These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease.

Eur J Appl Physiol. 2002 Jul;87(3):290-5. Epub 2002 May 28

Carbohydrate loading in human muscle: an improved 1 day protocol.

Bussau VA, Fairchild TJ, Rao A, Steele P, Fournier PA.

Department of Human Movement and Exercise Science, The University of Western Australia, Crawley, Western Australia, Australia, 6009.

It is generally acknowledged that even without a glycogen-depleting period of exercise, trained athletes can store maximal amounts of muscle glycogen if fed a carbohydrate-rich diet for 3 days. What has never been examined is whether under these conditions this many days are necessary for the content of muscle glycogen to attain these high levels. To examine this issue, eight endurance-trained male athletes were asked to eat 10 g.day(-1).kg(-1) body mass of high-carbohydrate foods having a high glycaemic index over 3 days, while remaining physically inactive. Muscle biopsies were taken prior to carbohydrate loading and after 1 and 3 days of eating the carbohydrate-rich diet. Muscle glycogen content increased significantly ( P<0.05) from pre-loading levels of [mean (SE)] 95 (5) to 180 (15) mmol.kg(-1) wet mass after only 1 day, and remained stable afterwards despite another 2 days of carbohydrate-rich diet. Densitometric analyses of muscle sections stained with periodic acid-Schiff not only supported these findings, but also indicated that only 1 day of high carbohydrate intake was required for glycogen stores to reach maximal levels in types I, IIa, and IIb muscle fibres. In conclusion, these findings showed that combining physical inactivity with a high intake of carbohydrate enables trained athletes to attain maximal muscle glycogen contents within only 24 h.

J Sports Sci. 2006 Jul;24(7):687-97.

Nutrition on match day.

Williams C, Serratosa L.

School of Sport and Exercise Sciences, Loughborough University, UK. c.williams@lboro.ac.uk

What players should eat on match day is a frequently asked question in sports nutrition. The recommendation from the available evidence is that players should eat a high-carbohydrate meal about 3 h before the match. This may be breakfast when the matches are played around midday, lunch for late afternoon matches, and an early dinner when matches are played late in the evening. The combination of a high-carbohydrate pre-match meal and a sports drink, ingested during the match, results in a greater exercise capacity than a high-carbohydrate meal alone. There is evidence to suggest that there are benefits to a pre-match meal that is composed of low-glycaemic index (GI) carbohydrate foods rather than high-GI foods. A low-GI pre-match meal results in feelings of satiety for longer and produces a more stable blood glucose concentration than after a high-GI meal. There are also some reports of improved endurance capacity after low-GI carbohydrate pre-exercise meals. The physical demands of soccer training and match-play draw heavily on players’ carbohydrate stores and so the benefits of good nutritional practices for performance and health should be an essential part of the education of players, coaches, and in particular the parents of young players.

Nutrition. 2004 Jul-Aug;20(7-8):651-6.

Fluids and hydration in prolonged endurance performance.

Von Duvillard SP,Braun WA, Markofski M, Beneke R, Leithauser R.

Human Performance Laboratory, Department of Health, Kinesiology and Sports Studies, Texas A and M University–Commerce, Commerce, Texas 75429, USA. serge_vonduvillard@tamu-commerce.edu

Numerous studies have confirmed that performance can be impaired when athletes are dehydrated. Endurance athletes should drink beverages containing carbohydrate and electrolyte during and after training or competition. Carbohydrates (sugars) favor consumption and Na(+) favors retention of water. Drinking during competition is desirable compared with fluid ingestion after or before training or competition only. Athletes seldom replace fluids fully due to sweat loss. Proper hydration during training or competition will enhance performance, avoid ensuing thermal stress, maintain plasma volume, delay fatigue, and prevent injuries associated with dehydration and sweat loss. In contrast, hyperhydration or overdrinking before, during, and after endurance events may cause Na(+) depletion and may lead to hyponatremia. It is imperative that endurance athletes replace sweat loss via fluid intake containing about 4% to 8% of carbohydrate solution and electrolytes during training or competition. It is recommended that athletes drink about 500 mL of fluid solution 1 to 2 h before an event and continue to consume cool or cold drinks in regular intervals to replace fluid loss due to sweat. For intense prolonged exercise lasting longer than 1 h, athletes should consume between 30 and 60 g/h and drink between 600 and 1200 mL/h of a solution containing carbohydrate and Na(+) (0.5 to 0.7 g/L of fluid). Maintaining proper hydration before, during, and after training and competition will help reduce fluid loss, maintain performance, lower submaximal exercise heart rate, maintain plasma volume, and reduce heat stress, heat exhaustion, and possibly heat stroke.

