Rapid Re-activation of Functionally Inhibited Hamstring Muscles via Real-Time EMG Visual Feedback in an Asymptomatic Masters Sprinter: A Case Report.

A 41-year-old male masters sprinter (183 cm, 62 kg) with a 20-year history of subjective hamstring activation failure during Romanian deadlifts, no pain, no structural injury, and no neurological history, underwent a single-session crossover assessment. Three conditions — a control condition, an exercise routine (specific exercises not detailed in the provided text), and real-time EMG visual feedback (VFB) — were performed in randomized order on the same day with 5-minute rest intervals between them. Surface EMG was recorded on the right (dominant) leg using a Delsys Trigno wireless system; the hardware gain of 909 V/V was corrected in post-processing to estimate physiological amplitude in millivolts. The average peak amplitude across five repetitions was the primary EMG measure. The athlete also rated his perceived hamstring engagement on a 10-cm visual analog scale after each condition. The study was approved by the Kanagawa University Ethical Review Committee (No. 202222-2).

The main question was whether real-time EMG visual feedback could acutely restore hamstring activation in a person with long-standing functional inhibition. EMG waveforms went from near-silence in the control condition to distinct high-amplitude bursts during VFB. The authors report an approximately 40-fold increase in proximal hamstring EMG amplitude during VFB compared to control, with a baseline amplitude of about 0.014 mV in the control condition. Subjective ratings tracked the same pattern: 3.8 cm (control), 5.8 cm (exercise routine), 7.8 cm (VFB) on a 0–10 cm scale. The authors note that a change of this magnitude within a single session cannot reflect muscle growth and instead points to a neural-drive problem.

If a patient — particularly an athlete or active adult — reports that a muscle simply will not fire despite no structural damage and no pain, and conventional coaching cues or strengthening have not helped over months or years, real-time EMG visual feedback is a low-risk, immediately available tool worth trying. The technique converts invisible muscle activity into a visible waveform the patient can learn to 'grow,' which may bypass the inhibitory loop that internal-focus cues cannot. This is a single-person observation, not a proven protocol, but the mechanism (external visual focus replacing a failed internal cue) is plausible and the setup is straightforward. It does not replace a full assessment to rule out structural or neurological causes.

This is one person, one session. There is no way to know whether the effect would replicate in another individual, let alone in a group. The athlete was not blinded: he knew which condition was the control, which was the exercise routine, and which was the visual feedback, so expectation and attention effects cannot be separated from the physiological effect. No follow-up was performed. The authors themselves note that long-term retention of the reactivated pathway is unknown. Surface EMG is subject to crosstalk from neighbouring muscles and to skin-impedance variation, which the authors acknowledge. The athlete was at roughly 80–90% of peak condition with some residual fatigue from a minor injury two months earlier and a hill-sprint session the day before testing, so his baseline state was not fully rested. The specific exercises used in the 'exercise routine' condition are not described in the provided text, making it impossible to judge whether that condition was an adequate active comparator. The presentation is very specific: 20 years of activation failure in one muscle group, no pain, no injury, no neurological history. It is unclear whether the finding extends to post-injury inhibition, multi-muscle deficits, or older, less active populations.

The authors declare no commercial or financial relationships that could be construed as conflicts of interest. The research was funded by the Tokyo Metropolitan Industrial Technology Research Institute (no grant number).