Review article
Wearable activity trackers for promoting physical activity: A systematic meta-analytic review

https://doi.org/10.1016/j.ijmedinf.2021.104487Get rights and content

Highlights

  • We conduct a systematic meta-analytic review to synthesize the existing evidence on the effectiveness of wearable activity trackers (WATs) for promoting physical activity (PA).

  • Interventions with WATs significantly increased daily steps and weekly moderate-to-vigorous physical activity (MVPA) but had no impact on light physical activity (LPA) or sedentary behavior.

  • Two PA outcomes (daily steps and weekly MVPA) were associated with participants’ characteristics (i.e., gender, age, health status, and baseline PA level) and intervention features (i.e., technology features, types of expert support, and intervention length.

Abstract

Purpose

Although wearable activity trackers hold a promise of nudging people toward a more active lifestyle, current research reveals inconsistent findings regarding the effectiveness of them. The objectives of this paper are two-fold: (1) to synthesize evidence on the effects of wearable activity trackers for improving physical activities, and (2) to identify potential moderators of effect size.

Methods

A systematic meta-analytic review was conducted. Forty-eight eligible papers based on forty-four distinct trials were identified through a systematic literature search process. Two authors independently extracted information from each study based on predefined data fields. Random-effects meta-analysis, subgroup analysis, and meta-regression analysis were employed.

Results

First, interventions with wearable activity trackers significantly increased daily steps and weekly moderate-to-vigorous physical activity but had no impact on light physical activity or sedentary behavior. Second, daily steps and weekly moderate-to-vigorous physical activity were associated with participants’ characteristics (i.e., gender, age, medical condition, and baseline physical activity level) and intervention features (i.e., sensors, modes of expert support, and intervention duration). The identified factors explained 53 % of the total variance for weekly moderate-to-vigorous physical activity.

Conclusions

The use of wearable activity trackers effectively improves conscious exercise behavior, including daily steps and weekly moderate-to-vigorous physical activity, but not effective for modifying habitual behavior, such as light physical activity and sedentary behavior. We also explicitly show that the extent to which the interventions with wearable activity trackers help users is contingent on the type of users and the design and delivery of interventions. Future studies are called to validate the findings and to offer theoretical explanations.

Introduction

In modern society, many people are habitually inactive during commuting, work, and leisure [1]. Insufficient physical activity (PA) is a leading risk factor for chronic diseases, mental health problems, and quality of life [2]. For substantial health benefits, PA guidelines recommend that adults do at least 150 min of moderate-to-vigorous physical activity (MVPA) per week, accumulate 10,000 steps per day, and reduce sedentary behavior [3,4]. Nevertheless, according to a global survey across 168 countries [2], over one-quarter of people do not meet the PA level recommendations.

Wearable activity trackers (WATs) have the potential to nudge people toward a more active lifestyle. By integrating sensors, algorithms, and human-computer interaction designs, WATs could benefit users in two ways. First, WATs support self-monitoring of PA, such as steps taken, timing and intensity of PA, distance walked, and calories burned. Second, WATs help build self-regulatory skills, including goal-setting, action plans, behavior control, and goal achievement [5,6].

Despite the increasing popularity of WATs (e.g., Fitbit, Mi Band, Apple Watch, Garmin) in the consumer market, formal adoption of them in public health practice is scarce [7]. One exception was a national public health project carried out by Fitbit and Singapore’s Health Promotion Board in 2019. Some empirical studies have been conducted to assess the effectiveness of WATs, albeit with mixed findings (e.g. [8,9]). The extent to which WATs are able to promote PA remains unclear in the literature. Hence, a meta-analysis method has been employed by several review studies. This approach can overcome the equivocation in the existing literature by calculating the weighted average value [10]. Although several relevant meta-analytic papers have come out in recent years [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]], there are still two research gaps.

First, previous review articles did not examine all types of PA. Existing meta-analytic reviews found that WATs are effective for improving PA by assessing step counts [11,12,14,16,17,19,[22], [23], [24]], MVPA [12,14,17,19,[22], [23], [24]], or overall PA [13,15,16,18,20,21]. However, there is a lack of in-depth analysis of light PA (LPA) and sedentary behavior, leading to an incomplete understanding of the WATs’ effectiveness. To fill this gap, we propose the first research objective.

