120-OR: Muscle Lipid Turnover Predicts Aerobic Training Effects on Body Composition

Aerobic exercise utilizes muscle lipid. We hypothesize that high pre-training muscle lipid turnover, suggesting high muscle lipid utilization, predicts the effects of aerobic training. Obese, insulin-resistant subjects [mean(SD), BMI:37.7 kg/m²(6.2), VO₂max 25 ml/kg/min (6.3)] underwent a 16 week of supervised, weight-stable, aerobic training (n=16). Body composition (DXA), fitness level (VO₂max) and insulin sensitivity (hyperinsulinemic-euglycemic clamp) were performed at baseline and end-training. Two muscle biopsies (Bx) were acquired during a pulse-chase experiment using [U-¹³C]palmitate and [9-²H]palmitate infusions (6 h each), overlapping by 1 hour. Bx#1 captured muscle lipid incorporation and was performed during the infusion overlap [last hour of 6 h [U-¹³C]palmitate infusion, 1 hour after starting [9-²H]palmitate. Bx#2 captured muscle lipid breakdown and was performed at study conclusion [last hour of [9-²H]palmitate infusion, 6 hours after stopping [U-¹³C]palmitate]. As expected, aerobic training increased VO₂max, fat-free mass, insulin sensitivity and hepatic insulin sensitivity while decreasing fat mass and visceral fat (Table 1). Baseline measures, especially muscle palmitate incorporation and breakdown, best predicted training effects on body composition. Muscle lipid turnover, along with other baseline measures, predicts aerobic training effects on body composition.

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