We evaluated the hypotheses that endurance training decreases arterial lactate concentration ([lactate] a ) during continuous exercise by decreasing net release (L˙) and appearance rates (R increasing metabolic clearance rate (MCR). Measurements were made at two intensities before [45 65% peak O 2 consumption (V˙o )] after [65% pretrainingV˙o , same absolute workload (ABT), posttrainingV˙o relative intensity (RLT)]. Nine men (27.4 ± 2.0 yr) trained for 9 wk on cycle ergometer, 5 times/wk...

To test the hypothesis that lactate plays a central role in distribution of carbohydrate (CHO) potential energy for oxidation and glucose production (GP), we performed clamp (LC) procedure during rest moderate intensity exercise. Blood [lactate] was clamped at ≈4 m by exogenous infusion. Subjects 90 min exercise trials 65 % peak rate oxygen consumption (V̇ O2 ,peak ; %), 55 V̇ (55 %) with to blood measured %‐LC). Lactate rates appearance ( R ), disappearance d ) ox were combination [3‐ 13...

We examined the hypothesis that glucose flux was directly related to relative exercise intensity both before and after a 12-wk cycle ergometer training program [5 days/wk, 1-h duration, 75% peak O 2 consumption (V˙o )] in healthy female subjects ( n = 17; age 23.8 ± 2.0 yr). Two pretraining trials (45 65% of V˙o ) two posttraining [same absolute workload (65% oldV˙o same newV˙o were performed on nine by using primed-continuous infusion [1- 13 C]- [6,6- H]glucose. Eight additional studied...

We sought to determine whether lipolysis, fatty acid (FA) mobilization, and plasma FA oxidation would remain elevated for hours following isoenergetic exercise bouts of different intensities. Ten men eight women received a primed‐continuous infusion [1,1,2,3,3‐ 2 H 5 ]glycerol continuous [1‐ 13 C]palmitate measure glycerol kinetics. On Day 1 (D1), participants were studied under one three conditions, assigned in random order: (1) before, during 3 h after 90 min at 45% (E45), (2) 60 65%...

We evaluated the hypothesis that lactate shuttling helps support nutritive needs of injured brains. To end, we utilized dual isotope tracer [6,6-2H2]glucose, is, D2-glucose, and [3-13C]lactate techniques involving arm vein infusion along with simultaneous cerebral (arterial [art] jugular bulb [JB]) blood sampling. Traumatic brain injury (TBI) patients nonpenetrating injuries (n=12) were entered into study following consent patients' legal representatives. Written informed was obtained from...

To understand the meaning of lactate threshold (LT) and to test hypothesis that endurance training augments kinetics [i.e., rates appearance disposal (Ra Rd, respectively, mg·kg(-1)·min(-1)) metabolic clearance rate (MCR, ml·kg(-1)·min(-1))], we studied six untrained (UT) trained (T) subjects during 60-min exercise bouts at power outputs (PO) eliciting LT. Trained performed two additional a PO 10% lower (LT-10%), one which involved clamp (LC) match blood concentration ([lactate]b) achieved...

Because the maintenance of glycemia is essential during prolonged exercise, we examined effects endurance training, exercise intensity, and plasma lactate concentration ([lactate]) on gluconeogenesis (GNG) hepatic glycogenolysis (GLY) in fasted men exercising at, just below, threshold (LT), where GNG precursor availability high. Twelve healthy (6 untrained, 6 trained) completed 60 min constant-load at power outputs corresponding to their individual LT. Trained subjects two additional 60-min...

We examined the effects of exercise intensity and training [12 wk, 5 days/wk, 1 h, 75% peak oxygen consumption (V˙o 2 )] on lipolysis plasma free fatty acid (FFA) flux in women ( n = 8; 24.3 ± 1.6 yr). Two pretraining trials (45 65% ofV˙o ) two posttraining [same absolute workload (65% oldV˙o ; ABT) same relative newV˙o RLT)] were performed using infusions [1,1,2,3,3- H]glycerol [1- 13 C]palmitate. Pretraining rates FFA appearance (R a ), disappearance d oxidation ox p similar between (6.8...

The hypothesis that endurance training increases gluconeogenesis (GNG) during rest and exercise was evaluated. We determined glucose turnover with [6,6- 2 H]glucose lactate incorporation into by use of [3- 13 C]lactate 1 h cycle ergometry at two intensities [45 65% peak O consumption (V˙o )] before after [65% pretrainingV˙o ], same absolute workload (ABT), posttrainingV˙o , 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 ergometer 5...

Friedlander, Anne L., Gretchen A. Casazza, Michael Horning, Melvin J. Huie, and George Brooks. Training-induced alterations of glucose flux in men. Appl. Physiol. 82(4): 1360–1369, 1997.—We examined the hypothesis that was directly related to relative exercise intensity both before after a 10-wk cycle ergometer training program 19 healthy male subjects. Two pretraining trials [45 65% peak O 2 consumption (V˙o )] two posttraining (same absolute intensities as pretraining) were performed for...

To evaluate the hypothesis that exposure to high altitude would reduce blood glucose and total carbohydrate utilization relative sea level (SL), 16 young women were studied over four 12-day periods: at 50% of peak O(2) consumption in different menstrual cycle phases (SL-50), 65% SL (SL-65), 4,300 m (HA). After 10 days each condition, rate disappearance (R(d)) respiratory exchange ratio measured rest during 45 min exercise. Glucose R(d) exercise HA (4.71 +/- 0.30 mg. kg(-1). min(-1)) was not...

