## 4 Discussion  
The present systematic review described the state of the art regarding the rehabilitation efficacy in the fatigue treatment in people affected by PCS. The findings underlined that nearly all patients showed COVID-19-related fatigue, with a mean hospital LOS of  
Figure 3: Funnel plot of the included studies. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**Author and Year** & **Q1** & **Q2** & **Q3** & **Q4** & **Q5** & **Q6** & **Q7** & **Q8** & **Q9** \\ \hline [PERSON] et al. [44] & N/A & N/A & Y & N & Y & Y & Y & Y & Y \\ [PERSON] et al. [45] & N/A & N/A & Y & N & Y & Y & N & Y & Y \\ [PERSON] et al. [46] & N/A & N/A & Y & N & Y & Y & Y & Y & Y \\ [PERSON] et al. [47] & Y & Y & Y & Y & Y & Y & Y & Y & Y \\ [PERSON] et al. [48] & Y & Y & Y & Y & Y & Y & Y & Y & Y \\ [PERSON] et al. [49] & N/A & N/A & Y & N & Y & Y & N & Y & N/A \\ \hline \end{tabular} Legend: Q1 = Is it clear in the study what is the ‘cause’ and what is the ‘effect’ (i.e., there is no confusion about which variable comes first)?; Q2 = Were the participants included in any comparisons similar?; Q3 = Were the participants included in any comparisons receiving similar treatment/care, other than the exposure or intervention of interest?; Q4 = Was there a control group?; Q5 = Were there multiple measurements of the outcome both pre and post the intervention/exposure?; Q6 = Was follow-up complete, and if not, were differences between groups in terms of their follow up adequately described and analyzed?; Q7 = Were the outcomes of participants included in any comparisons measured in the same way?; Q8 = Were outcomes measured in a reliable way?; Q9 = Was appropriate statistical analysis used?; N = no, Y = yes; N/A = not applicable.  
\end{table} 
Table 5: Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies (non-randomized experimental studies). 15.6 days (in two studies [46; 49], the rehabilitation program was conducted at home). Specifically, after the rehabilitation treatment, only 17% of subjects stated the symptoms persistency, with a significant reduction in their severity. The studies included in our review performed different rehabilitation interventions: high-intensity exercise was administered in one study [44]; a combination of aerobic and resistance exercise was performed in one study [45]; one study [47] administered aerobic training and breathing exercise training; in one study [48], patients underwent a program with aerobic exercise, strength training of upper and lower limbs, and educational discussions; in one study, patients underwent a program with posture changes, passive mobilization of the limbs, breathing control exercises, and passive muscle stretching and pumping exercises; finally, in two studies [46; 47], an individual telerehabilitation program was applied. In this scenario, telerehabilitation was applied successfully during the first wave of the epidemic [50]. Moreover, it may also be a valid support for the management over time of patients suffering from PCS. The biological mechanisms of chronic fatigue occurrence in COVID-19 patients are still unclear, with a recent review hypothesizing inflammatory overregulation, increased resistance to cerebrospinal fluid drainage, and even impaired metabolism in the cerebellum and frontal lobe [51; 52]. Our meta-analysis showed a statistically significant decrease in Borg Scale (\(p<0.001\)), though the high heterogeneity (74%; \(p=0.67\)) of the included studies should be considered [44; 45; 46; 47; 48; 49]. The statistical methodology applied in our paper, the proportional meta-analysis, was recently introduced in the literature and only allowed the evaluation of the Borg Scale variation. However, as demonstrated in the funnel plot, the studies are homogenous concerning publication bias.