TRAINING-INDUCED ALTERATIONS OF GLUCOSE FLUX IN MEN

We examined the hypothesis that glucose flux was directly related to r elative exercise intensity both before and after a 10-wk cycle ergomet er training program in 19 healthy male subjects. Two pretraining trial s [45 and 65% of peak O-2 consumption (VO2peak)] and two posttraining trials (same absolute and relative intensities as 65% pretraining) wer e performed for 90 min of rest and 1 h of cycling exercise. After trai ning, subjects increased VO2peak by 9.4 +/- 1.4%. Pretraining, the int ensity effect on glucose kinetics was evident with rates of appearance (R(a); 5.84 +/- 0.23 vs. 4.73 +/- 0.19 mg . kg(-1) . min(-1)), disapp earance (R(d); 5.78 +/- 0.19 vs. 4.73 +/- 0.19 mg . kg(-1) . min(-1)), oxidation (R(ox); 5.36 +/- 0.15 vs. 3.41 +/- 0.23 mg . kg(-1) . min(- 1)), and metabolic clearance (7.03 +/- 0.56 vs. 5.20 +/- 0.28 ml . kg( -1) . min(-1)) of glucose being. significantly greater (P less than or equal to 0.05) in the 65% than the 45% VO2peak trial. When Rd was exp ressed as a percentage of total energy expended per minute (R(dE)), th ere was no difference between the 45 and 65% intensities. Training did reduce R(a) (4.63 +/- 0.25), R(d) (4.65 +/- 0.24), R(ox) (3.77 +/- 0. 43), and R(dE) (15.30 +/- 0.40 to 12.85 +/- 0.81) when subjects were t ested at the same absolute workload (P less than or equal to 0.05). Ho wever, when they were tested at the same relative workload, R(a), R(d) , and R(dE) were not different, although R(ox) was lower posttraining (5.36 +/- 0.15 vs. 4.41 +/- 0.42, P less than or equal to 0.05). These results show 1) glucose use is directly related to exercise intensity ; 2) training decreases glucose flux for a given power output; 3) when expressed as relative exercise intensity, training does not affect th e magnitude of blood glucose use during exercise; 4)training alters th e pathways of glucose disposal.