How many adults have sufficient muscle-strengthening exercise and the associated factors: A systematic review consisting of 2,629,508 participants.

Purpose: The aim of this systematic review was to (1) estimate the prevalence of adhering to the MSE guidelines (at least 2 times/days a week) among adults; and (2) synthesize evidence on the correlates of adhering to the MSE guidelines. Methods: Five electronic databases were searched (March 2022), with a total of 30 observational studies consisting of 2,629,508 participants meeting the eligibility criteria. A meta-analysis was conducted to pool the prevalence of adhering to the MSE guidelines using the results of 21 eligible studies (study aim 1); and data reporting correlates of adhering to the MSE guidelines using 12 eligible studies were synthesized and categorized based on the Socioecological Model Framework (study aim 2). Results: Overall, 22.8 % (95%CI: 18.18 % ─ 27.77 %) of adults adhered to the MSE guidelines, and 23 potential correlates at five levels were examined. Five variables (i.e., sex, age, education level, socioeconomic status) at the sociodemographic level and two variables (i.e., body mass index, self-rated health) at the physical related level were identified as consistent correlates, but displaying weak to moderate association strengths. Conclusions: Less than a quarter of adults meet the MSE guidelines and multidimensional correlates are associated with the adherence to the guidelines, particularly sociodemographic correlates (e.g., sex, age, and educational level). Findings highlight the need to further promote the importance of engaging in MSE among adults and investing effective interventions that not only provide opportunities for MSE for adults, but also facilitate the development of skills and confidence to engage in MSE.