Carbohydrate and exercise

A 12-week aerobic exercise intervention results in improved metabolic function and lower adipose tissue and ectopic fat in high-fat diet fed rats

Investigations of long-term exercise interventions in humans to reverse obesity is expensive and is hampered by poor compliance and confounders. In the present study, we investigated intrahepatic and muscle fat, visceral and subcutaneous fat pads, plasma metabolic profile and skeletal muscle inflammatory markers in response to 12-week aerobic exercise in an obese rodent model. Six-week-old male Wistar rats (n=20) were randomized to chow-fed control (Control, n=5), sedentary high-fat diet (HFD, n=5), chow-fed exercise (Exercise, n=5) and HFD-fed exercise (HFD+Exercise, n=5) groups. The exercise groups were subjected to 12 weeks of motorized treadmill running at a speed of 18 m/min for 30 min/day. Differences in post-intervention measures were assessed by analysis of covariance (ANCOVA), adjusted for baseline bodyweight and pre-intervention measures, where available. Post-hoc analyses were performed with Bonferroni correction. Plasma metabolic profile was worsened and fat pads, ectopic fat in muscle and liver and inflammatory markers in skeletal muscle were elevated in sedentary HFD-fed animals relative to chow-fed controls. HFD+Exercise animals had significantly lower leptin (P=0.0004), triglycerides (P=0.007), homeostatic model assessment of insulin resistance (HOMA-IR; P=0.065), intramyocellular lipids (IMCLs; P=0.003), intrahepatic lipids (IHLs; P<0.0001), body fat% (P=0.001), subcutaneous adipose tissue (SAT; P<0.0001), visceral adipose (P<0.0001) and total fat mass (P<0.0001), relative to sedentary HFD-fed animals, despite only modestly lower bodyweight. Messenger RNA (mRNA) expression of inflammatory markers Interleukin 6 (IL6) and Tumor necrosis factor α (TNFα) were also reduced with aerobic exercise in skeletal muscle. Our results suggest that 12 weeks of aerobic exercise training is effective in improving metabolic health, fat depots, ectopic fat and inflammation even against a high-fat dietary background.

Exercise and Cardiovascular Risk among Masters Athletes with Type 2 Diabetes

PURPOSE OF REVIEW

This review was designed to provide a scientific and clinical framework for the care of physically active men and women with an emphasis on the management of T2DM.

RECENT FINDINGS

The preventative and therapeutic benefits of physical activity (PA) on adult onset or Type 2 Diabetes Mellitus (T2DM) are well established. Individuals diagnosed with or are at risk for T2DM should be counseled and maximally supported to pursue an active or athletic lifestyle. Optimally, this translates into the adoption of an athletic lifestyle. "Masters athletes", men and women above the age of 35 who regularly train for and/or participate in competitive sport, represent a rapidly growing segment of the population. Although the high level of exercise characteristic of this population has numerous health benefits, it does not confer immunity from T2DM or cardiovascular (CV) disease. Providing effective care for men and women above the age of 35 who regularly train for and/or participate in competitive sport requires an understanding of the interplay between basic exercise physiology and the pathogenesis of insulin resistance.

Nutritional implications for ultra-endurance walking and running events

This paper examines the various nutritional challenges which athletes encounter in preparing for and participating in ultra-endurance walking and running events. Special attention is paid to energy level, performance, and recovery within the context of athletes' intake of carbohydrate, protein, fat, and various vitamins and minerals. It outlines, by way of a review of literature, those factors which promote optimal performance for the ultra-endurance athlete and provides recommendations from multiple researchers concerned with the nutrition and performance of ultra-endurance athletes. Despite the availability of some research about the subject, there is a paucity of longitudinal material which examines athletes by nature and type of ultra-endurance event, gender, age, race, and unique physiological characteristics. Optimal nutrition results in a decreased risk of energy depletion, better performance, and quicker full-recovery.

