Nutrition Tips from Greg Shaw – AIS Sports Dietitian
Carbohydrate Intake
Carbohydrate is a fascinating nutrient and has a large impact on sporting performance but there is a lot of conflicting information floating around about carbohydrate and how much you need during training. To determine your carbohydrate requirements for an individual exercise session you need to ask yourself a few important questions.
1) How long will the session be for?
If the session is longer than 90 minutes it is important to take carbohydrate out on the bike with you. The muscles have a set store of carbohydrate called muscle glycogen. Muscle glycogen is finite and can be depleted. When this store runs out you “Hit the Wall” or “Bonk”. This is your body saying I have no more carbohydrate left in the muscles so I have to drop back my intensity.
2) What intensity is the session you are doing?
If you are doing an efforts session or a high intensity session then you will use your stores up faster and carbohydrate from food or fluids can be beneficial in maintaining your effort. Most cyclist would not think of taking carbohydrate out with them if they were doing a session of 8 x 5min efforts, but it may be beneficial in maintaining intensity in the last few repetitions of the session. This goes for racing as well. Most people doing a criterion of 45min plus 3 laps may not think that carbohydrate intake during a race would have a benefit, but a small amount around 20min in, may improve your ability to perform in the sprint at the end of the race. In very general terms it takes around 15-30min for a gel or sports drink to be absorbed and the body to be able to utilise the carbohydrate. So if it is a short race, get the carb in earlier rather than later. It is generally recommended that a person exercising at high intensity should consume around 30-60g/hr or ~1g of carbohydrate per kg per hour. This figure is based on absorption of carbohydrate during exercise and the bodies ability to utilise that carbohydrate being absorbed.
3) What form of Carbohydrate should you use?
Recently scientists have started to look at manipulating the type of carbohydrate in sports drinks and gels to see if they can increase the rate at which carbohydrate is absorbed. They have found that by including other types of carbohydrate mainly “Fructose” and “Maltodextrins” along with “Glucose” they can increase the rate of absorption and hence the body’s ability to burn carbohydrate to a higher level. Taking the potential rate of carbohydrate oxidation (burning of fuel) to around ~1.5g per min equating to around 90g of carbohydrate per hour. Products like lollies, soft drink, cordial, most gels and sports drinks contain only glucose. Products that integrate this research are starting to appear on the shelf and cyclists should be looking for products that use this latest research to maximise performance.
So before heading out onto the bike next time ask yourself these few simple questions and you will ensure you have enough high octane fuel to train at the red line.
Eat up the Road.
Greg Shaw, Australian Institute of Sport, Sports Dietitian
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