A variety of beverages are commonly used by active individuals during and after physical activity, ranging from tap and bottled water to traditional carbohydrate–electrolyte replacement drinks to more novel beverages such as milk (41,55). Indeed, in 2007, the beverage industry estimated that sports drinks alone accounted for >$1.5 billion in sales in the United States (55). Given the widespread consumption of these beverages, practical recommendations on their optimal nutrient composition and use are needed, particularly for endurance and team-sport athletes, who often compete or train with only a few hours of rest in between sessions. Thus, the purpose of this article is to summarize current research on the use of recovery beverages as it might be applied to endurance activities and to make recommendations on the optimal formula and timing of use for endurance and team-sport athletes. The literature search for the review was conducted using the PubMed, ProQuest, Journal of Strength and Conditioning Research, and MEDLINE databases and combining the search terms exercise and recovery beverages with carbohydrate electrolyte, milk, energy drink, water, juice, soda and cola, and the nutrients carbohydrates, fat, protein, amino acids, antioxidants and vitamins. In keeping with the purpose of the article, the major focus of the search was on recent studies (published between 2000 and 2009) discussing recovery from endurance exercise.
Fatigue and Recovery in Endurance Activity
Fatigue during endurance activities may result from a combination of factors, including lactate and hydrogen ion accumulation, warm temperatures, neural factors, and depletion of glycogen stores (52). During the first few minutes of intensive exercise, muscle glycogen stores are rapidly broken down to adenosine triphosphate (ATP) and quickly become depleted. Liver glycogen stores are also limited, and hypoglycemia can occur during prolonged activity if glucose uptake by exercising muscle exceeds hepatic glucose production. Thus, glycogen resynthesis is a critical part of recovery from competition and training, and when sessions are scheduled close together (e.g., championship games or multiple daily practices), recovery must be as complete as possible in a matter of hours (13).
Rehydration is also an important part of recovery. The American College of Sports Medicine recommends that athletes drink before, during, and after competition to prevent excessive fluid loss (>2% of body weight) and avoid large changes in electrolyte balance (38). A recent joint position statement by the American Dietetic Association, Dietitians of Canada, and American College of Sports Medicine recommended that athletes drink about 5–7 ml per kilogram body weight of water or a sports beverage at least 4 hours before exercise and adopt individualized hydration strategies during exercise that account for body size, sweat rate, and activity intensity to avoid a fluid deficit (1). When the recovery period is brief, athletes are encouraged to drink 1.5 L of fluid for each kilogram of body weight lost to rapidly and fully rehydrate and to choose beverages such as sports drinks that replenish electrolyte losses with about 0.3–0.7 g sodium per liter of fluid at the same time (11,38). Although solid foods can also be used to restore glycogen and electrolytes, and to some extent, fluid losses over a longer recovery period, beverages can aid in rapid restoration of these, beginning immediately after exercise, when appetite may be suppressed (38,39).
Carbohydrate and Glycogen Resynthesis during Recovery
After exercise, glycogen resynthesis occurs in 2 phases: The first occurs rapidly and without insulin for 30–60 minutes (14,26), and the second occurs more slowly and in the presence of high insulin levels over a period of several hours (17). Consequently, when a fast recovery is needed, athletes can maximize glycogen resynthesis during the insulin-independent phase by consuming carbohydrate immediately after exercise, when insulin sensitivity, glucose uptake, and glycogen synthesis are increased (13,28,45). Indeed, a study of 12 male cyclists found that rates of glycogen synthesis were 45% slower (p < 0.05) when a carbohydrate solution (1.0 g glucose·per kilogram body weight·per hour) was consumed 2 hours postexercise compared to when it was consumed immediately after the exercise (19). The rate of carbohydrate consumption throughout recovery may also affect glycogen synthesis. For example, researchers administered varying amounts of carbohydrate at 2-hour intervals during the first 6 hours after an exhaustive bout of cycling (7). They found that the rate of glycogen synthesis was greater when 0.70 g per kg body weight of glucose was given compared to when 0.35 g· per kilogram body weight of glucose was given and that there was no difference between doses of 0.70 and 1.4 g per kilogram body weight (7). The authors suggested that a “threshold” for glycogen synthesis occurs between 0.35 and 0.70 g per kilogram body weight of glucose administration (7,21). To better understand what amount of carbohydrate promotes maximal glycogen synthesis, another research team compared supplements with differing amounts of carbohydrates given at 2-hour intervals over a 4-hour recovery period after exhaustive cycling (20). Glycogen resynthesis reached its peak and plateaued with carbohydrate intakes of 1.0–1.5 g per kilogram body weight (28). The authors speculated that when postexercise carbohydrate feeding occurs at 2-hour intervals, amounts below this level of intake may be too small to maintain blood glucose and insulin adequately to promote glycogen synthesis; thus, smaller amounts of carbohydrate consumed more frequently would be required (10,28).
