METHODS: wild type (WT, ~20) mice and mice with muscle-specific overexpression of PGC-1?1 (MCK-PGC-1?, ~20) were given Western Diet (WD) at 8 wks of age and allowed to consume food ab libitum throughout the course of the study. At 12 wks of age, animals were further divided into sedentary (SED) and physical activity (voluntary wheel running [VWR]) interventions. At ages 7, 11, and 15 wks animals underwent glucose tolerance tests (GTT). At 16 wks of age animals were humanely euthanized and tissues collected for analysis. Results were analyzed by 2X2X3 repeated measures ANOVA with an ?=0.05. RESULTS: MCK-PGC-1? animals were lighter and had less epididymal fat compared to WT (~6% and ~28% respectively). Food efficiency (weight gained:food consumed) was ~17% lower in MCK-PGC-1? animals. While there was no difference at 7 wks age, at 11 wks age MCK-PGC-1? had ~50% greater GTT integrated area under the curve (IAUC) compared to WT. Yet at 15 wks, VWR had 30% lower IAUC compared to SED, regardless of genotype. MCK-PGC-1? -VWR ran ~3X more per day compared to WTVWR. Correlations for wheel running distance per day v. IAUC, body weight, and epididymal fat were significant and moderately strong (r=-0.67--0.71) for WT-VWR, but in MCK-PGC-1? there was no correlation between these variables and wheel running distance per day (r=0.10-0.20). CONCLUSION: These results suggest increasing PGC-1?1 promotes exercise-induced adaptations regardless of exercise volume, but overexpression of PGC-1?1 during lipid overload without physical activity does not mitigate insulin resistance and may in fact exacerbate the condition. 3580 Board #27 June 3 8:00 AM - 9:30 AM Differential Metabolic Responses to Acute Fatmax and Lactate Threshold Exercise Timothy D. Allerton1, Kate Early2, Carl Lavie, Jr3, Neil Johannsen1. 1Louisiana State University, Baton Rouge, LA. 2Columbus State, Columbus, GA. 3Ocshner, New Orleans, LA. Email: firstname.lastname@example.org (No relationships reported) Improvements in glucose tolerance and insulin action with aerobic exercise may be the result of increase glucose utilization and/or more complete oxidation of intramuscular triglycerides. PURPOSE: To investigate the effect of acute aerobic exercise at an intensity that maximizes the rate of fat oxidation (FM) on glucose tolerance, insulin action, and metabolic flexibility (MF) compared to acute aerobic exercise at lactate threshold (LT) resulting in greater carbohydrate (CHO) oxidation. METHODS: Participants (aged 20.5�5y, BMI 29.5�7kg/m2) performed a VO2max and baseline 2hr OGTT (n=8). Isocaloric (400 kcal) exercise sessions at FM (41�%VO2max) and LT (68�%VO2max) were performed with an OGTT ~24-hrs post-exercise. RESULTS: FM exercise elicited significantly (p<0.01) greater fat utilization (18.6�.1g) than LT (10.1�.3g) during exercise. Accordingly, LT (82.8�.1g) exercise elicited significantly (p<0.05) greater CHO utilization than FM (62.4�.3g) exercise. There was no significant difference in total energy expenditure between FM (416.1�.4) and LT (422.1�.4) exercise (p=0.2). However, AUC for glucose was significantly higher for LT exercise than baseline and FM exercise (p<0.05). MF was significantly (p<0.05) reduced post-FM (?120-min RER=0.04�03) exercise when compared to baseline (0.13�04). CONCLUSION: LT exercise appears to have deleterious effects on oral glucose tolerance acutely, however, FM exercise does not confer improved MF. These results suggest a disconnect between glucose tolerance and MF and that preferential substrate utilization does not promote comprehensive metabolic improvements acutely in young overweight men. 3581 Board #28 June 3 8:00 AM - 9:30 AM The Relationship Between Sedentary Bout Duration And Glucose In Adults With Type 2 Diabetes Kathryn A. McMillan1, Alison Kirk1, Allan Hewitt1, Sandra MacRury2. 1University of Strathclyde, Glasgow, United Kingdom. 