It's a horrible feeling to have a dramatic lack of energy in the second half of your bike ride. That sudden tiredness is called "hitting the wall". Even if you are fit and healthy, poor food choice before and during the ride can really slow you down.
Foods naturally high in carbohydrates are crucial for topping up the muscle fuel, known as glycogen, used in cycling. Glycogen is your muscle 'petrol tank'. When a muscle contracts and works hard during a ride, especially during hill climbing or sprint work, it burns the glucose that has been released from the glycogen stored in muscles.
The glucose and glycogen comes primarily from the carbohydrate in the food we eat. If the pre-ride meal is low in carbohydrate, the muscles become low in glycogen, and you run out of energy before you finish. When that happens the body starts to break down muscle protein for extra glucose. You can see why low carbohydrate diets do not help you to keep active and fit.
High carbohydrate foods that are a favourite with cyclists are pasta, bread rolls, breakfast cereal, smoothies, baked beans and fruit. Choose good quality carbohydrate foods, that is, those that have been least-processed, like wholegrains, fresh fruits and starchy vegetables. The all-time favourite fruit of cyclists is the banana because it is easy-to-peel on the bike, rich in carbohydrates, tasty and easy-to-eat.
Bars, gels and snacks
In addition, many cyclists like to take food bars, carbohydrate gels and confectionery on the ride. Food bars should be relatively low in fat (say, less than 5 grams of fat per bar) so they can be quickly digested on the bike, allowing the carbohydrates to be quickly absorbed into the blood and transported to the muscles.
If you take a carbohydrate gel, I strongly advise that you wash it down with some water because the sugars in the gel are easier to absorb into the blood when they are dilute. Some gels have caffeine. These can be useful in very long rides as they can increase endurance near the end of a ride. In other words, take them in the last one third of a ride.
Confectionery, especially jelly snakes, are commonly eaten by cyclists during endurance rides. They provide easy-to-digest sugars and are a tasty treat during a long, tough ride. Remember that when the ride is over to restock your muscle fuel with good quality carbohydrate foods, along with protein foods to repair the small amount of muscle damage that happens with all long rides.
Finally, remind yourself that you will likely need 600-1200 mL of fluids for every hour you ride. Because sweat quickly evaporates from your skin during cycling, you may not even see or feel any sweat. Rest assured you are losing water as you will sweat with each turn of the pedal. Water is perfect for rides one hour or less. If you are cycling for 90 minutes or more consider a sports drink because they provide sugars to replace those burned as you cycle. So, water is all you need for the 10 and 25 km rides, but you will likely benefit from a sports drink, a gel and a banana during the 100 km ride.
Accredited Practising Dietitian & Sports Dietitian
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