Physiologic and performance effects of sago supplementation before and during cycling in a warm-humid environment

The present study determined whether 0.8g/kg bodyweight sago ingested before (Pre-Sago) or during (Dur-Sago) exercise under warm-humid conditions (30 ± 2°C, 78 ± 3 % RH; 20 km·h⁻¹ frontal airflow) conferred a performance and/or physiological benefit compared to a control (Control) condition. Eight trained, male cyclists/triathletes (45 ± 4 y, VO₂peak: 65 ± 10 ml·kg⁻¹·min⁻¹, peak aerobic power: 397 ± 71 W) completed 3 15-min time-trials (∼75% VO₂peak) pre-loaded with 45 min of steady-state (∼55% VO₂peak) cycling following > 24 h standardization of training and diet. Measures of work completed, rectal and mean skin temperatures, heart rate, expiratory gases and venous blood samples were taken. Compared to Control, Pre-Sago resulted in a smaller rise in rectal temperature (0.3 ± 0.5°C) while heart rate increased to a greater extent (6 ± 13 beats·min⁻¹) during exercise (both P < 0.05), however, compared to Control time-trial performance remained unaffected (Pre-Sago: −0.5 ± 4.0%, P > 0.05). During exercise, plasma glucose concentrations were maintained higher for Dur-Sago than Control (P < 0.05), however substrate oxidation rates remained similar (P > 0.05). Dur-Sago also resulted in a higher plasma sodium concentration (2 ± 2 mmol·l¹) and lower whole-body sweat loss (544 ± 636 g) and, therefore, reduced plasma volume contraction (all P < 0.05). Heart rate increased to a greater extent (5 ± 13 beats·min⁻¹) during Dur-Sago, yet compared to Control time-trial performance remained unaffected (+0.9 ± 2.3%, P > 0.05). Uniquely, these results indicate that during exercise heat stress feeding sago can result in some ‘beneficial’ physiological responses, however these do not translate to changes in exercise performance when performed in a post-prandial state.

Exercise Inducible Lactate Dehydrogenase B Regulates Mitochondrial Function in Skeletal Muscle

Lactate dehydrogenase (LDH) catalyzes the interconversion of pyruvate and lactate, which are critical fuel metabolites of skeletal muscle particularly during exercise. However, the physiological relevance of LDH remains poorly understood. Here we show that Ldhb expression is induced by exercise in human muscle and negatively correlated with changes in intramuscular pH levels, a marker of lactate production, during isometric exercise. We found that the expression of Ldhb is regulated by exercise-induced peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). Ldhb gene promoter reporter studies demonstrated that PGC-1α activates Ldhb gene expression through multiple conserved estrogen-related receptor (ERR) and myocyte enhancer factor 2 (MEF2) binding sites. Transgenic mice overexpressing Ldhb in muscle (muscle creatine kinase (MCK)-Ldhb) exhibited increased exercise performance and enhanced oxygen consumption during exercise. MCK-Ldhb muscle was shown to have enhanced mitochondrial enzyme activity and increased mitochondrial gene expression, suggesting an adaptive oxidative muscle transformation. In addition, mitochondrial respiration capacity was increased and lactate production decreased in MCK-Ldhb skeletal myotubes in culture. Together, these results identified a previously unrecognized Ldhb-driven alteration in muscle mitochondrial function and suggested a mechanism for the adaptive metabolic response induced by exercise training.

Sago supplementation for exercise performed in a thermally stressful environment: Rationale, efficacy and opportunity

Sago (Metroxylin sagu), a carbohydrate (CHO) based dietary staple of Southeast Asia is easily digestible and quickly absorbed, and thus has potential to be prescribed as an affordable pre-and post-exercise food in this part of the world. Compared to other CHO staples, research into the physiological response to sago ingestion is sparse, and only a few recent studies have investigated its value before, during, and after exercise. The purpose of this review is to describe the published literature pertaining to sago, particularly as a supplement in the peri-exercise period, and suggest further avenues of research, principally in an environment/climate which would be experienced in Southeast Asia i.e. hot/humid.

Nutritional behaviour and beliefs of ski-mountaineers: a semi-quantitative and qualitative study

BACKGROUND

Endurance athletes are advised to optimize nutrition prior to races. Little is known about actual athletes' beliefs, knowledge and nutritional behaviour. We monitored nutritional behaviour of amateur ski-mountaineering athletes during 4 days prior to a major competition to compare it with official recommendations and with the athletes' beliefs.

METHODS

Participants to the two routes of the 'Patrouille des Glaciers' were recruited (A, 26 km, ascent 1881 m, descent 2341 m, max altitude 3160 m; Z, 53 km, ascent 3994 m, descent 4090 m, max altitude 3650 m). Dietary intake diaries of 40 athletes (21 A, 19 Z) were analysed for energy, carbohydrate, fat, protein and liquid; ten were interviewed about their pre-race nutritional beliefs and behaviour.

