Nutrition and hydration
Nutrition and hydration
Nutrition
The body’s use of food as fuel is more clearly demonstrated on a bicycle than perhaps any other aspect of modern life.
Cardiovascular demands or pain in the muscles or joints is likely to stop you running long before you exhaust your glycogen reserves. Not so with cycling. Riding without replenishing your fuel reserves is like driving a car and watching the needle on the fuel gauge fall inexorably towards empty. Setting off for a ride longer than about ninety minutes without fuel reserves is ill-advised, to say the least.
The body’s natural glycogen reserves will only fuel effort in the saddle for a maximum of 90 minutes, according to Emma Barraclough, SIS nutritionist and Ironman triathlete. Increase effort to something like that demanded by a 25-mile time trial, and that window could be reduced to as little as an hour. Carrying fuel supplies with you if you’re riding for a longer period is therefore essential if the dreaded ‘bonk’ is to be avoided. “Optimally, our bodies can absorb up to 60g of carbohydrate per hour,” says Barraclough.
Intensity is the guide when deciding on bars or gels, she continues. Low and medium intensity exercise will leave sufficient spare capacity from working muscles for blood flow to the stomach to aid digestion. High intensity efforts will place working muscles first in the queue, and so gels might be easier to digest.
“The dreaded bonking or hitting the wall happens when you’ve exhausted your glycogen stores. You’re pedalling squares,” Barraclough explains. “where you just haven’t got the energy to keep going, you feel very fatigued, and possibly dizzy.”
Much as running a car until the last drop of fuel has been used can damage the engine, so running the body until glycogen reserves have been utterly depleted can also cause harm, she continues. The immune system is fuelled by carbohydrate in the bloodstream, so what Barraclough describes as ‘upper respiratory tract infections’ – colds and flu symptoms – can also become more common. More immediately, power outputs can drop as glycogen reserves fall, but mental tiredness can also ensue as muscles search elsewhere for fuel, typically from the energy source used by the brain – glucose in the bloodstream.
Hydration
Hydration is another key consideration when preparing your ‘ready to ride’ checklist. In short, don’t leave home without some form fluid supply, whether it be water, juice, or either with added electrolyte. The latter helps the body to maintain an optimum fluid balance between salts and sugars in ‘extra-cellular’ fluid, Barraclough says. Electrolytes such as potassium help carry glucose to the cells of exercising muscles.
“Temperature and humidity will make a huge difference,” she continues, “but we generally work on [a recommendation of] 500ml to a litre of fluid per hour.” Seasonal variations and the difference in clothing can also have an effect, she continues. Compensating for colder temperatures by wearing more is an entirely sensible course of action, but reducing fluid intake as a result can be shortsighted. More and warmer clothes will mean you’ll continue to sweat, even in reduced ambient temperatures.
A lack of hydration can cause a drop in what Barraclough describes as “plasma volumes”.
“As you become dehydrated, your blood volume drops,” she explains. The detrimental effect on performance is easily understood: impaired oxygen delivery to working muscles will prevent them performing at their optimum. Severe dehydration will present the body with issues in regulating core temperature.