Physical activity – assessment of objective measurements and its associations to cardiometabolic health and healthy aging

Physical activity (PA) alongside a varied diet are the two cornerstones of a healthy life. A sufficient volume of PA with high enough intensity leads to a plethora of favorable modifications in the human body. In this thesis, first, the connection between PA at an old age and the telomere length (TL) as a marker of biological age was studied in the Oulu cohort 1945 to assess the effect of PA on cellular aging. At the same age, women had longer telomeres than men. Physical activity was correlated to TL with the longest TL observed in moderately active participants. Next, objective PA measurement methods using accelerometers were assessed, compared, and based on this; a novel method for step detection and energy expenditure (EE) estimation was validated in a laboratory setting. Comparisons and validation were conducted with participants of varying body characteristics and ages. New algorithms for step detection and EE were developed and optimized using machine learning. The predominant research-grade accelerometer (ActiGraph) was detected to be only accurate with speeds above 4 km/h. The optimized step detection algorithm for the self-developed Sartorio Xelometer was shown to be accurate at assessing step numbers and intensities, especially at the lower range of speeds (1.5 – 4 km/h), which is important for participants with obesity or at an advanced age. All accelerometry-based EE estimation methods were found to be inaccurate. Finally, these newly developed algorithms were used on the Northern Finland Birth Cohort 1986 (NFBC1986) data collection to assess step numbers and PA intensity. A correlation analysis was conducted between these physical variables and multiple cardiometabolic risk factors to determine beneficial PA thresholds using SI-unit standard gravity (g) as the determinant of intensity. The total PA was significantly correlated with anthropometric measures. Triglycerides, total cholesterol, and LDL were significantly associated with PA, indicating that the accumulative effects of a sedentary lifestyle on health results were early pathophysiological changes. The objective measurement of PA is extremely important to create general recommendations and personalized PA prescriptions to prevent obesity and cardiometabolic diseases, and to ensure an active, independent, and healthy life while aging.