Most adults recognize exercise and physical activity is good for them, so why do so many individuals struggle to weave this important lifestyle behavior into their life? Further, among individuals motivated to enroll in exercise interventions, 20-30% drop out and return to their previously sedentary lifestyles. Unfortunately, there is a lack of researcher follow-up among these individuals who drop out, especially in collecting information regarding why they drop out, when they drop out and the association between the two.

The three Studies of Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) randomized trials — which examined the differential effects of exercise amount, mode, and intensity on cardiometabolic health — clearly defined dropout and collected information regarding when and why individuals did so. Thus, providing an opportunity to explore these important questions. 

Within the three STRRIDE trials, 69% of individuals completed the exercise intervention, and 31% dropped out. Following our analyses, we found two-thirds (66%) of individuals who dropped out did so prior to the end of month one of the exercise intervention — primarily during the ramp period that was put in place to allow for gradual adaption to the exercise prescription.

Not surprisingly, the most common reported reason for dropping out was lack of time (40%), with lack of time being attributed to work, family, motivation, travel and overall time. Intriguingly, individuals who dropped out because they changed their mind (9%), did so earlier on in the study period — during the inactive control period or run-in phase  — compared to individuals who dropped out due to lack of time and other measured reasons.

We also assessed if there was variation in adherence to exercise training across the STRRIDE trials among individuals who completed one of the interventions. We found adherence generally remained constant across the duration of the six- to eight-month exercise interventions.

We believe this study provides several translational takeaways, especially for those involved in designing and implementing exercise interventions:

1. First, most individuals will drop out before or within two to three months of exercise training onset. Placing greater targeting efforts during this early exercise adoption period may promote better exercise intervention adherence.
2. Second, the majority of individuals dropped out during the ramp phase of the exercise intervention, suggesting the way current interventions ramp up to exercise prescriptions may be too lofty for sedentary individuals with overweight or obesity. Researchers and interventionists should consider adjusting the design of the ramp-up phase of the exercise intervention to compensate for individuals who struggle incorporating exercise into their daily routine.
3. Third, those individuals who changed their mind did so during the inactive control or run-in period of the exercise intervention. When designing an exercise intervention, avoiding a long inactive control period and starting the exercise portion immediately may prevent these individuals from changing their minds. In addition, further exploration of participant perceptions during the inactive control and ramp phases may assist with improved intervention design and in turn adherence.
4. Fourth, once individuals make it past the initial two- to three-month ramp period (i.e., adoption period), they typically are consistent in adhering to a six- to eight-month exercise intervention. Furthering efforts on inactive control and ramp periods can leverage this new evidence that once an individual adopts the exercise behavior, they will most likely adhere to the intervention for at least six to eight months.

To read more about our findings and gain further insight into how variability of behavior change can lead to variation in when and why individuals dropout from an exercise intervention, view the full article in the Translational Journal of the American College of Sports Medicine (TJACSM).

Katherine A. Collins, Ph.D., is a postdoctoral fellow at the Duke Molecular Physiology Institute in the Duke University School of Medicine. She completed both her master of science (M.S.) and doctoral degrees in exercise physiology at the University of Pittsburgh. Her research focuses on identifying predictors of dropout and adherence to lifestyle interventions, characterizing phenotypic and genotypic profiles of individuals at risk for dropout and poor adherence, and utilizing personalized-medicine approaches to target these at-risk individuals.