Pre-exercise ingestion of carbohydrate and transient hypoglycemia during exercise

Int J Sports Med. 1999 May;20(4):227-31. doi: 10.1055/s-2007-971122.


To study the occurrence and contributing factors of transient hypoglycemia after pre-exercise ingestion of glucose after a 4-hour fast, 19 well-trained cyclists ingested 50 grams of glucose dissolved in water around noon after having a normal breakfast. The ingestion of the glucose solution was followed by 30 minutes rest after which the subjects cycled for 40 minutes at 60% of the predetermined maximal power output. Every 10 minutes blood was sampled for determination of glucose, catecholamines, and insulin concentrations. In 6 subjects (hypo-group) plasma glucose levels dropped transiently below 3.0 mmol/l, while in the other 13 subjects (non-hypo group) plasma glucose level remained above this level. Although at the onset of exercise the plasma glucose levels were lower in the hypo-group, insulin levels were similar in both groups, suggesting a higher insulin sensitivity in the hypo-group. During exercise, norepinephrine was lower in the hypo-group, indicating a lower sympathetic activity in the hypo-group. The lowest plasma glucose levels in both groups were observed after 20 minutes of exercise, after which plasma glucose concentration returned to normal levels. It is concluded that pre-exercise carbohydrate ingestion after a 4-hour fast is sufficient to induce a transient hypoglycemia. The data suggest that the occurrence of hypoglycemia is determined by a combination of a high insulin sensitivity, a small amount of ingested glucose, and a low sympathetic activity.

MeSH terms

  • Adult
  • Bicycling / physiology
  • Blood Glucose / physiology
  • Dietary Carbohydrates / administration & dosage*
  • Eating
  • Exercise / physiology*
  • Fasting
  • Humans
  • Hyperinsulinism / physiopathology
  • Hypoglycemia / physiopathology*
  • Male


  • Blood Glucose
  • Dietary Carbohydrates