This is an excerpt from Nutrition for Sport, Exercise, and Health-Loose-Leaf Edition by Marie Spano,Marie Spano,Laura Kruskall,Laura Kruskall,D. Travis Thomas & D. Travis Thomas.
The main purpose of the preexercise meal, consumed within an hour or less before resistance training, is to hydrate the athlete, top off glycogen stores, and decrease hunger. In addition, adding protein to one's preexercise meal or snack might be advantageous if the athlete hasn't consumed protein for several hours prior, or if their daily protein needs are high and the preexercise meal represents an important opportunity to help them meet their daily protein needs. For instance, a 280-pound male athlete who is trying to gain 20 pounds will have substantial daily protein needs and might find it challenging to consume the quantity of food (including protein) necessary to gain weight, particularly if he is training for several hours a day (more time spent training means less available hours to eat).
Staying hydrated is important for resistance training. Hypohydration compromises resistance-training performance and recovery. However, methodological considerations in study design make it difficult to clearly distinguish the mechanism through which hypohydration affects strength, power, and high-intensity exercise. Cardiovascular strain such as decreases in maximal cardiac output and blood flow to muscle tissue (and thus a decline in the delivery of nutrients and metabolite removal) are plausible contributing factors. The studies to date indicate dehydration of 3 to 4 percent body weight loss reduces muscle strength by approximately 2 percent, muscular power by approximately 3 percent, and high-intensity endurance activity (maximal repeated activities lasting >30 seconds but
Hypohydration also impacts the hormonal response to exercise. In one resistance training study, increasing levels of hypohydration (from 2.5% of body weight to 5% of body weight) led to progressive increases in the stress hormones cortisol and norepinephrine, and a subsequent increase in blood glucose, presumably to cope with increased physiological demands (the stress response leads to greater energy availability). These results suggest hypohydration significantly enhances stress from resistance exercise and could impair training adaptations. Over time, these changes could decrease training adaptations to resistance training if consistently performed in a hypohydrated state.
Given the impact of hypohydration on strength, power, and repetitive activity lasting more than 30 seconds but less than 2 minutes, athletes engaging in resistance-training sessions or participating in sports that require these variables, such as American football, soccer, wrestling, ice hockey, and rugby, should ensure they are adequately hydrated prior to training or competition. There are no specific pretraining guidelines for resistance exercise because any recommendations depend on hydration status prior to exercise.
Carbohydrate, from circulating blood sugar and muscle glycogen, is the primary source of fuel used during resistance training. In addition, maintaining adequate glycogen stores can help attenuate muscle breakdown during exercise and keep both the immune and nervous system functioning normally. Low carbohydrate intake can acutely suppress immune and central nervous system functioning.
Do You Know?
Muscle breakdown increases when resistance training is performed on an empty (fasted) stomach.
Consuming carbohydrate prior to training can help decrease muscular fatigue, particularly in fast-twitch muscle fibers, which tire quickly compared to slow-twitch muscle fibers; spare the use of protein as a source of energy; and perhaps also improve performance. This strategy is particularly important for athletes who exercise first thing in the morning after an overnight fast; those who haven't consumed enough carbohydrate in the time period since their last training session; and those who are lifting weights right after speed work, endurance exercise, or any other type of training that requires a significant amount of carbohydrate for energy. Like many aspects of nutrition, there is a caveat to the need for carbohydrate prior to resistance training. The body can adapt to sustained alterations in the intake of energy-yielding macronutrients (carbohydrate, protein, fat), and thus individuals on a low-carbohydrate diet might not experience any negative effects or performance decrements once adapted to this diet, provided their diet contains enough protein to build and repair muscle and energy to help spare protein losses (from protein breakdown in muscle as a source of energy). However, there is a paucity of data on this topic, so at this time low-carbohydrate diets are not recommended for those engaging in a resistance-training program.
In one study, six trained men were given either a carbohydrate supplement (1 g of carbohydrate per kg body mass before exercise and 0.17 g of carbohydrate per kg body mass every 6 minutes during the session) or a placebo sweetened with saccharin and aspartame (nonnutritive sweeteners). They performed a series of static contractions of the quadriceps at 50 percent maximum contraction with 40 seconds of rest between sets until muscle failure (i.e., they couldn't do anymore). Time to exhaustion and force output were significantly higher in the group receiving carbohydrate compared to the group consuming the placebo.
Carbohydrate loading is a technique endurance athletes have used for several decades to super-compensate glycogen stores and improve performance. In general, the athlete will taper their training program for a specified period of time - from a few days to weeks prior to an event - while consuming a higher-carbohydrate diet, generally between 8 and 10 grams of carbohydrate per kilgram body weight each day. Few studies have looked at the effect of carbohydrate loading on resistance exercise performance. However, in one study, healthy young men were randomized to receive either a moderate-carbohydrate diet (4.4 g of carbohydrate per kg body weight) or higher-carbohydrate diet (6.5 g of carbohydrate per kg body weight) for 4 days before a resistance exercise test, including 4 sets of 12 repetitions of maximal-effort jump squats with a load of 30 percent of 1 repetition maximum (1RM) and a 2-minute rest period between sets. Power performance didn't differ between groups, indicating a higher-carbohydrate diet did not enhance power-endurance performance over four sets of exercise. However, it isn't clear if an even greater intake of carbohydrate, reaching 8 to 10 grams per kilogram body weight, would have led to a performance difference or if the diet used would have made a difference over the course of several sets.
Bodybuilders might carbohydrate-load prior to competition to increase muscle size, a practice that makes sense physiologically (particularly if they consume a lower-carbohydrate diet for a few days, followed by carbohydrate loading), yet only one study to date has examined this practice. There was no change in muscle size following a low- versus high-carbohydrate diet; however, study subjects consumed the same amount of total energy during the period of low-carbohydrate intake (3 days of 10% energy from carbohydrate) as they did during the 3-day period of carbohydrate loading (80% energy from carbohydrate). Thus it is possible that a difference might have been noted if they also increased total energy intake.
Do You Know?
Muscle size and strength do not increase together in a direct linear fashion.
Protein and Amino Acids
Research shows that protein or essential amino acids (EAAs) consumed prior to resistance training will stimulate muscle protein synthesis, and prolonged supplementation can improve lean mass, body fat percentage, and muscle hypertrophy. Protein can be taken pre- or postexercise to enhance acute muscle protein synthesis.