Implementation of a workplace intervention using financial rewards to promote adherence to physical activity guidelines: a feasibility study

Setting, eligibility, and enrollment

B-Well was conducted at Brigham and Women’s Hospital, an academic medical center in Boston, Massachusetts. The study ran from July 2014 to June 2015 and was funded to include 300 participants. All participants received the financial incentives intervention; there was no control arm. Employees were recruited via a limited number of hospital-wide emails and advertisements. Eligible individuals were older than 21 years, reported ≤30 min of exercise per week, and had access to a computer. Weekly minutes of exercise were assessed with a question asking participants if they exercised for 30 min on 0, 1, 2, 3, or ≥4 days of the week. Physicians and nurses were not eligible for participation, as they had access to other similar PA programs. Pregnant women were excluded.

Eligible employees formed three-person teams, created independently or by B-Well staff, to provide peer support. Each team met with study staff to review the study protocol, PA monitoring schedule, and financial incentive details. At this meeting, each participant was given a Fitbit Flex activity monitor (Fitbit Inc., San Francisco, California) and instructions for its use.

Baseline assessments

Trained research staff collected health data at the baseline visit. Participants provided written informed consent and completed an online questionnaire containing questions related to general health, healthcare utilization, quality of life (measured by EQ-5D), and perceptions of PA. Participants self-reported comorbidities including heart disease, hypertension, diabetes, osteoarthritis, and others. Musculoskeletal disease was assessed with a validated musculoskeletal index [24].

Participants also completed an assessment to determine their degree of delay discounting. Delay discounting, a measure of impulsivity, describes the extent to which individuals prefer immediate, smaller rewards to larger, long-term gains [12, 25, 26]. Based on choices between receiving a specified monetary amount now or receiving a larger amount later, participants were assigned a value on a delay discounting index, with higher values indicating greater preference for immediate rewards. We used a method developed by Kirby and Petry to estimate the index [27].

Intervention and financial incentives structure

Participants were asked to wear their Fitbits continuously for 26 weeks. During the first 2 weeks, participants were in the pre-intervention period and were compensated for wearing the Fitbit. They received $20 for wearing the Fitbit for at least 10 days and an additional $10 for wearing it for all 14 days. Teams in which all members met the 10 day criterion received an additional $10 per member. Results from these 2 weeks were considered baseline levels of PA.

Financial incentives, chosen to be meaningful but not coercive, were available for the subsequent 24 weeks. Participants could receive $10 per week for increasing minutes of moderate-to-vigorous PA (MVPA) by at least 10% from the preceding week or for meeting Centers for Disease Control and Prevention (CDC) PA guidelines (150 min of moderate PA per week) [8]. Individuals meeting their MVPA goal every week for one, three, or 6 months received an additional $15, $25, or $50 respectively. If all team members successfully met their MVPA goals, each individual’s reward was doubled that week. In total, participants could receive up to $860 by meeting MVPA goals. These amounts fall within the range identified by a 2013 systematic review on financial incentives for exercise session attendance, which noted that successful programs had weekly incentives ranging from $2.79 to $46.82 [19].

Participants received individualized weekly emails during the intervention detailing their levels of recent MVPA, their weekly goals, and their recent rewards. While participants could view activity data (e.g. step counts) on the Fitbit website, this data did not include the minutes of MVPA that counted toward their goals. Participants could visit the B-Well study website to monitor current and past individual and team progress.

Measuring MVPA

The Fitbit Flex is a commercial accelerometer that records the number of steps taken each minute. We chose the Fitbit Flex because it presents an adequate trade-off between validity and expense; it is less expensive than medical grade accelerometers and has moderate validity for measuring step count and physical activity [28–30]. We downloaded minute-by-minute step counts weekly and defined thresholds of 100 and 175 steps/min for moderate and vigorous PA, respectively. The threshold of 100 steps/min was selected as it corresponds with an intensity of ≥3 metabolic equivalents of task (METs) [31, 32]. As there is limited data on the association between step count and vigorous activity, we used the conservative threshold of 175 steps/min. We weighted minutes of vigorous activity as twice that of moderate activity, as CDC guidelines recommend either 150 min of moderate activity, 75 min of vigorous activity, or an equivalent combination per week [8]. Days with fewer than 10 h of wear time were excluded from analysis. To count towards the weekly goal, activity had to be performed in bouts of at least 10 min, in accordance with the CDC PA guidelines [8]. Within a single bout, we allowed up to two ‘grace’ minutes during which the participant’s step count could fall below the thresholds.

Our algorithm identified the start of potential bouts of moderate PA either as a minute with more than 100 steps preceded by a minute of fewer than 100 steps or as 100 steps in the first minute of the day. Bout length was defined as the number of consecutive minutes during which the step count met the 100 steps/min threshold before the two grace minutes were exceeded. Bouts of fewer than 10 min were not counted. The algorithm then conducted consecutive pair-wise comparisons of each bout of at least 10 min. When two bouts overlapped, the shorter of the two was discarded and the pair-wise comparison continued until no bouts were overlapping. The algorithm repeated with a 175 steps/min threshold to identify bouts of vigorous PA.

Outcomes

We assessed intervention efficacy on several domains. First, we calculated the average number of minutes spent in bouts of MVPA on a weekly basis and compared these values during the intervention period to those during the pre-intervention period. Second, we measured Fitbit adherence among enrolled participants by counting weeks in which participants wore the Fitbit for at least 10 h per day for at least 4 days of the week. We defined adherent Fitbit wearers as participants with at least 20 adherent intervention weeks (out of 24). Third, we evaluated the number and proportion of study participants who met their weekly MVPA goals or CDC PA guidelines during the intervention.

