Introduction: Critically ill patients frequently suffer from significant muscle wasting, or sarcopenia. Electrical muscle stimulation (EMS) offers potential as a rehabilitation tool, having been shown to improve muscle strength and neural drive; both commonly reduced in deconditioned patients. However, EMS research has predominantly focused on limb muscles; thus, the effect of EMS on trunk muscles, particularly in relation to neural drive, remains unclear. Given the vital role of the trunk in maintaining stability, balance and posture, this knowledge could be crucial for improving the recovery of such patients. This study represents the first to assess the impact of a 4-week EMS programme on the neural drive to trunk muscles.
Methods: With ethical approval (SETREC No. 6948844), healthy adult participants were randomly assigned to Intervention (n=6, mean±SD age=21.5±0.55 years) or Control (n=6, mean±SD age=21.7±0.52 years) groups. Intervention participants completed a 25-minute, home-based EMS programme (DiPulse) targeting Rectus Abdominis (RA) and Erector Spinae (ES) three times a week, for four weeks. Control participants continued their usual activity levels. Neural drive was assessed via Transcranial Magnetic Stimulation-induced twitch interpolation, pre- and post-intervention in both muscles. Maximum Voluntary Contraction (MVC) torque, Motor Evoked Potential (MEP) amplitudes and time-to-peak (TTP) twitch amplitude were recorded pre- and post-intervention, at three different contraction strengths (50%, 75% and 100% of MVC). Trunk function was also assessed. Differences between parameters were assessed using two-way analysis of variance (ANOVA) with factors group (intervention/control) and time (pre/post) or contraction strength (50%, 75% and 100% MVC). The level of significance was set at p<0.05.
Results: Following 4-weeks of EMS, statistically significant increases in
the mean ES MEP amplitudes were observed, at all contraction strengths levels (50%-pre:
0.679±0.499mV, post: 0.901±0.466mV, p=0.02; 75%-pre: 0.870±0.811mV, post: 1.365±0.861mV, p<0.0001; MVC-pre: 0.655 ± 0.394mV, post: 1.272 ± 0.589mV, p<0.0001). No significant changes were observed in control group. These results imply increased corticospinal excitability to ES, suggestive of EMS-induced neuromodulation. Although no statistically significant improvements in neural drive, trunk muscle strength, function, or TTP amplitude were seen, similar discrepancies have been reported in the literature, where MEP amplitude changes fail to align with functional outcomes. Thus, the increase in corticospinal excitability in ES, whilst significant, may have been inadequate to produce any measurable functional benefits over 4-weeks. This could be attributed to insufficient EMS parameters used, inclusion of healthy participants with limited potential for neurophysiological improvement, or inherent differences in neural control between trunk and limb muscles, where greater effects have previously been demonstrated.
Conclusion: A 4-week EMS programme targeting RA and ES resulted in a significant increase in ES MEP amplitudes but did not alter neural drive or MVC strength in either muscle. These findings indicate that EMS may induce neural adaptations in the trunk musculature, although further investigation with greater sample sizes is needed to determine the underlying neuromodulatory mechanisms. While the utility of this intervention lies with sarcopenic patients, this preliminary study in healthy individuals demonstrates, for the first time, the feasibility of using EMS to increase corticospinal drive to trunk muscles.