This is an excerpt from NSCA's Guide to Sport and Exercise Nutrition-2nd Edition by NSCA -National Strength & Conditioning Association & Bill I. Campbell.
By Chad K. Kerksick and Shawn M. Arent
For many years, preexercise nutrient administration focused on delivering carbohydrate sources at various points before the start of exercise. Most of this initial research centered on aerobic endurance exercise, specifically cycling. In recent years, researchers have begun to explore the potential of ingesting protein, amino acids, or both (and sometimes in combination with carbohydrate) before exercise to enhance training adaptations to resistance exercise and to modulate the process of recovery to damaged muscle tissue.
Carbohydrate supplementation before resistance exercise is commonly advocated because of the known patterns of carbohydrate use that are observed in response to resistance exercise (85, 92). Although studies have clearly reported that resistance training can decrease intramuscular glycogen stores, the extent to which muscle glycogen is depleted is less than what is commonly observed for prolonged endurance exercise. But when carbohydrate supplementation was provided before resistance exercise, most studies have not reported an improvement in performance (31, 45, 78). When carbohydrate (35 g sucrose) and essential amino acids (6 g) were provided in combination either immediately before or immediately after the resistance training bout, ingestion immediately beforehand increased levels of muscle protein synthesis to a greater extent (110). A few years later, Fujita and investigators (42) completed a similar study using a slightly different isotope model and concluded that although rates of muscle protein synthesis were elevated, the timing of nutrient delivery did not affect the outcome. Later, the same authors compared the changes in muscle protein metabolism after ingesting 20 g whey protein immediately before, or immediately after, a single bout of resistance exercise. They found that whey protein ingestion (before or after) but not timing significantly increased the rate of muscle protein synthesis (107). Collectively, results from these two studies suggest that pre- or postexercise whey protein ingestion can stimulate significantly greater levels of muscle protein synthesis. But how these acute changes in protein synthesis relate to chronic adaptations, such as hypertrophy, has not been well established.
For athletes who are performing resistance training, increases in strength, power, or lean muscle mass are often the primary desired outcomes. A study by Kraemer and colleagues (75) suggested that preexercise ingestion of a multinutrient compound may modulate performance during explosive, powerful movements. In a double-blind format, subjects ingested a 25 kcal multivitamin mineral supplement containing 3 g creatine and other bioactives (e.g., 70 mg caffeine, 2 g arginine) or an isoenergetic maltodextrin placebo for seven days before reporting for two consecutive days of resistance training (75). On both exercise days, they ingested the supplement 30 minutes before the exercise bout. When compared with the placebo, the multinutrient supplement significantly improved vertical jump power and the number of repetitions performed at 80% 1RM while also increasing serum levels of hormones closely linked to muscle hypertrophy and enhanced training adaptations (i.e., growth hormone and free and total testosterone) (75). In this respect, multi-ingredient preworkout supplements (MIPS) such as those used in the study by Kraemer and colleagues have increased in popularity. Many of these formulations contain various blends or combinations of ingredients that have been purported to enhance performance. A narrative review by Harty (48) concluded that acute dosing of various MIPS can increase many indicators of performance and mood, whereas studies involving several weeks of exercise training and dosing differences are less clear and require more investigation.
Although acute studies provide detailed information about immediate responses, the additive effect of nutrient provision and several weeks of following a resistance training program are of the greatest practical interest. A small number of studies have used heavy resistance training programs over 8- to 12-week periods in conjunction with nutrient timing to determine the changes in strength and body composition. Longer-duration studies are more applicable to real-life training cycles in which athletes engage in preseason training and then lighten their training load during the season in favor of skill work and simulation of game-time situations. For example, Coburn and colleagues (23) reported that supplementation of 26 g whey protein and 6 g leucine before and after eight weeks of unilateral lower body resistance training resulted in greater increases in maximal strength (30.3% increase) over a six-week period than 26 g carbohydrate alone (22.4% increase). Similar conclusions were reached by Andersen and colleagues (1), who had healthy males resistance train for 14 weeks while supplementing with either 25 g protein or 25 g carbohydrate immediately before and again immediately after each workout. Although performance differences were modest, greater increases in markers of muscle growth were more apparent in the group that supplemented with protein.
Further research has examined the effects of protein (21, 117) taken before and after 8 and 10 weeks of resistance training, respectively. The Candow study (21) compared equal doses of whey protein and soy protein taken before and after each resistance training bout over an eight-week resistance training period. Both forms of supplementation increased strength and lean muscle mass when compared with a placebo, but no differences were found between the two sources of protein. Similarly, Willoughby and colleagues (117) had subjects resistance train four days per week for 10 weeks and ingest either 20 g protein or 20 g carbohydrate before and after each exercise bout for a daily total of 40 g. Impressively, protein supplementation increased body weight, lean muscle mass, strength, and several markers of muscle hypertrophy. Combined, these studies indicate that providing protein before and after resistance exercise is associated with greater improvements in strength, lean muscle mass, body fat percentage, serum levels of important anabolic (muscle building) hormones, and intramuscular markers of muscle hypertrophy. The additional impact of carbohydrate on these effects is somewhat unclear.
Cribb and Hayes (27) also investigated the effect of nutrient timing strategies over several weeks of supplementation and resistance training.