(The information in this article was taken or adapted from the High Performance Coaching Program Study Guide.)
As previously mentioned, carbohydrates and fats are the primary energy sources utilized during a tennis practice or match. However, carbohydrate and water are the only principal nutrients that need to be consumed while playing tennis. For some players, salt intake during play is important for maintaining fluid balance and preventing heat-related muscle cramps.
Even if a player eats well the night before and has a good pre-match meal, after 60 to 90 minutes of intense singles, carbohydrate stores within the body will be significantly reduced. This will generally cause the player’s blood sugar level to begin to drop off. This could prompt lower performance and accelerate feelings of fatigue. Therefore, ingesting carbohydrates during play becomes necessary. Most adult players can burn off up to 60 grams of carbohydrate per hour during play. To offset this, a player can readily get 60 grams of carbohydrate by drinking about a liter (35 ounces) of a carbohydrate-electrolyte drink.
Carbohydrate-electrolyte sport drinks can have several distinct advantages over water alone: They
a) Provide energy in the form of carbohydrate,
b) Have been shown to delay the onset of fatigue and perception of effort,
c) Increase voluntary fluid intake, and
d) Provide electrolytes that help to maintain mineral and fluid balance.
All of these factors are important in maintaining performance, especially when playing in a hot environment (carbohydrates are used faster and a player loses more fluid through sweating). Sport drinks, designed for consumption during play, generally should have a carbohydrate concentration of 5% to 7%. This means, for each liter consumed, a player will get 50 to 70 grams of carbohydrate, respectively. Higher carbohydrate concentrations (i.e., > 10%) slow down emptying of the stomach, which, in turn, delays water and carbohydrate from getting into the bloodstream where they are needed.
When a player drinks more than 1 liter (35 ounces) during each hour of play, it is often better to drink a sport drink and plain water at each changeover (usually with an emphasis on the sport drink). Drinking just a sport drink (even if the carbohydrate content is in the 5% to 7% range) in large volumes (e.g., 1.5-2.0 liters/hour) might not be well tolerated, because too much carbohydrate could be ingested. Ingesting a high amount of fructose (via a sport drink or solid food) could also cause gastrointestinal distress, since fructose is absorbed more slowly than other carbohydrates in sport drinks like glucose, sucrose, and glucose polymers. Again, for a quick energy “boost”, a small, easily digestible, high-glycemic index snack (e.g., crackers, a plain bagel, raisins, jelly beans, etc.) can be very effective during competition or practice.
If a player has a very high sweating rate (e.g., > 2 liters per hour), it may be impossible to avoid a progressive fluid deficit. However, most older adolescents and adults can comfortably drink up to 48 ounces (~1.4 liters) per hour, which can match sweating rates (and thus prevent significant fluid deficits) for most people. Again, if a player is prone to heat cramps, a little salt can be added to their on-court sport drink (about ¼ tsp. per 32 ounces).