Investigating the effects of Theta Burst Stimulation (TBS) on experimentally-induced hamstring pain

Abstract

Background: Maximising recovery and facilitating return to sport following a hamstring injury are key considerations for athletes and rehabilitation providers. Interventions that can accelerate pain resolution following a hamstring injury may allow earlier exposure to hamstring rehabilitation and accelerate return to sport. Recently, non-invasive stimulation of the primary motor cortex (M1) has been shown to expedite recovery following acute musculoskeletal pain. However, previous research has involved prolonged stimulation sessions that require multiple days of treatment, which may not be feasible for many athletes. Theta burst stimulation (TBS) is a novel paradigm that has been shown to produce comparable effects to other brain stimulation modalities in a fraction of the time. Accordingly, this study aimed to investigate the effect of theta burst stimulation (TBS) on the recovery of pain severity and sensitivity following experimentally-induced hamstring pain. Methods: Twenty pain-free people participated in this randomised controlled trial. All participants attended two sessions (Day 0 and 2). On Day 0, participants performed an eccentric exercise protocol (resisted unilateral knee flexion, 10 x 10 repetitions) to induce delayed onset muscle soreness. On Day 2, participants received 4 blocks of either active or sham TBS (approximately 3 minutes each) over M1 contralateral to the painful leg. Pain severity (visual analogue scale) and sensitivity (pressure pain thresholds [PPTs]) over the painful site were assessed before and after the TBS intervention. Pain severity was assessed during functional tasks including walking up and down stairs, forward bending with extended knees, and removing shoes using the contralateral foot. Results: The eccentric protocol induced comparable pain in both groups across all functional tasks (mean pain intensity of 4.5 for both groups when walking upstairs).There was a significant increase in PPTs amongst the active TBS group when compared to sham (p = 0.03). No differences were observed between groups following TBS in pain severity during any of the functional tasks (p > 0.05 for all). Discussion: A single session of TBS reduced pain sensitivity (an increase in PPTs) associated with experimentally-induced hamstring pain but did not reduce pain severity during functional tasks. This treatment may assist in expediting the resolution of peripheral sensitisation observed following an acute hamstring injury, an effect that could translate to earlier engagement with rehabilitation. Further exploration of the effects of TBS on acute clinical hamstring injury, and whether improvements in pain sensitivity translate into shorter recovery time, is warranted. Conflict of interest statement: My co-authors and I acknowledge that we have no conflict of interest of relevance to the submission of this abstract.