Nutrition for High Intensity Exercise
- Carbohydrate stores are limited.
- At threshold intensity and higher, carbohydrate is your primary fuel source (90-100 percent).
- Carbohydrate cannot be assimilated at the same rate it is consumed.
Your fueling/hydrating goal for intermediate distance racing is not to replace everything your body consumes, but to delay glycogen depletion and dehydration/electrolyte imbalance at least until the finish line.
The sympathetic (fight/flight) and parasympathetic (resting and digesting) nervous systems are often thought of as opposing forces since they have almost exact opposite effects on many body functions. So during sustained, high intensity exercise, skeletal muscles can increase blood flow by 15 to 20 times that of resting muscle, which shunts blood flow away from non-essential functions such as digestion. So taking in nutrients during a race is not only uncomfortable, but also not as effective compared to an easy, long endurance ride. Determining how much you can handle and from what sources is something you need to experiment with during training and lower priority races.
A well thought out strategy doesn’t need to be complex, but needs to be effective and familiar. First, start with how long the race should take you. Shoot for about 240-320 calories per hour at least while you are on the bike. If you prefer to think in grams, then about 60-80 grams of CHO per hour. This can be a combination of a drink mix, energy gel, and/or solid food. If the concentration is too high then it will delay gastric emptying (sit in your stomach) until it is diluted by either water you ingest or water pulled from your body, further dehydrating you. So make sure to take in enough fluids and with a high electrolyte content. Sodium is the primary electrolyte your body loses so make sure your drink mix is formulated with at least 200 mg or more per serving. The EFS drink mix I use has 500 mg of sodium per serving.
For XTERRA racing I like to keep it simple. If the race will take around 2 hours, then I can make more mistakes with my nutrition and rely exclusively on liquid calories from my EFS drink mix. I don’t need to maximize calorie intake, but I will race better if I stay hydrated and take in some calories. If the course is more dynamic with less sustained climbing, then intensity is not as sustained which can allow you to dip back into your fat burning zones and spared some carbohydrate.
For the championship races, especially those with massive amounts of elevation gain, the energy output is the highest, most sustained, and generally race times can be 3+ hours. So for those races, shooting to maximize the amounts of water, calories and electrolytes is critical, but also needs to be practiced. I like to start with my familiar EFS drink mix and then have a 400 calorie liquid gel flask taped on my top tube that I will take during the second half of the bike along with water from aid station(s). Another thing to consider is not transporting excessive amounts of water long distances (in racing and in life). Use the aid stations, that’s what they are for. Consider carrying more than one water bottle when you have determined there is too much time between aid stations to rely on only one bottle. I personally don’t use solid food during my races, but many prefer some solids or semi-solids, especially if the intensity will be slightly lower or if you know you will be out there longer.
Write down your nutrition plan before big races so that you know exactly what to do. Seeing it on paper will help you remember it on race day. It also allows you to revisit your plan later. I know many athletes that go back to their nutrition plan after their race and make notes on how they performed and how they felt that day. This analysis can help you nail down your nutrition and will make putting together your next plan much easier.