Nutrition
Fluid and Carbohydrate Replacement
Prepared by Dr. Denis Bourke
- During prolonged exercise in hot weather, fluid loss can be between one to two litres per hour - equivalent to 1-2 Kilos in body weight
- Possible consequences of even low levels of dehydration include:
- Increased heart rate (a pulse rate increase of 8/minute for 1 litre fluid loss)
- Decreased cardiac output -causing reduced performance capacity.
- Body temperature to rise by 0.3°C
- Fluid replacement with added carbohydrate during prolonged exercise for a 70Kg competitor should be at the rate of about one litre/hour with about 40-60 gms of carbohydrate: this equates to a drink with 4-6% carbohydrate content. It has been demonstrated in research that performance in exercise lasting about 50 minutes is improved by ingestion of fluids with a carbohydrate content of 4-6%.
- The prime purpose in the intake of carbohydrates during exercise is to maintain blood glucose levels and to sustain a high rate of production of energy from blood glucose and glycogen stores in muscle.
- A study by Montain and Coyle in Texas, USA in 1993 clearly demonstrated that in the 40 minutes after intake of fluid there was during exercise a definite stabilisation of heart rate and body temperature.
- Individual variation occurs in that the capacity of athletes to tolerate large volumes of fluid can vary enormously.
SUMMARY:
Although the research quoted is from cycling and running in which it is possible to ingest fluid during competition, the broad principles can be applied to rowing. Intake of 40-60gms of carbohydrate in one litre of fluid for each hour of exercise will generally be sufficient to maintain high rates of blood glucose late in exercise thus delaying fatigue.
REFERENCES:
http://www.smartplay.com.au/vic/DocLib/Pub/DocLibDetail.asp?lngDocLibID=4
http://www.ianr.unl.edu/pubs/foods/nf72.htm
http://www.ausport.gov.au/fulltext/1998/sda/factsheet1.pdf