Equally important is the type of carbohydrate provided. In general, carbohydrates with a higher glycemic index (i.e., those that cause a rapid increase in postprandial blood glucose, such as glucose and sucrose) also promote greater muscle glycogen storage compared with carbohydrates that have a lower glycemic index (such as fructose) (9). Moderate– to high–glycemic index carbohydrates are therefore often recommended postexercise (48). Sucrose and fructose are metabolized differently by the body and thus have different effects on resynthesis of muscle glycogen. Although fructose is metabolized in the liver, most glucose is stored or oxidized by muscle so that providing either glucose or sucrose appears to yield a higher rate of skeletal muscle glycogen storage (28). When provided as a low-osmolality solution, glucose may also promote rapid gastric emptying and delivery to the intestine, thereby providing another mechanism for speeding restoration of muscle glycogen (32,42). However, recent work has also reported that consumption of a high–glycemic index meal before exercise increases glycogen use during exercise (50); thus, further work is needed before recommendations about the ideal type of carbohydrate for a recovery beverage can be made.
Carbohydrate–Electrolyte Recovery Beverages
Carbohydrate–electrolyte drinks are among the most common supplements used by athletes to replenish fluid and electrolyte losses and restore carbohydrate reserves during and between exercise sessions (24), and research has demonstrated their effectiveness in promoting recovery. For example, in a study of 16 runners completing a 90-minute run at 70% maximal oxygen uptake (O2max) followed by a 4-hour recovery and a subsequent run to exhaustion, time to fatigue during the second run was significantly longer when consuming a 6.9% carbohydrate electrolyte beverage compared to when consuming an isovolumetric placebo during the recovery (mean run time 62.0 ± 6.2 vs. 39.8 ± 6.1 minutes, p < 0.05) (12). A similar randomized, double-blind trial conducted with 90 men reported that consuming a 6.9% carbohydrate–electrolyte solution during the 4-hour recovery significantly improved subsequent run time by 24.3 ± 4.4 minutes compared to an electrolyte-free placebo and was as effective as the placebo in enabling participants to achieve positive fluid balance between exercise bouts (53). Carbohydrate–electrolyte drinks consumed after physical activity may also promote recovery from exercise in the heat. A study of 13 men running at 60% O2max for 90 minutes in a warm environment followed by a 4-hour recovery and a subsequent run to fatigue found that run time was significantly longer with the carbohydrate–electrolyte solution compared to that with a placebo (60.9 ± 5.5 vs. 44.9 ± 3.0 minutes, p < 0.01) (6).
Addition of Protein to Recovery Beverages
The consumption of other nutrients, such as protein, may also further enhance recovery and promote muscle glycogen storage after exercise. In particular, arginine and carbohydrate together increase insulin secretion 5 times as much compared to carbohydrate or arginine alone (28), and including protein with a carbohydrate-rich meal or drink likewise magnifies insulin response without causing gastrointestinal distress (28). Several other amino acids also appear to increase insulin secretion (21). For example, consuming a mixture of wheat protein hydrolysate, leucine, and phenylalanine (0.4 g·kg−1·h−1) and carbohydrate (0.8 g·kg−1·h−1) every 30 minutes for 3 or 5 hours after an exhaustive cycle ride caused a significant increase in insulin (p < 0.05) compared to when consuming the carbohydrate-only control (46,47). In particular, the branched-chain amino acids (valine, isoleucine, and leucine) may have an anabolic effect during recovery and increase the rate of protein synthesis or decrease protein degradation (8). Further work is needed to evaluate this hypothesis.
