853 for changes in measures of maximal muscle strength (1 repetition maximum [1RM] for the bench press and leg press), upper body muscular endurance (50% of 1RM for the bench press), and body composition (fat free mass, skeletal muscle mass, and body fat percentage) assessed via multifrequency bioelectrical impedance analysis. The level of enjoyment of the respective exercise programs was assessed post-study using the modified 8-item Physical Activity Enjoyment Scale. RESULTS: Main effects for time were observed for 1RM bench press (F = 71.030; p < 0.001), 1RM leg press (F = 64.021; p < 0.001), upper body muscular endurance (F = 43.059; < 0.001), lean body mass (F = 5.345; p = 0.034) and skeletal muscle mass (F = 6.968; p = 0.017). No main effects for time were noted with respect to changes in body fat. A time-group interaction was observed for tests of 1RM leg press (p = 0. 004) and upper body muscular endurance (p = 0.033), with TE showing significantly greater increases compared to VR. No between-group differences were noted for any other outcome variable. CONCLUSIONS: Despite greater improvements in some performance-related measures for TE, our findings suggest that the specific VR program studied is a viable strategy to improve muscular fitness and lean mass while requiring a limited time commitment in a young, untrained population. Moreover, participants in VR reported a high level of enjoyment with the program, which may help to foster long-term adherence. 3091 Board #137 May 31 3:30 PM - 5:00 PM Student Engagement in Classroom Physical Activity Breaks Jeanne Barcelona 1 , Yen Chen 2 , Darla Castelli 2 . 1 Wayne State University, Detroit, MI. 2 University of Texas at Austin, Austin, TX. (No relationships reported) PURPOSE: Students are sedentary for approximately 92% of the day. Classroom physical activity (PA) breaks are known to decrease sedentary behavior (SB). However, little consideration has been given to the environmental and behavioral factors influencing how students engage in classroom PA breaks. Therefore the purpose of this study was to understand how perceived classroom climate and sedentary behavior impact students’ total moderate to vigorous physical activity (MVPA). METHODS: Students (n=112) housed in 1 st and 2 nd grade classrooms across two school districts participated in a one-day study protocol using a classroom climate survey and accelerometers to investigate student engagement in a five minute classroom PA break. Descriptive statistics, bivariate correlation analyses between variables and mediation analyses using linear regression were conducted to explore direct and indirect effects. RESULTS: Over half of the students were females (56.3%) and second graders (51.8%). Correlations were found between perceived classroom climate to sedentary behavior (r = -.31, p = .001) and total MVPA (r = .34, p < .001). Sedentary behavior was negatively correlated with total MVPA (r = -.71, p < .001). The mediation model explained 27% of the total MVPA variance (p < .001). Perceived classroom climate had a direct effect on sedentary behavior ( B = -.04, SE = .01, t = -3.09, p < .05). Sedentary behavior had a direct effect on total MVPA (B = -.45, SE = .06, t = -7.69, p < .05). Student perceived classroom climate did not have a significant direct effect on total MVPA ( p = .09) but did have significant indirect effect through sedentary behavior (indirect effect = .02, bootstrap SE = .007, 95% bootstrap CI = .005, .030), meaning that a participant who scores 1 point higher on perceived classroom climate survey, on average, .02 minutes higher on total MVPA through sedentary behavior. Grade, sex, and PA break type were controlled in the analyses. CONCLUSIONS: Providing students with classroom PA breaks may not be enough. Student’s PCC shape how they engage in classroom PA breaks. Te achers must develop a positive classroom climate where PA is encouraged and affirmed. 