Muscle strength, muscle morphology, and oxidative capacity in normal weight versus overweight and obese youth: a systematic review with meta-analysis

Abstract

Abstract The World Health Organization (WHO) defined youth overweight and obesity as pandemic due to a large global overweight and obesity prevalence of 14.8% and 8.1% in 2023. However, the impact of overweight and obesity on youth muscle strength, morphology, and oxidative capacity is unclear despite increased research efforts. To systematically review the literature and meta-analyze findings on muscle strength, morphology, and oxidative capacity in youth with overweight and/or obesity (OW) versus those with normal-weight (NW). Following PRISMA guidelines, electronic databases (i.e., PubMed, Web of Science, Scopus, CINAHL, MEDLINE) were searched for cross-sectional studies that compared OW with NW regarding the outcomes muscle strength (e.g., absolute, relative [e.g., to fat-free mass, body mass]), morphology (e.g., muscle cross-sectional area [CSA]), and oxidative capacity (e.g., phase II of volume of oxygen [VO 2 ] kinetics). The risk of bias (RoB) was assessed using the Joanna Briggs Institute 8-item checklist. A random-effects three-level meta-analysis was used, and within- as well as between-group effect sizes (Hedges’ g [g]) were computed. Study heterogeneity was assessed using I 2 statistics. The Grading Recommendation Assessment Development and Evaluation (GRADE) approach was used to evaluate the certainty of evidence. Overall, 15 studies were meta-analyzed, including 1,475 participants aged 8.4 to 16.6 years. The mean RoB amounted to 6.1 on a 0 to 8 scale. Muscle absolute strength (n = 346; g = 0.68; p  = 0.011; I 2  = 59.3% [ p  < 0.001]) and CSA (n = 1,024; g = 1.12; p  < 0.001; I 2  = 73% [ p  < 0.001]) was significantly greater in OW versus NW. However, relative muscle strength tended to be larger in NW versus OW (n = 320; g = -0.455; p  = 0.165; I 2  = 92.7% [ p  < 0.001]). Moreover, muscle oxidative capacity was significantly greater in NW versus OW (n = 105; g = -0.58; p  = 0.019; I 2  = 37.5% [ p  = 0.18]). GRADE revealed very low (absolute and relative strength and muscle oxidative capacity) to moderate (muscle CSA) certainty of evidence. Absolute muscle strength and CSA seem larger in OW versus NW, potentially related to the chronic overload during every day and sports-related tasks imposed by overweight and/or obesity. However, relative muscle strength tended to be lower in OW versus NW, suggesting impaired muscle quality in OW. Further, muscle oxidative capacity seems lower in OW versus NW, which might be indicative of muscle mitochondrial dysfunction and impaired oxygen supply, with a potential negative impact on exercise tolerance. However, the cross-sectional nature of included studies, results heterogeneity, and reduced control of confounders among the included studies (e.g., biological maturation) preclude a robust conclusion, due to a low certainty of evidence.