Feed for speed
Get your glucose right and you can go further, faster
Next time you’re out for a ride, tip your cap to Andreas Marggraf, the German chemist who first isolated the simple sugar glucose in raisins in 1747. These days glucose is the vital ingredient in gels, bars and drinks, promising peak performance and sustained endurance. But what exactly is it and how can it be manipulated to benefit performance?
The ABC of ATP
Like an engine, muscles convert chemical energy into kinetic energy. They achieve this via three energy systems – two anaerobic, one aerobic – the duration and intensity of cycling dictating which one dominates. For each, the power to contract the muscle comes from adenosine triphosphate, or ATP.
The first system uses creatine phosphate to produce enough energy for around 10 seconds of really hard effort and utilises ATP in the muscle.
But it’s the next two that are of more interest to the road cyclist. One is anaerobic glycolysis (creating energy without oxygen present), and the other is aerobic respiration (creating energy with oxygen), but essentially both create ATP by breaking down glucose.
If you have sufficient glucose and are riding at an easy enough tempo, your limbs can keep on pedalling almost indefinitely. Up the intensity, however, and you start burning through not only your blood- glucose stores but also glycogen, which is glucose stored in the liver and muscles. How much you store is down to genetics and fitness but will be around 300-500g. As each gram generates four calories of energy, that’s as little as 1,200 calories to fuel your ride. And that’s only if you follow a textbook fuelling regime.
‘Cyclists training for an hour a day should aim for 5-7g carbohydrate per kilogram of body mass per day, while those doing one to three hours should aim for 6-10g,’ says sports scientist James Carter. ‘This may represent up to 60% of total energy intake, with protein contributing 15-20% and fat the rest.’
Healthy carbs come from staples such as fruit, vegetables, beans, legumes and wholegrains. These provide a wide range of nutrients as well as stabilising blood-sugar levels by preventing insulin spikes. However, rather cleverly, you can play around with your macronutrient ratios dependent on physical goal.
‘To ensure fat loss is optimised and lean tissue maintained, daily protein intake should be increased to around 25-35%,’ says Carter. ‘Carbs can be reduced to between 40-45% of the total intake and there should be a shift towards lower glycaemic index choices. Just ensure carb intake isn’t so low that it won’t support specific training demands, especially high-intensity efforts.’
Manipulating carbohydrate and glucose intake for these specific training demands is a balancing act – one of achieving your goal without falling ill. Cue one of the more popular nutritional strategies of recent times: fasted training. The idea is that by ‘starving’ the body of carbohydrates, it adapts to burning more fat for fuel. In turn, you spare precious glycogen stores for key high-intensity moments of races, whether that’s ascending a hill or sprinting to the finish line.
How do you safely ‘starve’ yourself? If you’re an elite rider you might look at doing a morning ride to reduce muscle glycogen followed by several hours of reduced carbohydrate intake so that the evening session starts with low glycogen levels. A more practical option for most riders is to simply wait until after your morning ride to have breakfast. The most effective but most debilitating method is to perform an evening training session, restrict post-exercise carbohydrate intake during overnight recovery and then complete a fasted session before breakfast. One study showed that three weeks of this latter effort in elite triathletes and cyclists improved 20km cycling time-trial performance by 3.2%.
Research by
James Morton, formerly of Team
Sky, shows physiological adaptations are optimised with fasted sessions taking up 30-50% of training time, but that is unrealistic for recreational riders. Once a week would be a good start. Just note there are potential pitfalls to long-term low-carb training that include impaired immune function, reduced ability to train at a high intensity and increased muscle protein breakdown. In short, this type of session must be managed carefully.
Be specific
Arguably a safer management of glucose to optimise gains is proficient fuelling during rides. Research suggests you can assimilate around 60g of glucose (two gels) per hour before the transporter SGLT1, which ships glucose from the small intestine to the bloodstream, becomes saturated. But research by Professor Asker Jeukendrup showed that by adding fructose to the energy product you can tap into the fructose transporter GLUT5 and deliver more energy, up to around 90g per hour. However, this figure might be too much for many, leading to stomach issues.
If you can stomach that amount, however, work by nutritionist Kevin Currell showed you could enjoy an 8% improvement in endurance performance because of the greater amount of more readily accessible energy. Increasing
‘There are at least 42 variables that can affect blood glucose including nerves, sickness, stress, sleep, altitude, temperature and metabolism’
from 60g to 90g means you’ll ingest an extra 120 calories over the glucose-only option – 360 calories per hour against just 240 calories. Add that up over a five-hour ride and theoretically that’s an extra 600 calories you could consume without becoming bloated or nauseous.
It depends on the individual, because the breakdown of foods and glucose is influenced by myriad factors.
‘There are at least 42 variables that can affect blood glucose including nerves, sickness, stress, sleep, altitude, temperature and speed of metabolism,’ says Phil Southerland, co-founder of diabetic pro cycling outfit Team Novo Nordisk. ‘If 60g carbs an hour is what you feel you need as a rider, most of the time if that system has been working for you it’s going to be fine, but if you show up to race day and your metabolism is a little faster, so you’re burning fuel more quickly, you might need 80g an hour.’
Time to experiment
Southerland is also the co-founder of Supersapiens, a blood-glucose measuring company that has linked up with Ineos Grenadiers. He has a vested interest in highlighting the individuality of glucose absorption but independent research, plus anecdotal experience, supports his thinking.
‘Glucose is a tough thing to control and we’ve seen in the diabetes world that a plate of pasta given to four riders with similar body composition will see one person need six units of insulin, one four units, one two units and one five units. Everyone is different.’
To determine how increasing or decreasing glucose intake impacts performance, Southerland says, if you have a Tuesday afternoon set of intervals, try one fuelling strategy and see how you feel. ‘Try a different strategy the following week and compare. You’ll be able to see if a highcarb diet, for example, works for you. Do the same with base rides and you’ll become an expert on your own body.’
Glucose management helps you generate peak power output, reach race weight and protect your immune system. That’s not to mention how it impacts decision-making, boosts protein uptake and influences mood. Don’t let Marggraf’s work go to waste this summer – become a glucose expert and enjoy the sweet taste of success.