The influence of gender on aerobic energy expenditure (EE) during weight training has not been systematically researched. We determined the absolute and relative EE during the performance of two weight training programs of different intensities, durations and total work in males and females. Eight male and seven female recreational weight trainers (20-29 y) completed two randomly ordered weight training sessions involving 2 sets of 8 standard upper and lower body lifts at a set cadence separated by 45 seconds rest between sets and lifts (48 hrs apart). Heavy (H) at 100% 8 Repetition Maximum (8RM), 8 reps, ~19 min duration and light (L) at 85% 8RM, 15 reps, ~23 min duration. VO₂ was determined continuously throughout the training sessions. Lean body mass (LBM) was estimated from skin fold measures and body weight. Energy expenditure was estimated from breath-by-breath metabolic measurements using portable metabolic assessment equipment (Cosmed K4b²). Absolute EE (total kJ) and rate of energy expenditure per minute (kJ per min) were not significantly different between H and L intensities and male and female subjects. The rate of EE averaged between approximately 10-12 kJ per min. However, relative EE (J per kg LBM per min per unit work) were significantly higher (p < 0.02) for females compared to males in both H: (26.46±8.06 females vs 14.36±3.02 males) and L: (19.91±4.28 females vs. 9.83±3.28 males), intensities. It was concluded that females rely on a greater relative aerobic EE than males when performing recreational type weight lifting programs.