Physical activity is closely linked with health and well-being; however, many Americans do not engage in regular exercise. Only one in five adults in the US meets the CDC physical activity guidelines of 150 min of aerobic activity and 2 days of muscle strengthening activity per week [1]. This trend of inactivity increases with age and can interfere with an individual’s capacity to work. The consequences of these trends are that the average worker can no longer deliver a full day’s effort in a physically, psychologically, and cognitively demanding job. Degenerative diseases associated with inactivity and obesity are epidemic. The benefits of physical activity and fitness extend beyond job performance and work capacity and include longer life and enhanced quality of life. Fit workers are more productive, are absent fewer days, and have a more positive attitude toward work and life in general [2].

Physical activity and fitness can be quantified by leveraging the available, affordable fitness technology. Fitness technology, including trackers and smartphone applications (apps), have become increasingly popular for measuring and encouraging physical activity in recent years. Such technology encompasses individual fitness trackers that can stand alone, a fitness tracker paired with a companion app, or an app that can be downloaded onto a smartphone without the need for an extra device. The fitness tracker market is currently thriving, with estimates of almost 1.5 billion dollars in revenue last year alone [3] and is expected to increase to a five-billion-dollar industry by 2019 [4]. A 2013 analysis revealed that there are over 41,000 health and fitness apps currently available to the public via iTunes (e.g., Map My Walk, Runkeeper, My Fitness Pal) [5] and over half of smartphone users report having downloaded such an app [6]. Other personalized QoL technologies exist to assess and improve physical activity and work capacity such as heart rate monitors, sleep trackers, and smart scales, to name a few.

These physical activity and fitness trackers and apps are among the increasing number of Quality of Life Technologies (QoLT) for the assessment or improvement of an individual’s QoL. QoLT leverage the increasing availability of miniaturized computing, storage, and communication sensor- and actuator-based, context-rich technologies that can be embedded within various personal devices, for example, smartphones and wearables. They rely on hardware technologies (i.e., devices or physical interaction elements) or software technologies (e.g., apps or web-based interfaces) or, most likely, a combination of both. QoLT on an increasing scale can be personalized to satisfy the intended needs of the user anywhere and anytime and can be used in a continuous and longitudinal yet minimally intrusive way, in the individual’s daily life [7]. Overall personalized, and miniaturized computing QoL technologies have the potential to be change agents for an individual’s physical work capacity and health- related quality of life and significantly impact public health, research, and policy.

This chapter addresses (1) the factors associated with variations in work capacity and quality of life; (2) the state-of-art of personalized, miniaturized computing QoL technologies for measuring and improving individual work capacity; (3) the use of activity trackers to quantify work capacity; and (4) strategies to enhance use of Web-based and non-Web-based tools and fitness technology for behavioral change, health management, and rehabilitation interventions for the self-management of work capacity and enhancement of health-related quality of life across the lifespan. This chapter concludes with guidelines for the monitoring and evaluating of digital health technologies and eHealth interventions and suggestions for future development of tools for the assessment and remediation of working capacity. The research question that guides this literature review is: How does the use of self-management QoL technologies affect work capacity and reported health-related quality of life?

Definition and Measurement of Work Capacity

According to the WHOQOL theoretical model, working capacity is the facet of physical health that examines a person’s use of his or her energy for work. “Work” is defined as any major activity in which the person is engaged. Major activities might include paid work, unpaid work, voluntary community work, full-time study, care of children and household duties. This facet focuses on a person’s ability to perform work, regardless of the type of work [8].

In the past, many research studies on physical activity and work capacity have relied on self-report instruments. However, such subjective measures of activity can be highly unreliable, stemming from memory, social acceptability and other biases, revealing both higher and lower estimates than an objective measurement [9, 10]. Since then, several standardized instruments have been developed to measure work capacity.

