Objective:This study examines the impact of a short-term exercise programme, prescribed on the basis of current exercise recommendations, on energy balance in males and females to assess whether this type of exercise induces compensatory changes in spontaneous activity energy expenditure (SAEE) and energy intake (EI).Design:Individuals were monitored for 16 days, 8 days of habitual physical activity (C) and 8 days when exercise was imposed (E). Total energy expenditure (TEE) was calculated from individual relationships of [Vdot ]O2 and [Vdot ]CO2 to heart rate (HR) records of HR and physical activity obtained during waking hours of the C and E periods and basal metabolic rate (BMR) measurements (Deltatrac System, Datex Instrumentation). Changes in nude body mass (BM) were estimated by using a digital scale (Sartorius AG, Gottigen, Germany).Setting:Laboratory and free-living.Subjects:Eight lean females (body fat: 17.5±4.5%) and eight males of similar percentage body fat participated in this study. All subjects were Caucasian and aged between 20 and 25 years.Intervention:During the E period, a supervised exercise session was conducted every second day, each consisting of a total net energy expenditure of 2092 kJ+BMR at 90% lactate threshold.Results:During the E period, TEE was higher than C in males and females (exercise: 95.2±13.9, 78.3±15.9 MJ; control: 82.4±10.4, 68.8±16.7 MJ, respectively; P<0.00; P=0.02). SAEE, calculated as TEE minus the energy expended during exercise, was not significantly different between C (males: 82.4±4.8 MJ; females: 68.8±7.6 MJ) and E (males: 86.8±6.3 MJ; females: 70.0±7.2 MJ) periods in either gender. Males showed no change in BM over the C (pre-intervention: 83.4±7.2 kg; post-intervention: 83.1±6.8 kg) or E (pre-intervention: 83.4±6.8 kg; post-intervention: 83.4±6.8 kg) periods. Females’ BM over the C period did not alter (pre-intervention: 63.3±2.8 kg; post-intervention 63.7±3.1 kg); however, there was a significant decrease (P<0.00) in BM over the E period (pre-intervention: 63.0±2.7 kg; post-intervention: 62.4±2.7 kg).Conclusion:The exercise programme was achieved in males and females without any impact on SAEE. Therefore, differences between genders in relation to BM reduction can be explained by differences in the EI response to exercise.