3092 Board #138 May 31 3:30 PM - 5:00 PM Osteogenic Response After Six Months of High-Intensity, Low-Impact Exercise Malcolm Jones, Alberto F. Vallejo, E. Todd Schroeder, FACSM. University of Southern California, Los Angeles, CA. (No relationships reported) PURPOSE: Lagree Fitness exercise offers high-intensity, low impact workouts that combine resistance, endurance, core, and cardio training. These classes are offered as alternatives to traditional weight bearing resistance training; however, it is unknown whether this training method has osteogenic effects on bone similar to traditional resistance training. To provide such insight, we assessed changes in bone after six months of the high-intensity training using the Lagree Fitness Megaformer in men and women. METHODS: 31 healthy participants began a 6 month, 3x per week, 25 minute group lead, Lagree Fitness training course on the Megaformer. The data from 19 women and 4 men (45.1 ± 20.9 years of age), weight (150.5 ± 41.5 lb), height (66.5 ± 6.5 in) were analyzed; eight participants did not complete the course and were excluded from data analysis. All participants completed a lumbar spine, bilateral hip, and total body scan on a GE Lunar iDXA dual-energy x-ray absorptiometer at baseline and within 10 days of completing 72 training sessions. RESULTS: There were no significant osteogenic effects on lumbar spine bone mineral density (BMD) (P=.102), femoral neck BMD (P=.519), or total hip BMD (P=.481) in this sample. There was also no significant changes in total body bone mineral content (BMC). While there were no statistically significant changes in total body BMD (P= .186), total arm BMD (P=.125) and total leg BMD (P=.111), there were apparent positive increases that may be promising and suggests the necessity for further data collection with a larger sample. There were similar positive effects on total arm BMC (P=.292) with statistically significant increases in total leg BMC (P <.035). The increase from baseline of total arm lean mass (LM) (P < .009) was significant, and increases in total body LM (P=.069) approached significance. Change in total leg LM (P=.382) was not significant. CONCLUSION: In the absence of weight bearing exercise, high-intensity exercise on the Lagree Fitness Megaformer provided significant increase in total leg BMC, and promising increases in BMC and BMD across other body regions. However, there were no significant osteogenic effects on the hips and lumbar spine typically of importance in osteopenic populations. 3093 Board #139 May 31 3:30 PM - 5:00 PM Physical Activity Breaks in the College Classroom: Student Engagement Factors Maria del Mar Chavarria-Soto 1 , Megan Babkes Stellino 1 , Lyndsie M. Koon 2 , Jessica B. Kirby 1 , Taylor Polson 1 . 1 University of Northern Colorado, GREELEY, CO. 2 University of Illinois, Champaign, IL. Email: mariadelmcr@yahoo.com (No relationships reported) Most college classes require long periods of sedentary behavior and attention demanding tasks. College students, as emerging adults, are moving through a key developmental stage, in which it is critical to instill lifelong health behaviors. Physical activity breaks (PABs) in college settings are novel, but have been shown to be potentially beneficial regarding concentration and academic performance (Babkes Stellino, et al., 2017). PURPOSE: To explore college students’ barriers to, and reasons for, engagement in a PABs intervention. METHODS: College students were invited to participate in video-led or live instructor-led PABs consisting of cardio-strength based exercises or yoga during a 6-week summer college course. Students were asked to write out the reason(s) they chose to engage in the PAB, or not, each day a PAB was offered. At the end of the 6-week course, students also completed an open-ended survey intended to understand their overall reasons for engagement, and barriers to participation in PABs. Basic thematic analysis was conducted to explore why students chose to engage in PABs or chose to opt out. RESULTS: Common reasons reported for engaging in PABs were enjoyment, needing a break from lecture, and contributing to the research. Enjoyment levels were higher when various modes of PABs were offered. Students mentioned a greater personal connection, and a desire to put forth more effort when a live instructor led the activity, particularly for yoga PABs. PABs were viewed as a break from class, and considered a valid exercise bout for some students. This was motivating for some students, but reported as a limitation for others who had already exercised or were going to exercise later that day. Not feeling well, being unprepared or just not wanting to participate, were reported as the main barriers to engagement in the PABs. CONCLUSION: It is important to understand what motivates college students to engage, or not, in PABs, in order to better tailor future programs that will appeal to a greater majority of students. Findings will contribute to the continued exploration of the benefits that PABs can have for college students in the college classroom. Copyright © 2019 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited.