Background There is limited information about the impact of coronavirus disease (COVID‐19) on the muscular dysfunction, despite the generalized weakness and fatigue that patients report after overcoming the acute phase of the infection. This study aimed to detect impaired muscle efficiency by evaluating delta efficiency (DE) in patients with COVID‐19 compared with subjects with chronic obstructive pulmonary disease (COPD), ischaemic heart disease (IHD), and control group (CG). Methods A total of 60 participants were assigned to four experimental groups: COVID‐19, COPD, IHD, and CG ( n = 15 each group). Incremental exercise tests in a cycle ergometer were performed to obtain peak oxygen uptake (VO 2 peak). DE was obtained from the end of the first workload to the power output where the respiratory exchange ratio was 1. Results A lower DE was detected in patients with COVID‐19 and COPD compared with those in CG ( P ≤ 0.033). However, no significant differences were observed among the experimental groups with diseases ( P > 0.05). Lower VO 2 peak, peak ventilation, peak power output, and total exercise time were observed in the groups with diseases than in the CG ( P < 0.05). A higher VO 2 , ventilation, and power output were detected in the CG compared with those in the groups with diseases at the first and second ventilatory threshold ( P < 0.05). A higher power output was detected in the IHD group compared with those in the COVID‐19 and COPD groups ( P < 0.05) at the first and second ventilatory thresholds and when the respiratory exchange ratio was 1. A significant correlation ( P < 0.001) was found between the VO 2 peak and DE and between the peak power output and DE ( P < 0.001). Conclusions Patients with COVID‐19 showed marked mechanical inefficiency similar to that observed in COPD and IHD patients. Patients with COVID‐19 and COPD showed a significant decrease in power output compared to IHD during pedalling despite having similar response in VO 2 at each intensity. Resistance training should be considered during the early phase of rehabilitation.

Worldwide, healthcare systems had to respond to an exponential increase in COVID-19 patients with a noteworthy increment in intensive care units (ICU) admissions and invasive mechanical ventilation (IMV). The aim was to determine low intensity respiratory muscle training (RMT) effects in COVID-19 patients upon medical discharge and after an ICU stay with IMV. A retrospective case-series study was performed. Forty COVID-19 patients were enrolled and divided into twenty participants who received IMV during ICU stay (IMV group) and 20 participants who did not receive IMV nor an ICU stay (non-IMV group). Maximal expiratory pressure (PEmax), maximal inspiratory pressure (PImax), COPD assessment test (CAT) and Medical Research Council (MRC) dyspnea scale were collected at baseline and after 12 weeks of low intensity RMT. A greater MRC dyspnea score and lower PImax were shown at baseline in the IMV group versus the non-IMV group (p < 0.01). RMT effects on the total sample improved all outcome measurements (p < 0.05; d = 0.38–0.98). Intragroup comparisons after RMT improved PImax, CAT and MRC scores in the IMV group (p = 0.001; d = 0.94–1.09), but not for PImax in the non-IMV group (p > 0.05). Between-groups comparison after RMT only showed MRC dyspnea improvements (p = 0.020; d = 0.74) in the IMV group versus non-IMV group. Furthermore, PImax decrease was only predicted by the IMV presence (R2 = 0.378). Low intensity RMT may improve respiratory muscle strength, health related quality of life and dyspnea in COVID-19 patients. Especially, low intensity RMT could improve dyspnea level and maybe PImax in COVID-19 patients who received IMV in ICU.