HD-EMG Captures Muscle-Specific Fatigue Patterns During Sustained Contractions: A Comparison of Participants with ALS and Healthy Controls

Summary: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease of the motor unit that leads to physical disability, communication difficulties, respiratory failure, and ultimately death. Muscle fibers can be broadly categorized into fast-twitch fibers, which produce high force but fatigue rapidly, and slow-twitch fibers, which are more fatigue-resistant. In mouse models of ALS, fast-twitch fibers are selectively vulnerable, resulting in altered fiber composition as the disease advances [1–2]. High-density electromyography (HD-EMG) has been shown to detect motor unit changes in paralyzed patients [3], suggesting its potential as a non-invasive tool for monitoring ALS progression. Our goal is to integrate HD-EMG with clinical evaluations to assess disease severity, track progression, identify biomarkers, and support personalized treatment strategies. Here we present findings from our ongoing study comparing individuals with ALS to healthy controls. We collected HD-EMG recordings from the biceps brachii, triceps brachii, tibialis anterior, and soleus/gastrocnemius during sustained contractions in 6 ALS participants and 4 healthy controls matched by age and sex. Participants first completed a maximum voluntary contraction (MVC), followed by sustained contractions at intensities 20–50% of their MVC for up to 5 minutes to induce fatigue. We measured Root Mean Square (RMS) amplitude and mean power frequency across four equal-duration blocks. Then we used paired t-tests to assess changes in these metrics with muscle fatigue, which would indicate a shift in muscle fiber recruitment. In healthy control participants, RMS amplitude as well as both low- and high-frequency power decreased during higher-intensity contractions, while remaining stable or increasing at lower intensities. These results are consistent with fatigue-induced adaptation. In contrast, ALS participants exhibited variable responses. Some muscles in the ALS patients mirrored healthy patterns while others showed uniform decreases in all measures regardless of contraction intensity. Our preliminary findings suggest impaired recruitment of both fast- and slow-twitch muscle fibers in ALS, contributing to the fatigue and motor decline observed in this patient population. Ongoing decomposition analysis will assess composition changes in fast- and slow-twitch muscle fibers. Longitudinal data collection is also ongoing, with ALS participants assessed every 2–3 months to track changes in muscle fibers with disease progression. HD-EMG may serve as a valuable and non-invasive tool for characterizing these muscle alterations, offering clinical potential as a biomarker platform for monitoring disease progression and guiding personalized treatment strategies. Ernesto Bedoy, Michael Christofidis, Maia Brown, Tawfiq Al-Lahham, Douglas Weber, and Christi Kolarcik