title: Effect of carbohydrate ingestion and ambient temperature on muscle fatigue development in endurance-trained male cyclists.
abstract: The aim of the present study was to determine the effect of carbohydrate (CHO; sucrose) ingestion and environmental heat on the development of fatigue and the distribution of power output during a 16.1-km cycling time trial. Ten male cyclists (Vo(2max) = 61.7 +/- 5.0 ml.kg(-1).min(-1), mean +/- SD) performed four 90-min constant-pace cycling trials at 80% of second ventilatory threshold (220 +/- 12 W). Trials were conducted in temperate (18.1 +/- 0.4 degrees C) or hot (32.2 +/- 0.7 degrees C) conditions during which subjects ingested either CHO (0.96 g.kg(-1).h(-1)) or placebo (PLA) gels. All trials were followed by a 16.1-km time trial. Before and immediately after exercise, percent muscle activation was determined using superimposed electrical stimulation. Power output, integrated electromyography (iEMG) of vastus lateralis, rectal temperature, and skin temperature were recorded throughout the trial. Percent muscle activation significantly declined during the CHO and PLA trials in hot (6.0 and 6.9%, respectively) but not temperate conditions (1.9 and 2.2%, respectively). The decline in power output during the first 6 km was significantly greater during exercise in the heat. iEMG correlated significantly with power output during the CHO trials in hot and temperate conditions (r = 0.93 and 0.73; P < 0.05) but not during either PLA trial. In conclusion, cyclists tended to self-select an aggressive pacing strategy (initial high intensity) in the heat.
authors.affiliation: School of Exercise, Biomedical and Health Sciences, Edith Cowan Univ., 100 Joondalup Dr., Joondalup, WA, Australia. c.abbiss@ecu.edu.au
authors.forename: Chris R
authors.initials: CR
authors.lastname: Abbiss
authors.forename: Jeremiah J
authors.initials: JJ
authors.lastname: Peiffer
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Peake
authors.forename: Kazunori
authors.initials: K
authors.lastname: Nosaka
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Suzuki
authors.forename: David T
authors.initials: DT
authors.lastname: Martin
authors.forename: Paul B
authors.initials: PB
authors.lastname: Laursen
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D001831:Body Temperature / Q000187:drug effects / Q000502:physiology; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D004298:Dopamine / Q000097:blood; D004558:Electric Stimulation; D004576:Electromyography; D005230:Fatty Acids, Nonesterified / Q000097:blood; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D018763:Muscle Fatigue / Q000187:drug effects / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D011388:Prolactin / Q000097:blood; D012881:Skin Temperature / Q000187:drug effects / Q000502:physiology; D013696:Temperature
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D005230:Fatty Acids, Nonesterified; D019344:Lactic Acid; D011388:Prolactin; D004298:Dopamine