Muscle Strain Injury has been notorious for its high incidence and high recurrent ratio in a wide variety of sports. Severe muscle strain alters morphological properties of the connective tissue. Connective tissue, especially fascia which surrounds muscles, is highly sensory innervated. Therefore, we hypothesize that previous muscle strain injury affects sensory nerve transmission. Altered proprioceptive feedback will affect the muscle function which consequently may lead to muscle strain re-injury.PURPOSE: This pilot study aimed to compare the differences between injured and uninjured leg in sensory nerve excitability of the tibial nerve in professional rugby players. Moreover, we wanted to compare it with muscle-tendon junction stiffness of gastrocnemius muscles.
METHODS: Five male professional rugby players (age/ height/ weight, ± 3.9/181.2±10.5/101±12.46) who have a history of calf strain ( confirmed by MRI) were selected. The measurement was performed at least 6 weeks after injury. To evaluate sensory excitability, we examined somatosensory evoked potentials (SEPs) elicited by tibial nerve stimulation on both injured and uninjured side. Muscle stiffness (strain ratio) was also assessed by strain elastography in both injured and uninjured leg. The relationship between SEPs and strain ratio was analyzed.
RESULTS: The SEPs of the injured side was lower than that of the uninjured side (mean latency injured side/uninjured side, 7.26 m/s±1.21/9.34 m/s±2.01, p<0.05). However, there was no difference in muscle stiffness between the legs (mean strain ratio injured side/uninjured side, 0.128/0.124, p=0.37). The relationship between SEPs and muscle stiffness was found on non-significant (p=0.74).
CONCLUSIONS: SEP of injured gastrocnemius muscle was lower than uninjured one in professional rugby players. However, muscle stiffness did not differ.