Metabolic profile of 4 h cycling in the field with varying amounts of carbohydrate supply

Eur J Appl Physiol. 2003 Jan;88(4-5):431-7. doi: 10.1007/s00421-002-0712-3. Epub 2002 Nov 19.


Several laboratory studies have demonstrated a performance-enhancing effect of carbohydrate (CHO) supplementations during endurance sessions of long duration. However, the transferability of these results to real training and competition circumstances has not been conclusively shown. Therefore, we tried to test the influence of graded CHO substitution on substrate utilization and selected physiological parameters under standardized but practically orientated field conditions. Fourteen endurance-trained male subjects [mean (SD): 25 (5) years, 72 (9) kg, .VO(2max) 67 (6) ml.min(-1).kg(-1), individual anaerobic threshold (IAT) 269 (30) W] after a stepwise increasing pre-test had to perform three 4-h endurance rides on their own bicycles with simultaneous spiroergometry: constant workload 70% IAT (monitoring by SRM-System). Before and during exercise, solutions without (0%), with 6% or 12% CHO were administered double-blindly and in randomized order (total volume: 50 After cessation of exercise, significant differences between 0% and both CHO concentrations were detected for blood glucose (GLU; 75 mg dl(-1) for 0% vs 101 mg dl(-1) for 6% vs 115 mg dl(-1) for 12%; P<0.001) and respiratory exchange ratio (0.84 vs 0.88 vs 0.90; P<0.01; correlation to GLU: r=0.46, P<0.05). Free fatty acids (0.19 vs 0.16 vs 0.10 mmol l(-1)) and glycerol (0.41 vs 0.22 vs 0.12 mmol l(-1)) were significantly different between the endurance trials in a dose-dependent manner (both P<0.001). Lactate concentration ( P=0.42) and heart rate ( P=0.12) had no significant influence from CHO substitution. We conclude that CHO substitution during 4-h endurance training inhibits lipolysis in a dose-dependent manner and enhances aerobic glycolysis. This proves that earlier laboratory findings can be replicated under field conditions using modern portable equipment.

Publication types

  • Clinical Trial
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Anaerobic Threshold
  • Bicycling / physiology*
  • Blood Glucose / analysis
  • Carbohydrates / administration & dosage*
  • Dose-Response Relationship, Drug
  • Double-Blind Method
  • Glycolysis / drug effects
  • Humans
  • Lipolysis / drug effects
  • Male
  • Oxygen Consumption
  • Physical Education and Training
  • Physical Endurance
  • Pulmonary Gas Exchange / drug effects
  • Time Factors


  • Blood Glucose
  • Carbohydrates