The Influence of Resistance Training on Joint Flexibility in Healthy Adults: A Systematic Review, Meta-analysis, and Meta-regression

Abstract

Favro, F, Roma, E, Gobbo, S, Bullo, V, Di Blasio, A, Cugusi, L, and Bergamin, M. The influence of resistance training on joint flexibility in healthy adults: A systematic review, meta-analysis, and meta-regression. J Strength Cond Res 39(3): 386-397, 2025-Joint flexibility is a key component of physical fitness. Despite the large body of evidence regarding the effectiveness of muscle stretching exercises, little is known about the effect of resistance training on flexibility. A systematic search was conducted on 9 academic search instruments; inclusion criteria were as follows: healthy adult participants (age ≥18 years); resistance training intervention (duration ≥4 weeks); at least one flexibility outcome. Risk of bias was assessed using the RoB-2 and ROBINS-I tools. A 3-level meta-analysis was conducted, with multiple outcomes nested within each study. A moderator analysis was conducted by fitting a meta-regression model. Significance level was set at p < 0.05. We included 36 studies (1,469 participants). None of the included papers resulted at a low risk of bias. The pooled effect size for resistance training on flexibility was g = 0.6325, with 95% CI: 0.4762 to 0.7888 ( p < 0.0001). There was a substantial amount of heterogeneity between studies. Exercise intensity was a significant moderator ( p < 0.0225, high vs low), based on 129 and unique effect sizes, and sex ( p = 0.0429). Activity level and age were nonsignificant moderators. Resistance training could be implemented as a strategy to improve joint flexibility, with high-intensity protocols resulting in a magnified effect. However, the high overall risk of bias and substantial heterogeneity limit our ability to draw definitive conclusions.

Figure 1.

PRISMA flow diagram.

Figure 2.

Risk of bias summary for randomized studies, reported as percentage of the total on the x-axis.

Figure 3.

Exercise intensity grouped as “low”, “moderate”, and “high”. ES = Hedge’s g.

Figure 4.

Forest plot, 95% CI: 95% confidence intervals, ES: standardized mean change with raw score standardization, n. of Estimates: the number of unique effect sizes nested within each study. Arrows in confidence intervals denote that they continue beyond the limits of the forest plot. Dotted lines indicate the prediction intervals.

Figure 5.

Funnel plot, centered on the pooled estimate. Every point represents the combined ES of all outcomes nested within each study.

Figure 6.

Contour-enhanced funnel plot, centered at 0. Every point represents the combined ES of all outcomes nested within each study; shaded areas represent different levels of significance.

Figure 7.

Strength outcomes funnel plot. Every point represents the combined ES of all outcomes nested within each study.