Magnes Res. 1990 Jun;3(2):93-102. Links

New experimental and clinical data on the relationship between magnesium and sport.

Rayssiguier Y, Guezennec CY, Durlach J.

INRA, Laboratoire des Maladies Metaboliques, Ceyrat, France.

Exercise under certain conditions appears to lead to Mg depletion and may worsen a state of deficiency when Mg intake is inadequate. Whereas hypermagnesaemia occurs following short term high intensity exercise as the consequence of a decrease in plasma volume and a shift of cellular magnesium resulting from acidosis, prolonged submaximal exercise is accompanied by hypomagnesaemia. Discordant findings on the effect of physical exercise on erythrocyte concentrations have been reported. A mechanism for the observed decrease in plasma magnesium concentration after long term physical exercise could be a shift of Mg into the erythrocyte. However, in several studies the decrease in plasma Mg was not accompanied by an increase in RBC Mg, but a decrease in cellular Mg was observed. Urinary Mg losses during an endurance event could play a role in this depletion but are often reduced, reflecting renal compensation. Loss of Mg by sweating takes place only when there is a failure in sweat homeostasis, a situation which arises when exercise is made in conditions of damp atmosphere and high temperature. Stress caused by physical exercise is capable of inducing Mg deficit by various mechanisms. A possible explanation for decreased plasma Mg concentration during long endurance events is the effect of lipolysis. Since fatty acids are mobilized for muscle energy, lipolysis would cause a decrease in plasma Mg. In developed countries Mg intake is often marginal and sport is a factor which is particularly likely to expose athletes to Mg deficit through metabolic depletion linked to exercise itself, which can only aggravate the consequences of a frequent marginal deficiency. Mg depletion and deficiency therefore play a role in the pathophysiology of physical exercise. Experiments on animals have shown that severe Mg deficiency reduces physical performance and in particular the efficiency of energy metabolism. These data, however, do not correspond to those of marginal deficiency most commonly observed in humans. Clinical symptomatology, both in athletes and in other patients, is dominated by the symptomatology of neuromuscular hyperexcitability. Medical authorities in sport have enforced obligatory tests for latent tetany in athletes, with ionic assessment. The effects of the correction of magnesium deficiency are judged from clinical signs, Chvosteck sign, electromyogram and echocardiogram findings and plasma Mg, erythrocyte and urine analysis. These may also be complemented by cardiac and respiratory investigations after exercise. The positive effects (analysis after a minimum period of one month) of a simple oral supplement administered in physiological doses (5 mg/kg body weight/day) provides evidence for the existence of a deficiency

Cinar V, Nizamlioglu M, Mogulkoc R.

The effect of magnesium supplementation on lactate levels of sportsmen and sedanter.

Acta Physiol Hung. 2006 Jun;93(2-3):137-44.

Comment: Low dietary intakes of magnesium are common and insufficient magnesium intake decreases physical performance, furthermore physical activity increases magnesium loss through sweating and urination. Magnesium is thus an important a mineral for increasing physical performance. While previous research has shown the benefit of magnesium supplementation on physical performance this study demonstrates that the effect of magnesium may be related to improved energy metabolism and reduced lactic acid production

Schweiz Rundsch Med Prax. 2004 Mar 17;93(12):457-68.

Energy turnover in endurance exercise

Knechtle B. Thurgauer Klinik St. Katharinental, Diessenhofen. beat.knechtle@ecr.ch

During endurance exercise energy derives mainly from oxidation of carbohydrates and fat. Carbohydrates are stored in muscle and liver glycogen, fat is stored in adipose subcutaneous tissue and in intramuscular triglycerides. The intramuscular stores are the preliminary sources of fuel during muscular exercise. The principles of fat loading and carbo loading are useful in increasing the intramuscular stores before exercise. The increased muscular reserves enable the athlete to maintain a higher intensity for longer time. During exercise depletion of glycogen may be delayed by ingestion of carbohydrates. Due to the limited resorption and oxidation of carbohydrates, efficacy of ingested carbohydrates is clearly limited. Due to the limitation in energy stores in the muscles and the limitation of energy ingestion during exercise, a considerable energy deficiency in long lasting events over days has to be considered.

Curr Sports Med Rep. 2002 Aug;1(4):214-21. Links

The role of protein and amino acid supplements in the athlete’s diet: does type or timing of ingestion matter? Lemon PW, Berardi JM,Noreen EE.

