Among coronavirus disease 2019 (COVID‐19) patients, physically active individuals may be at lower risk of fatal outcomes. However, to date, no meta‐analysis has been carried out to investigate the relationship between physical activity (PA) and fatal outcomes in patients with COVID‐19. Therefore, this meta‐analysis aims to explore the hospitalisation, intensive care unit (ICU) admissions, and mortality rates of COVID‐19 patients with a history of PA participation before the onset of the pandemic, and to evaluate the reliability of the evidence. A systematic search of MEDLINE/PubMed, Cumulative Index to Nursing and Allied Health Literature, Scopus, and medRxiv was conducted for articles published up to January 2022. A random‐effects meta‐analysis was performed to compare disease severity and mortality rates of COVID‐19 patients in physically active and inactive cases. Twelve studies involving 1,256,609 patients (991,268 physically active and 265,341 inactive cases) with COVID‐19, were included in the pooled analysis. The overall meta‐analysis compared with inactive controls showed significant associations between PA with reduction in COVID‐19 hospitalisation (risk ratio (RR) = 0.58, 95% confidence intervals (CI) 0.46–0.73, P = 0.001), ICU admissions (RR = 0.65, 95% CI 0.52–0.81, P = 0.001) and mortality (RR = 0.47, 95% CI 0.38–0.59, P = 0.001). The protective effect of PA on COVID‐19 hospitalisation and mortality could be attributable to the types of exercise such as resistance exercise (RR = 0.27, 95% CI 0.15–0.49, P = 0.001) and endurance exercise (RR = 0.41, 95% CI 0.23–0.74, P = 0.003), respectively. Physical activity is associated with decreased hospitalisation, ICU admissions, and mortality rates of patients with COVID‐19. Moreover, COVID‐19 patients with a history of resistance and endurance exercises experience a lower rate of hospitalisation and mortality, respectively. Further studies are warranted to determine the biological mechanisms underlying these findings.

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One aspect of skeletal muscle memory is the ability of a previously trained muscle to hypertrophy more rapidly following a period of detraining. Although the molecular basis of muscle memory remains to be fully elucidated, one potential mechanism thought to mediate muscle memory is the permanent retention of myonuclei acquired during the initial phase of hypertrophic growth. However, myonuclear permanence is debated and would benefit from a meta-analysis to clarify the current state of the field for this important aspect of skeletal muscle plasticity. The objective of this study was to perform a meta-analysis to assess the permanence of myonuclei associated with changes in physical activity and ageing. When available, the abundance of satellite cells (SCs) was also considered given their potential influence on changes in myonuclear abundance. One hundred forty-seven peer-reviewed articles were identified for inclusion across five separate meta-analyses; (1-2) human and rodent studies assessed muscle response to hypertrophy; (3-4) human and rodent studies assessed muscle response to atrophy; and (5) human studies assessed muscle response with ageing. Skeletal muscle hypertrophy was associated with higher myonuclear content that was retained in rodents, but not humans, with atrophy (SMD = À0.60, 95% CI À1.71 to 0.51, P = 0.29, and MD = 83.46, 95% CI À649.41 to 816.32, P = 0.82; respectively). Myonuclear and SC content were both lower following atrophy in humans (MD = À11, 95% CI À0.19 to À0.03, P = 0.005, and SMD = À0.49, 95% CI À0.77 to À0.22, P = 0.0005; respectively), although the response in rodents was affected by the type of muscle under consideration and the mode of atrophy. Whereas rodent myonuclei were found to be more permanent regardless of the mode of atrophy, atrophy of ≥30% was associated with a reduction in myonuclear content (SMD = À1.02, 95% CI À1.53 to À0.51, P = 0.0001). In humans, sarcopenia was accompanied by a lower myonuclear and SC content (MD = 0.47, 95% CI 0.09 to 0.85, P = 0.02, and SMD = 0.78, 95% CI 0.37-1.19, P = 0.0002; respectively). The major finding from the present meta-analysis is that myonuclei are not permanent but are lost during periods of atrophy and with ageing. These findings do not support the concept of skeletal muscle memory based on the permanence of myonuclei and suggest other mechanisms, such as epigenetics, may have a more important role in mediating this aspect of skeletal muscle plasticity.

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Objective Although neuromuscular electrical stimulation (NMES) has been used as a safe and relevant complement to voluntary resistance training, its effectiveness in increasing quadriceps femoris muscle strength and mass in healthy young and older adults has not been determined. The aim of this scoping review was to assess the effects of NMES on quadriceps muscle strength and mass in healthy young and older adults. Methods CENTRAL, Pedro, MEDLINE, PubMed were searched from inception to September 2019. Randomized controlled trials (RCTs) that compared NMES with control group or voluntary resistance training for healthy young and older adults were included. Study characteristics, primary and secondary outcome parameters, and details of the NMES intervention were extracted by 2 reviewers. Only studies for which full text was available in English were included. Results Thirty-two RCTs including 796 healthy participants were identified as being eligible for young adults, and 5 RCTs including 123 healthy participants were identified as being eligible for older adults. The available evidence strongly suggests that NMES improves quadriceps muscle strength as compared with control group in young adults, but its efficacy seems lower than that of voluntary resistance training. The available limited evidence regarding the effects of NMES on quadriceps muscle mass compared to control in young adults is inconclusive, with 3 RCTs showing positive effects and 3 RCTs not showing positive effects. The very limited available evidence from 2 RCTs in older adults suggests that NMES might be beneficial for increasing quadriceps muscle strength and mass. Conclusion Overall, the evidence indicates that NMES is an efficacious method for increasing quadriceps muscle strength in young adults, whereas its impact on muscle mass requires further investigations. In addition, the effectiveness of NMES needs to be confirmed in older adults on the basis of more high-quality RCTs with larger sample sizes. Impact This scoping review of 87 RCTs including 919 people is the first study to show that the use of NMES increases quadriceps muscle strength in young adults and might improve quadriceps muscle strength as compared to control interventions in older adults. In both young and older adults, the effects of NMES on quadriceps muscle mass are still unclear.