Nutrition Publication

NNIW75 - Nutritional Coaching Strategy to Modulate Training Efficiency

Editor(s): K. Tipton, L. van Loon. Sports Nutrition Series 75

Nutrition plays a key role in allowing the numerous training hours to be translated into useful adaptive responses of various tissues in the individual athlete. Research over the last decade has shown many examples of the impact of dietary interventions to modulate the skeletal muscle adaptive response to prolonged exercise training. Proper nutritional coaching should be applied throughout both training and competition, each with their specific requirements regarding nutrient provision. Such dietary support will improve exercise training efficiency and, as such, further increase performance capacity. Here we provide an overview on the properties of various nutritional interventions that may be useful to support the adaptive response to exercise training and competition and, as such, to augment exercise training efficiency.

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Nutritional Strategies to Modulate the Adaptive Response to Endurance Training

Author(s): J. Hawley

 In recent years, advances in molecular biology have allowed scientists to elucidate how endurance exercise training stimulates skeletal muscle remodeling (i.e. promotes mitochondrial biogenesis). A growing field of interest directly arising from our understanding of the molecular bases of training adaptation is how nutrient availability can alter the regulation of many contraction-induced events in muscle in response to endurance exercise. Acutely manipulating substrate availability can exert profound effects on muscle energy stores and patterns of fuel metabolism during exercise, as well as many processes activating gene expression and cell signaling. Accordingly, such interventions when repeated over weeks and months have the potential to modulate numerous adaptive processes in skeletal muscle that ultimately drive the phenotype-specific characteristics observed in highly trained athletes. In this review, the molecular and cellular events that occur in skeletal muscle during and after endurance exercise are discussed and evidence provided to demonstrate that nutrient availability plays an important role in modulating many of the adaptive responses to training. Emphasis is on human studies that have determined the regulatory role of muscle glycogen availability on cell metabolism, endurance training capacity and performance.

Practical Considerations for Bicarbonate Loading and Sports Performance

Author(s): L. Burke

Consumption of sodium bicarbonate (300 mg/kg 1–2 h before exercise) can temporarily increase blood bicarbonate concentrations, enhancing extracellular buffering of hydrogen ions which accumulate and efflux from the working muscle. Such ‘bicarbonate loading’ provides an ergogenic strategy for sporting events involving high rates of anaerobic glycolysis which are otherwise limited by the body’s capacity to manage the progressive increase in intracellular acidity. Studies show that bicarbonate loading strategies have a moderate positive effect on the performance of sports involving 1–7 min of sustained strenuous exercise, and may also be useful for prolonged sports involving intermittent or sustained periods of high-intensity work rates. This potential to enhance sports performance requires further investigation using appropriate research design, but may be limited by practical considerations such as gut discomfort or the logistics of the event. The effect of chronic use of bicarbonate supplementation prior to high-intensity workouts to promote better training performance and adaptations is worthy of further investigation. While this relatively simple dietary strategy has been studied and used by sports people for over 80 years, it is likely that there are still ways in which further benefits from bicarbonate supplementation can be developed and individualized for specific athletes or specific events.

Nitrate Supplementation and Exercise Performance

Author(s): A. Jones

Several recent studies indicate that supplementation of the diet with inorganic nitrate results in a significant reduction in pulmonary O 2 uptake during sub-maximal exercise, an effect that appears to be related to enhanced skeletal muscle efficiency. The physiological mechanisms responsible for this effect are not completely understood but are presumably linked to the bioconversion of ingested nitrate into nitrite and thence to nitric oxide. Nitrite and/or nitric oxide may influence muscle contractile efficiency perhaps via effects on sarcoplasmic reticulum calcium handling or actin-myosin interaction, and may also improve the efficiency of mitochondrial oxidative phosphorylation. A reduced O 2 cost of exercise can be observed within 3 h of the consumption of 5–6 mmol of nitrate, and this effect can be preserved for at least 15 days provided that the same ‘dose’ of nitrate is consumed daily. A reduced O 2 cost of exercise following nitrate supplementation has now been reported for several types of exercise including cycling, walking, running, and knee extension exercise. Dietary nitrate supplementation has been reported to extend the time to exhaustion during high-intensity constant work rate exercise by 16–25% and to enhance cycling performance over 4, 10, and 16.1 km by 1–2% in recreationally active and moderately trained subjects. Although nitrate appears to be a promising ‘new’ ergogenic aid, additional research is required to determine the scope of its effects in different populations and different types of exercise. 