Although there is limited research on the role of individual amino acids during recovery, the addition of carbohydrate and protein together to a recovery beverage and their effects on muscle glycogen synthesis have been studied in greater detail. For instance, a study of 9 trained male cyclists assessed the effects of drinking a mixture of milk and whey protein equivalent to about 1.0 L (about 32 oz.) of milk with carbohydrate (1.5 g per kilogram body weight) immediately after and 2 hours after an exhaustive cycle ride (54). Muscle glycogen storage rates were significantly faster than when carbohydrate or protein alone was consumed (54). However, because the milk had provided additional calories compared to the carbohydrate beverage, Ivy et al. conducted a subsequent experiment with isocaloric treatments and with an isocaloric lipid–carbohydrate drink containing 6 g of fat (18). Four hours after exercise, total glycogen storage was significantly higher with the carbohydrate–protein drink compared to that with the other beverages (18), suggesting that the carbohydrate–protein beverage was more effective in replenishing muscle glycogen stores postexercise compared to a carbohydrate or lipid–carbohydrate supplement of equal calorie content. More recent research has also proposed that postexercise stimulation of glycogen synthase by insulin rather than increased plasma glucose uptake may increase muscle glycogen synthesis during recovery (22) and that the addition of protein to a carbohydrate recovery beverage may promote carbohydrate oxidation, thereby delaying fatigue during a second exercise session (4). Others have suggested that increasing the rate of carbohydrate intake from 0.8 to 1.2 g·kg−1·h−1 may promote higher rates of muscle glycogen synthesis (46) but that consuming additional protein with these amounts does not increase muscle glycogen synthesis further (21). In addition, recent work comparing nitrogen balance after ingestion of 1.2 g·kg−1·h−1 of carbohydrate with 0.4 g·kg−1·h−1 of hydrolyzed whey protein during recovery to carbohydrate only or high carbohydrate (1.6 g·kg−1·h−1) conditions over 3 hours of recovery reported increased muscle glycogen synthesis and whole-body net protein balance with the carbohydrate–protein condition (16). Collectively, these data indicate that providing carbohydrate–protein at regular intervals postexercise may be more effective than providing a single bolus, although further research is needed to compare the effects of various feeding schedules and determine which is optimal for glycogen synthesis (21).
In theory, a carbohydrate- and protein-rich recovery beverage that promotes muscle glycogen resynthesis should improve endurance performance during subsequent exercise. This has been demonstrated in several, but not all, investigations examining the topic. In one study, 10 fasted male endurance runners ran for 30 minutes at 80% of their O2max and then for 15–20 minutes at 70–75% of their O2max to deplete glycogen stores (31). Immediately after the run and 1 hour later, they received 600 ml of either a carbohydrate–protein beverage (112 g dextrose and maltodextrin with 40.7 g milk and whey protein isolate) or a carbohydrate drink (152.7 g dextrose and maltodextrin) of a similar calorie content. Each subject then completed a performance test, which involved running to exhaustion at a O2 that was 10% above his anaerobic threshold. Time to exhaustion was significantly longer after consumption of the carbohydrate–protein beverage compared to after consumption of the carbohydrate drink (540 ± 91.56 vs. 446.1 ± 97.09 seconds, p < 0.05) (31). Williams et al. compared the effects of consuming a carbohydrate–protein beverage (which included 0.42 g of glutamine and 1.42 g or arginine) or a typical carbohydrate-rich sports drink during the recovery between a glycogen-depleting exercise session and a subsequent cycling session at 85% O2max (51). They reported a 55% greater time to exhaustion with the carbohydrate–protein solution compared to that with the sports drink (51), although because the control beverage was not matched for calories, the improvements may have been because of the additional energy.
