Individually Tailored Physical Activity Intervention for Latina Adolescents: Chicas Fuertes
Phase: NA
Conditions: Physical Activity
Sponsor: University of California, San Diego

 
 
 
Physical Activity Intervention for Adolescent Girls 
Clinical Trials NCT04190225 
Study Protocol and Statistical Analysis Plan 
September 4, 2024

Trial Design and Setting 
 Chicas Fuertes is a parallel group randomized trial. Adolescent Latinas (N=200) living in San 
Diego County are randomized 1:1 to receive either the mobile technology-based MVPA 
intervention or only a wearable tracker (control group); analyses will test the superiority of the 
intervention over the control condition in increasing MVPA. Participants assigned to the 
intervention first receive a face-to-face counseling session to learn behavior change techniques. 
These sessions are conducted in a number of settings such as local parks, classrooms, and 
community-based organizations. They then receive a Fitbit and access to a tailored intervention 
website to reinforce goal setting and self-monitoring. Participants also are connected to a study 
Instagram account, and receive regular text messages automatically generated by data from 
wearable trackers that update participants on goal progress and encourage adaptive goal 
setting. Activity is measured at baseline and follow-up via accelerometers and the 7-Day 
Physical Activity Recall (PAR) Interview, and throughout the study using Fitbits. Measures are 
taken again at 12 months to evaluate maintenance of activity gains. The sponsor and funder, 
the National Institutes of Health, played no part in study design. They have no role in the 
collection, management, analysis, and interpretation of data. They played no part in writing of 
the protocol and the decision to submit the protocol for publication. The study protocol uses 
SPIRIT reporting guidelines 1. 
Participants 
Eligibility criteria 
Potential participants must self-identify as Latina, be 13-18 years old, read, write, and speak 
English, and be underactive, defined as regularly participating in MVPA for less than 150 
minutes per week. Participants must also have regular (≥2 times/week) access to the Internet 
and to a cell phone that can receive and send text messages. Interested participants who do not 
have access to a smartphone are provided equipment to sync the Fitbit with a computer and 

use the Fitbit website dashboard rather than the smartphone app.  
 
Intervention 
Intervention description 
The intervention utilizes the same theory-based intervention strategies we have shown to 
successfully increase MVPA in non-Latino White men and women 2, Latina adults 3-5, Latino 
men 6, and which showed good potential efficacy with Latina adolescents in our pilot trial 7.  The 
current intervention focuses on the same core theoretical components and behavior change 
strategies from multiple psychosocial theories, including Social Cognitive Theory (SCT) and the 
Transtheoretical Model (TTM), i.e., goal-setting, self-monitoring, problem-solving barriers, 
increasing social support, social norms, and rewarding oneself for meeting goals, which are 
reinforced by various technology channels: the Fitbit Inspire HR wrist monitor and Fitbit app, 
interactive automated text messaging, motivational content on social media (Instagram), and an 
interactive website. In order to leverage the tools of each channel and avoid fatigue with the 
technologies, different channels are emphasized at different time points. The schedule and 
content of the intervention components were refined through an intensive iterative process 
involving multiple interviews, focus groups, and design workshops with Latina girls (N=50) and 
beta testing with a Youth Advisory Board; this has been described in detail elsewhere. 
Intervention components are summarized in Table 1.   
At the baseline one-on-one counseling session with a trained interventionist, the participant 
learns about MVPA (e.g. guidelines, benefits, intensity, duration) and engages in an individual 
goal setting. This session is based on principles of motivational interviewing, and teaches 
individuals to set realistic, specific short-term goals to build up to the long-term goal of meeting 
national guidelines (300 minutes/week of MVPA for children aged 12-17) 8. The interventionist 

