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Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by skeletal muscle atrophy and weakness, ultimately leading to respiratory failure. The purpose of this study was to assess changes in skeletal muscle excitation-contraction (E-C) coupling and intracellular Ca²⁺ handling during disease progression in the G93A*SOD1 ALS transgenic (ALS Tg) mouse model. To assess E-C coupling, single muscle fibers were electrically stimulated (10–150 Hz), and intracellular free Ca²⁺ concentration was assessed using fura-2. There were no differences in peak fura-2 ratio at any stimulation frequency at 70 days (early presymptomatic). However, at 90 days (late presymptomatic) and 120–140 days (symptomatic), fura-2 ratio was increased at 10 Hz in ALS Tg compared with wild-type (WT) fibers (0.670 ± 0.02 vs. 0.585 ± 0.02 for 120–140 days; P < 0.05). There was also a significant …