One of these standardized instruments, The Work Ability Index (WAI) , is an instrument consisting of seven items, which takes into consideration the demands of work and the worker’s health status and resources and is used to assess the work ability of workers during health examinations and workplace surveys. The purpose of the WAI is to help define necessary actions to maintain and promote work ability. The validity and reliability of the WAI has been assessed in correlation analyses. The WAI and all its items have been shown to reliably predict work disability, retirement, and mortality [11]. More recently, the validity of WAI has been studied by Radkiewich [12] and WAI’s test–retest reliability by de Zwart [13]. The WAI has become the standard for assessing work capacity in occupational health research and the daily practice of occupational health care and has been translated into 24 languages.

Another instrument, The Work-ability Support Scale (WSS) , is a newer tool designed to assess vocational ability and support needs following onset of acquired disability to assist decision-making in vocational rehabilitation. It is designed to be used both for people who are working, or, as a planning tool for those considering returning to work. The tool has 16 items across three domains of work functioning: physical/environment, thinking and communicating, and social/behavioral. Scores ranges from 1 for constant support to 7 for independence. There are also an additional seven items related to contextual factors outside the workplace that could affect work functioning. Its scoring accuracy and rater reliability has been supported [14, 9].

Work capacity can also be assessed through a Functional Capacity Evaluation (FCE) which evaluates an individual’s capacity to perform work activities related to his or her participation in employment. The FCE process is a set of tests, practices and observations highly specific for a type of job for which the individual is being assessed, as it compares the individual’s health status, and body functions and structures to the demands of this job and the work environment. It can provide an accurate measurement of an individual’s ability to perform critical work tasks. This can help to determine an individual’s capability/ability to return to work or their employability. An FCE is performed on a one-on-one basis and can last up to 4 hours. A well-designed FCE should consist of a battery of standardized assessments that offer results in performance-based measures and demonstrates predictive value about the individual’s return to work. The FCE report includes an overall physical demand level, a summary of job-specific physical abilities, a summary of performance consistency and overall voluntary effort, job match information, adaptations to enhance performance, and treatment recommendations, if requested [15].

Two self-reports have been utilized to assess the physical aspects of work capacity in cross-cultural settings. One instrument, The International Physical Activity Questionnaire- Long (IPAQ-L) is a 27-item questionnaire for use by either telephone or self-administered methods that can be used to obtain internationally comparable data on health–related physical activity in theses domains (domestic physical activity (PA), occupational PA, leisure-time PA, active transportation and sitting time) and intensities of PA (vigorous, moderate, and walking). The instrument has undergone extensive reliability and validity testing across 12 countries (14 sites). IPAQ has high reliability and moderate criteria validity in comparison with accelerometers. Good test-retest reliability for total PA, occupational PA, active transportation, and vigorous intensity activities was shown. The results suggest that these measures have acceptable measurement properties for use in many settings and in different languages and are suitable for national population-based prevalence studies of participation in physical activity [16, 17].

Another instrument, The Global Physical Activity Questionnaire (GPAQ) is a 16-item test developed by WHO as an improvement of the International Physical Activity Questionnaire (IPAQ) for use in cross-cultural settings. It collects information on physical activity participation in three settings or domains (activity at work, travel to and from places, and recreational activities) and sedentary behavior. It assesses work-related abilities such as able to “perform work involve vigorous-intensity activity that causes large increases in breathing or heart rate like [carrying or lifting heavy loads, digging or construction work] for at least 10 minutes continuously” and “time spent walking or bicycling for travel on a typical day.” Studies have shown fair-to-moderate validity of the GPAQ in a self-administered format in German, French, and Italian [18].

A few questionnaires have been designed for wide-scale, population-based surveillance of occupational physical activity (PA) behaviors. The Occupational Physical Activity Questionnaire (OPAQ) is a seven-item survey that identifies the average time per week spent in occupational tasks, e.g., sitting or standing, walking, and heavy labor activities. The modifications made when designing OPAQ improved its reliability for persons with stable work patterns, but at the expense of poorer reliability for persons with more variable PA. OPAQ did not have superior validity to IPAQ. OPAQ showed moderate to high 2-week test–retest reliability and moderate criterion validity when compared with detailed occupational PA records. The validity of the OPAQ is similar to other established occupational PA questionnaires [19].

