CHO and Exercise Research task 30 minutes

The role of CHO in Sport

CHO and the Body

CHO in Sport & Exercise Capacity for endurance exercise related to pre-exercise muscle glycogen stores. A high CHO diet will increase glycogen stores. After exercise glycogen stores need to be replenished . For most athletes/ active people 5-10g CHO per kg body weight will maximise muscle glycogen recovery

How much CHO? Activity level # 3-5 hours per week 4-5 g CHO/kg body weight/day 3-5 hours per week 4-5 5-7 hours per week 5-6 1-2 hours per day 6-7 2-4 hours per day 7-8 More than 4 hours /day 8-10 #No. of hours of moderate intensity exercise or sport

Which type of CHO is best? ‘Simple’ and ‘complex’ based on their chemical structure. In practice, many foods contain a mixture of both. Glycaemic Index (G I) describes the effect different foods have on blood sugar levels.

Before Exercise Consuming a low GI meal 2-4 hours before provides slow release energy and delays fatigue. There is still some controversy over whether to eat high or low GI just before exercise. High GI foods are more ‘risky’ to performance.

During Exercise First hour of exercise most of your energy comes from muscle glycogen After an hour fuel comes from blood sugar supplied by liver glycogen as well as some muscle glycogen.  Glycogen depletion = low blood sugar “hypoglycaemia” Hypoglycaemia = feelings of tiredness and light-headedness, and your legs begin to feel very heavy “hitting the wall”

During Exercise Consuming CHO can maintain your blood sugar levels so you could exercise for longer Muscles can take up about 30g to 60g an hour of carbohydrate from the bloodstream (Anita Bean 2003) It takes 30 minutes for the carbohydrate to reach your bloodstream To promote quick absorption high to moderate GI CHO’s are the best choices In practice if you consume about 500ml an hour of an isotonic sports drink containing 7g of carbohydrate per 100ml, then you will consume about 35g of carbohydrate per hour, which will roughly maintain your blood sugar levels.

After exercise The length of time it takes to refuel depends upon: How depleted glycogen stores are Extent of muscle damage Amount and timing of CHO eaten Training experience and fitness levels

After exercise consume CHO quickly –within half an hour and certainly within 2 hours high GI CHO can be absorbed quickly Water is needed for storage of CHO Protein and fats aids absorption of the carbohydrates More experienced athletes refuel quicker and can store up to 20% more glycogen. The minimum time for refuelling is 20 hours (Coyle 1991)

After exercise 1g high GI CHO per kg bodyweight in the two hours post exercise It makes no difference whether the CHO is liquid or solid Once stores are replenished in the 6 hour post ex window CHO intake is still important Low GI meals eaten regularly maintain a steady supply of CHO into the blood stream and avoid fluctuations in blood sugar.