High-Density Surface Electromyography Allows for Longitudinal Assessment of the Neural Drive to Muscle in Individuals with Acute Stroke.

Previous work on neuromuscular impairments following stroke has mainly focused on the chronic phase of recovery, and relatively little is known regarding the acute phase. Studies demonstrating impairments in muscle activation have typically used single bipolar surface electromyography $(\text{sEMG})$ recordings, which may lead to a mischaracterization of muscle excitation. In this study, we assessed neuromuscular function of patients undergoing rehabilitation therapy in the acute phase post-stroke, combining high-density $\text{sEMG (IIDsEMG)}$ decomposition with isometric force recording to quantity changes in force production and motor unit discharge rates in comparison with global amplitude of a single bipolar sEMG signal. Seven patients with acute hemiparetic stroke were tested, beginning when a detectable dorsi- and plantarflexion movement could be observed (T0) and then again 15 and 30 days later (T15 and T30). The isometric maximal voluntary contraction (MVC) in dorsi- and plantarflexion were measured at these time points. $\text{HDsEMG}$ signals recorded from tibialis anterior, gastrocnemius lateralis and medialis, and soleus muscles during isometric contractions at 10% and 30% MVC were decomposed into motor unit discharge offline. Our main results revealed significant impairments in maximal force production at T0, which improved over the 30 days of inpatient rehabilitation therapy. There were also increases in mean motor unit discharge rate for TA and SOL muscles at 10% MVC. These neuromuscular changes could not be captured by using the classical, bipolar sEMG approach. Our results suggest that the combination of force recordings with HDsEMG may provide useful information in the acute phase of stroke and, longitudinally, during inpatient rehabilitation therapy.