CYCLING PERFORMANCE TIPS
What is an endurance ride? Any ride done at moderate speed (70 to 80 percent VO2max) for long enough that without snacking would deplete your internal glycogen stores. You would then find yourself completely dependent on fat metabolism. You will have bonked.
Let's review the physiology.
Except in states of severe malnutrition, carbohydrates and fats provide the two major fuels for endurance cycling. Both provide the energy for the production of ATP, the immediate energy source that powers muscle contraction.
How much comes from each depends strongly on how hard you are riding.
At lower exercise intensities, more than 50% of ATP can be produced from fat. As intensity increases, the contribution from carbohydrate progressively increases. The maximum rate of fat oxidation generally occurs in the range of 45 to 65% VO2max. Above this point, carbohydrate becomes increasingly important while the absolute contribution from fat falls.
Why can't the muscles burn more fat as you ride harder? The problem is not the amount of fat available. Even a lean cyclist has tens of thousands of Calories stored as body fat. The limitation is how rapidly metabolic systems in the cell can convert fat into ATP. As demand increases with higher exercise intensities, fat metabolism cannot supply ATP rapidly enough to meet the demands.
As exercise intensity approaches VO2max, 90% or more of the energy being supplied from carbohydrate and fat comes from carbohydrate, with fat and other cellular backup systems contributing the remainder. These numbers are approximate and vary with training, diet, exercise duration, and the individual cyclist, but the direction of the change is consistent: the harder you ride, the more dependent you become on carbohydrate.
What happens when you ride harder than the power you can sustain at VO2max? Your aerobic system is already operating near its maximum, so the additional ATP must come from other energy systems. Anaerobic glycolysis can rapidly produce ATP from carbohydrate without requiring oxygen. During very short maximal efforts, stored ATP and the phosphocreatine system also contribute. These systems can produce ATP rapidly, but their capacity is limited, which is why efforts substantially above VO2max can be maintained for only a relatively short time.
Training modifies this relationship. Endurance training increases the ability of muscles to oxidize fat, allowing a trained cyclist to obtain more energy from fat and conserve glycogen at any given submaximal workload. But training does not eliminate the fundamental upper limit on how rapidly fat can provide ATP. High-intensity cycling remains heavily dependent on carbohydrate.
This leads to one of the most important concepts in endurance nutrition. Your body has an enormous reserve of energy stored as fat but only a limited reserve of carbohydrate, primarily as glycogen stored in the muscles and liver. You don't bonk because your body runs out of energy. You bonk because your limited carbohydrate reserves become depleted and fat alone cannot provide ATP rapidly enough to maintain your previous pace. Your level of exertion is now limited by the maximum rate at which fat metabolism can provide ATP.
For those interested in the underlying physiology, the science of fat metabolism is covered in more detail in this paper. The relationship between fat and carbohydrate use as exercise intensity increases is also illustrated in the graph below.
Let's review the ideal strategy to maximize and extend your internal glycogen (glucose) stores for an endurance ride. More detail on the physiology.
Four days prior: Adjust carbohydrate intake to arrive at the ride with full glycogen stores rather than a deficit accumulated during training. As training tapers, a reasonable range is 5 to 8 grams of carbohydrate/kg body weight/day, with 6 g/kg/day as a reasonable target for most cyclists. For a 75-kg (165-pound) cyclist, 6 g/kg is about 450 grams of carbohydrate per day. NOTE: This is not carbohydrate loading. For unusually long or demanding events, deliberate carbohydrate loading of 10 to 12 g/kg/day for the final 24 to 48 hours may provide an additional benefit and is discussed below.
Four hours prior: This is the time to top off the tank with a carbohydrate-rich meal of 2 to 3 grams of carbohydrate/kg body weight, or about 150 to 225 grams for a 75-kg (165-pound) cyclist. For an unusually long or demanding event, an increase to 3 to 4 g/kg may provide extra endurance. As the start of the ride gets closer, large amounts of rapidly absorbed carbohydrate, particularly glucose, can produce an insulin surge and, in some cyclists, transient reactive hypoglycemia. This is more likely when simple carbohydrates are consumed during the 30 to 90 minutes before exercise. Choose familiar, easily digested carbohydrate-rich foods such as rice, pancakes, bread, cereal, or fruit, while limiting large amounts of fat and fiber that can slow stomach emptying or cause gastrointestinal problems. A carbohydrate-rich sports drink can provide some of these Calories for cyclists who have difficulty eating a large pre-ride meal if drunk 2 to 4 hours before the event.
