Physical Activity Behaviours of a Middle-aged South African Cohort as Determined by Integrated Hip and Thigh Accelerometry

Descriptive studies of objectively measured physical activity behaviours in African populations are rare. We developed a method of combining hip and thigh accelerometery signals to quantify and describe physical behaviours in middle-aged South African men and women. We integrated signals from two triaxial accelerometers worn simultaneously during free-living, in a subsample of the Middle-aged Soweto Cohort (MASC) (n = 794;mean (SD) age:53.7( 6.3) years). Acceleration time-series from the accelerometers were combined and movement-related acceleration derived using Euclidean Norm Minus One (ENMO, milli-g), to determine total movement volume (mean ENMO) and non-movement time (85 mg); thigh pitch angle and a sleep diary were used to divide non-movement time (min/day) into sleep, awake sitting/lying, and standing. Socio-demographic factors were self-reported, and weight and height were measured. Mean (SD) wear time was 128 (48) hours. Movement volume was 15.0 (6.5) mg for men and 12.2 (3.4) mg for women. Men spent more time in MVPA and sitting/lying, while women spent more time standing. Age was inversely associated with movement volume, MVPA and LPA. When compared to their normal weight counterparts, men who were overweight or obese spent less time in MVPA, while women who were overweight or obese spent less time in LPA and more time sitting/lying. Socio-economic status was inversely associated with total movement volume, MVPA and time spent sleeping, and positively associated with time spent sitting/lying, in both men and women. Integrating signals from hip and thigh accelerometers enables characterisation of physical behaviours that can be applied in an African population.