Across 45 studies (58 circuit groups, n = 897; 34 control groups, n = 474), resistance circuit training raised VO2max by 6.3%, muscle mass by 1.9% and upper- and lower-body strength and cut fat mass by 4.3% after training, but raised maximal aerobic speed or power by only 0.3%; the abstract reports no risk-of-bias assessment and compares circuits only with controls and with baseline

Ramos-Campo and colleagues pooled studies of resistance circuit-based training to estimate what it does for strength, cardiorespiratory fitness and body composition. They searched three databases up to March 2020, found 830 records and included 45 studies, with 58 circuit groups (897 participants) and 34 control groups (474).

They analysed changes from before to after the circuits and differences from controls, with subgroup analyses. After training, muscle mass was up 1.9% and fat mass down 4.3%; VO2max rose 6.3%, maximal aerobic speed or power 0.3% and aerobic performance 2.6%; strength of the arms and legs increased.

Only the size of the strength gain appeared to vary with the number of sessions, the weekly frequency and the participants' training status, and fat loss was larger with low-to-moderate intensities and short rests between exercises. The authors conclude that circuit training improves body composition, cardiorespiratory fitness and upper- and lower-limb strength.