Background: Muscle triacylglycerols (TG) are known to be a source of energy during submaximal exercise.
Objective: The aim of this study was to assess whether an index of muscle fat content is related to maximal fat oxidation rate (FATOXmax) in 58 obese men (mean age 46.0+/-0.8 (s.e.) y, body weight 96.4+/-1.4 kg, percentage fat: 31.9+/-0.5%) [corrected].
Design: FATOXmax was defined as the highest value of fat oxidation rate, measured by indirect calorimetry, while walking on a treadmill (4.3 km/h) at three different slopes: 0% (40+/-1% of VO2max), 3% (47+/-1% of VO2max) and 6% (58+/-1% of VO2max). Fat-free mass (FFM) and fat mass (FM) were measured with the underwater technique and scans were obtained by computed tomography (CT) at the mid thigh level to assess areas of adipose tissue within skeletal muscle, ie deep adipose tissue (DAT), subcutaneous adipose tissue (SAT), skeletal muscle (M) and low attenuation skeletal muscle (LAM, range of attenuation values: 0-34 Hounsfield units). LAM and DAT were used as indices of skeletal muscle fat content.
Results: FATOXmax, adjusted for age, was correlated with FFM (r=0.26, P<0.05), LAM (r=0.29, P<0.05), abdominal visceral adipose tissue (r=0.30, P<0.05) and plasma free fatty acid (FFA) levels (r=0.33, P<0.05) but not with SAT (r=0.03) and DAT (r=0.21) [corrected]. In a stepwise linear multiple regression, plasma FFA, age and LAM significantly predicted FATOXmax (r2=0.27). Each independent variable explained about 9% of the FATOXmax variance.
Conclusion: LAM makes a significant but weak contribution to the modulation of fat oxidation during submaximal exercise in obese men.