In a study of 9 male recreational runners, participants completed a 90-minute run at 70% O2max followed immediately by a 4-hour recovery during which they consumed a solution of either 1.2 or 0.8 g·kg−1·h−1 glucose and fructose alone or with 1.5% wheat protein hydrolysate every 30 minutes (3). However, no significant differences in time to exhaustion during a run (85% O2max) at the end of the recovery period were reported with either beverage (5). The authors hypothesized that differences in the type of protein (wheat vs. whey) and timing of supplementation (consuming the last beverage 30 minutes before running) used in this study compared to others may account for the lack of significant results (3). When they repeated the study with 3.3% whey protein isolate instead of wheat protein and added a high carbohydrate treatment (13.3%), both matched for energy, time to fatigue significantly increased with both the carbohydrate–protein and high carbohydrate beverages compared to the lower carbohydrate drink (5).
In one of the few studies to evaluate the use of a carbohydrate–protein recovery beverage among female athletes, 18 participants were given 1.2 g·kg−1·h−1 carbohydrate alone or with 0.3 g·kg−1·h−1 whey protein or an isovolumetric amount of noncaloric placebo during the hour after 30 minutes of downhill treadmill running to induce muscle injury (15). No significant differences on isometric quadriceps strength, muscle soreness, or serum creatine kinase were reported (15). The authors suggested that controlling for total calories served in the beverage may lessen the performance effects of added protein. In addition, research comparing a carbohydrate–protein recovery beverage (containing whey protein isolate, milk protein concentrate and cream powder) and a bar (containing whey and soy protein isolates and calcium caseinate) with an isocaloric, low-protein control given after exhaustive cycling reported that mean sprint power was unchanged at 15 hours after feeding but was 4.1% higher 60 hours (day 4) after consumption of the protein-enriched meal, suggesting that consuming carbohydrate with protein during recovery may confer a delayed benefit on performance (35,36).
Further study is thus needed to better elucidate the effects of protein and carbohydrate on glycogen storage. Specifically, many of the studies conducted have used protocols with varying amounts and types of carbohydrate and protein, a variety of procedures and participants with different levels of training, making comparisons difficult. The majority of the studies have also used male cyclists as subjects; little is known about responses among women or athletes participating in other (noncycling) activities. Finally, there is limited evidence about how athletes respond in a practical setting. Most of the studies have involved fasted subjects; in contrast, athletes usually perform exercise in a fed, nonglycogen depleted state before consuming a recovery beverage.
Addition of Antioxidants to Carbohydrate–Protein Beverages
Recent interest in the possible effects of antioxidants in exercise has led to the investigation of their possible benefit when included in recovery beverages. In theory, the addition of antioxidants (e.g., vitamins E and C) may promote recovery by ameliorating the oxidative stress and muscle damage that occurs after exercise (44). However, results of studies examining the effects of antioxidant use before exercise have been mixed, and a review of this research concluded that further work is needed before recommendations can be made (27). For example, during a 6-day supplementation trial, 23 crosscountry runners consumed 10 mL· per kilogram body weight of a beverage with 1.46 ml·per kilogram carbohydrate (control) and 0.365 mL· per kilogram body weight whey and vitamin C and E (treatment) (25). Plasma creatine kinase levels (a marker of muscle damage) and ratings of muscle soreness after 5 days were significantly lower with the carbohydrate–protein beverage (p < 0.05) (28). Because the beverages were consumed before and after exercise and were not matched for calories, the mechanisms by which the carbohydrate–protein drink may have affected recovery are unclear, although among cyclists, consuming a carbohydrate–protein–antioxidant beverage during and between exhaustive training sessions caused significant decreases in postexercise muscle soreness compared to an isocaloric amount of carbohydrate control drink (p < 0.05) (34).
Recent interest on the use of chocolate milk during recovery has prompted study of the antioxidant properties that a cocoa-based protein and carbohydrate drink may provide (29). Seven men participated in 30 minutes of downhill treadmill running (−10% grade) at 75% O2max. The study used a randomized crossover design so that subjects received either the carbohydrate–protein drink (formulated with a ratio of 3.5:1 carbohydrate:protein) before or after exercise or were given water. No significant differences in inflammatory markers and measures of skeletal muscle damage, including interleukin-6, creatine kinase, interleukin-8, C-Reactive Protein, or urinary isoprostanes were noted with consumption of the test beverage (29). However, there was a significant decrease (p = 0.03) in perceived soreness from 24 to 48 hours after exercise when the drink was consumed during the recovery period (29), suggesting that the antioxidants in cocoa itself or the combination of cocoa with carbohydrate and protein may aid in recovery. The authors suggest that a longer protocol may be needed to see changes in blood markers of inflammation and that further study is warranted (29).
