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For Flux Sake: Isotopic Tracer Methods of Monitoring Human Carbohydrate Metabolism During Exercise

Javier T. Gonzalez and Andy J. King

specifically focuses on the theory and practice of employing isotopic tracers to study carbohydrate metabolism during exercise in humans. Tracers can be considered as “labels” which are used to track the trace of interest (e.g., ingested glucose). A common tracer method employs isotopes, which are elements

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Addition of Fructose to a Carbohydrate-Rich Breakfast Improves Cycling Endurance Capacity in Trained Cyclists

Tim Podlogar, Simon Cirnski, Špela Bokal, Nina Verdel, and Javier T. Gonzalez

.T. , & Betts , J.A. ( 2019 ). Dietary sugars, exercise and hepatic carbohydrate metabolism . Proceedings of the Nutrition Society, 78 ( 02 ), 246 – 256 . 10.1017/S0029665118002604 Gonzalez , J.T. , & Wallis , G.A. ( 2021 ). Carb-conscious: The role of

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The Influence of Biological Maturation on Fat and Carbohydrate Metabolism during Exercise in Males

Brooke R. Stephens, Andrew S. Cole, and Anthony D. Mahon

This study examined substrate use during exercise in early-pubertal (EP), mid-pubertal (MP), late-pubertal (LP), and young-adult (YA) males. Fuel use was calculated using the RER and VO2 response during cycling exercise at 30 to 70% of VO2peak. Significant group by intensity interactions were found for lactate, RER, percent CHO, and fat use, in addition to fat and CHO oxidation rates, which suggest a maturation effect on substrate use during exercise. While significance was not achieved at all intensities, post hoc analyses revealed greater fat use, lower CHO use, and lower lactate concentrations in EP and MP compared to LP or YA. No differences were noted between EP and MP or LP and YA at any intensity, suggesting the development of an adult-like metabolic profile occurs between mid- to late-puberty and is complete by the end of puberty.

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The Effect of Encapsulated Soluble Fiber on Carbohydrate Metabolism during Exercise

Allen C. Parcell, Melinda L. Ray, Kristine A. Moss, Timothy M. Ruden, Rick L. Sharp, and Douglas S. King

Previous investigations have reported that soluble fiber reduces the plasma glucose and insulin changes after an oral glucose load. To improve the payability of a soluble-fiber feeding, this study addressed how a combined, soluble fiber (delivered in capsule form) and a preexercise CHO feeding would affect metabolic responses during exercise. On 3 different days, participants ingested a placebo (CON), 75 g liquid CHO (GLU), or 75 g liquid CHO with 14.5 g encapsulated guar gum (FIB) 45 min before cycling for 60 min at 70% VO2peak. Peak concentrations of plasma glucose and insulin were similar and significantly greater than CON preexercise (p < .05). Similarities in carbohydrate reliance were observed in GLU and FIB. Muscle glycogen use did not differ significantly among trials. These results demonstrate that encapsulated soluble fiber delivered with a liquid CHO feeding does not affect plasma glucose, insulin, or muscle glycogen utilization during exercise.

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The Effect of a Carbohydrate-Arginine Supplement on Postexercise Carbohydrate Metabolism

Ben B. Yaspelkis III and John L. lvy

The effect of a carbohydrate-arginine supplement on postexercise muscle glycogen storage was investigated. Twelve well-trained cyclists rode for 2 hr on two separate occasions to deplete theirmuscle glycogen stores. At 0, l, 2, and 3 hr after each exercise bout, the subjects ingested either a carbohydrate (CHO) supplement (1 g carbohydrate/kg body weight) or a carbohydrate-arginine (CHO/AA) supplement (1 g carbohydrate/kg body mass and 0.08 g arginine-hydrochloride/kg body weight). No difference in rate of glycogen storage was found between the CHO/AA and CHO treatments, although significance was approached. There were also no differences in plasma glucose, insulin, or blood lactate responses between treatments. Postexercise carbohydrate oxidation during the CHO/AA treatment was significantly reduced compared to the CHO treatment. These results suggest that the addition of arginine to a CHO supplement reduces the rate of CHO oxidation postexercise and therefore may increase the availability of glucose for muscle glycogen storage during recovery.

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Effect of Preexercise Ingestion of Modified Cornstarch on Substrate Oxidation during Endurance Exercise

Neil M. Johannsen and Rick L. Sharp

The purpose of this study was to investigate differences in substrate oxidation between dextrose (DEX) and unmodified (UAMS) and acid/alcohol-modified (MAMS) cornstarches. Seven endurance-trained men (VO2peak = 59.1 ± 5.4 mL·kg−1·min−1) participated in 2 h of exercise (66.4% ± 3.3% VO2peak) 30 min after ingesting 1 g/kg body weight of the experimental carbohydrate or placebo (PLA). Plasma glucose and insulin were elevated after DEX (P < 0.05) compared with UAMS, MAMS, and PLA. Although MAMS and DEX raised carbohydrate oxidation rate through 90 min of exercise, only MAMS persisted throughout 120 min (P < 0.05 compared with all trials). Exogenous-carbohydrate oxidation rate was higher in DEX than in MAMS and UAMS until 90 min of exercise. Acid/alcohol modification resulted in augmented carbohydrate oxidation with a small, sustained increase in exogenous-carbohydrate oxidation rate. MAMS appears to be metabolizable and available for oxidation during exercise.

