Background. Dropouts and compliance to exercise interventions targeting bone mineral density (BMD) in adults are not well established. The purpose of this study was to address that gap. Methods. Meta-analysis of randomized controlled exercise intervention trials in adults ≥18 years of age. The primary outcomes were dropouts in the exercise and control groups as well as compliance to the exercise interventions. A random-effects model was used to pool results. Moderator analyses were conducted using mixed-effects ANOVA-like models and metaregression. Statistical significance was set at . Results. Thirty-six studies representing 3,297 participants (1,855 exercise, 1,442 control) were included. Dropout rates in the exercise and control groups averaged 20.9% (95% CI 16.7%–25.9%) and 15.9% (11.8%–21.1%) while compliance to exercise was 76.3% (71.7%–80.3%). For both exercise and control groups, greater dropout rates were associated with studies conducted in the USA versus other countries, females versus males, premenopausal versus postmenopausal women, younger versus older participants, longer studies (controls only), and high- versus moderate-intensity training (exercisers only). Greater compliance to exercise was associated with being female, home- or facility-based exercise versus both, and shorter studies. Conclusion. These findings provide important information for researchers and practitioners with respect to exercise programs targeting BMD in adults. 1. Introduction Osteoporosis and the fractures that result from osteoporosis are a major public health problem worldwide. For example, it has been estimated that osteoporosis causes more than 8.9 million fractures annually, resulting in an osteoporotic fracture every 3 seconds [1]. In the United States (USA), the prevalence of osteoporosis and low bone mass includes almost 44 million women and men 50 years of age and older [2]. This represents 55% of US adults aged 50 and older [2]. By the year 2020, it is estimated that more than 61 million women and men in the USA will have osteoporosis or low bone mass [2]. Exercise is a nonpharmacologic intervention that has been recommended for increasing and/or maintaining bone mineral density (BMD) in adults [3, 4]. However, the investigative team is not aware of any previous meta-analytic research that has focused on dropouts and compliance with respect to participants enrolled in nonbehaviorally focused randomized controlled exercise intervention programs targeting BMD in adults. This has important implications from both a research and practice perspective. From a
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