In addition, certain occupations have developed work capacity tests to assess the specific demands of their required work. An example, The Work Capacity Test (WCT) , is a family of tests to determine firefighters’ physical capabilities to perform the duties of wildland firefighting and to meet National Wildfire Coordinating Group (NWCG) standards for wildland firefighters. There are three levels of tests known as the “pack test” (arduous), “field test” (moderate), and “walk test” (light). The Arduous Pack Test is intentionally stressful as it tests the capacity of muscular strength and aerobic endurance of firefighters. Considerable effort has been spent on validating the test to the work demands of US wildland firefighters, for whom the test displays content validity; however, work is still needed to verify its reliability and criterion and construct validity [20].

Research Studies on Variations in Work Capacity and QoL

Studies have documented greater exercise and physical work capacity among people who are active compared with sedentary individuals [21, 22]. Individuals with self-rated good health are more likely to be employed [21]. Participants who had the capacity to work graded themselves as having both better health and HRQoL than those with a non-capacity to work [21].

Physical activity in older adults not only improves their physical work capacity but also reduces the risk of chronic diseases, such as cardiovascular disease, stroke, obesity, and hypertension; improves cognitive and mental health; lowers the chance of falls; and helps maintain a longer independent life. While a great deal of variation exists, significant declines in physical work capacity have been reported between the ages of 40 and 60 years due to decreases in aerobic and musculoskeletal capacity. These physical declines can lead to increases in work- related injuries and illness. Differences in habitual physical activity, among other factors, greatly influences the variability seen in individual physical work capacity and its components [23].

Chronic diseases have an enormous impact on the ability to work. Being able to work is particularly important for the quality of life of people with chronic diseases [24]. Among individuals diagnosed with chronic conditions such as multiple sclerosis (MS), a majority suffer with fatigue, which strongly influences their everyday life. Flensner [25] found that individuals with MS who had the capacity to work reported significantly less fatigue compared to those with no capacity to work. Additionally, the level of work capacity was significantly higher among those participants who were less sensitive to heat, while those who were sensitive to heat showed significantly more often a non-capacity to work. This study lends support to some existing evidence of the beneficial impact of good health on work ability in patients with MS.

The relationship between physical and functional capacity and quality of life among elderly people who have a chronic disease was demonstrated in a study by Oztürk. Oztürk [26]. found that there are differences among elderly female and male individuals with a chronic disease in terms of the number of chronic diseases, types of chronic disease, mobility level, functional status, and QoL. One difference, mobility level, is related to functional capacity and QoL particularly in females; the higher the mobility level, the higher the QoL in females Rehabilitation programs to improve physical and functional capability and participation in daily activities may improve quality of life.

Participation in regular physical activity has been associated with better cardiometabolic indices [27], skeletal health [28], and cognitive and academic performance [29] in young people aged 7–18 years. Conversely, doing little or no physical activity in youth has been related to poor health outcomes and decreased quality of life in adulthood resulting in extended medical care and associated costs [30]. One study showed that the cost of MS in Sweden is about €600 million a year, one third of which are indirect costs associated with loss of production [31].

Reduced capacity to work is a major cause of high medical care costs and personal care costs in the later stages of a disease [30].

The State-of-Art of Personalized Computing QoL Technologies for Measuring Physical Activity

Types of Wearable Activity Trackers and Other Devices

In the past, many research studies on physical activity and work capacity have relied on self- report and self-report instruments to assess exercise behavior and capacity. However, such subjective measures of activity can be highly unreliable, revealing both higher and lower estimates than an objective measurement. People may overestimate activity intensity or time spent to present a favorable impression. Self-reports often focus on discrete activities such as going for a run or working out at a gym. Objective measurement of physical activity can record activity that may be missed in a questionnaire or self-report. This may be especially relevant for older adults who are less likely to go to a gym on a regular basis [32]. Thus, there is an increased interest in using objective activity monitors and other available, affordable QoL technologies to quantify physical activity and work capacity.

