Background: Age-related loss of the muscle mass is linked to obesity and diabetes because the muscle is the major site for fat oxidation which is influenced by exercise. We aimed to explore the association between fat oxidation rates (FORs) and exercise intensity during age-related muscle loss.
Methods: A total of 224 healthy Chinese men aged 23-92 years were recruited. Fat and lean tissue masses were measured by DXA. The subjects were also tested using graded incremental exercise with an increased intensity of 10 W until maximal fat oxidation rate (Fatmax) was achieved. Real-time contribution (%) of fat to total energy expenditure were determined using indirect calorimetry.
Results: We found that appendicular skeletal muscle mass/weight (ASM/Wt) decreased during ageing and positively correlated with FORs during low-intensity exercise. In multiple linear regression models, FORs was positively related with ASM/Wt (β =0.446, P=0.0091) but negatively associated with exercise intensity (β =-0.573, P<0.0001), whereas fat oxidation rate did not show any association with age. Moreover, there was a significantly negative correlation between ASM/Wt and Fatmax.
Conclusions: Our findings highlight the importance of muscle mass in fat utilization during low-intensity exercise. A higher exercise intensity indicated by Fatmax is recommended for improving fat oxidation in Chinese men with decreased muscle mass.
Keywords: Muscle mass; ageing; exercise intensity; fat utilization.