Statistical analysis

We employed generalized linear modeling to determine factors associated with the number of weeks meeting CDC PA guidelines. The multivariable analyses included demographic and clinical variables and the delay discounting index, which was divided into the highest quartile (the highest degree of discounting future benefits) vs. the lowest three quartiles combined. Based on the multivariable model results, we estimated the adjusted mean number of intervention weeks during which subjects achieved MVPA levels consistent with CDC PA guidelines. We initially built bivariate models; covariates that reached a significance level of α = 0.15 were advanced to multivariable models. We used intraclass correlation to measure within-team correlation for meeting CDC guidelines. We calculated within-team correlation for minutes of MVPA over time to examine whether within team correlation was based on selection (active participants form teams with active participants) or adaption (teams are mixed with active and inactive participants at the start and correlation increases over time). All statistical analyses were done in SAS 9.4.

Sample characteristics

Fitbit wear adherence & physical activity

Ninety-four percent of participants wore the Fitbit ≥4 days at the end of the first month. By the end of the 6 months, 62% of the cohort wore the Fitbit ≥4 days. One hundred eighty-four study participants (63%) were adherent Fitbit wearers, wearing their Fitbit ≥4 days per week for at least 20 out of 24 intervention weeks.

The 292 participants self-reported a mean of approximately 15 min of PA per week prior to the start of B-Well; half reported no exercise and half reported 30 min of exercise. During the initial two-week pre-intervention period, the average weekly duration of MVPA was 54 (SD 64) minutes. One month into the intervention, the average duration of MVPA increased to 93 (SD 87) minutes, and 72% of participants were above their personal pre-intervention baseline levels of MVPA. By week 14 (halfway through the intervention), average weekly MVPA was 80 (SD 90) minutes. At the end of the intervention, the average duration of weekly MVPA was 62 (SD 89) minutes, and 41% of participants were above their personal baseline levels of MVPA by an average of 16 min. Over the intervention period, the average weekly duration of MVPA was 85 (SD 76) minutes (Fig. 1).

Compared to Fitbit non-adherers, adherent Fitbit wearers had higher pre-intervention levels of MVPA and achieved higher intervention levels of MVPA. The pre-intervention average duration of MVPA for adherent participants was 67 (SD 71) minutes; at week 14 (halfway), the average duration of MVPA increased to 111 (SD 94) minutes. Adherent participants completed, on average, 99 (SD 96) minutes of weekly MVPA at the end of the study, with an average duration of weekly MVPA of 113 (SD 80) minutes throughout the intervention.

Meeting goals & CDC guidelines

During the first week of the intervention, 58% of study participants increased their MVPA by at least 10% and met their weekly goal but did not meet CDC guidelines. An additional 16% of all participants met CDC guidelines. One month into the intervention, 37% of participants met their weekly goal but not CDC guidelines, and an additional 24% met CDC guidelines. By the end of the intervention, 23% of all participants met CDC guidelines (Fig. 2).

Eighty-six percent of the cohort met either their personal weekly goal or CDC guidelines for at least 6 individual weeks throughout the intervention period, and 52% met their goal or CDC guidelines for at least half of all intervention weeks. Six participants (2%) met their goal or CDC guidelines every week of the intervention.

Across the 24 intervention weeks, participants met CDC guidelines an average of 6.3 weeks (SD 7.8). Multivariable analyses showed that reporting an ability to walk at least 20 blocks (one mile) at baseline, African American race, non-obesity, and lower delay discounting index scores were associated with an increased number of weeks meeting CDC PA guidelines (Fig. 3). Participants reporting the ability to walk >20 blocks at baseline achieved CDC guidelines an average of 7 weeks, while participants unable to walk 20 blocks at baseline achieved CDC guidelines an average of 5 weeks (p = 0.010). African Americans achieved CDC guidelines an average of 8 weeks, while all other races met CDC guidelines an average of 6 weeks (p = 0.016). Non-obese persons achieved CDC guidelines an average of 7 weeks throughout the duration of the study, while obese participants achieved CDC guidelines an average of 5 weeks (p = 0.018). Participants in the lowest three quartiles of the delay discounting index achieved CDC guidelines approximately 7 weeks, while those in the highest quartile (those who attach most value to immediate rewards) achieved CDC guidelines an average of 5 weeks (p = 0.068).

We did not find an association between the method of team formation (independent versus matched by study staff) and number of weeks meeting CDC guidelines. However, the within-team correlation was estimated to be 0.5, suggesting that having one team member reach CDC guidelines was associated with increased likelihood of other team members meeting CDC guidelines. Within-team correlation for minutes of MVPA increased over time, ranging from 0.06 for week 1 (pre-intervention) to 0.32 at week 24.

Financial rewards and satisfaction

On average, participants earned $220 (SD $168) by meeting goals throughout the intervention. Three participants earned the maximum $860, and one participant did not achieve any goals and therefore did not receive any goal-based compensation.

Two hundred fifty-five out of 298 participants (86%) responded to the satisfaction survey. Sixty-six percent of participants were satisfied with the B-Well program overall, with 79% indicating that they would participate again if offered. The majority (72%) of participants thought that the program helped increase PA; 58% thought that being part of a team helped them increase their PA, and 73% of participants indicated that receiving financial incentives was beneficial for promoting activity. Those who were not satisfied were less likely to achieve daily PA goals and receive incentives.