The effect of exercise and improved physical fitness on basal metabolic rate

Abstract

1. The suggestion that there is a sustained enhancement in metabolic rate after exercise was investigated during the course of a study in which six normal-weight volunteers (three men, three women) took part in a 9-week training programme. Baseline values were assessed in a 3-5 week control period of minimal activity before training. At the end of the study the subjects were capable of running for I h/d, 5 d/week.2. Throughout the entire study the subjects were maintained on a constant diet. Measurement of energy expenditure by the doubly-labelled water (2H218O) method showed that the subjects had an energy imbalance of +3% in the control and -20% at the end of the training period. The subjects were in positive (1·1 (se 0·2) g) nitrogen balance in the second week of the control, and in negative (-0·6 (se 0·3) g) N balance in the last week of the exercise period.3. Over the course of the study maximum oxygen consumption (Vo2max) and high-density-lipoprotein-cholesterol levels increased by 30%. Heart rate at rest and when performing a standard step test fell significantly.4. Body composition was assessed weekly by40K counting and skinfold thickness measurements, in addition to2H2dilution at the beginning and end of the study. Fat-free mass was apparently gained in the early phases of the study, but there was lack of agreement between the different methods of assessing body composition. Changes in body-weight were not significant.5. Basal metabolic rate (BMR), overnight metabolic rate (OMR) and sleeping metabolic rate (SMR) were measured on three occasions: in the control period, and the beginning and end of the training periods. Average BMR in the control period was 5·91 (se 0·39) MJ/24 h and was not changed with activity. There were no changes in OMR (5·71 (se 0·27) MJ/24 h in the control) nor in SMR (5·18 (se 027) MJ/24 h in the control), nor in BMR, OMR or SMR when expressed per kg body-weight, or per kg fat-free mass.6. These results do not support the suggestion that there is a sustained increase in BMR following exercise that can usefully assist in weight-loss programmes.