Another study of runners (5 women and 3 men) compared a carbohydrate–protein recovery drink (8% sucrose, 2.3% whey protein isolate with branched-chain amino acids, glutamine and vitamins E and C), an isocaloric carbohydrate beverage (8% sucrose with 2.3% maltodextrin) and a carbohydrate–electrolyte drink (6% sucrose and glucose) (30). Participants completed a 21-km run at 70% O2max followed by a run to fatigue at 90% O2max. Beverages were fed so that participants received 1.0 g per kilogram body weight per hour during the 2-hour recovery and then repeated the run to fatigue. Twenty-four hours after the recovery protocol, participants completed a 5-km time trial after which subjective ratings of muscle soreness and plasma creatine kinase were measured. Blood glucose and insulin were significantly higher (p < 0.05) with the 10% carbohydrate drink compared to with the other beverages (30), but there were no significant differences in run time afterf the recovery or in creatine kinase. However, perceived soreness was significantly lower with the carbohydrate-protein drink compared to the 10% carbohydrate drink (rating of 2.1 ± 0.5 vs. 5.2 ± 0.7 on a scale of 0 not sore to 10 very, very sore, p < 0.05), perhaps because the carbohydrate–protein branched-chain amino acid mixture enhanced protein synthesis while limiting catabolism.
Few studies have assessed the effectiveness of antioxidants during recovery and in a beverage without added protein and carbohydrate. Thompson et al. supplemented 16 male runners with 400 mg of vitamin C per day dissolved in a noncaloric drink given immediately after and for 2 days after 90 minutes of intensive exercise but found no significant differences in muscles soreness or serum creatine kinase (44). Thus, further research is needed to clarify what role, if any, vitamins C and E or other antioxidants may play in recovery.
Other Types of Recovery Beverages and Ingredients
Several studies have also evaluated the effectiveness of novel beverages on recovery. For example, one study compared the use of a carbonated apple juice and water mixture or mineral water to plain water or a carbohydrate–electrolyte drink on restoring fluid and electrolyte balance after exercise in the heat (40). Four hours after rehydration, participants were in a negative hydration status compared to baseline with all beverages except the sports drink (40). A recent study compared the effects of 6 days of supplementation with 0.5 L beetroot juice per day vs. a placebo (black currant juice) on time to exhaustion during a cycling test to fatigue during day 6 and found a significant increase in time to exhaustion with beetroot juice (p < 0.05) (2). The authors suggested that the high concentration of nitrate in beetroot juice may, when converted to nitric oxide and nitrite, decrease the oxygen cost of low-intensity exercise by enhancing the efficiency of mitochondrial protein pumps or serving as an alternative electron acceptor during cell respiration (2).
Use of Milk during Recovery
Commercial recovery drinks typically come in 2 forms. Carbohydrate replacement drinks contain added carbohydrate to aid in glycogen resynthesis after exhaustive exercise, and fluid replacement drinks contain smaller amounts of carbohydrate with electrolytes to replace those lost during sweating (23). An ideal recovery beverage would provide both the carbohydrates and proteins needed for muscle glycogen synthesis and the fluid and electrolytes needed for rehydration, be easily obtained, palatable and well tolerated. Because milk, and in particular chocolate milk, with its high carbohydrate and protein content (including the amino acids leucine, isoleucine, phenylalanine, and arginine) and widespread popularity, meets all of these criteria and is also an excellent source of calcium, it has generated much interest as a possible recovery beverage (37).