Nutritional Strategies to Support Adaptation to High-Intensity Interval Training in Team Sports

Author(s): M. Gibala

Team sports are characterized by intermittent high-intensity activity patterns. Typically, play consists of short periods of very intense or all-out efforts interspersed with longer periods of low-intensity activity. Fatigue is a complex, multi-factorial process, but intense intermittent exercise performance can potentially be limited by reduced availability of substrates stored in skeletal muscle and/or metabolic by-products associated with fuel breakdown. High-intensity interval training (HIT) has been shown to induce adaptations in skeletal muscle that enhance the capacity for both oxidative and non-oxidative metabolism. Nutrient availability is a potent modulator of many acute physiological responses to exercise, including various molecular signaling pathways that are believed to regulate cellular adaptation to training. Several nutritional strategies have also been reported to acutely alter metabolism and enhance intermittent high-intensity exercise performance. However, relatively little is known regarding the effect of chronic interventions, and whether supplementation over a period of weeks or months augments HIT-induced physiological remodeling and promotes greater performance adaptations. Theoretically, a nutritional intervention could augment HIT adaptation by improving energy metabolism during exercise, which could facilitate greater total work and an enhanced chronic training stimulus, or promoting some aspect of the adaptive response during recovery, which could lead to enhanced physiological adaptations over time.

Dietary Strategies to Attenuate Muscle Loss during Recovery from Injury

Author(s): K. Tipton

Injuries are an unavoidable aspect of participation in physical activity. Nutrition is important for optimal wound healing and recovery, but little information about nutritional support for injuries exists. Immediately following injury, wound healing begins with an inflammatory response. Excessive anti-inflammatory measures may impair recovery. Many injuries result in limb immobilization. Immobilization results in muscle loss due to increased periods of negative muscle protein balance from decreased basal muscle protein synthesis and resistance to anabolic stimuli, including protein ingestion. Oxidative capacity of muscle is also decreased. Nutrient and energy deficiencies should be avoided. Energy expenditure may be reduced during immobilization, but inflammation, wound healing and the energy cost of ambulation limit the reduction of energy expenditure. There is a theoretical rationale for leucine and omega-3 fatty acid supplementation to help reduce muscle atrophy. During rehabilitation and recovery from immobilization, increased activity, in particular resistance exercise will increase muscle protein synthesis and restore sensitivity to anabolic stimuli. Ample, but not excessive, protein and energy must be consumed to support muscle growth. During rehabilitation and recovery, nutritional needs are very much like those for any athlete desiring muscle growth. The most important consideration is to avoid malnutrition and to apply a risk/benefit approach.

Role of Dietary Protein in Post-Exercise Muscle Reconditioning

Author(s): L. van Loon

 Dietary protein ingestion after exercise stimulates muscle protein synthesis, inhibits protein breakdown and, as such, stimulates net muscle protein accretion following resistance as well as endurance type exercise. Protein ingestion during and/or immediately after exercise has been suggested to facilitate the skeletal muscle adaptive response to each exercise session, resulting in more effective muscle reconditioning. A few basic guidelines can be defined with regard to the preferred type and amount of dietary protein and the timing by which protein should be ingested. Whey protein seems to be most effective to increase post-exercise muscle protein synthesis rates. This is likely attributed to its rapid digestion and absorption kinetics and specific amino acid composition. Ingestion of approximately 20 g protein during and/or immediately after exercise is sufficient to maximize post-exercise muscle protein synthesis rates. Additional ingestion of large amounts of carbohydrate does not further increase post-exercise muscle protein synthesis rates when ample protein is already ingested. Dietary protein should be ingested during and/or immediately after cessation of exercise to allow muscle protein synthesis rates to reach maximal levels. Future research should focus on the impact of the timing of protein provision throughout the day on the adaptive response to more prolonged exercise training.