Activity trackers refer to sensor-based personalized wearable devices that automatically track and monitor various indicators of physical activity, such as steps taken, stairs climbed, duration and quality of sleep, pulse or heart rate, and self-reported calories burned. Newer devices feature an electrodermal activity (EDA) sensor to help measure your stress level, an ECG sensor to assess your heart rhythm, an SpO2 sensor to measure the amount of oxygen in your blood, and a skin temperature sensor. Some include built-in GPS. Activity trackers synchronize this data with users’ personal accounts, ensuring easy access from any device by the user. Activity trackers provide relatively unbiased data about basic physical activities and have the advantage of boosting physical activity through the integration of empirically tested behavioral change techniques such as goal setting, self-monitoring, social support, social comparison, feedback, and rewards [33], in contrast to antecedent technologies, such as pedometers. Self-monitoring and goal setting using activity trackers have been especially effective in promoting self-efficacy and physical activity in interventions to improve capacity for work [28]. Studies have shown that physical activity and fitness is increased using wearable activity trackers [21, 23].

Good fitness level may increase the physical capacity for work as well as enable one to operationalize the factors important for self-reported work capacity. For example, wearable activity trackers data may enable one to quantify the answer for the WAI factor of “work ability in relation to the demands of the job” or “estimated work impairment due to diseases.” As for the WSS scale, fitness trackers may enable one to quantify the “physical and motor” or “mobility and access”, “community mobility” and even “stamina and pacing” factors. Also, activity trackers may be useful in quantifying physical capabilities and capacity for certain work functions.

Fitness Trackers

Fitness trackers are at the heart of the fitness technology movement and have broad appeal. Their main appeal is that they create a snapshot of an individual’s physical fitness, which can empower individuals to make healthy changes that impact their ability to engage in everyday work and nonwork activities. According to 2020 PCMag [33], a few examples of trackers that do a little of everything are the Fitbit Inspire HR and Fitbit Charge 3. Easy-to-use and easy-to-read collected data, they are both excellent options for first-time users. If an individual is more interested in having a full-fledged smartwatch that includes fitness tracking, then the AppleWatch Series 5 (which does a bit of everything except measure sleep) or Samsung Galaxy Fit are the best options. With a smartwatch, an individual gets apps and a lot more functionality, such as the ability to send text messages from one’s watch. One major disadvantage is battery life. The best fitness trackers can last a week or more, but smartwatches usually need to be charged once a day. For runners, cyclists, and anyone else who is already invested in fitness and monitoring peak work capacity, the best option is a runner’s watch that doubles as an all-day fitness tracker such as the Forerunner 45 .

Heart Rate Monitors (HRM)

HRMs read an individual’s pulse while working out or active and are usually either chest straps or watch-style devices. They are not meant for monitoring heart rate 24/7 for medical purposes; for that, one needs an HRM that is FDA- approved or the equivalent in another country. Polar’s heart rate monitors, including the Polar OH1, have excellent tools for finding heart rate zones as well as explaining the activity’s benefits for the heart and body. Some fitness trackers or running watches have a heart rate sensor built in and allow one to see their heart rate in real time. Some such as JBL’s Reflect Fit are headphones, which take the pulse from the ear. HRMs may enable better quantification of stamina and pacing contributing to increased work capacity (WSS).

Smartphone Fitness Apps

Smartphone fitness and exercise apps provide users with data to quantify physical activities such as their “physical and motor” capacity and “stamina and pacing” with the additional advantage of immediate data aggregation and analysis. Users can then modify their behaviors or work activities accordingly. Additionally, dedicated smartphone- based apps may enable one to quantify the “sensory and perceptual skills” (WSS) required by the job.

For free workouts, The Johnson & Johnson Official 7-Minute Workout app has a variety of workouts for people of all fitness levels and of different lengths which are great for people who are just getting started with exercise and for frequent travelers to use in their hotel room.

Run-tracking apps, such as Runkeeper and Strava , use the phone (or a compatible watch or fitness tracker) to record a runner’s pace, distance, mileage, and more. Apps such as MapMyFitness can track non-sport activities—for instance, shoveling snow, raking leaves, or walking briskly. MyFitnessPal app is one of the best apps for logging the foods one eats to count calories and get a nutritional breakdown. Weight Watchers and Noom include access to coaches through their apps as well as community aspects so the user will not be alone on your fitness journey. If one wants hardcore training by an MMA champion, Touchfit : GSP gives an individual a series of progressively harder videos by fighter George St-Pierre. Jillian.

