The purpose of this study is to test the effectiveness of On the Move (OTM) in terms of improving mobility among 502 older adults in 44 senior community centers and to evaluate intervention fidelity, including adherence and competence, and the impact of organizational, instructor, and participant level factors on intervention fidelity.

The investigators will conduct a Hybrid I trial, blending effectiveness and implementation research aims to: test the effectiveness of OTM, evaluate intervention fidelity, and determine the extent intervention fidelity moderates intervention effectiveness. The investigators will evaluate the effects of OTM taught by community instructors for improving mobility among 502 older adults in 44 community centers using a cluster randomized design with a delayed intervention control arm. Intervention fidelity will be assessed by instructor self-report (intervention diaries) and observation (fidelity checklist). Organizational, instructor, and participant level factors which may impact fidelity will be assessed via standard instruments, focus groups and interviews.

Specific Aims are as follows:

Aim 1: Establish the effectiveness of OTM on improvements in walking ability and post-intervention persistence of benefits.

Rationale: OTM delivered by research staff is effective. Establishing the effectiveness of OTM delivered by community instructors is necessary before wide-scale implementation.

Hypothesis: Compared to a randomized control group followed for 12 weeks, the OTM group will have greater gains in gait speed (primary outcome) and self-reported mobility at 12 and 24 weeks of follow-up.

Aim 2: Assess intervention fidelity (measures of adherence and competence) and identify the impact of organizational, instructor, and participant level factors on intervention fidelity.

Rationale: To inform future implementation efforts, it is critical to measure intervention fidelity and to identify factors associated with fidelity.

Hypothesis: Organizational, instructor, and participant level factors will impact fidelity. For example, instructors who utilize greater facilitation strategies will have higher fidelity, poor organizational acceptance of the program will be related to lower fidelity, and fewer organizational resources will lead to lower fidelity.

Aim 3: Determine the extent to which intervention fidelity, measured by adherence and competence, moderates the effectiveness of OTM.

Rationale: Intervention fidelity may influence the effectiveness of OTM. Understanding the consequences of differing levels of intervention fidelity on effectiveness will inform future implementation efforts.

Hypothesis: Higher fidelity will be associated with greater mobility gains, and there may be critical fidelity thresholds.

Inclusion Criteria:

• 60 years of age or older
• attend the senior center
• can ambulate household distances independently
• can participate in group exercise classes

Exclusion Criteria:

• impaired cognition (unable to understand consent process)
• plans to leave the area for an extended period of time
• any acute or unstable illness or medical condition

All collected individual participant data may be shared. Because the human subjects included in the project could potentially be identified, given the relatively limited geographic distribution of these subjects, investigators requesting data will be required to sign a data sharing agreement. For external requests, the agreement will be executed through the University's Office of Research; and for internal requests, through email.

Data sets will be available at the time the primary paper is accepted for publication or at 2 years after the last participant is followed whichever comes first.

Data will be available by secure transfer to investigators who complete a data sharing agreement for data from this project. The sharable data will be archived at the study's home site and will be available for sharing by submitting a request to the PI. Once a request is approved by the PI and the requester agrees to the conditions for data use, the data will be transferred.