 degrees) and legs straight. For this measurement, the researchers found no difference between baseline and after treatment.