Background and objectives: Sub-Saharan Africa (SSA) has an increasing burden of noncommunicable diseases (NCDs). Comprehensive and context-specific evidence on the major modifiable risk factors for NCDs, such as physical activity, is required to help inform strategies to address this burden. Accurate measurement of physical activity and other health indicators will be important to achieving these objectives. This thesis aims to contribute to the current understanding of physical activity in SSA, and the development of frameworks to objectively assess health indicators, including physical activity, in free-living populations.

Methods: Using existing large-scale population data from SSA (N=29606), I examined the prevalence and determinants of physical activity. The association between physical activity and key intermediate risk factors for NCDs was also assessed. Furthermore, I conducted a feasibility study (N=32) to assess the usability and validity of two commercial wrist-worn heart rate monitors as potential tools in the measurement of physical activity and related dimensions in free-living populations.

Results: Across these diverse sub-Saharan African populations, there was substantial variation in the prevalence of NCD risk factors, including insufficient physical activity. Women, older individuals, those with higher levels of education, overweight and obese individuals, the unemployed, and urban residents were more likely to be insufficiently active. Furthermore, there was strong evidence of sociodemographic differences in the domains within which physical activity is undertaken, with potential inequities observed for participation in leisure-time physical activity. A weak but statistically significant association was observed between physical activity and BMI, and physical activity and diastolic blood pressure. Finally, the commercial wrist-worn heart rate monitors examined demonstrated acceptable coverage, with minimal data loss over the study period, and comparable estimates for population-level estimates. However, there was evidence of systematic differences in individual heart rate measurements, potentially limiting their use in active populations.

Conclusions: This work provides key evidence on physical activity, its distribution and determinants, in 10 diverse populations in SSA. It also highlights opportunities for reducing the obesity and hypertension burden in these populations, and hence informs future directions for research and strategies to address the increasing NCD burden. Lastly, it provides the basis for further validation studies of commercial wearable devices in free-living populations and highlights the need for improvements to device algorithms.