For example, a study of 9 male endurance cyclists compared the effects of low fat chocolate milk to a fluid or carbohydrate replacement drink on postexercise recovery (23). The cyclists completed an interval workout followed by a 4-hour recovery and a subsequent cycle test to exhaustion at 70% of O2max on 3 separate occasions. During the recovery period, the subjects consumed 1 of the 3 beverages as part of a single-blind, randomized study design. Time to exhaustion and total work were significantly greater for both chocolate milk and the carbohydrate replacement drink with no significant differences in reported feelings of hunger, thirst, nausea, lightheadedness, or headache (23). Using a similar design, Thomas et al. repeated the study by Karp but this time provided the recovery beverages in isocaloric amounts so that the carbohydrate replacement beverage supplied 1.0 g carbohydrate per kilogram body weight. The other beverages were matched to the carbohydrate replacement drink so that an isocaloric amount of low fat chocolate milk and an isovolumetric amount of fluid replacement drink were given (43). During the second exercise bout, time to exhaustion was significantly longer (p = 0.01 for all) with low fat chocolate milk (32 ± 11 minutes) compared to the carbohydrate replacement drink (21 ± 8 minutes) or the fluid replacement drink (23 ± 8 minutes) (43). In contrast, a recent study comparing chocolate milk that supplied 1.0 g carbohydrate per kilogram body weight to an isocarbohydrate and isovolumetric control beverage consumed immediately and 2 hours after during exhaustive cycling found no significant differences in time to fatigue during an endurance cycle ride 15–18 hours later (33). Differences in the recovery period length make comparisons difficult, although, similar to previous findings (23), the milk was well tolerated: Participants preferred its taste and reported less gastrointestinal distress compared to the control (33).
Milk consumption during recovery also appears to effectively promote rehydration. A study of cyclists exercising at a workload of 55 ± 6% O2max in a climatic chamber at 35° C and 60–70% humidity until about 2% of total body mass was lost through sweat reported that, after consumption of skimmed milk equal to 150% of body mass lost, participants were in positive fluid and potassium balance and were euhydrated (49). In contrast, they were in negative potassium balance when an equal volume of carbohydrate–electrolyte beverage was consumed during the 3-hour recovery (49). Similarly, in a study of 5 men and 6 women cycling in a warm environment until losing about 1.7% of their body mass through sweat, urine volume was significantly increased with consumption of water and a sports drink compared to milk after exercise (p < 0.001), indicating that participants retained less of the fluid provided by the water and sports drink (41). Participants also remained in net positive fluid balance or euhydrated during the 4-hour recovery period after drinking milk but returned to a net negative fluid balance within one hour after drinking the sports drink or water (41). Collectively, these findings suggest that milk may promote rehydration better than sports drinks after heat-induced sweat loss with similar or improved outcomes during subsequent performance.
Based on the evidence to date, strength and conditioning personnel working with endurance and team-sports athletes needing to maximize glycogen resynthesis (e.g., during multiple, daily practices or tournaments) should suggest consuming about 1.2 g·kg−1 of carbohydrate as glucose and sucrose immediately after exercise and each hour thereafter or as multiple small meals for 4–6 hours postexercise (21). However, because these large amounts may be difficult to ingest when a rapid recovery is needed, a practical and equally effective alternative is to consume 0.8 g·kg−1·h−1 in combination with 0.4 g·kg−1·h−1 amino acids or protein (21). Comparisons of solid vs. liquid supplements have indicated that both are equally effective (28), but because appetite is often suppressed during the first few hours postexercise, strength and conditioning personnel should recommend liquids as the carbohydrate replacement of choice immediately after exercise (21). Liquids also provide valuable fluids for rehydration, and strength professionals should encourage athletes to use a recovery beverage that contains electrolytes, including potassium, chloride and about 0.3–0.7 g sodium·per liter of fluid, to help restore losses through sweat, retain ingested fluids and stimulate thirst to ensure continued drinking (11,38). Commercial beverages with this type of nutrient composition are effective, and recent work indicates that milk, particularly chocolate milk, may be as effective as or superior to these in promoting recovery. Current research regarding the effects of specific types of amino acids and antioxidants on recovery is mixed; thus, further investigation is needed before specific recommendations about these nutrients can be made. Future research should also include women and athletes representing a variety of sports, ages, and training levels. Consistent protocols are also needed to better understand the effects of postexercise intake on recovery.
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