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Roberson, KB, Chowdhari, SS, White, MJ, and Signorile, JF. Loads and movement speeds dictate differences in power output during circuit training. J Strength Cond Res 31(10): 2765–2776, 2017—Power training has become a common exercise intervention for improving muscle strength, power, and physical function while reducing injury risk. Few studies, however, have evaluated acute load changes on power output during traditional resistance training protocols. Therefore, the aim of this study was to quantify the effects of different loading patterns on power output during a single session of circuit resistance training (CRT). Nine male (age = 19.4 ± 0.9 years) and 11 female participants (age = 20.6 ± 1.6 years) completed 3 CRT protocols during separate testing sessions using 7 pneumatic exercises. Protocols included heavy load explosive contraction (HLEC: 80% one repetition maximum [1RM], maximum speed concentric-2 seconds eccentric), heavy load controlled contraction (HLCC: 80% 1RM, 2 seconds concentric-2 seconds eccentric), and moderate load explosive contraction (MLEC: 50% 1RM, maximum speed concentric-2 seconds eccentric). Protocols were assigned randomly using a counterbalanced design. Power for each repetition and set were determined using computerized software interfaced with each machine. Blood lactate was measured at rest and immediately postexercise. For male and female participants, average power was significantly greater during all exercises for HLEC and MLEC than HLCC. Average power was greatest during the HLEC for leg press (LP), hip adduction (ADD), and hip abduction (ABD) (p ≤ 0.05), whereas male participants alone produced their greatest power during HLEC for leg curl (LC) (p < 0.001). For male and female participants, significantly greater power was detected by set for LP, lat pull-down (LAT), ADD, LC, and ABD for the MLEC protocol (p < 0.02) and for LP, LAT, CP, and LC for the HLEC protocol (p < 0.03). A condition × sex interaction was seen for blood lactate changes (= 0.249; p = 0.024), with female participants producing a significantly greater change for MLEC than HLEC (Mdiff = 1.61 ± 0.35 mmol·L−1; p = 0.011), whereas male participants showed no significant differences among conditions. Performing a CRT protocol using explosive training patterns, especially at high loads for lower-body exercises and moderate loads for upper-body exercises, produces significantly higher power than controlled speed training in most exercises. These results provide exercisers, personal trainers, and strength coaches with information that can assist in the design of training protocols to maximize power output during CRT.