Abstract
The hypothesis that endurance training increases gluconeogenesis (GNG) during rest and exercise was evaluated. We determined glucose turnover with [6,6-2H]glucose and lactate incorporation into glucose by use of [3-13C]lactate during 1 h of cycle ergometry at two intensities [45 and 65% peak O2 consumption (V˙o 2 peak)] before and after training [65% pretrainingV˙o 2 peak], same absolute workload (ABT), and 65% posttrainingV˙o 2 peak, same relative intensity (RLT). Nine males (178.1 ± 2.5 cm, 81.8 ± 3.3 kg, 27.4 ± 2.0 yr) trained for 9 wk on a cycle ergometer 5 times/wk for 1 h at 75%V˙o 2 peak. The power output that elicited 66.0 ± 1.1% ofV˙o 2 peak pretraining elicited 54.0 ± 1.7% posttraining. Rest and exercise arterial glucose concentrations were similar before and after training, regardless of exercise intensity. Arterial lactate concentration during exercise was significantly greater than at rest before and after training. Compared with 65% pretraining, arterial lactate concentration decreased at ABT (4.75 ± 0.4 mM, 65% pretraining; 2.78 ± 0.3 mM, ABT) and RLT (3.76 ± 0.46 mM) ( P < 0.05). At rest after training, the percentage of glucose rate of appearance (Ra) from GNG more than doubled (1.98 ± 0.5% pretraining; 5.45 ± 1.3% posttraining), as did the rate of GNG (0.11 ± 0.03 mg ⋅ kg− 1 ⋅ min− 1pretraining, 0.24 ± 0.06 mg ⋅ kg− 1 ⋅ min− 1posttraining). During exercise after training, %glucose Rafrom GNG increased significantly at ABT (2.3 ± 0.8% at 65% pre- vs. 7.6 ± 2.1% posttraining) and RLT (6.1 ± 1.5%), whereas GNG increased almost threefold ( P < 0.05) at ABT (0.24 ± 0.08 mg ⋅ kg− 1 ⋅ min− 165% pre-, and 0.71 ± 0.18 mg ⋅ kg− 1 ⋅ min− 1posttraining) and RLT (0.75 ± 0.26 mg ⋅ kg− 1 ⋅ min− 1). We conclude that endurance training increases gluconeogenesis twofold at rest and threefold during exercise at given absolute and relative exercise intensities.