2212 3M Centre, The University of Western Ontario, London, Ontario, N6A 3K7, Canada. plemon@uwo.ca

Rather than the age-old debate regarding overall protein and amino acid needs of athletes, this paper focuses on the importance of timing and type of protein and amino acid ingestion relative to both muscle growth and exercise performance. Evidence discussed comes from definitive measurement techniques including net protein balance determinations (for acute studies) or quantification of muscle size or strength (for chronic studies) First, recent data indicate that consuming a small meal of mixed macronutrient composition (or perhaps even a very small quantity of a few indispensable amino acids) immediately before or following strength exercise bouts can alter significantly net protein balance, resulting in greater gains in both muscle mass and strength than observed with training alone. With aerobic exercise, some evidence suggests immediate postexercise (but perhaps not pre-exercise) supplementation is also beneficial. Second, protein type may also be important owing to variable speeds of absorption and availability, differences in amino acid and peptide profiles, unique hormonal response, or positive effects on antioxidant defense. In addition to athletes, many others who desire to regain, maintain, or enhance muscle mass or function, including those with muscle-wasting diseases, astronauts, and all of us as we age, need to ensure that nutrient availability is sufficient during the apparently critical anabolic window of time associated with exercise training sessions. Future studies are needed to fine tune these recommendations

: Aust J Sci Med Sport. 1997 Mar;29(1):3-10. Links

Nutrition for post-exercise recovery.

Burke LM.

Australian Institute of Sport, ACT, Australia.

Recovery after exercise poses an important challenge to the modern athlete. Important issues include restoration of liver and muscle glycogen stores, and the replacement of fluid and electrolytes lost in sweat. Rapid resynthesis of muscle glycogen stores is aided by the immediate intake of carbohydrate (I g.kg-1 BM each 2 hours), particularly of high glycemic index carbohydrate foods, leading to a total intake over 24 hours of 7-10 g.kg-1 BM. Provided adequate carbohydrate is consumed it appears that the frequency of intake, the form (liquid versus solid) and the presence of other macronutrients does not affect the rate of glycogen storage. Practical considerations, such as the availability and appetite appeal of foods or drinks, and gastrointestinal comfort may determine ideal carbohydrate choices and intake patterns. Rehydration requires a special fluid intake plan since thirst and voluntary intake will not provide for full restoration of sweat losses in the acute phase (0-6 hr) of recovery. Steps should be taken to ensure that a supply of palatable drinks is available after exercise. Sweetened drinks are generally preferred and can contribute towards achieving carbohydrate intake goals. Replacement of sodium lost in sweat is important in maximising the retention of ingested fluids. A sodium content of 50-90 mmol.L-1 may be necessary for optimal rehydration; however commercial sports drinks are formulated with a more moderate sodium content (10-25 mmol.L-1). It may be necessary to consume 150% of fluid losses to allow for complete fluid restoration. Caffeine and alcohol containing beverages are not ideal rehydration fluids since they promote an increased rate of diuresis.

Nutr Clin Care. 2002 Jul-Aug;5(4):191-6. Links

What are the dietary protein requirements of physically active individuals? New evidence on the effects of exercise on protein utilization during post-exercise recovery.

Fielding RA, Parkington J.

Human Physiology Laboratory, Department of Health Sciences, Boston University, Sargent College of Health and Rehabilitation Sciences, 635 Commonwealth Avenue, Boston, MA 02215, USA. fielding@bu.edu

Exercise and physical activity increase energy expenditure up to 10-fold. This brief review will focus on the effect of exercise on protein requirements. Evidence has accumulated that amino acids are oxidized as substrates during prolonged submaximal exercise. In addition, studies have determined that both endurance and resistance training exercise increase skeletal muscle protein synthesis and breakdown in the post-exercise recovery period. Studies using nitrogen balance have further confirmed that protein requirements for individuals engaged in regular exercise are increased. The current recommended intakes of protein for strength and endurance athletes are 1.6 to 1.7 g/kg and 1.2 to 1.4 g/kg per day, respectively. Presently, most athletes consume an adequate amount of protein in their diet. The timing and nutritional content of the post-exercise meal, although often overlooked, are known to have synergistic effects on protein accretion after exercise. New evidence suggests that individuals engaging in strenuous activity consume a meal rich in amino acids and carbohydrate soon after the exercise bout or training session.

FASEB J. 2005 May;19(7):786-8. Epub 2005 Feb 16.

Selective activation of AMPK-PGC-1alpha or PKB-TSC2-mTOR signaling can explain specific adaptive responses to endurance or resistance training-like electrical muscle stimulation.

Atherton PJ,Babraj J, Smith K, Singh J, Rennie MJ, Wackerhage H.

School of Life Sciences, University of Dundee, UK.

