Investigating interindividual variability in corticomotor reorganization during sustained hamstring pain: A randomized experimental study.

BACKGROUND: Increasing evidence suggests that pain drives maladaptive corticomotor changes that may increase susceptibility to injury and promote symptom recurrence. However, few studies have evaluated the influence of interindividual corticomotor responses to musculoskeletal pain. Existing research in this area has also been limited largely to the upper limb. This is a pertinent point, given the functional and neurophysiological differences between upper and lower limb muscles, as well as the fact that most acute sporting injuries occur in the lower limb. Accordingly, this study explored the variability of corticomotor responses to experimentally-induced sustained hamstring pain and whether specific patterns of corticomotor reorganization were associated with poorer outcomes (mechanical sensitivity, pain, or functional limitation). METHOD: Thirty-six healthy individuals participated. Following random allocation on Day 0, the experimental group performed an eccentric exercise protocol of the right hamstring muscles to induce delayed onset muscle soreness. The control group performed repetition-matched concentric exercise that did not induce soreness. Measures of mechanical sensitivity, pain, function, and corticomotor organization were collected at baseline and on Day 2. RESULTS AND CONCLUSIONS: Corticomotor responses to sustained hamstring pain were variable. Individuals who developed corticomotor facilitation in response to hamstring pain experienced greater mechanical sensitivity than those who developed corticomotor depression. These novel data could have implications for rehabilitation following lower limb pain or injury.

The Effect of Theta Burst Stimulation Over the Primary Motor Cortex on Experimental Hamstring Pain: A Randomized, Controlled Study.

Theta burst stimulation (TBS) over the primary motor cortex (M1) is an emerging technique that may have utility in the treatment of musculoskeletal pain. However, previous work exploring the analgesic effects of noninvasive brain stimulation has been limited largely to the arm or hand, despite 80% of acute musculoskeletal injuries occurring in the lower limb. This is a pertinent point, given the functional and neurophysiological differences between upper and lower limb musculature, as well as evidence suggesting that reorganization of corticomotor pathways is region-specific. This study investigated the effect of excitatory TBS on pain, function, and corticomotor organization during experimentally induced lower limb pain. Twenty-eight healthy participants attended 2 experimental sessions. On Day 0, participants completed 10 sets of 10 maximal eccentric contractions of the right hamstring muscles to induce delayed onset muscle soreness. Four consecutive blocks of either active or sham TBS were delivered on Day 2. Measures of mechanical sensitivity, pain (muscle soreness, pain intensity, pain area) function (single-leg hop distance, maximum voluntary isometric contraction, lower extremity functional scale), and corticomotor organization were recorded before and after TBS on Day 2. Pain and function were also assessed daily from Days 2 to 10. Active TBS reduced mechanical sensitivity compared to sham stimulation (P = .01). Corticomotor organization did not differ between groups, suggesting that improvements in mechanical sensitivity were not mediated by changes in M1. Subjective reports of pain intensity and function did not change following active TBS, contrasting previous reports in studies of the upper limb. PERSPECTIVE: M1 TBS reduces mechanical sensitivity associated with experimentally induced hamstring pain. Though further work is needed, these findings may hold important implications for those seeking to expedite recovery or reduce muscle sensitivity following hamstring injury.