Michaels has a similar app with video-based workouts and a diet plan. Then there are apps and sites that specialize in one type of class, such as ballet, barre, and yoga or where you get a personal trainer to work with you on a personal fitness plan. Additionally, these dedicated smartphone-based apps resources may assist in quantifying “work ability” (WAI) and “sensory and perceptual skills” (WSS) required by the job.

Sleep Trackers

Sleep may influence one’s stamina, pacing and physical capacity to work and thus is an important variable to assess. Sleep trackers can track the user’s sleep so that an individual can learn more about his/her sleep patterns. Most fitness trackers now include sleep tracking. There are also smart mattresses with tracking technology built in. The most advanced, such as the Sleep Number 36 makes adjustments during the night that are tailored to the user. Or one could consider a smart pillow that plays white noise and detects snoring, such as the REM- Fit Zeeq Smart Pillow.

Other Devices

There are other aspects of daily life and its relation to potential work capacity that are worth tracking and operationalizing. Smart water-bottles track your water consumption and remind an individual to drink to minimize dehydration. Smart clothing gives feedback to runners about their form in real time, commenting on heel strikes, cadence, etc.

Some fitness enthusiasts believe that the secret to maximizing their fitness potential is in their blood. A service called InsideTracker will send a phlebotomist to one’s home or office to collect a blood sample and send it to a lab. There is even a wearable DNAband that helps an individual choose groceries based on their DNA, but it is now only available in the UK.

Evidence for the Use and Effectiveness of Activity Trackers

Academic and industry research has shown that the use of activity trackers can increase physical activity through continuous monitoring of activity progress, motivational messages, social support, and many other empirically tested behavioral change techniques [34,35,36]. That, in turn, may influence the work capacity [2, 26].

Wearable activity trackers have been shown to be effective in measuring and increasing the types of physical activity (e.g., steps, distance, calories expended, heart rate) that lead to increase work capacity. Adults who started using wearable activity trackers have been shown to increase daily activity levels [21]. A 7-month study of 18 participants (aged 36 to 73 years) who were given a wearable tracker found that 16 participants continued to use it after 7 months. The benefits of use included weight loss, social connection, and increased activity awareness [37].

Participants aged 60 years and older who were given a tracker reduced waist circumference and increased step count during another 12-week study [35]. African American and Hispanic older female participants, who tested a newly developed tracking device in a 7-week study, increased their physical activity level, lost weight, and lowered blood pressure levels [21]. Activity trackers have been found to be more effective than their predecessors, where sedentary female older adults who used digital trackers significantly increased their physical activity compared with those who used pedometers [21]. A tracker that delivered prompts via a short message service has also been found effective in increasing moderate-to-vigorous physical activity among overweight and obese adults [38].

Activity trackers facilitate physical activity in both young and older adults and are particularly beneficial for older adults because of the protective power of physical activity against diseases associated with older ages [36]. Despite the evident benefits of activity trackers for older generations, digital care today is more available to younger populations, leaving older adults on the periphery of the industry [39]. As little as 7% of older adults owned an activity tracker in 2014 [40]. Although many adults are now aware of this technology and its increased popularity, this population still shows slow rates of adoption that depend on many factors, including activity tracker trial and price [41]. Almost 84% of older adults aged 65 years and older do not meet the aerobic and muscle-strengthening physical activity requirements [42], which makes activity trackers a particularly relevant technology for this age group. Physical activity recommendations for older adults tend to focus on moderate-intensity aerobic and muscle-strengthening activities such as walking, jogging, bicycle riding, yard work, and gardening [43]. Some of these activities are tracked by wearable technology.

Activity trackers have the advantage of boosting physical activity through the integration of empirically tested behavioral change techniques such as goal setting, self-monitoring, social support, social comparison, feedback, and rewards [36] in contrast to antecedent technologies, such as pedometers. Self-monitoring and goal setting have been especially effective in promoting self-efficacy and physical activity in functional capacity interventions. Although wearing a new piece of health technology is a novel activity for older adults, they appreciate the activity tracker’s contribution to self-awareness and goal setting. Activity trackers provide older adults with relatively unbiased data about basic activities. In addition, older adults view activity trackers as helpful motivators in achieving walking goals and competing with themselves [44].