Endurance training induces a partial fast-to-slow muscle phenotype transformation and mitochondrial biogenesis but no growth. In contrast, resistance training mainly stimulates muscle protein synthesis resulting in hypertrophy. The aim of this study was to identify signaling events that may mediate the specific adaptations to these types of exercise. Isolated rat muscles were electrically stimulated with either high frequency (HFS; 6×10 repetitions of 3 s-bursts at 100 Hz to mimic resistance training) or low frequency (LFS; 3 h at 10 Hz to mimic endurance training). HFS significantly increased myofibrillar and sarcoplasmic protein synthesis 3 h after stimulation 5.3- and 2.7-fold, respectively. LFS had no significant effect on protein synthesis 3 h after stimulation but increased UCP3 mRNA 11.7-fold, whereas HFS had no significant effect on UCP3 mRNA. Only LFS increased AMPK phosphorylation significantly at Thr172 by approximately 2-fold and increased PGC-1alpha protein to 1.3 times of control. LFS had no effect on PKB phosphorylation but reduced TSC2 phosphorylation at Thr1462 and deactivated translational regulators. In contrast, HFS acutely increased phosphorylation of PKB at Ser473 5.3-fold and the phosphorylation of TSC2, mTOR, GSK-3beta at PKB-sensitive sites. HFS also caused a prolonged activation of the translational regulators p70 S6k, 4E-BP1, eIF-2B, and eEF2. These data suggest that a specific signaling response to LFS is a specific activation of the AMPK-PGC-1alpha signaling pathway which may explain some endurance training adaptations. HFS selectively activates the PKB-TSC2-mTOR cascade causing a prolonged activation of translational regulators, which is consistent with increased protein synthesis and muscle growth. We term this behavior the “AMPK-PKB switch.” We hypothesize that the AMPK-PKB switch is a mechanism that partially mediates specific adaptations to endurance and resistance training, respectively.

Med Sci Sports Exerc. 2006 Nov;38(11):1965-70

Concurrent strength and endurance training: from molecules to man.

Nader GA.

Research Center for Genetic Medicine, Children’s National Medical Center, Washington, DC.

Strength and endurance training produce widely diversified adaptations, with little overlap between them. Strength training typically results in increases in muscle mass and muscle strength. In contrast, endurance training induces increases in maximal oxygen uptake and metabolic adaptations that lead to an increased exercise capacity. In many sports, a combination of strength and endurance training is required to improve performance, but in some situations when strength and endurance training are performed simultaneously, a potential interference in strength development takes place, making such a combination seemingly incompatible. The phenomenon of concurrent training, or simultaneously training for strength and endurance, was first described in the scientific literature in 1980 by Robert C. Hickson, and although work that followed provided evidence for and against it, the interference effect seems to hold true in specific situations. At the molecular level, there seems to be an explanation for the interference of strength development during concurrent training; it is now clear that different forms of exercise induce antagonistic intracellular signaling mechanisms that, in turn, could have a negative impact on the muscle’s adaptive response to this particular form of training. That is, activation of AMPK by endurance exercise may inhibit signaling to the protein-synthesis machinery by inhibiting the activity of mTOR and its downstream targets. The purpose of this review is to briefly describe the problem of concurrent strength and endurance training and to examine new data highlighting potential molecular mechanisms that may help explain the inhibition of strength development when strength and endurance training are performed simultaneously.

Med Sci Sports Exerc. 2006 Nov;38(11):1939-44.

Training for endurance and strength: lessons from cell signaling.

Baar K.

Division of Molecular Physiology, University of Dundee, Dundee, UNITED KINGDOM.

The classic work of Hickson demonstrated that training for both strength and endurance at the same time results in less adaptation compared with training for either one alone: this has been described as the concurrent training effect. Generally, resistance exercise results in an increase in muscle mass, and endurance exercise results in an increase in muscle capillary density, mitochondrial protein, fatty acid-oxidation enzymes, and more metabolically efficient forms of contractile and regulatory proteins. In the 25 yr since Hickson’s initial description, there have been a number of important advances in the understanding of the molecular regulation of muscle’s adaptation to exercise that may enable explanation of this phenomenon at the molecular level. As will be described in depth in the following four papers, two serine/threonine protein kinases in particular play a particularly important role in this process. Protein kinase B/Akt can both activate protein synthesis and decrease protein breakdown, thus leading to hypertrophy, and AMP-activated protein kinase can increase mitochondrial protein, glucose transport, and a number of other factors that result in an endurance phenotype. Not only are PKB and AMPK central to the generation of the resistance and endurance phenotypes, they also block each other’s downstream signaling. The consequence of these interactions is a direct molecular blockade hindering the development of the concurrent training phenotype. A better understanding of the activation of these molecular pathways after exercise and how they interact will allow development of better training programs to maximize both strength and endurance.