The use of wearable technology and digital health platforms to enable remote monitoring of physical activity and health.

Physical inactivity is a major risk factor for premature death and non-communicable diseases (NCDs). Participating in regular physical activity (PA) and reducing time spent in sedentary behaviour supports mental and physical health. Measurements of population PA are essential for understanding the influence of PA on NCD. Therefore, the overarching aim of this PhD was to determine validity and user experience of wearable technology to measure step count, energy expenditure (EE), heart rate and PA intensity. Twenty healthy adult men and women took part in the experimental trial study in chapter 4. Participants wore an iPhone 5S and GT3X+ in a waist-mounted pouch during bouts of treadmill walking, jogging, and other physical activities in the laboratory. Step counts were manually counted (MC), and EE was measured using indirect calorimetry (IC). During two weeks of free living, participants (n = 17) continuously wore a GT3X+ attached to their waist and were provided with an iPhone 5S to use as they would their own phone. The data showed that the iPhone accurately estimated step count during laboratory walking but recorded significantly lower daily steps compared with the GT3X+ during free living. In the next chapter, a mixedmethods study explored the use of participants’ own iPhone in estimating PA during free living compared to another iPhone and GT3X+ worn continuously on the waist. Results showed that the user’s own iPhone recorded significantly fewer steps than both devices attached to the waist. The usability of a novel digital health platform (DHP) was established in chapter 6 (study 3). A sample of healthy adults and health care professionals (HCPs) were recruited for this qualitative study. The data showed that both cohorts believed the DHP had the potential to be implemented within the NHS. Lastly, in chapter 7, the change in PA behaviours prior-to, during and post-COVID-19 lockdown was investigated with a mixed-methods approach in a sample of healthy adults. Data showed that PA and mental health was negatively affected by the lockdown, however, PA increased a month into lockdown, but not to pre-COVID-19 levels. The results of this PhD expand the knowledge of PA monitoring using mHealth technologies in both laboratory and free-living settings, provides “proof of concept” of a novel DHP and confirms previous findings of a reduction in PA at the commencement of the COVID-19 lockdown.