Ten days of exercise training reduces glucose production and utilization during moderate-intensity exercise
Mendenhall, L.A.; Swanson, S.C.; Habash, D.L.; Coggan, A.R.
American Journal of Physiology 266(1 Pt 1): E136-E143
1994
ISSN/ISBN: 0002-9513 PMID: 8304438 Document Number: 436988
We have previously shown that 12 wk of endurance training reduces the rate of glucose appearance (R.) during submaximal exercise (Coggan, A. R., W. M. Kohrt, R. J. Spina, D. M. Bier, and J. 0. Holloszy. J. Appl. Physiol. 68: 990-996, 1990). The purpose of the present study was to examine the time course of and relationship between training-induced alterations in glucose kinetics and endocrine responses during prolonged exercise. Accordingly, seven men were studied during 2 h of cycle ergometer exercise at apprx 60% of pretraining peak oxygen uptake on three occasions: before, after 10 days, and after 12 wk of endurance training. R-a was determined using a primed, continuous infusion of (6,6-2H)glucose. Ten days of training reduced mean R-a during exercise from 36.9 +- 3.3 (SE) to 28.5 +- 3.4 mu-mol cntdot min-1 cntdot kg-1 (P lt 0.001). Exercise-induced changes in insulin, C-peptide, glucagon, norepinephrine, and epinephrine were also significantly blunted. After 12 wk of training, R-a during exercise was further reduced to 21.5 +- 3.1 mu-mol cntdot min-1 cntdot kg-1 (P lt 0.001 vs. 10 days), but hormone concentrations were not significantly different from 10-day values. The lower glucose R-a during exercise after short-term (10 days) training is accompanied by, and may be due to, altered plasma concentrations of the major glucoregulatory hormones. However, other adaptations must be responsible for the further reduction in R-a with more prolonged training.