Impact of muscle glycogen availability on the capacity for repeated 1 exercise in man 2 3 4

30 31 Purpose: To examine whether muscle glycogen availability is associated with fatigue 32 in a repeated exercise bout following short-term recovery. 33 34 Methods: Ten endurance-trained individuals underwent two trials in a repeated 35 measures design, each involving an initial run to exhaustion at 70% (Run-1) 36 followed by a 4-h recovery and a subsequent run to exhaustion at 70% (Run37 2). A low-carbohydrate (L-CHO; 0.3 g·kg BM·h) or high-carbohydrate (H-CHO; 38 1.2 g·kg BM·h) beverage was ingested at 30-min intervals during recovery. Muscle 39 biopsies were taken upon cessation of Run-1, post-recovery and fatigue during Run-2 40 in L-CHO (F2). In H-CHO, the muscle biopsies were obtained post-recovery, the time 41 point coincident with fatigue in L-CHO (F2) and the point of fatigue during the 42 subsequent exercise bout (F3). 43 44 Results: Run-2 was more prolonged for every participant in H-CHO (80±16 min) 45 than L-CHO (48±11 min; p< 0.001). Muscle glycogen concentrations were higher at 46 the end of recovery in H-CHO (269±84 mmol·kg dm) versus L-CHO (157±37 47 mmol·kg dm; p= 0.001). The rate of muscle glycogen degradation during Run-2 was 48 higher in H-CHO (3.1±1.5 mmol·kg dm·min) than L-CHO (1.6±1.3 mmol·kg dm 49 ·min; p= 0.05). The concentration of muscle glycogen was higher in H-CHO than 50 L-CHO at F2 (123±28 mmol·kg dm; p< 0.01) but no differences were observed 51 between treatments at the respective points of exhaustion (78±22 versus 72±21 52 mmol·kg dm·min; H-CHO and L-CHO, respectively). 53 54 max 2 O V 