Outdoor gyms in Los Angeles public parks provide an alternative to costly indoor gyms for low-income populations. The purpose of this study was to compare the impact of non-adjustable outdoor gym (OG) equipment to similar adjustable indoor equipment (IG) on physical activity behavior and muscular fitness adaptations. Seven untrained healthy subjects performed repetitions to fatigue on four exercises in two experimental trials: 1) 60% of estimated 1-repetition maximum indoors; 2) non-standardized resistance based on machine mechanics outdoors. In addition, a total of 85 IG and OG users completed physical activity behavior surveys. Subjects performed a significantly greater number of repetitions on all four exercises outdoors relative to indoors (leg press: 80.17?2.89 vs. 18.67?1.15; leg extension: 65.43?6.53 vs. 12.43?1.25; chest press; 23.29?1.95 vs. 14.86?0.60; shoulder press: 6.14?1.57 vs. 13.29?0.84, P<0.05). Muscle activity measured by surface electromyography was also greater for all lower body muscles tested indoors (P<0.05). Although OG subjects perform strength training (ST) at the same frequency as IG subjects (median: 3-4 days/week, P>0.05), it is performed at a lower relative intensity (median RPE: 9-11 vs.15-17, P<0.05) and a greater percentage of OG subjects perform ST for durations ≤ 15 minutes (33.9% vs. 0.0%, P>0.05). Results from this study suggest that OG subjects are less likely to meet the physical activity recommendations for muscular strength when compared to IG subjects, in part due to machine mechanics. Additional studies are needed to determine whether the presence of outdoor gyms increase physical activity behavior in low-income populations.