and the participant review her activity from the baseline week (measured by the Fitbit), and the 
participant selects her own goal for the following week. The interventionist also helps her 
identify personal barriers to activity (e.g., time, motivation), and teaches problem-solving 
strategies. The participant is then oriented to the mHealth technology channels of the 
intervention. Health coaching sessions are recorded (with participant permission); a random 
subsample of recordings are evaluated by an external consultant to ensure fidelity of 
intervention delivery across participants.   
Website 
At the baseline study visit, participants assigned to the intervention group are provided with a 
unique login and password for the Chicas Fuertes website, which serves as a rich resource for 
MVPA tips and strategies, as well as the platform for MVPA goal setting and monitoring. The 
website includes a weekly calendar for planning out the upcoming week of activity, including 
which activities they plan to do, which days and times they plan to do them, where they plan to 
do them, and for how long. The calendar syncs with the participant’s Fitbit so that actual 
minutes of MVPA are directly imputed to allow participants to visualize planned vs. completed 
activity. The website also includes a monthly questionnaire, which measures participants’ 
attitudes, beliefs, and strategies for increasing MVPA. Responses to monthly questionnaires are 
fed into an expert system that automatically generates personalized reports, drawing from a 
bank of 330 messages addressing different levels of psychosocial and environmental factors 
affecting physical activity, such as stages of change, decisional balance, and self-efficacy, and 
tailors messages based on whether scores on these phenomena have increased, decreased, or 
remained stagnant. Tailored reports address: 1) their current stage of motivational readiness for 
physical activity; 2) increasing self-efficacy for physical activity; 3) cognitive and behavioral 
strategies associated with physical activity behavior change (processes of change); 4) how the 
participant compares to their prior responses (progress feedback); 5) how the participant 

compares to other adolescents who are physically active (normative feedback); and, 6) self-
monitoring of MVPA (use of online activity logging calendars). Participants complete the 
questionnaire each month for the first six months of the study, and every other month for the 
remaining six months, and receive $10 each time they complete the questionnaire.  
Other website features include maps of free or low-cost places to be active locally, strategies to 
overcome common barriers to MVPA, web links to free online workout videos, and a current 
activity leaders board that highlights the three most active participants that week (measured by 
Fitbit activity). The website also has an online message board, moderated by the interventionist, 
where participants can encourage each other to be active, congratulate and celebrate each 
other’s successes, and seek guidance or support. The website also scrolls the study Instagram 
feed (see below). To encourage regular use of the Chicas Fuertes website, participants receive 
“engagement points” for logging on, answering the weekly pop quiz question, and setting their 
weekly MVPA goals. Accrued points can be traded in for a variety of Chicas Fuertes branded 
prizes, such as water bottles, power banks, and Bluetooth speakers.  
Fitbit Inspire HR Monitor and app 
Participants in both the intervention and control groups are provided with a Fitbit Inspire HR 
monitor and free Fitbit app for the one-year study; however, only those in the intervention group 
receive coaching on how to navigate the features of the Fitbit App. At baseline, the 
interventionist walks the intervention participant through the Fitbit app, focusing on how to 
monitor PA metrics, such as steps, MVPA minutes, and heartrate, as well as how to set goals 
for MVPA. Participants are encouraged to monitor their progress regularly on both the Fitbit 
wrist-worn tracker as well as the Fitbit app, and to update their MVPA goals on the Fitbit app 
gradually over time as they work toward increasing their weekly MVPA minutes. 
Text messaging 

In the first month of the intervention, text messaging is primarily used to reinforce other 
intervention media channels. Participants receive text message reminders to use the website 
features, which includes a link to take them directly to the website. They receive additional 
weekly texts reminding them to set goals and wear & sync their Fitbits. In months 2-12, 
participants also receive algorithm-derived individually tailored text messages updating them on 
their goal progress mid-week and reviewing MVPA at the end of the week. Data are sourced 
from the Fitabase software program that monitors Fitbit data in real time and computes total 
active and very active minutes. Texts encourage adaptive goal setting, asking participants who 
meet their activity minute goal if they can increase their goal by 10% for the next week until 
national guidelines are met. Participants who do not meet their goal receive a text calculating 
how many more minutes they need to add per day to meet their goal and asking if they believe 
that they can do it for the coming week.  
Instagram posts 
Instagram posts are used to deliver short, visual, daily intervention content based on specified 
constructs of psychosocial theories. At baseline, participants assigned to the intervention group 
are invited to “follow” the study’s private Instagram account. Focus group results prior to the 
study launch directed the development of Instagram posts that contain brightly colored images 
and videos featuring relatable girls engaging in MVPA, couched in positive and inspirational 
messaging. Each day of the week features one post based on constructs from the 
aforementioned psychosocial theories: benefits/outcomes, social support, modeling, 
environment, self-efficacy, and a weekly challenge incorporating behavior change techniques 
for participants to try during the week (see Figure 3 for sample post). Along with daily posts, 
Instagram stories are posted throughout the week, which include interactive components such 
as a poll or quiz to engage users. Participants are encouraged to “like” the posts, which 
indicates to the study team that the post has been seen, and also ensures that Chicas Fuertes 
posts remain at the top of the participant’s Instagram feed.  