We examined the effects of exercise intensity and a 10-wk cycle ergometer training program [5 days/wk, 1 h, 75% peak oxygen consumption (V˙o 2 )] on plasma free fatty acid (FFA) flux, total fat oxidation, whole body lipolysis in healthy male subjects ( n= 10; age = 25.6 ± 1.0 yr). Two pretraining trials (45 65% ofV˙o ) two posttraining (same absolute workload, oldV˙o ; same relative newV˙o were performed by using an infusion [1- 13 C]palmitate [1,1,2,3,3- H]glycerol. An additional nine (age...

We evaluated the hypotheses that alterations in glucose disposal rate (R d ) due to endurance training are result of changed net uptake by active muscle and blood is shunted working during exercise requiring high relative power output. studied leg 1 h cycle ergometry at two intensities before [45 65% peak oxygen consumption (V˙o 2 )] after [65% pretrainingV˙o , same absolute workload (ABT), posttrainingV˙o (RLT)]. Nine male subjects (178.1 ± 2.5 cm, 81.8 3.3 kg, 27.4 2.0 yr) were tested 9 wk...

Lactate has been shown to be an important oxidative fuel. We aimed quantify the total lactate oxidation rate (Rox) and its direct vs. indirect (glucose that is gluconeogenically derived from subsequently oxidized) components (mg·kg(-1)·min(-1)) during rest exercise in humans. also investigated effects of endurance training, intensity, blood concentration ([lactate]b) on oxidation. Six untrained (UT) six trained (T) men completed 60 min constant load at power outputs corresponding their...

We examined the effects of oral contraceptives (OC) on glucose flux and whole body substrate oxidation rates during rest (90 min) two exercise intensities [60-min leg ergometer cycling at 45 65% peak O 2 uptake (V˙o )]. Eight healthy, eumenorrheic women were studied follicular luteal phases before OC inactive high-dose after 4 mo a low-dose, triphasic OC. Subjects in morning 3 h standardized (308 kcal) breakfast. There significant reductions appearance disappearance both with but not rest....

To evaluate the contribution of working muscle to whole body lipid oxidation, we examined effects exercise intensity and endurance training (9 wk, 5 days/wk, 1 h, 75% V̇o 2 peak ) on leg free fatty acid (FFA) kinetics in eight male subjects (26 ± yr, means SE). Two pretraining trials [45 65% max (45UT, 65UT)] two posttraining [65% (ABT), (RLT)] were performed using [1- 13 C]palmitate infusion femoral arteriovenous sampling. Training increased by 15% (45.2 1.2 52.0 1.8 ml·kg −1 ·min , P <...

We evaluated the hypothesis that nutritive needs of injured brains are supported by large and coordinated increases in lactate shuttling throughout body. To end, we used dual isotope tracer ([6,6-(2)H2]glucose, i.e., D2-glucose, [3-(13)C]lactate) techniques involving central venous infusion along with cerebral (arterial [art] jugular bulb [JB]) blood sampling. Patients traumatic brain injury (TBI) who had nonpenetrating head injuries (n=12, all male) were entered into study after consent...

We examined the effects of exercise intensity and menstrual cycle phase on glucose flux rates during rest in rested fed (3-h postabsorptive) women. Eight moderately active, eumenorrheic women were studied under conditions (90 min) (60 min, leg ergometer cycling at 45 65% peak oxygen consumption) follicular luteal phases. In both phases, an effect was evident with appearance disappearance metabolic clearance rates: < 45% ( P 0.05). addition, we observed no significant rate or either...

To evaluate the hypothesis that precursor supply limits gluconeogenesis (GNG) during exercise, we examined training-induced changes in glucose kinetics [rates of appearance (R a ) and disappearance d )], oxidation ox ), recycling r with an exogenous lactate infusion to 3.5–4.0 mM rest pretraining 65% peak O 2 consumption (V˙o levels exercise. Control clamped trials (LC) were performed at pre- (P R R, P R-LC) posttraining exercise E X absolute A B , -LC) relative L intensities. Glucose was...

For estimating the oxidation rates (Rox) of glucose and other substrates by use 13 C-labeled tracers, we obtained correction factors to account for label dilution in endogenous bicarbonate pools TCA cycle exchange reactions. Fractional recoveries C respiratory gases were determined during 225 min rest 90 leg ergometry at 45 65% peak oxygen uptake (V˙o 2 ) after continuous infusions [1- C]acetate, [2- or NaH CO 3 . In parallel trials, [6,6- H]glucose C]glucose given. Experiments conducted an...

The shuttling of intermediary metabolites such as lactate through the vasculature contributes to dynamic energy and biosynthetic needs tissues. Tracer kinetic studies offer a powerful tool measure metabolism substrates like that are simultaneously taken up from released into circulation by organs, but in each circulatory passage, entire cardiac output traverses pulmonary parenchyma. To determine whether transpulmonary affects whole-body kinetics vivo, we examined effects load (via clamp, LC)...

We examined the effects of exercise intensity and training on rates lipolysis, plasma free fatty acid (FFA) appearance (R a ), disappearance d reesterification s oxidation oxP ) in postmenopausal (PM) women. Ten sedentary but healthy women (55 ± 0.6 yr) completed 12 wk supervised endurance cycle ergometer [5 days/wk, 1 h/day, 65% peak oxygen consumption (V̇o 2peak )]. Flux were determined by continuous infusion [1- 13 C]palmitate [1,1,2,3,3- 2 H 5 ]glycerol during 90 min rest 60 one...