Background: The efficacy of Resistance training (RT) is highly dependent on the precise manipulation of training program variables, such as frequency, load, sets, repetitions, and rest intervals. However, the independent effect of frequency remains controversial, with existing systematic evidence primarily focused on muscle mass and muscle strength, and the potential moderating role of training protocols and participant characteristics is insufficiently examined in muscle mass and muscle strength. Critical gaps persist regarding its impact on functional performance and athletic performance. Therefore, the independent effects of RT frequency and its key moderators across these physiological and performance adaptations are still unclear. Objective: This study aims to (i) investigate the effects of lower frequency versus higher frequency (e.g., two vs. three sessions per week) of RT on physiological and performance adaptations, (ii) explore the moderating factors, including the training protocol (training volume, targeted body part, intervention duration, and outcome measurements), participant characteristics (RT experience, population, and gender), and study design. Methods: Systematic searches across multiple databases up to October 2024 identified 47 studies (1665 participants). A three-level meta-analysis was performed using Standardized Mean Difference (Hedges’ g ). Subgroup and meta-regression analyses examined moderators. Results: When comparing higher to lower frequency RT conditions, significantly greater improvement in muscle strength was found for higher frequency ( g = −0.17, I 2 = 0%, p < 0.0001). However, training frequency did not affect changes in muscle mass ( g = −0.13, I 2 = 77.29%, p = 0.34), functional performance ( g = −0.13, I 2 = 25.19%, p = 0.18), and athletic performance ( g = 0.00, I 2 = 68.30%, p = 0.69). Training protocol (e.g., body-part specific training), participant characteristics, and study design moderated strength improvements. Only intervention duration significantly moderated muscle mass (≥6 weeks needed). No moderators influenced functional or athletic performance. Conclusion: RT frequency independently predicts strength gains but not muscle mass or performance adaptations. Strength improvements are moderated by multiple factors, while muscle mass changes depend primarily on training specificity and duration.
Tao et al. (2026) studied this question.