One month call  
After one month, participants receive a brief (20-minute) phone call from intervention staff to 
review progress. The interventionist reviews their goals and progress and helps them set new 
goals for the coming week and address barriers they have experienced so far. The participant is 
instructed to fill out their next online questionnaire to generate an individually tailored report on 
the website. Reminders to fill out questionnaires in subsequent months are automatically sent 
via text message.   
 
6-month visit 
During the 6-month assessment, those in the Intervention arm also engage in a repeat goal 
setting session and learn strategies to maximize MVPA maintenance over the next six months. 
The interventionist emphasizes continued self-monitoring using the Fitbit and asks them to 
identify sources of support to help them stay active.  
Control group 
The control group receives a Fitbit Inspire HR wrist-worn tracker to wear throughout the 12-
month intervention. They are encouraged to wear the Fitbit every day, and sync at least every 
four days. They have access to all features built into the Fitbit monitor and app (see Table 1), 
but do not receive explicit instruction on how to use or personalize them. This control group is 
meant to serve as a “real world” control group, representing the large, growing population of 
individuals who purchase commercial fitness trackers and receive no additional guidance in 
using them.  
Intervention: adherence         
We examine adherence to the intervention through monitoring frequency of Fitbit wear and 
syncing, tracking logins on the website, and monitoring views and likes on the Instagram 

account. Participants receive text messages reminding them to sync their Fitbit if they have not 
synced for four days. They also receive engagement points for interacting with the website, 
which can be traded in for prizes.  
To increase enrollment and retention in the study, Fitbit devices and incentives in the form of 
cash payments and gift cards are provided to all participants. At baseline, each participant 
receives a Fitbit Inspire HR activity tracker to use throughout the study and keep after study 
participation is completed. Incentive payments of $25, $50, and $50 are provided at the 
baseline, 6-, and 12-month follow-up measurement visits, respectively. Additionally, participants 
receive an additional $25 bonus if they complete all measures at the 6- and 12-month visits.  
Lastly, while in-person research was suspended at UC San Diego (March 2020 – August 2020) 
and is limited (August 2020 – present) to mitigate the spread of COVID-19, remote follow-up 
measurement visits are offered to participants unable to return in-person. This includes 
completing self-report surveys online.  
 
Outcomes 
Primary outcome 
The primary outcome is change in weekly minutes of MVPA from baseline to six months 
measured by the ActiGraph GT3X+ accelerometer. The ActiGraph GT3X+ is a hip-worn triaxial 
accelerometer which measures movement and intensity of activity and has been validated 
against heart rate telemetry 9 and total energy expenditure 10, including in children.11 
Participants wear the ActiGraph for ≥12 hrs/day ≥7 days at baseline and follow-up. Participants 
receive regular text messages to remind them to wear the ActiGraph. Valid wear time is 
considered ≥3000 minutes on ≥4 days. Data is processed using Freedson’s age-specific cut 
points for children to identify activity at various intensities.12 We will evaluate total minutes of 
MVPA and total time in 10+ minute bouts. 

As an additional measure of MVPA change, at baseline and follow-up participants also engage 
in the 7-Day PAR interview. The 7-Day PAR is a semi-structured interview that assesses 
frequency, duration and intensity of MVPA. It has consistently demonstrated acceptable 
reliability, internal consistency, and congruent validity with objective MVPA measures 13,14 and 
sensitivity to changes over time.15,16. It has been validated in children as young as 11.17 
Administering the PAR requires annual certification. To ensure fidelity of PAR measures, a 
random sample of 5% of PAR interviews are recorded and assessed for fidelity by an external 
consultant.  
 