Another important advantage of activity tracker usage in the 65+ population is social connection. For a population that is characterized by social isolation and loneliness, technology such as activity trackers that addresses social connectivity needs is perceived as helpful in overcoming barriers to increase physical activity [45].

Although activity trackers can be helpful in increasing physical activity, this technology is not ideal. For example, in a study with 8 adults who were aged 75 years or older, 3 participants experienced technical problems with the activity trackers, preventing them from gathering any activity feedback. Participants reported that they could only get the activity tracker to work 78% of the time [46].

Thus, the full potential of quantifying and leveraging the available, affordable fitness technology in enhancing the capacity to work has only begun to be realized. Each year additional new and upgraded wearable devices and new apps with expanded tracking features such as monitoring blood oxygen saturation levels, feedback on sleep quality and stamina levels, and anxiety and panic attack tracking are being introduced to enhance the ability of these devices to monitor and facilitate major improvements in physical work capacity.

Validity and Reliability of Fitness Trackers for Measuring Physical Activity

Many studies have tested the utility of fitness trackers for measuring physical activity, with varied results [46, 47]. For each fitness tracker, there are many models, with a variety of algorithms that provide activity estimates. It is important to note the brand, model, and body placement used to facilitate comparisons across studies. Early studies found that fitness trackers including the wrist-worn Fitbit and Fitbit Ultra and the waist-worn Fitbit One have acceptable reliability and validity comparable to research–standard devices in the lab [47]. Van Remoortel.

[47] conducted a systematic review to identify whether available activity monitors (AM) have been appropriately validated for use in assessing physical activity in healthy populations and in those with chronic diseases. The latter population walk more slowly than healthy individuals which is reflected in their six-minute walking distance. This review suggests that most monitors (and pedometers) are less accurate during slower walking speeds. Validation studies of activity monitors are highly heterogeneous which is partly explained by the type of activity monitor and the activity monitor outcome. Since activity monitors are less accurate at slow walking speeds and information about validated activity monitors in chronic disease populations is lacking, proper validation studies in these populations are needed prior to their inclusion in clinical trials.

From Activity Trackers to Quantified Work Capacity

With respect to use of the evidence of fitness data and work capacity, wearable activity trackers data may enable one to quantify the answers for self-reports and self-report instruments.

Good fitness level may increase the physical capacity for work as well as enable one to operationalize the factors important for self-reported work capacity. For example, the wearable activity trackers data may enable one to quantify the answer for the WAI factor of “work ability in relation to the demands of the job” or “estimated work impairment due to diseases”. As for the WSS scale, the fitness trackers may enable to quantify the “physical and motor” or “mobility and access”, “community mobility” and even “stamina and pacing” factors. In addition, they may be useful in quantifying physical capabilities and capacity for certain work functions.

Evaluating the match between the physical, mental, social, environmental, and the organizational demands of a person’s work and his or her capacity to meet these demands are important in assessing work capacity. Measurement of workability requires consideration of a range of factors, including physical ability to perform tasks, ability to cope with the cognitive/communication demands of the job, and to function appropriately in the social and environmental context of the work. Wearable activity trackers can quantify many of these factors and are especially useful for individuals with physically demanding work such as a mail carrier/postman and a wildlands firefighter (see Table 8.1).

Table 8.1 Quantification of Work Capacity Using Wearable QoL Technologies

Strategies to Improve Work Capacity Using Behavioral Change Techniques and QoLT Interventions

Work capacity is the employee’s ability to accomplish production goals without undue fatigue, and without becoming a hazard to oneself or coworkers. It is a complex composite of aerobic and muscular fitness, natural abilities, intelligence, skill, experience, acclimatization, nutrition, and, of course, motivation. Even the most highly motivated workers may fail if they lack the strength or endurance required by the job. For prolonged arduous work, fitness is the most important determinant of work capacity [2]. While a great deal of variation exists, an average decline of 20% in physical work capacity has been reported between the ages of 40 and 60 years, due to decreases in aerobic and musculoskeletal capacity. These declines can contribute to decreased work capacity, and consequential increases in work-related injuries and illness [23].