RESULTS

Despite belief that pre-race carbohydrate, energy and fluid intake should be increased, energy consumption was 2416 ± 696 (mean ± SD) kcal · day(-1), 83 ± 17% of recommended intake, carbohydrate intake was only 46 ± 13% of minimal recommended (10 g · kg(-1) · day(-1)) and fluid intake only 2.7 ± 1.0 l · day(-1).

CONCLUSIONS

Our sample of endurance athletes did not comply with pre-race nutritional recommendations despite elementary knowledge and belief to be compliant. In these athletes a clear and reflective nutritional strategy was lacking. This suggests a potential for improving knowledge and compliance with recommendations. Alternatively, some recommendations may be unrealistic.

Acute nutritional ketosis: implications for exercise performance and metabolism

Ketone bodies acetoacetate (AcAc) and D-β-hydroxybutyrate (βHB) may provide an alternative carbon source to fuel exercise when delivered acutely in nutritional form. The metabolic actions of ketone bodies are based on sound evolutionary principles to prolong survival during caloric deprivation. By harnessing the potential of these metabolic actions during exercise, athletic performance could be influenced, providing a useful model for the application of ketosis in therapeutic conditions. This article examines the energetic implications of ketone body utilisation with particular reference to exercise metabolism and substrate energetics.

Acute effects of physical exercise in type 2 diabetes: A review

The literature has shown the efficiency of exercise in the control of type 2 diabetes (T2D), being suggested as one of the best kinds of non-pharmacological treatments for its population. Thus, the scientific production related to this phenomenon has growing exponentially. However, despite its advances, still there is a lack of studies that have carried out a review on the acute effects of physical exercise on metabolic and hemodynamic markers and possible control mechanisms of these indicators in individuals with T2D, not to mention that in a related way, these themes have been very little studied today. Therefore, the aim of this study was to organize and analyze the current scientific production about the acute effects of physical exercise on metabolic and hemodynamic markers and possible control mechanisms of these indicators in T2D individuals. For such, a research with the following keywords was performed: -exercise; diabetes and post-exercise hypotension; diabetes and excess post-exercise oxygen consumption; diabetes and acute effects in PUBMED, SCIELO and HIGHWIRE databases. From the analyzed studies, it is possible to conclude that, a single exercise session can promote an increase in the bioavailability of nitric oxide and elicit decreases in postexercise blood pressure. Furthermore, the metabolic stress from physical exercise can increase the oxidation of carbohydrate during the exercise and keep it, in high levels, the post exercise consumption of O_², this phenomenon increases the rate of fat oxidation during recovery periods after exercise, improves glucose tolerance and insulin sensitivity and reduces glycemia between 2-72 h, which seems to be dependent on the exercise intensity and duration of the effort.

Personal food systems of male collegiate football players: a grounded theory investigation

CONTEXT

Factors that affect food choices include the physical and social environments, quality, quantity, perceived healthfulness, and convenience. The personal food choice process was defined as the procedures used by athletes for making food choices, including the weighing and balancing of activities of daily life, physical well-being, convenience, monetary resources, and social relationships.

OBJECTIVE

To develop a theoretical model explaining the personal food choice processes of collegiate football players.

DESIGN

Qualitative study.

SETTING

National Collegiate Athletic Association Division II football program.

PATIENTS OR OTHER PARTICIPANTS

Fifteen football players were purposefully sampled to represent various positions, years of athletic eligibility, and ethnic backgrounds.

DATA COLLECTION AND ANALYSIS

For text data collection, we used predetermined, open-ended questions. Data were analyzed using the constant comparison method. The athletes' words were used to label and describe their interactions and experiences with the food choice process. Member checks and an external audit were conducted by a qualitative methodologist and a nutrition specialist, and the findings were triangulated with the current literature to ensure trustworthiness of the text data.

RESULTS

Time was the core category and yielded a cyclic graphic of a theoretical model for the food choice system. Planning hydration, macronutrient strategies, snacks, and healthful food choices emerged as themes.

CONCLUSIONS

The athletes planned meals and snacks around their academic and athletic schedules while attempting to consume foods identified as healthful. Healthful foods were generally lower in fat but high in preferred macronutrients. High-protein foods were the players' primary goal; carbohydrate consumption was secondary. The athletes had established plans to maintain hydration. Professionals may use these findings to implement educational programs on food choices for football players.