Secondary outcomes and covariates 
Participant demographic information is measured via self-report questionnaire at baseline, and 
includes age, race, and parents’ education, income, and marital status. 
We also will assess changes in trajectories of daily MVPA measured by the Fitbit Inspire HR. 
The Fitbit tracker measures physical activity intensity, energy expenditure, bouts of exercise, 
steps, distance traveled, and flights of stairs at varying resolutions. We will be evaluating the 
daily active minutes and steps recorded by the Fitbit.  
 
We will also measure technology engagement with the website, Fitbit, texting interactions, and 
Instagram. Engagement with the Chicas Fuertes website measures number of logins and use of 
specific features, including goal setting, the weekly quiz, and monthly questionnaire completion. 
Fitbit use is measured as days worn and sync frequency, while texting is based on the 
percentage of interactive texts the participants responded to. Instagram engagement is 
measured by the number of views and likes by participants.  
 

Questionnaires on the website are used to create individual intervention content, and also serve 
as measures of psychosocial constructs. Stages of Change for Physical Activity (SCPA) is used 
to stage-match participants, it has been successful in previous trials and has acceptable 
reliability (Kappa = 0.78; intraclass correlation r = 0.84) 18.  Processes of Change for Physical 
Activity (POC) was also administered monthly, POC contains 10 subscales on a variety of 
cognitive and behavioral processes related to MVPA change. Its subscale internal consistency 
ranges from .62 to .96. 19. Self-Efficacy for Physical Activity (SE) was used to measure self-
efficacy to become physically active across diverse contexts. The SE internal consistency is 
acceptable (alpha = .82) 18. We also administered the Social Support for Exercise (SSE) scale 
which has three subscales of family, friends, rewards and punishments and an acceptable 
internal consistency (alphas .61-.91) and criterion validity 20. To assess enjoyment for physical 
activity, the Physical Activity Enjoyment Scale (PACES) is used to evaluate the level of personal 
satisfaction from PA. PACES has high internal consistency (alpha = 0.96) and test-retest 
reliability 21. Lastly, we used the Outcome Expectations Scale to assess the beliefs regarding 
the consequences of physical activity participation will be examined by 9 items with internal 
consistency (alpha=.89) and validity based on confirmatory factor analysis and positive 
correlations with physical activity and self-efficacy. 
Neighborhood environment is measured using the Neighborhood Environment Walkability Scale 
for Youth (NEWS-Y). The NEWS-Y measures perceptions of neighborhood environment, 
including recreation facility availability, pedestrian traffic safety, and walking facilities. It has 
shown acceptable reliability and correlations with objectively measured activity 22.   
Participants also fill out the CES-D depression inventory at baseline and follow-up visits.  
Potential contamination is measured at six and 12 months through a contamination measure 
asking participants to indicate the number of people they know who were simultaneously in the 
study, how much contact they had with them, and if they changed any of their behaviors due to 
their contact with other participants. 

At 12 months, participants in the intervention group were asked to complete a consumer 
satisfaction measure to assess the acceptability of the intervention. This is modified from our 
previous studies.  
Screening and consenting 
Potential participants may contact research staff through Instagram direct message, Facebook, 
email, or text/call via the study phone number.  Interested participants are then called to 
participate in the telephone screener that includes a description of the study purpose, 
procedures, risks, benefits, and eligibility requirements.  If participant is under the age of 18, 
research staff first talk with her parent/guardian before screening her to ask basic eligibility 
questions and to receive parental consent to screen the daughter, then speak to the adolescent 
to complete screening.  If eligible, interested participants are invited to engage in an orientation 
session via Zoom. 
Orientation visit 
Prior to the orientation session, participants are instructed to download the Fitbit app and set up 
an account. They are also provided with an orientation packet via mail, including a Fitbit Inspire 
HR, a hip-worn accelerometer, and an orientation folder that includes a consent form, assent 
form, instructions on how to use the Fitbit, and instructions for wearing the accelerometer. The 
girl’s parent/guardian is invited to attend the first half of the orientation via Zoom to review a 
PowerPoint presentation that outlines the procedures, benefits, and expectations of the study. 
Following the presentations, the participant and their parent/guardian sign the written informed 
consent and assent forms, which are collected the following week at the baseline visit. The 
second half of the orientation is used to set up the Fitbit, including syncing it with a smartphone, 
connecting it to the study’s online Fitabase database, and temporarily blinding the Fitbit monitor 
and app to prevent feedback from influencing baseline activity. We also review the Fitbit and 
accelerometer expectations, and schedule the Baseline visit for 7 days after the orientation.  

