ABSTRACT
OBJECTIVE: The objectives of this study were to evaluate neuromuscular recruitment and efficiency in participants who recovered from COVID-19 and assess the association between neuromuscular efficiency and symptom-limited aerobic exercise capacity. METHODS: Participants who recovered from mild (n = 31) and severe (n = 17) COVID-19 were evaluated and compared with a reference group (n = 15). Participants underwent symptom-limited ergometer exercise testing with simultaneous electromyography evaluation after a 4-week recovery period. Activation of muscle fiber types IIa and IIb and neuromuscular efficiency (watts/percentage of root-mean-square obtained at the maximum effort) were determined from electromyography of the right vastus lateralis. RESULTS: Participants who had recovered from severe COVID-19 had lower power output and higher neuromuscular activity than the reference group and those who had recovered from mild COVID-19. Type IIa and IIb fibers were activated at a lower power output in participants who had recovered from severe COVID-19 than in the reference group and those who had recovered from mild COVID-19, with large effect sizes (0.40 for type IIa and 0.48 for type IIb). Neuromuscular efficiency was lower in participants who had recovered from severe COVID-19 than in the reference group and those who had recovered from mild COVID-19, with a large effect size (0.45). Neuromuscular efficiency showed a correlation with symptom-limited aerobic exercise capacity (r = 0.83). No differences were observed between participants who had recovered from mild COVID-19 and the reference group for any variables. CONCLUSION: This physiological observational study supports the notion that more severe COVID-19 symptoms at disease onset appear to correspondingly impair neuromuscular efficiency in survivors over a short time frame of 4 weeks after recovery, potentially contributing to reduced cardiorespiratory capacity. Further studies are needed to replicate and extend these findings with respect to their clinical implications for assessment/evaluation and interventions. IMPACT: After 4 weeks of recovery, neuromuscular impairment is particularly evident in severe cases; this problem may contribute to reduced cardiopulmonary exercise capacity.