LAUSR

Increased skeletal muscle fat infiltration (i.e. myosteatosis) is now recognized as a major risk factor for cardio-metabolic diseases. Therefore, a lifestyle modification that reduces myosteatosis would be of great public health importance. However, studies examining the association of relevant lifestyle factors with this ectopic fat depot are lacking, particularly in African ancestry populations who have a very high burden of cardio-metabolic diseases. The aim of this study was to examine the relation between objectively measured physical activity and sedentary behavior with computed tomography measured calf muscle attenuation among middle-aged and elderly African-Caribbeans from the population-based Tobago Health Study. Preliminary analyses were conducted among 134 women (mean age 59 yrs, mean BMI 31.6 kg/m 2 ) and 355 men (mean age 62 yrs, mean BMI 28 kg/m 2 ). Physical activity was measured using the SenseWear Pro armband worn for 4-7 days. We calculated the mean duration of waking time engaged in light physical activity (LPA), moderate to vigorous activity (MVPA), and sedentary behavior (SB) per day. Skeletal muscle attenuation (mg/cm 3 ) reflects the fat content of the muscle such that greater skeletal muscle fat infiltration is reflected by lower attenuation. Women spent less time in LPA (146 vs. 270 min/day) and MVPA (15 vs. 41 min/day), but more time in SB (789 vs. 647 min/day) than men (all p<0.0001) after adjustments for gender differences in age. Muscle attenuation was lower among women compared with men (70.5 vs. 72.7 mg/cm3; age and BMI adjusted p<0.0001). In both women and men, muscle attenuation was positively correlated with the LPA and MVPA, and inversely with time spent in SB (spearman correlation coefficients (r) ranged from 0.21 to 0.39, all p<0.006 adjusted for age). Upon additional adjustment for BMI, in both women and men, the association of muscle attenuation with MVPA remained significant (r=0.21 and r=0.18, respectively, both p<0.03), but there was no association with LPA. Percent time spent in SB was associated with muscle attenuation only among women after additional adjustment for BMI (women: -0.16, p=0.052), and we also found a significant sex interaction effect of SB on muscle attenuation (p=0.035). Our preliminary findings suggest that there is significant association between MVPA and myosteatosis among middle-aged and elderly African Caribbeans. However, SB may only be relevant for myosteatosis among women. Future analyses will be conducted in a larger sample from this cohort to confirm our findings and to test for independence from other potential confounding factors, such as diet, sleep patterns, adiposity distribution, and diabetes.