Dennis H. Passe

Fuel selection and cycling endurance performance with ingestion of [13C]glucose: evidence for a carbohydrate dose response

Endurance performance and fuel selection while ingesting glucose (15, 30, and 60 g/h) was studied in 12 cyclists during a 2-h constant-load ride [approximately 77% peak O2 uptake] followed by a 20-km time trial. Total fat and carbohydrate (CHO) oxidation and oxidation of exogenous glucose, plasma glucose, glucose released from the liver, and muscle glycogen were computed using indirect respiratory calorimetry and tracer techniques. Relative to placebo (210+/-36 W), glucose ingestion increased the time trial mean power output (%improvement, 90% confidence limits: 7.4, 1.4 to 13.4 for 15 g/h; 8.3, 1.4 to 15.2 for 30 g/h; and 10.7, 1.8 to 19.6 for 60 g/h glucose ingested; effect size=0.46). With 60 g/h glucose, mean power was 2.3, 0.4 to 4.2% higher, and 3.1, 0.5 to 5.7% higher than with 30 and 15 g/h, respectively, suggesting a relationship between the dose of glucose ingested and improvements in endurance performance. Exogenous glucose oxidation increased with ingestion rate (0.17+/-0.04, 0.33+/-0.04, and 0.52+/-0.09 g/min for 15, 30, and 60 g/h glucose), but endogenous CHO oxidation was reduced only with 30 and 60 g/h due to the progressive inhibition of glucose released from the liver (probably related to higher plasma insulin concentration) with increasing ingestion rate without evidence for muscle glycogen sparing. Thus ingestion of glucose at low rates improved cycling time trial performance in a dose-dependent manner. This was associated with a small increase in CHO oxidation without any reduction in muscle glycogen utilization.

Curvilinear dose-response relationship of carbohydrate (0-120 g·h(-1)) and performance.

BACKGROUND There is a lack of consensus regarding the optimal range of carbohydrate (CHO) ingestion rates recommended for endurance athletes. PURPOSE This study investigated the relationship between CHO dose and cycling time trial performance to identify an optimal range of CHO ingestion rates for endurance performance. METHODS Fifty-one cyclists and triathletes (28 ± 7 yr, mean ± SD) across four research sites completed four trials. Each trial consisted of a 2-h constant load ride at 95% of the workload that elicited a 4-mmol·L(-1) blood lactate concentration immediately followed by a computer-simulated 20-km time trial, which subjects were asked to complete as quickly as possible. Twelve CHO electrolyte (18 mmol·L(-1) Na, 3 mmol·L(-1) K, and 11 mmol·L(-1) Cl) beverages (three at each site) were tested in a double-blind manner, providing subjects 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, and 120 g CHO (1:1:1 glucose-fructose-maltodextrin) per hour during the 2-h constant load ride at a fluid intake rate of 1 L·h(-1). All subjects also consumed a noncaloric placebo on one counterbalanced test occasion. Data were natural log transformed, subjected to a mixed-model analysis, and are reported as adjusted treatment means. RESULTS We estimate incremental performance improvements of 1.0%, 2.0%, 3.0%, 4.0%, and 4.7% at 9, 19, 31, 48, and 78 g·h, respectively, with diminishing performance enhancement seen at CHO levels >78 g·h(-1). CONCLUSIONS CHO beverage ingestion and endurance (∼160 min) performance appear to be related in a curvilinear dose-response manner, with the best performance occurring with a CHO (1:1:1 glucose-fructose-maltodextrin) ingestion rate of 78 g·h(-1).

Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes

Abstract The purpose of this study was to establish normative data for regional sweat sodium concentration ([Na+]) and whole-body sweating rate in athletes. Data from 506 athletes (367 adults, 139 youth; 404 male, 102 female) were compiled from observational athlete testing for a retrospective analysis. The participants were skill/team-sport (including American football, baseball, basketball, soccer and tennis) and endurance (including cycling, running and triathlon) athletes exercising in cool to hot environmental conditions (15–50°C) during training or competition in the laboratory or field. A standardised regional absorbent patch technique was used to determine sweat [Na+] on the dorsal mid-forearm. Whole-body sweat [Na+] was predicted using a published regression equation (y = 0.57x+11.05). Whole-body sweating rate was calculated from pre- to post-exercise change in body mass, corrected for fluid/food intake (ad libitum) and urine output. Data are expressed as mean ± SD (range). Forearm sweat [Na+] and predicted whole-body sweat [Na+] were 43.6 ± 18.2 (12.6–104.8) mmol · L–1 and 35.9 ± 10.4 (18.2–70.8) mmol · L–1, respectively. Absolute and relative whole-body sweating rates were 1.21 ± 0.68 (0.26–5.73) L · h–1 and 15.3 ± 6.8 (3.3–69.7) ml · kg–1 · h–1, respectively. This retrospective analysis provides normative data for athletes’ forearm and predicted whole-body sweat [Na+] as well as absolute and relative whole-body sweating rate across a range of sports and environmental conditions.

Ingestion of transient receptor potential channel agonists attenuates exercise-induced muscle cramps

Introduction: Exercise‐associated muscle cramping (EAMC) is a poorly understood problem that is neuromuscular in origin. Ingestion of transient receptor potential (TRP) channel agonists has been efficacious in attenuating electrically induced muscle cramps. This study examines the effect of TRP agonist ingestion on voluntarily induced EAMC and motor function. Methods: Study 1: Thirty‐nine participants completed 2 trials after ingesting TRP agonist‐containing active treatment (A), or vehicle (V) control. Cramping in the triceps surae muscle was induced via voluntary isometric contraction. Study 2: After ingesting A or V, 31 participants performed kinematic and psychomotor tests of manual dexterity. Results: A increased precramp contraction duration (A, 36.9 ± 4.1 s; V, 27.8 ± 3.1 s), decreased cramp EMG area under the curve (A, 37.3 ± 7.7 %EMGmax·s; V, 77.2 ± 17.7 %EMGmax·s), increased contraction force to produce the cramp (A, 13.8 ± 1.8 kg; V, 9.9 ± 1.6 kg), and decreased postcramp soreness (A, 4.1 ± 0.3 arbitrary units (a.u.); V, 4.7 ± 0.3 a.u.). Kinematic and psychomotor tests were not affected. Discussion: TRP agonist ingestion attenuated EAMC characteristics without affecting motor function. Muscle Nerve 56: 379–385, 2017