Four minutes prior: Just before getting on the bike, take in about 20 to 30 grams of rapidly absorbed carbohydrate. At this point, simple carbohydrates are appropriate. Once you begin exercising, contracting muscles rapidly increase their uptake and use of glucose, substantially reducing the concern about an insulin surge and reactive hypoglycemia that can occur when simple carbohydrates are eaten 30 to 90 minutes before exercise. A sports drink, gel, chews, or another easily digested source of simple carbohydrate works well. The goal is to have carbohydrate entering the bloodstream as the ride begins and then continue carbohydrate replacement throughout the ride.
During the ride: Carbohydrate needs depend primarily on how long and how hard you are riding.
Start carbohydrate intake early rather than waiting until you begin to fade. Divide it into smaller amounts every 15 to 30 minutes using drinks, gels, chews, bars, or familiar foods.
Four hours after: Glycogen replacement is most rapid during the first few hours after exercise, making the first four hours an especially effective time to begin replacing the carbohydrate used during a long ride. If rapid recovery is important, aim for 1.0 to 1.2 grams of carbohydrate/kg body weight/hour for the first 3 to 4 hours post ride. For a 75-kg (165-pound) cyclist, that is about 75 to 90 grams per hour. For most recreational cyclists, a carbohydrate-rich meal after the ride followed by adequate carbohydrate during the remainder of the day will generally restore glycogen stores before the next day's ride.
The carbohydrate targets above can be met with sports drinks, gels, chews, bars, ordinary foods, or a combination. There is no physiologic requirement that carbohydrate be consumed as a liquid. The best choice is one that provides the carbohydrate you need, is easy to eat while riding, and doesn't cause gastrointestinal problems.
For lower carbohydrate intakes of 30 to 60 grams/hour, almost any easily digested carbohydrate source can work. As intake approaches 60 to 90 grams/hour, the type of carbohydrate becomes more important. Glucose absorption through the intestine begins to reach its practical limit at about 60 grams/hour. Combining glucose with fructose uses an additional intestinal transport pathway and can increase total carbohydrate absorption and oxidation to roughly 90 grams/hour or more.
This gives cyclists considerable flexibility:
Don't experiment with a new fueling strategy during an important ride or event. Practice it during training. If 60 to 90 grams/hour causes bloating, nausea, or diarrhea, begin with a lower intake and progressively increase it over several weeks. The gastrointestinal tract adapts to repeated carbohydrate intake during exercise, allowing many cyclists to tolerate higher carbohydrate delivery rates.
Here are some on-the-bike snack ideas.
How many extra dietary carbohydrates do you need to restore glycogen reserves after a long ride or during training? And is it possible to overdo replacement?
As a general rule, cycling uses 20 to 40 Calories per mile, with 30 Calories per mile a reasonable working estimate for most recreational cyclists. Actual energy expenditure varies with rider weight, speed, climbing, wind, riding position, drafting, and other factors. At typical endurance intensities, 40 to 70% of those Calories come from carbohydrate. This gives a useful estimate of 3 to 6 grams of carbohydrate used per mile, with 4 grams per mile a reasonable middle estimate.
For a more individualized estimate of your ride's energy and carbohydrate needs, use the CPTIPS Ride Needs Calculator.
On-the-bike nutrition will affect how much carbohydrate you need to replace after the ride. You will not need to eat another 3 to 6 grams of carbohydrate for every mile you rode. Carbohydrate consumed while riding has already supplied some of your energy needs and reduced the amount taken from stored glycogen. After the ride, the goal is to replace the glycogen actually depleted, not every Calorie expended during the ride. For most recreational cyclists, a carbohydrate-rich post-ride meal followed by their normal carbohydrate intake during the rest of the day will accomplish this.