Variations in work capacity over time can be quantified and self-monitored using quality of life technologies. The increasing availability of miniaturized computing, storage, and communication sensor-and actuator-based, context-rich technologies that can be embedded within various personal devices, such as smartphones and wearables, offer the opportunity to increase physical activity and lessen some work capacity declines through the continuous measuring, monitoring, and modifying of lifestyle behaviors such as the type, duration, and intensity of exercise, nutrition, sleep quality, and water hydration [48,49,– 50].

Use of Digital Fitness Devices and Behavioral Change Management Techniques

One strategy to improve work capacity is by using personalized, wearable activity tracking and physical monitoring devices with behavioral change techniques (BCTs) and evidence-based behavioral interventions [51]. Some of the more common behavioral change techniques are goal setting, feedback, rewards, social support, coaching, identifying barriers/problem solving, and action planning. Self-regulatory behavior change techniques such as goal setting, self- monitoring, and social support have been associated with greater increases in physical activity than those that did not [32]. The extent that fitness trackers can enhance physical capacity to work may be dependent on goal setting such as the daily step goal of 10,000 steps or 250 steps within an hour. Feedback and rewards, another set of behavior change techniques closely tied to goal setting, include the activity tracker reminders, text messages, and real-time alerts when the user has met a goal or has been sedentary for too long which have been reported to be effective in motivating and increasing physical activity and fitness [52, 53]. Social factors such as social support or competition have been shown to increase engagement, adherence, and completion in physical activity interventions beneficial to modifying work capacity [52, 54]. Coaching is often used in fitness technologies and interventions to motivate increases in physical activity through weekly information sessions that encouraged healthy behaviors and a weekly 30-min group walking session [52]. BCT techniques used with fitness technology can lead to increases in physical activity, endurance, muscle strength, and decreases in physical work fatigue [32].

However, certain BCT strategies may be more effective for different age groups in enhancing the physical aspects of work capacity using wearable personal activity devices. A critical analysis by Mercer [54] noted that self-regulation techniques present in wearable activity trackers such as goal setting, feedback, and social support are effective for younger adults, whereas older adults may benefit more from problem-solving, rewards for successful behavior, and modeling or demonstrating behavior.

Some of these behavioral change techniques are included in fitness technology. An analysis of seven commercially available fitness trackers (Jawbone UP24, Nike Fuelband, Polar Loop, Misfit Shine, Withings Pulse, Fitbit Zip, and Spark) revealed that most or all of these trackers included goal setting, feedback, rewards, self-monitoring, and social support [54]. Many fitness trackers include a “mobile coach” within their connected application or website for encouraging increases in physical activity, stamina, and endurance. More recently, Lyons [36] used BCTs to systematically analyze 13 wearable activity trackers and found that all of these trackers helped users to self-monitor behavior, obtain feedback on behavior, and add objects to the environment while also generally support users in goal setting and comparing their behavior with their goal. However, many health and fitness apps do not include BCT strategies thus their impact on the physical activity and the strength, and endurance aspects of work capacity may be limited [32].

Challenges Using Quality of Life Technologies in the Improvement of Work Capacity

Several challenges exist in using quality of life technologies in the improvement of work capacity. One challenge for the use of wearable activity trackers for BCT for physical activity and work capacity interventions is that there is no guarantee that the user will encounter a technique even if it is present on the device. Another challenge is that trackers are complex tools with multiple features and different users are likely to have different experiences. Similarly, a user who has a lower health or technology literacy may not explore the features as deeply as a health professional or expert technology user, regardless of age. Thus, the potential of wearable activity trackers to increase fitness behaviors through BCTs leading to improved capacity for physical activity and work can vary greatly.