Over the next week, participants wear the Fitbit wrist monitor, and a hip worn GT3X+ 
accelerometer, with instructions to wear it 12 hours per day for seven days. Before the baseline 
visit, they also fill out online psychosocial measures, including self-efficacy, stage of change for 
activity, and social support (see Measures). 
Baseline visit  
One week after the orientation visit, participants attend an in-person baseline visit. Due to 
COVID-19 restrictions, in-person visits are conducted outdoors at parks close to the 
participant’s home. Participants return the accelerometer, which is assessed for sufficient wear 
time (≥3000 minutes on ≥4 days). After performing a short walk to demonstrate activity of a 
moderate intensity level, participants complete the 7-Day PAR interview 13,17. Once all baseline 
measures are completed, including all online psychosocial questionnaires, participants are 
randomized to either the multi-media MVPA intervention, or to a control group receiving only a 
Fitbit.  
Follow-up visits 
The primary outcome is change in MVPA from baseline to six months, with maintenance of 
activity at 12 months serving as a secondary outcome. Follow-up visits are conducted remotely 
via Zoom software. Prior to the six- and 12-month visits, participants are mailed the 
accelerometer for one week of wear, similar to baseline. Accelerometers are mailed back and 
checked for wear time, after which participants complete the PAR interview over Zoom, and fill 
in online psychosocial questionnaires. Participants also complete a contamination measure at 
six and 12 months to assess amount and type of contact with participants in other conditions. At 
12 months, a consumer satisfaction measure is completed by those in the Intervention arm to 
assess the acceptability of the Chicas Fuertes MVPA intervention, and a subset of participants 
engage in a one-on-one interview to give additional feedback about the program. Participants 
receive $50 for completing the baseline, 6- and 12-month measures, $25 for correctly wearing 

and returning the accelerometer, and $25 for completing all other measures. Participants 
receive an additional $25 bonus at month 12 if they complete all measures at all visits.  
Recruitment 
Over three years, we are recruiting a total of 200 adolescent girls (age 13-18) who self-identify 
as Latina and/or belong to groups considered Latino by the US Census Bureau. Recruitment is 
done through a variety of approaches including social media advertisements, providing health 
presentations in classes at local middle and high schools in San Diego County, conducting 
information sessions at community organization sites, distributing flyers through Latino-serving 
organizations, and contacting Latina women who have participated in previous studies and 
given permission to be contacted again to ask if they have family or friends who may be 
interested in participating. 
Randomization, allocation concealment and blinding 
Randomization is performed using a random number sequence (generated based on a stratified 
block randomization procedure) programmed into REDCap clinical trials software. 
Randomization is stratified by baseline stage of change according to the TTM (pre-
contemplation, contemplation, or preparation) to ensure equal motivational readiness for MVPA 
adoption across groups. Study group assignment is placed in a sealed envelope based on an 
order determined by the randomization sequence, with different envelopes designated for each 
baseline stage of change. Randomization is performed by an interventionist who is not blinded 
to participant study condition, while staff members completing baseline and follow-up measures 
remain blinded to condition. Siblings or close friends who enroll together are yoked together into 
a study arm to minimize contamination between arms; yoked groups are stratified across 
conditions to ensure equal distribution. After being randomized, participants’ Fitbit monitors and 
app are unblinded to allow for normal use. Participants in the Intervention group then undergo a 

goal setting session; those in the control group receive no more direct staff contact until the six-
month follow-up visit.  