Use of β-Alanine as an Ergogenic Aid

Author(s): W. Derave

Despite the large variety of so-called ergogenic supplements used by the sporting community, only few of them are effectively supported by scientific proof. One of the recent evidence-based supplements that entered the market is β-alanine. β-Alanine is the ratelimiting precursor for the synthesis of the dipeptide carnosine (β-alanyl- L -histidine) in human muscle. The chronic daily ingestion of β-alanine can markedly elevate muscle carnosine content, which results in improved exercise capacity, especially in sports that include high-intensity exercise episodes. The use of β-alanine is exponentially growing in recent years. This chapter aims to (1) discuss the scientific basis and physiological background of β-alanine and its synthesis product carnosine, and (2) translate these scientific findings to practical applications in sports.

Vitamin D Supplementation in Athletes

Author(s): E. Larson-Meyer

It is well recognized that vitamin D is necessary for optimal bone health. Emerging evidence is finding that vitamin D deficiency can have a profound effect on immunity, inflammation and muscle function. Studies in athletes have found that vitamin D status varies among different populations and is dependent on skin color, early- or late-day training, indoor training and geographic location. Although dietary assessment studies have found that athletes worldwide do not meet the dietary intake recommendations for vitamin D, the most probable reason for poor status is inadequate synthesis due to lack of sun exposure. Studies in athletic populations suggest that maintaining adequate vitamin D status may reduce stress fractures, total body inflammation, common infectious illnesses, and impaired muscle function, and may also aid in recovery from injury. Given that compromised vitamin D status can potentially impact an athlete’s overall health and training efficiency, vitamin D status should be routinely assessed so that athletes can be coached to maintain serum 25(OH)D concentration of ≥ 30 and preferably ≥ 40 ng/ml. Recommendations will be dependent on the athlete’s current 25(OH)D concentration, but can include regular safe sun exposure and/or dietary supplementation combined with increased vitamin D intake.

Weight Management in the Performance Athlete

Author(s): M. Manore

Management of weight is an ever-increasing challenge in societies where good tasting food is convenient, relatively inexpensive, and abundant. Developing a weight management plan is essential for everyone, including athletes that expend high amounts of energy in their sport. This brief review addresses the concept of dynamic energy balance and dietary approaches that can be successfully used with active individuals to facilitate weight loss, while retaining lean tissue and minimizing risks for disordered eating. Emphasis is placed on teaching athletes the benefits of consuming a low-energy-dense diet (e.g. high-fiber, high-water, low-fat foods), which allows for the consumption of a greater volume of food that is satiating but reduces energy intake. Other dietary behaviors important for weight loss or weight maintenance after weight loss are also emphasized, such as eating breakfast, spreading food and protein intake throughout the day, eating after exercise, elimination of sweetened beverages, and avoiding fad diets. As the general population becomes heavier, more young athletes will come to their sport needing to alter bodyweight or composition to perform at their peak. Health professionals need to be prepared with effective and evidence-based dietary approaches to help the athletes achieve their bodyweight goals. 

The new carbohydrate intake recommendations

Author(s): A. Jeukendrup

Carbohydrate intake during prolonged exercise has been shown to increase endurance capacity and improve performance. Until recently, the advice was to ingest 30–60 g of carbohydrate per hour. The upper limit was based on studies that demonstrated that intakes greater than 60–70 g/h would not result in greater exogenous carbohydrate oxidation rates. The lower limit was an estimated guess of the minimum amount of  carbohydrate required for ergogenic effects. In addition, the advice was independent of the type, the duration or the intensity of the activity as well as the level of athlete. Since 2004,  significant advances in the understanding of the effects of carbohydrate intake during exercise have made it possible to be much more prescriptive and individual with the advice. Studies revealed that oxidation rates can reach much higher values (up to 105 g/h) when multiple transportable carbohydrates are ingested (i.e. glucose:fructose). It has also been observed that carbohydrate ingested during shorter higher intensity exercise (1 h, 80%VO 2max) can improve performance, although mechanisms are  distinctly different. These findings resulted in new recommendations that are dependent on the duration and intensity of exercise and not only specify the quantity of carbohydrate to be ingested but also the type