RO 1: To synthesize evidence on the effects of WATs for promoting PA in terms of steps, LPA, MVPA, and sedentary behavior.

Second, although a large heterogeneity of WATs’ effect sizes was observed, potential moderators were not systematically investigated. Specifically, by comparing between reviews with a focus on at-risk populations (e.g., chronic disease patients, older adults) [13,[15], [16], [17], [18], [19]] and those without a specific population focus [[21], [22], [23], [24]], we noticed that the former often reported larger PA effect sizes (reflected by standard mean difference, SMD) (See Table 1)

In addition to health status, past research suggested that participants’ gender, age, and baseline PA level were associated with PA outcomes [11,25,26]. Such findings indicated that different target populations could respond diversely to WATs. Notably, previous articles mainly focused on a particular population, with a lack of comparisons between multiple groups.

Even if focusing on a particular target population, previous meta-analytic reviews reported a large heterogeneity of effect sizes across trials [11,12,14,16,19,20]. However, the sources of the heterogeneity were not well explained. The heterogeneity of effect sizes could stem from intervention features, such as functionalities of WATs, intervention duration, and intervention delivery [23,27]. Unfortunately, there is a lack of comprehensive evidence on how intervention features could moderate the effects of WATs.

Therefore, we propose the second research objective.

RO 2: To explore potential moderators of WATs’ effects through examining participants’ characteristics and intervention features.

This article is important in three ways. First, by considering the PA outcome at various intensity levels (i.e., steps, MVPA, LPA, and sedentary behavior), we analyze the influence of WATs use on PA thoroughly. This helps to understand the role of WATs from a fine-grained perspective. Second, by reporting eligible studies on a wide range of populations (see Table A.1 for details), we provide a holistic view of the effectiveness of WATs. This allows for comparing the role of WATs in promoting PA across different target user groups. Third, by analyzing the moderating role of participants’ characteristics and intervention features, we fill a common gap in previous review articles: lacking a systematic investigation into the cross-studies heterogeneity.

Section snippets

Methods

We conducted and reported this review according to the Cochrane Handbook for Systematic Reviews of Interventions [28] and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [29]. The details of the applied methods were described as following.

Study selection

The initial search on the six databases resulted in 13,791 records. Of them, 6298 were remained after removing duplicates. After screening of article types, titles, and abstracts, 6131 ineligible records were excluded. The remaining 167 articles were assessed based on the full-texts, resulting in 35 articles that met the eligibility criteria. Besides, 9 eligible articles were retrieved from reference searching. Also, 4 studies were identified through database updating (from March 25, 2020, to

RO1

Overall, we found that interventions with WATs had a medium effect on daily steps and a small effect on MVPA. The positive findings were consistent with some previous reviews [13,17,20,22]. By involving studies on a broad range of populations, this review provides evidence with greater generality in supporting the use of WATs for improving steps and MVPA.

However, this paper could not support the use of WATs for improving LPA or reducing sedentary behavior. Comparison of findings of LPA was not

Conclusion

This systematic meta-analytic review analyzed 48 papers (based on 43 distinct trials) involving 5,808 participants. We found promising evidence on the effects of WATs for promoting daily steps and weekly MVPA. The extent to which the WATs help was contextual—that is, the effect of WATs for promoting PA was contingent on the type of users and the design and delivery of interventions. As the emerging of more empirical studies, future work is needed to examine the validity of the findings from the

CRediT authorship contribution statement

Caining Li: Conceptualization, Methodology, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Xiaoyu Chen: Conceptualization, Data curation, Writing - original draft, Writing - review & editing. Xinhua Bi: Supervision, Writing - review & editing.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgments

The first author (C. Li) would like to thank the assistance in data collection from the Wee Kim Wee School of Communication and Information, Nanyang Technological University, Singapore, where she worked as a visiting PhD student from 2019 to 2020. This work is partly supported by the China Scholarship Council (CSC No.: 201906170120).

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