Background: Recurrent hamstring injuries are a major problem in sport. Despite extensive research regarding risk factors underlying hamstring injury, recurrence rates remain high, suggesting our current understanding may be overlooking important neurophysiological factors. Recent evidence demonstrates disruptions in tactile, proprioceptive, and spatial neural (cortical) representations in athletes who develop persistent posterior thigh pain following a hamstring injury. It is possible these disruptions may contribute to poor recovery and hamstring injury recurrence. However, due to the cross-sectional nature of existing research, it remains unknown if the disruption in neural representations are driven by pain, or other factors. We explored whether experimentally-induced posterior thigh pain is associated with impairments in tasks that are thought to interrogate neural representations. If so, this may spark new investigations into potential mechanisms underlying hamstring injury recurrence.
Methods: Healthy participants were recruited and attended two experimental sessions (Days 0 and 2). On Day 0, all participants performed an eccentric hamstring exercise protocol to induce delayed onset muscle soreness. Tactile neural representations were assessed using two-point discrimination (TPD) and accuracy of tactile localisation, proprioceptive neural representations were assessed using a motor imagery task (left/right body part judgement task), and spatial processing was assessed using an auditory detection task. These outcomes were recorded before the exercise protocol on Day 0 and after on Day 2. Pain-free control group data (concentric exercise) is currently being collected and will be included in the final presentation.
Results: 20 participants completed the protocol and all participants developed posterior thigh pain on Day 2 (mean ± SD VAS: 6.6±1.8). TPD thresholds, tactile localisation, and accuracy in detecting auditory stimuli did not differ between baseline and Day 2 (p>0.6). Participants were quicker and more accurate to judge whether an image of a foot was a left or right sided body part when the image corresponded to their leg (irrespective of side), but unaffected when they were asked to judge hand images (left/right hand judgement task p>0.3).
Discussion: Experimentally-induced posterior thigh pain appears to improve the response time and accuracy of left-right discrimination, but did not impact tactile or auditory detection performance. These findings raise the possibility that hamstring pain may alter proprioceptive neural representations. Comparison with the concentric group will assist in revealing whether these results are due to pain or learning. Understanding the implications of these findings on the recovery, and risk of recurrence, following a hamstring injury appears 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 or a statement of disclosure of any financial and/or personal relationships that could potentially bias your research"