STATISTICAL ANALYSIS 
As a preliminary step, the study sample was summarized with respect to baseline socio-
demographics and PA rates and compared between groups using t-tests, chi-squared tests and 
non-parametrics as appropriate. Both participant and parent characteristics at baseline are 
reported for socio-demographics.   
As min/week of MVPA was skewed and attempts to transform towards normality were 
unsuccessful, a series of quantile regression models with bootstrapped standard errors (10,000 
bootstrapped samples) were used to regress median min/week MVPA on baseline values, 
group, and covariates.  Models were run separately for self-reported MVPA (via the PAR) and 
objectively measured (using accelerometry). Models for the latter further adjusted for 
accelerometer wear time. As a small proportion of study participants were yoked together during 
the randomization process (siblings, cousins, or close friends who enrolled together), we 
adjusted for clustering by yoked group in each of our models (to ensure standard errors were 
adjusting for non-independence of outcomes within-cluster).  All other covariates were balanced 
at baseline and tested for significance in the model before being dropped. 
To understand the group differences in minutes of PA as collected via the Fitbit, we 
examined data from the weeks corresponding to measurement of PA via the PAR and 
accelerometer. Using a longitudinal mixed effects model with subject-specific intercepts, we 
examined group differences adjusting for clustering by yoked pair.   
All analyses were carried out in R, with significance level set at .05 a priori.   
 
 
 

1. 
Chan A-W, Tetzlaff JM, Gøtzsche PC, et al. SPIRIT 2013 explanation and elaboration: guidance for 
protocols of clinical trials. BMJ : British Medical Journal. 2013;346:e7586. doi:10.1136/bmj.e7586 
2. 
Marcus BH, Napolitano MA, King AC, et al. Telephone versus print delivery of an individualized 
motivationally tailored physical activity intervention: Project STRIDE. Health Psychol. Jul 2007;26(4):401-
9. doi:10.1037/0278-6133.26.4.401 
3. 
Marcus BH, Dunsiger SI, Pekmezi DW, et al. The Seamos Saludables study: A randomized 
controlled physical activity trial of Latinas. Am J Prev Med. Nov 2013;45(5):598-605. 
doi:10.1016/j.amepre.2013.07.006 
4. 
Marcus BH, Hartman SJ, Larsen BA, et al. Pasos Hacia La Salud: a randomized controlled trial of 
an internet-delivered physical activity intervention for Latinas. Int J Behav Nutr Phys Act. May 28 
2016;13:62. doi:10.1186/s12966-016-0385-7 
5. 
Pekmezi DW, Neighbors CJ, Lee CS, et al. A culturally adapted physical activity intervention for 
Latinas: a randomized controlled trial. Am J Prev Med. Dec 2009;37(6):495-500. 
doi:10.1016/j.amepre.2009.08.023 
6. 
Larsen B, Dunsiger S, Hartman S, et al. Activo: Assessing the Feasibility of Designing and 
Implementing a Physical Activity Intervention for Latino Men. International Journal of Men s Health. 
04/01 2014;13:60-71. doi:10.3149/jmh.1301.60 
7. 
Larsen B, Benitez T, Cano M, et al. Web-Based Physical Activity Intervention for Latina 
Adolescents: Feasibility, Acceptability, and Potential Efficacy of the Niñas Saludables Study. J Med 
Internet Res. 2018/05/09 2018;20(5):e170. doi:10.2196/jmir.9206 
8. 
Piercy KL, Troiano RP, Ballard RM, et al. The Physical Activity Guidelines for Americans. JAMA. 
2018;320(19):2020-2028. doi:10.1001/jama.2018.14854 
9. 
Janz KF. Validation of the CSA accelerometer for assessing children's physical activity. Med Sci 
Sports Exerc. Mar 1994;26(3):369-75.  
10. 
Melanson EL, Jr., Freedson PS. Validity of the Computer Science and Applications, Inc. (CSA) 
activity monitor. Med Sci Sports Exerc. Jun 1995;27(6):934-40.  
11. 
Trost SG, Pate RR, Freedson PS, Sallis JF, Taylor WC. Using objective physical activity measures 
with youth: how many days of monitoring are needed? Med Sci Sports Exerc. Feb 2000;32(2):426-31. 
doi:10.1097/00005768-200002000-00025 
12. 
Troiano RP, Berrigan D, Dodd KW, Mâsse LC, Tilert T, McDowell M. Physical activity in the United 
States measured by accelerometer. Med Sci Sports Exerc. Jan 2008;40(1):181-8. 
doi:10.1249/mss.0b013e31815a51b3 
13. 
Pereira MA, FitzerGerald SJ, Gregg EW, et al. A collection of Physical Activity Questionnaires for 
health-related research. Med Sci Sports Exerc. Jun 1997;29(6 Suppl):S1-205.  
14. 
Rauh MJ, Hovell MF, Hofstetter CR, Sallis JF, Gleghorn A. Reliability and validity of self-reported 
physical activity in Latinos. Int J Epidemiol. Oct 1992;21(5):966-71. doi:10.1093/ije/21.5.966 
15. 
Dunn AL, Garcia ME, Marcus BH, Kampert JB, Kohl HW, Blair SN. Six-month physical activity and 
fitness changes in Project Active, a randomized trial. Med Sci Sports Exerc. Jul 1998;30(7):1076-83. 
doi:10.1097/00005768-199807000-00009 
16. 
Dunn AL, Marcus BH, Kampert JB, Garcia ME, Kohl III HW, Blair SN. Comparison of Lifestyle and 
Structured Interventions to Increase Physical Activity and Cardiorespiratory FitnessA Randomized Trial. 
JAMA. 1999;281(4):327-334. doi:10-1001/pubs.JAMA-ISSN-0098-7484-281-4-joc80889 
17. 
Sallis JF, Buono MJ, Roby JJ, Micale FG, Nelson JA. Seven-day recall and other physical activity 
self-reports in children and adolescents. Med Sci Sports Exerc. Jan 1993;25(1):99-108. 
doi:10.1249/00005768-199301000-00014 
18. 
Marcus BH, Selby VC, Niaura RS, Rossi JS. Self-efficacy and the stages of exercise behavior 
change. Res Q Exerc Sport. Mar 1992;63(1):60-6. doi:10.1080/02701367.1992.10607557 

