Sports nutrition is the practical science of hydrating and fueling before and during exercise, and promoting recovery afterwards. Applied properly, it can help make you a better athlete.
But are you up on the latest developments in sports nutrition, and are you leveraging that knowledge to be your best?
If you start exercise fully fueled and well hydrated, you'll be able to go harder for longer. That translates to better workouts and more personal bests when competing.
Understanding Muscle Fueling
Appreciating the importance of being fully fueled before exercise requires an understanding of how muscle fueling takes place.
Muscles use a biochemical called
adenosine triphosphate, or ATP, as the energy source for contractions. However, your body's entire supply of ATP lasts for only a few seconds. Thus, ATP constantly needs to be reformed. At rest and during endurance exercise, ATP is continually regenerated by the breakdown of a combination of fat and carbohydrate. During low-intensity effort and when you're resting, fat is the primary energy source for ATP regeneration, and carbohydrates take a back seat. But during moderate-to-vigorous endurance exercise, carbohydrates become the primary fuel to meet the heavy demands for ATP, and fat takes more of a back seat.
At first glance, this appears to be a perfect system. Indeed, each of us has fat stores aplenty — over 80,000 calories worth are stored throughout your body! However, carbohydrate stores are in much shorter supply. Fully loaded, you have only about 2,000 calories worth stored in the liver and muscle as bundles of glucose called glycogen, and circulating in the bloodstream as glucose.
During long endurance training sessions or competitions, muscle glycogen reserves start to run dry, and glucose from the bloodstream gets tapped as a fuel source. While this is occurring, glycogen stores in the liver are gradually broken down to help maintain your blood glucose concentration. However, eventually liver glycogen stores dry up and blood glucose can no longer be maintained. At this point your blood sugar starts falling and a profound sense of fatigue sets in. Runners call it "hitting the wall" and cyclists call it "bonking" or "hunger flatting." While the names may differ by sport, the underlying cause of this fatigue is the same. You're forced to slow your pace, or even stop altogether, because all that your muscles have left to rely on is fat stores.
Given the importance of carbohydrate for fueling endurance exercise, it's critical to begin competitions or long workouts with fully loaded glycogen stores.
Variations on Pre-Exercise Fueling
So, what is the state-of-the science for loading up your glycogen stores before competing or working out?
On the day of your event, your pre-exercise meal is the opportunity to top-off muscle fuel stores, and to restore liver glycogen levels which get depleted after an overnight fast. The latest recommendations call for a pre-exercise meal of about 200–300 grams of carbohydrates about 2–4 hours prior to exercise. This can be followed by a carbohydrate snack about 1–2 hours beforehand.
But what about early-morning competitions or workouts, when you can't afford to sacrifice much-needed sleep? In that situation, consume your high-carbohydrate meal the evening before, and have a carbohydrate-rich snack in the morning, 1–2 hours before exercise.
If nerves have your stomach in a knot before the event, don't skip carbohydrates entirely. Instead, try a fruit smoothie or a liquid meal replacement supplement as a light meal alternative.
Need ideas for high-carbohydrate foods and beverages? Try some of these:
Carbohydrate-Loading
If your event requires carbohydrate loading to supermaximize muscle glycogen stores, you have a few options:
- For endurance events of less than 90 minutes in duration, rest and 7–10 grams of carbohydrate per kg body weight (3.2–4.5 grams per pound) for 24 hours before your event will load you up with muscle glycogen.
- For some athletes, combining a typical high-carbohydrate eating pattern with a rest day is all that's needed. But not all athletes eat sufficient carbohydrates in their everyday diets to maximize glycogen storage, particularly female athletes who may be restricting their calorie intake to control body fat. If you fall into this camp, temporarily raise the ceiling on total calories, and use those extra calories on carbohydrates for 1–2 days before a competition to fully replenish glycogen stores.
- For events lasting 90 minutes or longer, where glycogen stores will get depleted, tapered training and 10 grams of carbohydrates per kg body weight (4.6 grams per pound) for 2–4 days before the event is recommended.
Where athletes typically stumble with either carbohydrate-loading regimen is not tapering sufficiently, and consuming too few carbohydrates. To effectively load up on muscle fuel stores, rest or at most do light training a day or two before the event, and definitely avoid training sessions that cause significant muscle damage, as this can interfere with glycogen storage. Also, really strive to boost your intake of carbohydrates. Don't use carbohydrate loading as an exercise in loading up on fat calories.
Carbohydrate-loading isn't just for marathon runners and triathletes. Athletes in team sports like soccer and hockey have been shown to benefit from boosting muscle glycogen stores, and athletes in other sports may benefit as well. For any sport requiring endurance, attention to loading muscle glycogen stores prior to important games and tournament competitions is worth considering. And practice your loading regimen prior to a long training session or a competition of minor importance.
Understanding Hydration
Your body functions best within a relatively narrow temperature range. As you exercise, your muscles generate heat internally. That heat needs to be dissipated or you'll overheat and quickly shut down. The blood that circulates through muscle carries that internal heat to the skin where it can be released. You also sweat during exercise, and as sweat evaporates from the skin, a cooling effect takes place. In order to maintain your cooling system you need to maintain your fluid volume. That means replacing the fluid you lose as sweat.
But fluid isn't the whole story. You also lose dissolved minerals in sweat known as electrolytes. While sweat contains a handful of these electrolytes, the one lost in the greatest concentration by far, is sodium. So when your fluid losses are high, such as in high heat/humidity conditions, you're also losing lots of sodium. This sodium needs to be replaced along with fluids. If you replace those lost fluids without sodium, you'll quickly dilute the electrolyte concentration in your blood. This then signals the brain to turn off your thirst since your fluid needs have ostensibly been met. The problem is, this shutting down of the drive to drink occurs long before your true fluid needs have been met. By consuming sodium along with fluids, you retain more of that fluid, and your drive to continue to drink fluids is maintained. Thus, the combination of sodium and fluid together are more effective for rehydrating.
Most athletes lose more fluid than they are able to consume during exercise. Try not to carry fluid deficits from one workout to the next, as this increases the risk of dehydration which impairs athletic performance and poses serious health risks. To replace lost fluids after exercising and before your next workout or competition, gradually drink about 700 mL fluid (23 oz) for every pound (0.45 kg) of weight you lose during exercise. And be sure to consume sources of sodium along with the fluid.
Pre-Exercise Hydration
On the day of a competition, follow a pre-exercise hydration plan, especially if you are competing in hot/humid weather. Consume 400–600 mL fluid (14–20 oz) 2–3 hours before the start of exercise. This will allow sufficient time for urine to be eliminated before the start of the event. A hydration plan is important because, in the short-term, thirst often isn't a very accurate indicator of your true fluid needs. So don't rely on thirst to drive your fluid intake before or during exercise.
For some athletes, hydration during exercise can be enhanced by priming the stomach with about 300 mL fluid (10 oz) immediately before the event. The idea is to take advantage of the effect of distending the stomach on the rate at which fluid is released from the stomach. However, this is not something you try for the first time on event day. Practice this technique first during training sessions.
Putting it into Practice
While these recommendations reflect the cutting-edge of sports nutrition, they are guidelines, and they need to be individualized to your specific requirements and tolerances. Use your training sessions to try variations on timing and amounts of carbohydrates and fluids to identify what works best for you.
Topics:
Hydration, Energy
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