Design of an Intelligent Wearable to Assess Physical Activity and Health Related Outcomes - the DIWAH Study

Globally, the life expectancy is gradually increasing, which leads to a demographic shift towards an increasing proportion of older people. For example, in Sweden, the number of individuals over the age of 75 will double during the next 50 years and the proportion will increase by more than 60% (Statistics Sweden, publicly available data). This means that more people will live longer and less people will be available to care for them. One of our major societal challenges to meet this demographic transition is to develop strategies for maintaining good health and quality of life in that age group and then when they inevitably become ill, how to treat them in the best possible way? One way forward is to capitalize on the opportunities the technological evolution have provided. In fact, Sweden have adopted a very ambitious goal as outlined in Vision2025 (www.ehalsa2025.se): In 2025, Sweden will be best in the world at using the opportunities offered by digitalization and eHealth to make it easier for people to achieve good and equal health and welfare, and to develop and strengthen their own resources for increased independence and participation in the life of society. However, digital technology alone is not sufficient to reach such a goal, other strategies that uses the technology to increase the health of individuals must also be present. One such strategy is to maintain a healthy level of physical activity through life. Physical activity is one of few behaviors that a human can change, on its own and to a low cost, that simultaneously produces significant physical and mental health benefits. To that end the ability to assess a person's habitual physical activity level, defined as "the hypothetical average around which that individual's physical activity varies" has for a long time been considered as the holy grail among physical activity researchers. For 30 years researchers have used accelerometers to objectively quantify free-living physical activity but in the last decade wearables have become hugely popular among the general population (Apple and Fitbit being the largest brands). Wearables, here defined as small portable devices with embedded sensors that measure health-related variables, claim to be able to collect long-term high-resolution data regarding health-related behaviour e.g., body posture, PA intensity, sleep, and much more. Wearables can also capture important aspects related to the cardiometabolic system such as heart rate, blood pressure, as well as support behaviour change. Thus, they can be viewed as a "Swiss army knife", since they provide a wide range of tools in one device. In theory, wearables hold a huge promise to be used to create evidence-based personalized PA in health promotion, disease prevention, and disease treatment. Compared to most research grade monitors the commercial wearables have several advantages that make them attractive for use in the healthcare system. They contain multiple sensors of relevance for the assessment of PA and related health outcomes, notably an accelerometer to detect biomechanical aspects of movement and an optical sensor to detect the physiological response to movement e.g., heart rate. Additional strengths of the commercial monitors compared to research grade monitors are that they are designed to be worn for a long time which gives an even better opportunity to assess the individual level of physical activity, especially among those the least active. However, during the last decade, there have been an explosion of different wearables and data processing methods without an established framework to evaluate their validity or reliability. This have caused great confusion driven by nonrobust device development and evaluation methods that do not reflect how they will be used in practice. Moreover, the divergence in summary estimates of physical activity within and between different brands prohibits an opportunity to pool data or to make direct comparisons between different studies. Other limitations that wearables have that makes them unsuitable for use, even among healthy individuals is that they are primarily designed for the fitness market and not for use within the health care system, they have not been evaluated in a transparent manner, they do not accurately capture physical activity among individuals with altered motorical pattern, e.g., elderly. Even though the hardware in most wearables are similar, the algorithms that translates the signals from the sensors to different interpretable outcomes (e.g., steps) are often proprietary and update with irregular intervals. Other important limitations include questionable patient confidentiality and data ownership. Neither the commercial nor research grade monitors can today assess physical activity at individual level since they make limited use of the wealth of data collected. If wearables can overcome these limitations, they hold much promise towards expanding the clinical repertoire of patient-specific measures, and they are considered an important tool for the future of precision health and personalized medicine. Considering the wealth of new wearable PA trackers entering the market without prior proof of validity it is fundamental to provide consumers, patients, health professionals and researchers with an open-source, evidence-based wearable with excellent validity and reliability.

Purpose and aims This project will start to merge the strengths of the commercial wearables with those of research grade monitors and modern data processing methods to overcome these limitations. The combination of information from accelerometry (biomechanics) and heart rate from the optical sensor (physiological response) improves the predictions regarding PA intensity and physical activity related energy expenditure on individual level. In addition, the optical sensor that are fitted in a wearable can estimate the blood pressure of an individual. The signals from the sensors will be analysed using artificial intelligence and machine learning to take better advantages of the rich data collected. Normally PA and health outcomes are being measured at different times, but wearables can collect data from multiple variables simultaneously and in real-time. This ability may provide novel details about the association between the physical activity behavior and the individuals clinical status. This have not yet been studied, most likely due to the complexity of acquiring and analyzing these data. However, the field have now moved to a point where the technology along with processing power and analytical tools exists. Thus, the time has come to explore the full possibility of combining real-time data on physical activity behaviour, health related outcomes and artificial intelligence. So that in the future citizens may be able to improve and maintain their health through device-based services and to make informed decisions that are based upon their personal health data.

The overarching purpose of DIWAH is to develop and validate artificial intelligence/machine learning based algorithms to assess physical activity and health related variables on individual level in real time for use within the health care system using open-source wearables.

This project will take the first steps by conducting a rigorous development and validation of the algorithms using a transparend phase-based framework. More specifically the project aim to develop algorithms for assessing:

• Physical activity
• Heart Rate
• Health related variables e.g., blood pressure and energy expenditure But also identify what underlying factors that improves the predictions such as age sex body composition and health related fitness levels.