Maximizing Post-Exercise Recovery with Carbohydrate plus Protein: How and Why It Works Lisa Ferguson-Stegall, PhD The University of Texas at Austin Exercise Physiology & Metabolism Laboratory The critical role of proper post-exercise nutrition has been well established through decades of scientific research and practical application. While the importance of carbohydrate intake has been well documented, recent investigations have demonstrated the effectiveness of carbohydrate plus protein supplementation in improving exercise performance in an acute bout, as well as in a second bout the same day. In addition, carbohydrate+protein supplementation post-exercise has been shown to be effective in restoring muscle glycogen, repairing muscle damage, attenuating protein degradation and initiating protein synthesis all positive outcomes that lead to improved rate of recovery and adaptation to exercise training. In this article, we describe the mechanisms by which carbohydrate+protein supplementation can improve recovery and increase training adaptations more effectively than when ingesting either nothing at all or carbohydrate only following an intense endurance exercise session. THE POST-EXERCISE STATE The body is in a catabolic state after an intense exercise session. Stress hormones are high, muscle tissues is damaged, and fuel stores such as muscle glycogen are low or
possibly depleted. Making a shift to an anabolic, or rebuilding, state must happen quickly in order to recover from the bout and adapt to the training stimulus. Endurance athletes must often compete in multiple events per day, such as in cycling stage races, or train twice per day, which means that there is little time to recover in between each bout. Therefore, to facilitate this shift quickly and adequately, proper post-exercise nutrition must be ingested, and the timing of intake must also be performed properly. We have known for many years that carbohydrate intake can maintain blood glucose and extend time to exhaustion during endurance exercise (4, 5), attenuate cytokine & immune cell perturbations (20), increase glucose & insulin levels, and restore glycogen levels (14, 29). In recent years, however, carbohydrate+protein has been shown to increase time to exhaustion in endurance exercise beyond that of carbohydrate alone, increase insulin and glycogen storage, and increase the rate of recovery such that subsequent performance later in the same day is improved. Also, carbohydrate+protein can increase the activation of pathways responsible for increased protein synthesis (11, 13, 24, 25). This is important for repairing damaged tissue and adapting to the training stimulus through the synthesis of new proteins. THE IMPORTANCE OF TIMING
The 30-60 minutes after an intense exercise session is often called the recovery window, and for a good reason. Immediately post-exercise, the muscles are more sensitive to nutritional stimuli, so this is the ideal time to take in nutrients in order to restore muscle glycogen and activate protein synthesis. Nutrient intake during this time can also help prevent additional protein breakdown that occurs in the absence of nutrient intake post-exercise (2), and can attenuate the cortisol response, which if left unchecked leads to further catabolism (19). The co-ingestion of carbohydrate and protein is more effective than either of the macronutrients alone because they activate different but cooperative signaling pathways that control glucose uptake, glycogen synthesis, and protein synthesis, as well as protein degradation. This is illustrated in the figure below. Just as skeletal muscle is most sensitive to insulin and nutritional substrate for glycogen resynthesis immediately post-exercise, the stimulation of protein synthesis, which will be discussed more below, is most responsive immediately after exercise as well. One group of researchers assessed the role of supplement timing on protein synthesis by providing a carbohydrate+protein supplement either immediately after, or 3 hours after a moderate-intensity cycling exercise bout (18). They found that when the supplement was ingested immediately post-exercise, whole body protein synthesis was increased by 300%, compared to only 12% when the supplement was delayed by 3 hours (18). This illustrates the importance of ingesting carbohydrate+protein immediately postexercise, rather than delaying supplementation.
