title: Manipulating Carbohydrate Availability Between Twice-Daily Sessions of High-Intensity Interval Training Over 2 Weeks Improves Time-Trial Performance.
abstract: Commencing some training sessions with reduced carbohydrate (CHO) availability has been shown to enhance skeletal muscle adaptations, but the effect on exercise performance is less clear. We examined whether restricting CHO intake between twice daily sessions of high-intensity interval training (HIIT) augments improvements in exercise performance and mitochondrial content. Eighteen active but not highly trained subjects (peak oxygen uptake [VO2peak] = 44 ± 9 ml/kg/min), matched for age, sex, and fitness, were randomly allocated to two groups. On each of 6 days over 2 weeks, subjects completed two training sessions, each consisting of 5 × 4-min cycling intervals (60% of peak power), interspersed by 2 min of recovery. Subjects ingested either 195 g of CHO (HI-HI group: ~2.3 g/kg) or 17 g of CHO (HI-LO group: ~0.3 g/kg) during the 3-hr period between sessions. The training-induced improvement in 250-kJ time trial performance was greater (p = .02) in the HI-LO group (211 ± 66 W to 244 ± 75 W) compared with the HI-HI group (203 ± 53 W to 219 ± 60 W); however, the increases in mitochondrial content was similar between groups, as reflected by similar increases in citrate synthase maximal activity, citrate synthase protein content and cytochrome c oxidase subunit IV protein content (p > .05 for interaction terms). This is the first study to show that a short-term "train low, compete high" intervention can improve whole-body exercise capacity. Further research is needed to determine whether this type of manipulation can also enhance performance in highly-trained subjects.
authors: Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
authors: Andrew J
authors: AJ
authors: Cochran
authors: Frank
authors: F
authors: Myslik
authors: Martin J
authors: MJ
authors: MacInnis
authors: Michael E
authors: ME
authors: Percival
authors: David
authors: D
authors: Bishop
authors: Mark A
authors: MA
authors: Tarnopolsky
authors: Martin J
authors: MJ
authors: Gibala
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D054874:Athletic Performance / Q000502:physiology*; D002950:Citrate (si)-Synthase / Q000378:metabolism; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004734:Energy Metabolism; D005080:Exercise Test / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008931:Mitochondria, Muscle / Q000201:enzymology; D010101:Oxygen Consumption; D011897:Random Allocation; D064133:Sports Nutritional Physiological Phenomena / Q000187:drug effects*; D013997:Time Factors; D055815:Young Adult
chemical_list: D004040:Dietary Carbohydrates; D003576:Electron Transport Complex IV; D002950:Citrate (si)-Synthase