Endurance training provides two important glycogen-related adaptations. First, trained muscles can obtain a greater percentage of their energy from fat at a given submaximal workload, conserving their limited glycogen supply. Second, training increases the amount of glycogen the muscles can store.
A typical cyclist may carry roughly 300 to 500 grams of muscle glycogen plus another 80 to 120 grams in the liver, for a total carbohydrate reserve of approximately 400 to 600 grams, or 1,600 to 2,400 Calories. With endurance training and high carbohydrate availability, muscle glycogen storage can increase substantially, and total glycogen stores can approach 800 to 1,000 grams under favorable conditions.
Thus training helps from both directions: you start the ride with a larger carbohydrate fuel tank and you empty it more slowly at the same riding intensity.
One study illustrates the effect of endurance training on glycogen storage. After 10 weeks of endurance training, subjects replenished muscle glycogen substantially faster following glycogen-depleting exercise. After 48 hours of recovery on a high-carbohydrate diet, muscle glycogen reached approximately 170 mmol/kg compared with about 95 mmol/kg before training, an increase of almost 80%. Training therefore not only helps conserve glycogen during exercise but also improves the muscle's ability to replenish and store it afterward.
Carbohydrate loading has been used by endurance athletes for decades. Athletes would first exercise hard enough to deplete their glycogen stores and follow that depletion phase with several days of a very high-carbohydrate diet. The theory was that the depleted muscles would respond by storing more glycogen than usual.
Experience has shown that the depletion phase isn't necessary. You can achieve much the same increase in glycogen stores by reducing your training and increasing carbohydrate intake for the day or two before an endurance event. For rides lasting less than about 90 minutes, carbohydrate loading provides little additional benefit for riders starting with normal glycogen stores. But as an event extends beyond 90 minutes, and particularly into the 2- to 4-hour plus range, the potential benefit increases.
A practical carbohydrate-loading program is to decrease your training load as you increase dietary carbohydrate to 10 to 12 grams of carbohydrate/kg body weight/day for the final 24 to 48 hours before the event. For a 75-kg (165-pound) cyclist, that means 750 to 900 grams of carbohydrate per day. It's a lot of carbohydrate and one reason not to carbohydrate load routinely when there is little to be gained.
Carbohydrate loading doesn't eliminate the need to eat during a long ride. Think of the two strategies as complementary. Carbohydrate loading lets you start with a larger glycogen fuel tank. On-the-bike carbohydrate helps you empty that tank more slowly.
For most recreational training rides, deliberate carbohydrate loading is unnecessary. Instead, maintain adequate carbohydrate intake while training, taper before an important event, and follow the on-the-bike fueling guidelines discussed above.
Bottom line: Carbohydrate loading does work. The question is whether the ride you have planned is long and demanding enough to make the extra attention it requires worthwhile.
Continuous glucose monitors (CGMs) measure glucose in the interstitial fluid surrounding cells. They are invaluable for managing diabetes, but their usefulness for guiding nutrition in healthy endurance athletes is much less certain.
The fundamental limitation is that blood or interstitial glucose is not the same as muscle glycogen. A cyclist can have a normal glucose reading while muscle glycogen stores are becoming depleted. Conversely, a high glucose reading during exercise does not necessarily mean that the muscles have adequate glycogen or that additional carbohydrate will not be needed later in the ride.
Low glucose can impair performance, but for most healthy cyclists there is little evidence that continuously monitoring glucose improves performance compared with a well-planned fueling strategy. Ride duration and intensity, combined with carbohydrate targets such as the 30 to 60 and 60 to 90 grams/hour ranges discussed above, remain more useful guides to on-the-bike fueling.
CGM can still be interesting for athletes who want to observe their individual glucose responses to food and exercise. But it should not be viewed as a fuel gauge telling you how much carbohydrate remains available to your exercising muscles.
Newer technology is also beginning to combine continuous glucose monitoring with continuous ketone monitoring (CKM). Whether adding ketone measurements will provide useful information for endurance athletes remains uncertain.
Bottom line: For most cyclists, a sound fueling plan is more useful than continuously watching a glucose number.
For a more detailed discussion of both technologies, see the CPTIPS Continuous Glucose and Ketone Monitoring page.
