It’s no secret that hydration plays a crucial role during the intense days spent training on and off the bike, but what is the proper way to prehydrate, hydrate during exercise, and rehydrate during the hottest months of the year? Aside from acclimatization to hot and humid weather, hydration status plays the biggest part in thermoregulation for motocross racers. Expecting your body to perform at the highest level without enough water and electrolytes is like expecting your bike to make it through two mud motos with half the coolant the bike requires, and we saw how that went last weekend at the second round of the motocross season at Loretta’s II. But unlike a modern 4-stroke that can run with no coolant for a bit of time, a 2% loss in body weight due to sweating can result in noticeable performance decrement. Larger losses of water through sweat, as can happen during a single 35 minute moto, can result in a significant decrease in blood plasma volume, increase core body temperature, and increase heart rate (HR) and rating of perceived exertion (RPE). What all that means is poor performance, lost positions and points, and possibly lost championships and income.
Let’s talk about the heat acclimatization portion real fast. The first two to four weeks of workouts and riding need to be scaled back, or at least broken up into shorter, more manageable chunks of training to account for the body’s reduced ability to deal with heat stress. These two to four weeks are the time at which the body is most vulnerable to exertional heat illnesses. As the athlete trains in hot and humid environments, the body will acclimatize to the heat by increasing the amount of sweat produced, lower the electrolyte concentration of sweat, and decrease the temperature at which sweating starts, among other adaptations. Refer to the NSCA, ACSM, and NATA’s recommendations on returning to activity in hot environments for more in-depth information from people way smarter than myself.
Now for the MAIN EVENT: HYDRATION.
If we know that a 2% decrease in body weight can lead to performance decrements, we obviously have to try to prevent that, or replenish fluids in order to get back to pre-exercise body weight. The simplest way to “measure” hydration status after a workout or moto is the difference in body weight. Weigh yourself or your athlete “in minimal, lightweight clothing, after drying off and urinating, immediately before and after their workout,” (Haff and Triplett, 2016) and make sure any sweaty clothing is removed. Once the difference in weight from pre- to post-workout is calculated, the amount of fluid required to rehydrate can be determined. More on that later.
To get a bit more specific, you can calculate the sweat rate of your athlete during an intense one-hour workout or moto. Sweat rate = pre-exercise body weight - post-exercise body weight + fluid intake during exercise - urine produced. Once sweat rate is determined, you can ballpark how much your athlete sweats during a 35 minute moto through simple math, and make rehydrating between motos much easier.
Everybody handles the heat differently, so determining a hydration plan for yourself or your athletes is an important process of trial and error that can be conducted on training days; never try something new on a competition day! But thankfully, amazing scientists have done research to provide general recommendations for hydration science for hot environments. Sawka et al (2007) provide recommendations for pre-, during-, and post-event hydration.
Pre-event/training:
The pre-event recommendation is to drink 0.05-0.08 ounces/lb body weight in the two hours before exercise/race, or 0.08-0.12 oz/lb in the four hours before. For myself at 190lbs that comes out to about 10-15oz in the two hours before, or 15-23oz in the four hours before. This recommendation ensures you won’t be dehydrated or hyperhydrated leading up to training or racing, but will need to be tailored to each person.
During-event/training:
The during-event recommendation for prolonged activity in hot weather is to have 3-8oz of a carbohydrate/electrolyte drink every 10-20 minutes for exercise lasting 60 minutes or longer. Do any motocross athletes wear hydration packs? Heck no. Should they? Heck yes. Will they? Probably not--I’ve only seen it once (Aaron Plessinger you da man!) Of course I realize a 35 minute moto does not fall into the recommendation that I just listed because it’s shorter than 60 minutes, but the fact that there’s a second moto shortly after the first emphasizes the need for between-moto hydration with a carb/electrolyte drink. That carb/electrolyte drink should have a carbohydrate concentration of 6-8%, 460-690 mg sodium (with chloride as the anion) per liter, 78-195 mg potassium per liter, and be between 50-59°F. For example, one serving of a favorite of mine, Nuun Sport provides enough electrolytes to meet the recommendation, but has no carbs. One supplement popular in the sport is Ryno Power Hydration Fuel, which meets the electrolyte and carb recommendations, whereas Arma Blitz doesn't meet either recommendation.
Post-event/training:
The recommendation for rehydration is to drink 16-24 ounces of fluid per pound of body weight lost. You can drink just water to rehydrate in this 12-24 hour recovery period, or a sports drink with electrolytes with meals. Also remember that the foods you eat have water in them that contribute to rehydration.
General Recommendations
Here are a few things I have learned in my education, time spent racing, training, and watching the pros:
- Use water bottles with measured volumes so you are completely knowledgeable on your fluid intake and leave nothing to chance.
- Put a strip of tape on said water bottle every day and mark each time you finish a bottle so you can keep track of hydration.
- Prevent hyponatremia (low sodium concentration in the blood) by reaching for an electrolyte beverage before, during, and after training or competition instead of just water.
- Skip the moto 1 podium unless contractually obligated to do a podium speech! With only about an hour between motos, each minute not spent on recovery is one minute too many.
- Strip gear immediately and cool your body down! Whether that is done via cold water immersion, sitting in an air conditioned environment, or sitting in front of a fan, your core temperature needs to cool down between motos.
Could I go on all day about this? Yes I really could. This post is long, but for good reason. I believe that hydration science is one portion of training and racing that is lacking for most riders and trainers. As hydration science continues to become increasingly complex, these recommendations will change but they are a great place to start. I hope you have learned something by reading this! Tune in soon for my next blog post.
-Jared
References
Campbell, BI, and Spano, MA (Eds.). (2011). NSCA’s guide to sport and exercise nutrition. Human Kinetics.
Haff, GG, and Triplett, NT (Eds.). (2016). Essentials of strength training and conditioning (2nd ed.). Human Kinetics.
Sawka, MN, Burke, LM, Eichner, ER, Maughan, RJ, Mountain, SJ, and Stachenfeld, NS. American College of Sports Medicine position stand: Exercise and fluid replacement. Med Sci Sports Exerc 39:377-390, 2007.
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