Discussion and Recommendations

The Quantified Self Movement (QS) is a relatively recent trend wherein QS practitioners rely on the wealth of digital data originating from wearables, applications, and self-reports to enable them to assess diverse domains of daily life---physical state, (e.g., mobility, steps), psychological state (e.g., mood), social interactions (e.g., number of Facebook “likes”) and environmental context they are in (e.g., pollution) which contribute to an individual’s Quality of Life (QoL). The collected QS data enables an individual’s state and behavioral patterns to be assessed through these different QoL domains, based on which individualized feedback can be provided, in turn enabling the improvement in the individual’s state and QoL [55, 56].

Continuous monitoring is at the heart of the Quantified Self movement since it often gives a more accurate picture of human motion realities than short periods of laboratory testing and may provide a more accurate assessment of individual work capacity across different time periods and work-related activities. The long-term vision of QS activity is that of a systemic monitoring approach where an individual’s continuous personal information climate provides real-time performance optimization suggestions. The availability of powerful, personalized, and wearable mobile devices facilitates the provision of ubiquitous computing applications that enable clinicians and employers to better assess and monitor work capacity in the workplace and everyday life and to develop more effective interventions to enhance the physical and emotional aspects of capacity to work than previously possible.

While the concept of the quantified self may have begun with self-tracking at the individual level, the term is quickly being extended to include “group data” and the idea of aggregated data from multiple quantified selves as self-trackers share and work collaboratively with their data. Using QS group device data could be helpful in quantifying potential healthcare cost reductions and savings and for verifying user behaviors in behavioral change management programs in the public and private sectors. QS group data has the potential to benefit society by going beyond data creation and information generation to meaning-making and action-taking strategies with applications for impacting work capacity on the population level.

However, more research on the effectiveness of QS monitoring with QoL technologies is needed. To date, relatively few high-quality studies have been conducted examining the correlation between physical activity and work capacity and the overall effectiveness of physical activity trackers and smartphone interventions. Future studies should describe these interventions, the device and app features, and the AI and algorithms used with adequate detail so results can be reproduced, and lessons learned to advance work capacity and QoLT research.

Future research should also be directed toward enhancing an understanding of the time course of intervention effects in enhancing one’s capacity for work. Of particular interest is a better understanding of the timepoint at which peak effect size is reached, the timepoint at which user engagement decreases, and the factors that underpin these phenomena. The relatively short- term nature of positive effects suggest that additional efforts are required to design app features which help sustain user engagement with the app over time, perhaps through modules, unlockable content, gaming, and rewards. Sustaining user engagement is particularly important for smartphone-based interventions quantifying the physical aspects of work capacity due to the absence of human support and minimal supportive accountability.

Mobile technology used for assessing and monitoring work capacity should continue to emphasize ease of use, function, feedback, tailored information, ability to personalize design, and design-aesthetic as highly ranked engagement strategies. It will be useful for future app designs to incorporate long-term engagement strategies as increased exposure to the intervention can lead to larger, longer lasting effects in improving physical fitness and in turn, influencing work capacity.

Fitness technology should continue to include theoretically derived behavior change techniques that are useful for their intended population. Strategies such as goal setting, self- monitoring, feedback, rewards, social support, and coaching seem to be especially helpful in increasing activity and healthy behaviors that impact the work capacity of younger adults; while older adults may benefit more from problem-solving, rewards for successful behavior, and modeling or demonstrating behavior. The use of QS technologies as different types of affordances supporting the goal-oriented actions by individuals can, in turn, improve capacity to work and their QoL.

Regardless of the type of intervention, efforts should be made to address the barriers that keep inactive people, especially older adults and low-SES populations, from using wearable activity devices to better help them engage in regular physical activity resulting in decreased sedentary behaviors and increased work capacity especially work requiring physical fitness and endurance.

It is recommended that app and mobile device developers and behavior change experts collaborate when developing apps used to monitor physical activity, physical fitness, or the physical aspects of work capacity. By understanding app usage, guidelines can be developed to create apps based on health behavior research to better quantify and promote long-term physical activity and sustainable work capacity.

Lastly, the use of digital, mobile, and wireless QoL technologies and tools in an evidence-based, structured environment can lead to a fundamental transformation of the patient- professional relationship and employer-employee relationship into collaborative partnerships focused on quantifying and improving work capacity and enhancing the overall health-related quality of life of individuals.