19. 
Marcus BH, Rossi JS, Selby VC, Niaura RS, Abrams DB. The stages and processes of exercise 
adoption and maintenance in a worksite sample. Health psychology : official journal of the Division of 
Health Psychology, American Psychological Association. 1992;11(6):386-95.  
20. 
Sallis JF, Grossman RM, Pinski RB, Patterson TL, Nader PR. The development of scales to 
measure social support for diet and exercise behaviors. Prev Med. Nov 1987;16(6):825-36. 
doi:10.1016/0091-7435(87)90022-3 
21. 
Kendzierski D, DeCarlo K. Physical Activity Enjoyment Scale: Two validation studies. Journal of 
Sport & Exercise Psychology. 1991;13 (1), 50-64 
22. 
Rosenberg D, Ding D, Sallis JF, et al. Neighborhood Environment Walkability Scale for Youth 
(NEWS-Y): reliability and relationship with physical activity. Prev Med. Aug-Sep 2009;49(2-3):213-8. 
doi:10.1016/j.ypmed.2009.07.011 
23. 
Kovacs M. The Children’s Depression Inventory (CDI) Manual Multi-Health Systems North 
Tanawanda;; 1992. 
24. 
Leon AC, Davis LL, Kraemer HC. The role and interpretation of pilot studies in clinical research. J 
Psychiatr Res. May 2011;45(5):626-9. doi:10.1016/j.jpsychires.2010.10.008 
25. 
Kraemer HC, Mintz J, Noda A, Tinklenberg J, Yesavage JA. Caution regarding the use of pilot 
studies to guide power calculations for study proposals. Arch Gen Psychiatry. May 2006;63(5):484-9. 
doi:10.1001/archpsyc.63.5.484 
26. 
Wang JB, Cadmus-Bertram LA, Natarajan L, et al. Wearable Sensor/Device (Fitbit One) and SMS 
Text-Messaging Prompts to Increase Physical Activity in Overweight and Obese Adults: A Randomized 
Controlled Trial. Telemed J E Health. Oct 2015;21(10):782-92. doi:10.1089/tmj.2014.0176