The purpose of this study was to determine the effect variations in the percent of one repetition maximum bench presses have on weight training economy (total net kcal consumed divided by J work) and blood lactate. Seventeen subjects participated in a number of bench press experiments at various intensities, 20 percent to 80 percent of one repetition maximum (1 RM). Oxygen uptake ((formula presented)) was measured continuously both during and following the experiments. Arterialized capillary blood was sampled and analyzed for lactate both prior to and at 4.5 minutes following exercise. Exercise and recovery net (formula presented) were summed to determine the total exercise (formula presented) requirement. Metabolism was estimated by assuming 5 kcal of energy released for each liter of oxygen used. Work was calculated by summing the work performed on the barbell and body segments. Economy of the weight training exercise decreased as exercise intensity increased. For example, subjects used almost 12 times as much energy (kcal) doing one repetition at 80 percent 1 RM as opposed to one repetition at 20 percent 1 RM even though work only increased by a magnitude offour. Significantly more lactate was found in the blood following the 60 percent 1 RM bench press experiments than after the 30 percent 1 RM bench press experiments. No significant difference in blood lactates was found between the 60 percent 1 RM and the two 70 percent 1 RM bench press experiments. Within each bench press intensity there was a high relationship between work performed and energy expended (r values ranged from.83 to.99). The amount of work performed in an exercise and the percent of 1 RM at which work was performed in an exercise have a marked effect on energy used to perform weight training tasks. Both of these factors must be considered in prescription of weight training exercise. © 1988 Journal of Applied Sport Science Research. All rights reserved.