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The Influence of Ingesting a Carbohydrate-Electrolyte Beverage during 4 Hours of Recovery on Subsequent Endurance Capacity

Joanne L. Fallowfield, Clyde Williams, and Rabindar Singh

Recovery from prolonged exercise involves both rehydration and replenishment of endogenous carbohydrate stores. The present study examined the influence of ingesting a carbohydrate-electrolyte (CE) solution following prolonged running, on exercise capacity 4 hr later. Twelve men and 4 women were divided into two matched groups, which were randomly assigned to either a control (P) or a carbohydrate (CHO) condition. Both groups ran at 70% of maximal oxygen uptake ( VO 2 max ) on a level treadmill for 90 min or until volitional fatigue (R,), and they ran at the same % VO 2 max to exhaustion 4 hr later to assess endurance capacity ( R 2 ). The CHO group ingested a 6.9% CE solution providing 1.0 g CHO · kg body weight−1 immediately post-R, and again 2 hr later. The P group ingested equal volumes of a placebo solution. Run times (mean ± SEM) for Rj did not differ between the groups (P 86.3 ± 3.8 min; CHO 87.5 ± 2.5 min). The CHO group ran 22.2 (±3.5) min longer than the P group during R 2 (P 39.8 ± 6.1 min; CHO 62.0 ± 6.2 min) (p < .05). Thus, ingesting a 6.9% carbohydrate-electrolyte beverage following prolonged, constant-pace running improves endurance capacity 4 hr later.

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The Influence of a High Carbohydrate Intake during Recovery from Prolonged, Constant-Pace Running

Joanne L. Fallowfield and Clyde Williams

The present study examined the influence of ingesting 3.0 g CHO · kg 1 body mass ⋅ 2  hr 1 after prolonged exercise on recovery and running capacity 4 hr later. Nine men and 8 women completed two trials in a counterbalanced design. Each trial consisted of a 90-min run on a level treadmill at 70% VO 2 max ( R t ) followed by 4 hr recovery (REC) and a further exhaustive run at 70% VO 2 max (R2). During REC, subjects ingested either two feedings of a 6.9% glucose-polymer (GP) solution (D trial) or two feedings of a 19.3% GP solution (C trial). There were no differences in mean (±SE) R 2 run times between the C and D trials or between the male and female subjects. More stable blood glucose concentrations were maintained during REC in the C trial, such that blood glucose was elevated in the C trial in comparison with the D trial after 210 min of REC. It was concluded that increasing postexercise carbohydrate intake from 1.0 to 3.0 g CHO ⋅ Kg 1 body mass 2  hr 1 does not improve endurance capacity 1 hr later.

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Carbohydrate Intake and Recovery of Intermittent Running Capacity

Ceri W. Nicholas, Paul A. Green, Richard D. Hawkins, and Clyde Williams

The purpose of the present study was to examine the influence of an increased carbohydrate intake on the recovery of endurance running capacity after exhaustive intermittent running. Six male subjects were randomly assigned to two dietary recovery conditions, each involving two running tests separated by 22 hr. The protocol comprised a prolonged, intermittent, high-intesity shuttle run test (I–HI). One week later subjects repeated the I–HI on consecutive days under different dietary conditions. During the 22-hr recovery, either the carbohydrate in take of the subjects was increased (CHO) or they ate an isocaloric diet by supplementing their normal diet with extra protein and fat (CON). Intermittent running capacity was improved when subjects increased their carbohydrate intake to 10 g · kg-1 bm during the 22-hr recovery between trials, but an isocaloric diet without additional carbohydrate did not bring about the same improvements.

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Maximal Lactate Steady State’s Dependence on Cycling Cadence

Ralph Beneke and Renate M. Leithäuser

The maximal lactate steady state (MLSS) depicts the highest blood lactate concentration (BLC) that can be maintained over time without a continual accumulation at constant prolonged workload. In cycling, no difference in the MLSS was combined with lower power output related to peak workload (IMLSS) at 100 than at 50 rpm. MLSS coincides with a respiratory exchange ratio (RER) close to 1. Recently, at incremental exercise, an RER of 1 was found at similar workload and similar intensity but higher BLC at 100 than at 50 rpm. Therefore, the authors reassessed a potential effect of cycling cadences on the MLSS and tested the hypothesis that the MLSS would be higher at 105 than at 60 rpm with no difference in IMLSS in a between-subjects design (n = 16, age 25.1 ± 1.9 y, height 178.4 ± 6.5 cm, body mass 70.3 ± 6.5 kg vs n = 16, 23.6 ± 3.0 y, 181.4 ± 5.6 cm, 72.5 ± 6.2 kg; study I) and confirmed these findings in a within-subject design (n = 12, 25.3 ± 2.1 y, 175.9 ± 7.7 cm, 67.8 ± 8.9 kg; study II). In study I, the MLSS was lower at 60 than at 105 rpm (4.3 ± 0.7 vs 5.4 ± 1.0 mmol/L; P = .003) with no difference in IMLSS (68.7% ± 5.3% vs 71.8% ± 5.9%). Study II confirmed these findings on MLSS (3.4 ± 0.8 vs 4.5 ± 1.0 mmol/L; P = .001) and IMLSS (65.0% ± 6.8% vs 63.5% ± 6.3%; P = .421). The higher MLSS at 105 than at 60 rpm combined with an invariance of IMLSS and RER close to 1 at MLSS supports the hypothesis that higher cadences can induce a preservation of carbohydrates at given BLC levels during low-intensity, high-volume training sessions.