Effects of Resistance Circuit-Based Training on Body Composition, Strength and Cardiorespiratory Fitness: A Systematic Review and Meta-Analysis

SIMPLE SUMMARY: Resistance circuit-based training is an effective training method to decrease total body fat and increase muscle mass in adults. Resistance circuit-based training promotes concurrent improvements in strength performance and cardiorespiratory fitness variables in adults. If training load is managed properly, a greater effect on body composition and strength adaptations is possible. Regarding 1-RM improvements, the effect of this type of training is influenced by the training status, obtaining greater effects in untrained and active adults, and by the training characteristics, showing a larger effect in protocols with three sessions and a duration of >20 training sessions. For body fat mass decreases, the effect of resistance circuit-based training was significantly greater in protocols that used low (<60% 1-RM) or moderate intensity (60–80% 1-RM) and short periods or rest between exercises (10–30 s). ABSTRACT: We assessed the effects of resistance circuit-based training (CT) on strength, cardiorespiratory fitness, and body composition. A systematic review with meta-analysis was conducted in three databases, ending on March, 2020. Meta-analysis and subgroup analysis were used to analyze the effects of pre–post-intervention CT and differences from control groups (CG). Of the 830 studies found, 45 were included in the meta-analysis (58 experimental groups (n = 897) and 34 CG (n = 474)). The CT interventions led to increases in muscle mass (1.9%; p < 0.001) and decreases in fat mass (4.3%; p < 0.001). With regard to cardiorespiratory fitness, CT had a favorable effect on VO2max (6.3%; p < 0.001), maximum aerobic speed or power (0.3%; p = 0.04), and aerobic performance (2.6%; p = 0.006) after training. Concerning strength outcome, the CT increased the strength of the upper and lower extremities. Only the magnitude of strength performance appears to be influenced by the training (number of sessions and frequency) and the training status. Moreover, low and moderate intensities and short rest time between exercise increase the magnitude of change in fat mass loss. Therefore, CT has been shown to be an effective method for improving body composition, cardiorespiratory fitness, and strength of the lower and upper limbs.