What these coaches and triathletes are missing is that not only can you not consume as much nutrition on the run, but you also cannot tolerate as much in your stomach or absorb it as quickly, so stocking up on nutrition before the run is a recipe for disaster.
In fact, one of the reasons the bike-run bonk is so common is that this advice is so frequently given, and followed.
2. Stay Liquid
Fluids are absorbed into the bloodstream more quickly than solid foods. Therefore I recommend you get as much of your nutrition as possible from fluids (where energy gels taken with water count as fluids) throughout the bike leg. This will not only minimize your chances of getting blocked up after the bike-run transition, but it will also maximize the rate of nutrient delivery to your blood and muscles throughout the bike leg itself.
You may swallow more calories if you chow down on a lot of energy bars during a triathlon, but you will absorb more calories if you avoid solids and stick to liquids, because they are absorbed more quickly.
3. Choose Fast-Absorbing Nutrition
Not all fluids are equal when it comes to absorption and retention. By consuming fluids that are absorbed more quickly and retained more effectively, you can actually get better hydration and faster energy delivery from less fluid. This will help you go light during the final 30 minutes of the bike leg, and throughout the run, with less risk of experiencing severe dehydration or glycogen depletion.
Two nutrients, sodium and protein, help you get more hydration per ounce of fluid consumed, while caffeine helps you absorb carbohydrate faster. Ounce for ounce, sports drinks with higher sodium concentrations provide better hydration, because they accelerate gastric emptying and improve fluid balance in the body. For this reason, use a sports drink that contains at least 15 mg of sodium per ounce.
Protein appears to enhance both fluid absorption and fluid retention. In a recent Spanish study, a carb-protein sports drink was found to empty from the stomach significantly faster than a carb-only sports drink in cyclists pedaling at 70 percent of VO2 max. And in a new study from St. Cloud State University in Minnesota, a carb-protein sports drink was retained in athletes 15 percent better than a carb-only sports drink (meaning 15 percent less of it wound up in the bladder).
Finally, the results of a new study published in the Journal of Applied Physiology suggest that caffeine may enhance the effectiveness of sports drinks consumed during exercise by accelerating the absorption of carbohydrate in the intestine.
So it's a good idea to use an energy gel with caffeine or to supplement your sports drink with caffeine from another source, especially in light of the fact that caffeine is also proven to enhance endurance performance and reduce perceived effort.
There's an easy way and a hard way to discover your personal fueling limitations. The hard way to find them is by experiencing the bike-run bonk in a long-distance race. The easy way is to do some long, race-pace brick workouts in training. In preparing for a half-Ironman, build up to at least a two-hour ride followed by a one-hour run. In preparing for a full Ironman, build up to at least a four-hour ride followed by a one-hour run.
During these workouts, fuel yourself at the maximum comfortable rate until 30 minutes remain in your ride, then go light and observe your body's response during the run. If you experience gastrointestinal distress, you know you need to go even lighter.
If you experience no GI symptoms but suffer an energy bonk, try taking in a little more nutrition next time, but don't count on being able to get away with it. You may actually have to reduce your pace to avoid both the bike-run bonk and the energy bonk.
Too Much Is no Better Than too Little
Triathletes are often panicked about getting in enough nutrition in these events, but it's actually quite easy to consume fluid and calories at the maximum rate your body can absorb them. And on the run, it's all too easy to exceed your limits, because they are so much lower than on the bike.
Make every effort to stay on the safe side of your limits, and don't fret about not getting enough nutrition. Although it may seem paradoxical, by focusing more on emptying your stomach than on filling it, you will have a better chance of avoiding both Paul's fate and the classic energy bonk in your next long-distance race.
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