Impaired Neuromuscular Efficiency and Symptom-Limited Aerobic Exercise Capacity 4Weeks After Recovery From COVID-19 Appear to Be Associated With Disease Severity at Onset.

Abstract

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. 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. 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. 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 4weeks 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. After 4weeks of recovery, neuromuscular impairment is particularly evident in severe cases; this problem may contribute to reduced cardiopulmonary exercise capacity.