Long-term Effects of the Use of a Step Count-Specific Smartphone App on Physical Activity and Weight Loss: Randomized Controlled Clinical Trial

Abstract

Background: Some studies on weight loss promotion using smartphone apps have shown a weight loss effect but not an increase in physical activity. However, the long-term effects of smartphone apps on weight loss and increasing physical activity have not been rigorously examined to date.

Objective: The aim of this study was to assess whether the use of a smartphone app will increase physical activity and reduce body weight.

Methods: In this parallel randomized clinical trial, participants recruited between April 2018 and June 2019 were randomized in equal proportions to a smartphone app group (n=55) or a control group (n=54). The intention-to-treat approach was used to analyze the data from December 2019 through November 2021. Before the intervention, an hour-long lecture on weight loss instruction and increasing physical activity was conducted once for both groups. Participants in both groups were instructed to weigh themselves immediately after waking up at least once daily from the start of the intervention. Monthly emails were sent advising the participants in both groups on how to lose weight and increase physical activity in order to maintain or increase motivation. Participants in the smartphone app group were instructed to open the app at least once a day to check their step count and rank. The primary outcome was daily accelerometer-measured physical activity (step count) and the secondary outcome was body weight. Since there was a significant difference in the wear time of the accelerometer depending on the intervention period (P<.001), the number of steps and moderate-to-vigorous physical activity were also evaluated per wear time.

Results: The mean age of the 109 participants in this study was 47 (SD 8) years. At baseline, the mean daily total steps were 7259 (SD 3256) steps per day for the smartphone app group and 8243 (SD 2815) steps per day for the control group. The difference in the step count per wear time between preintervention and postintervention was significantly different between the app group and the control group (average difference [95% CI], 65 [30 to 101] steps per hour vs -9 [-56 to 39] steps per hour; P=.042). The weight loss was -2.2 kg (SD -3.1%) in the smartphone app group and -2.2 kg (SD -3.1%) in the control group, with no significant difference between the groups. In addition, when divided into weekdays (Monday through Friday) and weekends (Saturday and Sunday), there was a significant interaction between step counts (P=.004) and MVPA (P=.003) during the intervention, with the app group showing higher interaction on weekends than the control group.

Conclusions: In this trial, the group with the smartphone app intervention showed increased physical activity, especially on weekends. However, this increased physical activity did not lead to increased weight loss.

Trial registration: University Hospital Medical Information Network UMIN000033397; https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000037956.

Keywords: lifestyle intervention; mHealth; mobile app: mobile phone; moderate-to-vigorous intensity physical activity; physical activity; smartphone app; step counts; step count–specific mobile app; weight loss.

Figure 1

Study flow diagram.

Figure 2

Study protocol. Wk: weeks.

Figure 3

Changes in body weight during the intervention period (32 weeks). The change in the body weight of the participants is shown by the solid line for the smartphone app group and the dotted line for the control group. (A) Values are shown as average and (B) as the moving average over 1 week. The change in body weight before and after the intervention (preintervention, 12 weeks, and 32 weeks) was not significantly different between the groups.

Figure 4

Intraweek variation in (A) body weight, (B) step counts, and (C) moderate-to-vigorous physical activity before the intervention. Missing data were taken into account and analyzed using two-way repeated measures mixed analysis of variance to examine the interaction between the groups. Values are presented as means and standard errors. MVPA: moderate-to-vigorous physical activity.

Figure 5

Intraweek variation in (A) body weight, (B and C) step counts, and (D and E) moderate-to-vigorous physical activity during the intervention. Data were combined from 12 and 32 weeks to analyze the relationship between physical activity and intraweek variability. Missing data were taken into account and analyzed using two-way repeated-measures mixed analysis of variance to examine the interaction between the groups. Values are presented as means and standard errors. MVPA: moderate-to-vigorous physical activity.