Two key intracellular signaling pathways are activated when a supplement containing both carbohydrate and protein is ingested post-exercise. Blood glucose rises due to the carbohydrate, which stimulates an increase in blood insulin. When insulin binds to its receptor of the membrane of the muscle cells, it activates a signaling cascade, which reaches downstream targets AS160 and GSK-3. AS160 normally inhibits the process through which glucose enters the cell, but when the signaling protein Akt phosphorylates it, the inhibition is relieved and cellular glucose uptake can occur. In a similar fashion, the enzyme glycogen synthase, which controls glycogen synthesis, is normally inhibited by GSK-3. When GSK-3 is phosphorylated by Akt, the inhibition is removed and the process of glycogen synthesis can proceed. Phosphorylation of GSK-3 also affects mrna translation initiation and protein synthesis by relieving the inhibition of eif2b, which is a critical initiation factor. The protein component of the supplement increases the level of blood amino acids, which leads to activation of the mtor pathway. This pathway ultimately controls protein synthesis, which is at the heart of recovery and adaptation to the exercise stimulus. Arrows between the pathways show that the pathways interact, which amplifies the signals further. OPTIMIZING GLYCOGEN RESYNTHESIS A long, intense endurance exercise session can leave your body s carbohydrate stores (e.g., muscle and liver glycogen) extremely low or even depleted, and without adequate
carbohydrate intake, very little glycogen resynthesis and storage can occur (12, 13, 30). Ingesting carbohydrate immediately after exercise is beneficial because it provides an immediate source of fuel for muscle to use to replace the glycogen that has been used. We know that ingesting a carbohydrate supplement immediately post-exercise doubles the rate of glycogen synthesis compared to ingesting the very same supplement 2 hours following exercise (12). Although some studies have shown that more frequent supplementation such as every 15 to 30 minutes results in rates of synthesis 25-30% higher than when supplementing every two hours (8, 28), this is a high amount of carbohydrate to ingest, and simply may not be practical for many individuals. A more realistic and practical strategy is simply to ingest a supplement immediately postexercise, and again about 2 hours later. Generally, the amount of carbohydrate and protein that is most effective after prolonged endurance exercise ranges between 1.2-1.5 grams of carbohydrate per kg body weight and 0.4-0.6 grams protein per kg when provided immediately post-exercise and 2 hours later. This can be achieved in the form of commercial supplements or as a meal. TURNING ON PROTEIN SYNTHESIS FOR REPAIR AND ADAPTATION Increased muscle protein synthesis is at the heart of adaptation to exercise training. The increased proteins include contractile fibers, oxidative enzymes, mitochondria, membrane receptors, hemoglobin, substrate transporters, and many other important cellular and molecular factors that have key functions related to exercise performance.
Many investigations have shown that the addition of protein, especially the essential amino acids, to a post-exercise carbohydrate supplement can optimize protein synthesis, create a positive protein balance, repair muscle damage, and stimulate positive training adaptations (1, 7, 9, 10, 16, 17, 21, 26). Carbohydrate+protein can reduce muscle protein breakdown, primarily due to increased insulin levels. Insulin, known for its key role in clearing glucose from the blood and stimulating its uptake into cells, is one of the body s most anabolic hormones. Insulin s most powerful role postexercise is in reducing protein degradation (2, 3). Therefore, when a supplement containing carbohydrate causes an increase in insulin and the protein component provides the amino acids as building blocks for tissue repair and protein synthesis, the result is that the net protein balance shifts because the rate of synthesis now exceeds the rate of breakdown (26). Several investigations have demonstrated reduced muscle damage following intense endurance exercise in response to carbohydrate-protein supplementation compared to carbohydrate alone or a placebo treatment (6, 22-25). In one such study, trained cyclists performed an intense cycling ride to exhaustion while receiving carbohydrate, carbohydrate+protein or a placebo during the ride (27). After a 24-hour recovery period, the cyclists performed leg extensions to fatigue. The cyclists were able to perform a greater number of leg extension repetitions after having the carbohydrate+protein treatment compared to the carbohydrate or placebo treatments. In addition, the time to exhaustion during the initial cycling session was longer during the carbohydrate+protein treatment, and a significant decrease in markers of muscle damage was detected with
the carbohydrate+protein supplement after the cycling bout (27). While the mechanisms by which carbohydrate+protein may reduce muscle damage are yet to be completely elucidated, it is likely that insulin s role in reducing muscle protein degradation is a key factor. APPLYING THIS TO YOUR TRAINING AND NUTRITIONAL PLAN We all know that recovery from intense endurance exercise is a multifaceted process, and is very important. Ingestion of carbohydrate+protein supplementation after exercise can optimize many aspects of the recovery process, as well as facilitate adaptations to training. Providing carbohydrate+protein supplementation immediately and 2 hours post exercise can increase the rate and amount of muscle glycogen restoration, reduce muscle damage, and increase the rate of muscle protein synthesis to a greater degree than when ingesting carbohydrate or protein alone. This means that you can both recover and adapt better to the training stimulus. Therefore, in order to apply this nutritional strategy to your post-endurance exercise routine, ingest a beverage or a meal containing 1.2-1.5 grams of carbohydrate plus 0.4-0.6 grams protein per kg of body weight immediately after exercise and again about 2 hours later. (Whenever possible, the protein source should contain whey, as this has been found to be most effective in stimulating protein synthesis (51).) For a 70 kg
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