Testing Interventions for Mobility through Exercise (TIME): Study protocol for a randomized trial comparing a novel, brief home-based exercise program and a standard home-based group exercise for older adults with mobility disability.

One in four older adults report difficulty walking, greatly increasing the risk of future disability and death. Though exercise improves mobility, too few older adults do it. While studies show that brief exercise sessions provide most of the benefit of longer sessions and that older adults note that "time" is a critical barrier to being active, what remains unknown is whether briefer RT sessions can improve mobility as well as, or better than, longer traditional sessions, possibly due to greater adherence. We present the design of a 12-month randomized controlled trial of 700 older adults with self-reported walking difficulty. Participants will be randomly assigned, in a 2 × 2 factorial design, to one of two home-based exercise programs: 1) Standard of Care: 45-min, three-times weekly sessions or 2) Experimental: 5-min daily sessions and to one of two doses of behavior change techniques (Standard or Enhanced) as part of their exercise program. The primary outcome measure is self-reported physical function. Secondary outcome measures include objectively measured lower extremity physical performance, walking endurance, balance, walking speed, strength and physical activity as well as self-reported falls, pain, fatigue and balance. This is one of the first studies to examine the clinical outcomes of brief exercise sessions, which may lead to a new generation of exercise programs that are optimized not only for impact, but for adherence as well.