2University of Highlands and Islands, Inverness, United Kingdom. (Sponsor: David Rowe, FACSM) Email: email@example.com (No relationships reported) Physical activity is important for blood glucose management in people with Type 2 diabetes (T2D). Little research has explored the relationship between sedentary behaviour and mean glucose and glucose variability in people with T2D using objective and continuous measurements. AIMS: To explore the relationship between sedentary bout duration and mean glucose and glucose variability in people with T2D using objective continuous measurement. METHODS: 16 participants with T2D managed with diet, Metformin or DPP4 inhibitors were recruited (mean age 64.1�.9 yr & BMI 29.4�9 kg/m2). Participants completed a demographic questionnaire and wore an activPAL accelerometer and FreeStyle Libre continuous glucose monitor for 3-14 days whilst documenting sleep, food and medication. Average proportion of time spent sitting/lying, during the waking day were calculated. Bouts of wake time sedentary behaviour were identified and defined as a period of at least 30 minutes continuous, uninterrupted sitting/lying during the waking day. Correlation analysis was conducted to investigate the relationships between sedentary bout duration and mean glucose, glucose range and glucose coefficient of variation. RESULTS: On average, participants spent 65% of their day sitting/lying, 76% of sedentary bouts were ?30minutes and 29% of bouts were ?60minutes. Mean glucose was negatively (r = -0.08, p <0.01) associated with sedentary bout duration. Glucose range (r =0.47, p <0.001) and glucose coefficient of variation (r = 0.26, p <0.001) both positively correlated with sedentary bout duration. Participant characteristics such as age, gender and BMI appear to influence the relationship between sedentary bout duration and glucose response. CONCLUSIONS: Results indicate increased sedentary time leads to improved mean glucose and increased glucose variability. 3582 Board #29 June 3 8:00 AM - 9:30 AM Effect of Short-term Exercise Training on Novel Diabetes Risk Biomarkers in Overweight/Obese Adolescents Kevin R. Short, Lauren V. Pratt, April M. Teague. University of Oklahoma Health Sciences Center, Oklahoma City, OK. Email: firstname.lastname@example.org (No relationships reported) Several novel biomarkers of risk for diabetes in adults have been reported that have not been carefully examined in adolescents with metabolic risk factors. We previously reported that pigment epithelial derived factor (PEDF) is increased in obese adolescents and associated with insulin resistance. 2-aminoadipic acid (2AAA) was shown to predict future diabetes onset in the Framingham study, and to decline in adults following insulin sensitizer treatment. Exercise can also increase insulin sensitivity but it is unknown whether PEDF or 2AAA are altered by exercise in adolescents. PURPOSE: To determine whether a short-term exercise program could alter insulin sensitivity, PEDF, and 2AAA in adolescents. METHODS: 22 habitually inactive, overweight/obese boys and girls (15�y, BMI-z 1.62�9, BMI 94�%ile, 36� body fat) performed 2 supervised and 1 home-based exercise session per week for 5 weeks. Half of the group performed continuous moderate intensity exercise (CME; 45-min walking at 70% HRmax) while the other half performed aerobic interval training of matched total energy expenditure (AIT; 4 x 4-min at 90% HRmax with 3-min recovery intervals at 60% HRmax plus 5-min warm up and cool down). A mixed meal test with blood sampling was performed at baseline and 40 hours after the final exercise session. RESULTS: At baseline, 2AAA and PEDF were positively correlated with HOMA-IR (r = 0.54 and 0.43, respectively) and inversely correlated with insulin sensitivity (r = -0.60 and -0.62, respectively). After the exercise program, body mass and composition were unchanged. The AIT group increased peak cycling power 11% and absolute VO2peak 8% (p<0.05, effect size 0.3 for both) but the CME group did not increase aerobic fitness. HOMA-IR was unchanged in either group but insulin sensitivity during the meal was 1019 Copyright � 2017 by the American College of Sports Medicine. 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