It is well established that carbohydrate during exercise can improve performance. But how do you know what sessions to fuel? Well…it depends. It depends on two main factors; the duration and intensity.
During exercise, we burn a combination of fuels; the main two being carbohydrate and fat.
At low intensity ~25% VO2 max (the intensity of walking), we burn mostly plasma free fatty acids, i.e. the fat kicking around in our blood stream.
At moderate intensity, ~65% VO2 max, (the intensity of an easy pedal on the flat), we burn roughly half carbohydrate and half fat source.
At high intensities, ~85% Vo2 max (the intensity of sprint efforts and hill climbing), we burn predominantly carbohydrate as a fuel source.
While we burn proportionally more fat at lower intensities, the overall calories burnt per minute are significantly less compared to higher intensities. So if you want to lose fat mass, rather than trundle along for hours at low intensity trying to burn fat, smash out a high intensity session to burn more calories overall.
Alright, now that technical stuff is out of the way, let’s talk about when we need to eat on the bike.
We know that our muscle glycogen stores (our fuel tank), last around 75-90 minutes during sustained exercise. They will run out faster if the intensity is higher (see above) and in untrained individuals. If you’re fit and well-trained, with a well tuned energy system, they may last you a little longer. Keep this duration in the back of your mind when determining if you need to eat during a ride.
Short sessions, <30-60minutes
For a ride less than 30-60 minutes, there generally isn’t a need to eat. In this short time, you are unlikely to completely run out of fuel (glycogen) and your blood sugar levels won’t drop significantly. It’s not harmful or performance limiting if you do eat, (unless it causes gut upset), but it’s not a necessity.
Longer rides, ~60-90minutes duration
It depends on the intensity. If you’re heading out for an easy spin at low intensity, you’ll be burning a combination of fat and carbohydrate as a fuel source. It’s unlikely you’ll deplete your fuel tank completely at this rate. However, if the intensity is higher e.g. sprint efforts or hills, where performance in that session is important, you would benefit from consuming carbohydrate during exercise. If you have difficulty eating on the bike, even a mouth rinse of carbohydrate appears to trigger a central nervous system effect and improve exercise performance. An accredited Sports Dietitian will be able to assist in developing a fuelling plan for you specifically.
Long sessions, >90 minutes
Our fuel tank is starting to red line around 75-90minutes. At this duration and longer, eating on the bike is important to prevent “bonking” or “hitting the wall” where your fuel tank is completely empty. A good rule of thumb is to start eating at the 45-60 minute mark for long rides so you’ve never in the red. The longer the duration, the more carbohydrate we need, with evidence of a dose response relationship. So for those epic weekend rides, make sure you fuel up appropriately. Glucose takes 15-30mins to be digested, absorbed and utilised by the body, so it’s important to commence your carbohydrate intake early, rather than wait until you’re feeling woozy.
Time and time again I see athletes under-fuelling on the bike. They think that by getting through a ride with minimal nutrition they’ll burn more calories and lose more weight. It may be hard to get your head around, but fuelling sessions well, will help you train harder and overall burn more calories. Work with an Accredited Sports Dietitian to plan a fuelling strategy that’s best for you.
Taryn Richardson, APD, AccSD Bach Hlth Sc (Nut & Diet) Hons; IOC dip sport nutr.
Taryn is an Accredited Sports Dietitian and Director of her private practice, Dietitian Approved. She spends half of her time on the Gold Coast working with the triathlon program at the Australian Institute of Sport (dream job!). The other half is spent consulting in Brisbane (or over Skype) spreading the good word on nutrition and helping everyday exercisers perform at their best.