Post-COVID-19 Muscle Weakness and Recovery Patterns After Mild-to-Moderate Infection: A Retrospective Analysis of a Structured Rehabilitation Program Using the MRC Scale

<b>Background/Objectives</b>: Post-COVID-19 muscle weakness is common even after mild or moderate infection, driven by systemic inflammation, prolonged inactivity, and reduced functional reserve. This study aimed to describe changes in global muscle strength assessed using the Medical Research Council (MRC) scale in adults recovering from mild or moderate COVID-19 who participated in a structured two-week rehabilitation program, and to compare these changes with those observed under standard medical follow-up. <b>Methods</b>: This retrospective study included 193 adults recovering from mild or moderate COVID-19: 160 who completed a structured inpatient rehabilitation program (study group) and 33 who received no supervised rehabilitation (control group). Muscle strength was assessed using the MRC scale at baseline and at follow-up. Non-parametric analyses (Wilcoxon signed-rank test, Mann-Whitney U test, and Spearman correlation) were used to evaluate within-group changes, between-group differences, and associations with age and sex. <b>Results</b>: Both groups showed significant within-group improvements in muscle strength. In the study group, median MRC scores increased from 50 (IQR 40-56) to 52 (IQR 50-56), with a mean ΔMRC of 2.76 ± 8.72 (<i>p</i> < 0.001). In the control group, MRC scores rose from 50 (40-56) to 52 (43-56), corresponding to a mean ΔMRC of 1.00 ± 2.09 (<i>p</i> = 0.005). The between-group comparison of ΔMRC did not reach statistical significance overall; however, age-stratified analyses indicated greater muscle strength gains in the rehabilitation group among participants aged ≥60 years. <b>Conclusions</b>: Short-term improvements in global muscle strength were observed both after structured rehabilitation and under standard medical follow-up, indicating a substantial contribution of natural recovery. Although participants in the rehabilitation group showed numerically larger gains-most notably in the ≥60-year subgroup-between-group differences in ΔMRC were not statistically significant. Overall, these findings support the feasibility and potential functional value of early, individualized rehabilitation while underscoring the need for adequately powered prospective studies to clarify its incremental benefit beyond spontaneous recovery.