The nuclear receptor PPARβ/δ programs muscle glucose metabolism in cooperation with AMPK and MEF2

To identify new gene regulatory pathways controlling skeletal muscle energy metabolism, comparative studies were conducted on muscle-specific transgenic mouse lines expressing the nuclear receptors peroxisome proliferator-activated receptor α (PPARα; muscle creatine kinase [MCK]-PPARα) or PPARβ/δ (MCK-PPARβ/δ). MCK-PPARβ/δ mice are known to have enhanced exercise performance, whereas MCK-PPARα mice perform at low levels. Transcriptional profiling revealed that the lactate dehydrogenase b (Ldhb)/Ldha gene expression ratio is increased in MCK-PPARβ/δ muscle, an isoenzyme shift that diverts pyruvate into the mitochondrion for the final steps of glucose oxidation. PPARβ/δ gain- and loss-of-function studies in skeletal myotubes demonstrated that PPARβ/δ, but not PPARα, interacts with the exercise-inducible kinase AMP-activated protein kinase (AMPK) to synergistically activate Ldhb gene transcription by cooperating with myocyte enhancer factor 2A (MEF2A) in a PPARβ/δ ligand-independent manner. MCK-PPARβ/δ muscle was shown to have high glycogen stores, increased levels of GLUT4, and augmented capacity for mitochondrial pyruvate oxidation, suggesting a broad reprogramming of glucose utilization pathways. Lastly, exercise studies demonstrated that MCK-PPARβ/δ mice persistently oxidized glucose compared with nontransgenic controls, while exhibiting supranormal performance. These results identify a transcriptional regulatory mechanism that increases capacity for muscle glucose utilization in a pattern that resembles the effects of exercise training.

Effects of high-dose large neutral amino acid supplementation on exercise, motor skill, and mental performance in Australian Rules Football players

This study investigated the effects of high-dose large neutral amino acid (LNAA) supplementation on attenuating fatigue-induced decrements in exercise and motor skill performance in Australian Rules Football (ARF) players. Fifteen subelite ARF players participated in 3 testing sessions separated by 7 days. Players completed an initial control trial involving a reactive motor skills test (RMST) and a reactive agility test (RAT) carried out before and after fatiguing exercise. In the subsequent experimental trials, players ingested a serotonin-depleting or protein control (PC) LNAA mixture 3 h before testing, allocated in a double-blind randomized cross-over design. Blood samples were taken at presupplementation and pre- and postexercise for analysis of plasma amino acid, insulin, and metabolite concentrations. The effect of the LNAA was established as the difference in the change in the mean RMST and RAT test scores among the depleting, PC, and baseline (BL) trials. Mean overall repetition time of the RAT was moderately improved by -5.2% ± 3.4% (mean ± 90% confidence limits; effect size -0.45 ± 0.28) after ingestion of the serotonin-depleting mixture compared with the BL trial. Serotonin-depleting and PC supplements had a divergent effect on mean repetition time after fatiguing exercise in RMST: depleting serotonin elicited a small improvement (-3.0% ± 2.7%) in motor skill performance in contrast to a small decrement (2.4% ± 2.7%) after ingestion of the PC mixture, when compared to the BL. High-dose serotonin-"depleting" LNAA supplementation given 3 h prior to intermittent high-intensity exercise improved reactive motor skill and agility performance in ARF players.

Exercise and type 2 diabetes: American College of Sports Medicine and the American Diabetes Association: joint position statement. Exercise and type 2 diabetes

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes mellitus (T2DM), many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay T2DM, along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower T2DM risk by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. The benefits of physical training are discussed, along with recommendations for varying activities, PA-associated blood glucose management, diabetes prevention, gestational diabetes, and safe and effective practices for PA with diabetes-related complications.

Exercise and type 2 diabetes: the American College of Sports Medicine and the American Diabetes Association: joint position statement

Although physical activity (PA) is a key element in the prevention and management of type 2 diabetes, many with this chronic disease do not become or remain regularly active. High-quality studies establishing the importance of exercise and fitness in diabetes were lacking until recently, but it is now well established that participation in regular PA improves blood glucose control and can prevent or delay type 2 diabetes, along with positively affecting lipids, blood pressure, cardiovascular events, mortality, and quality of life. Structured interventions combining PA and modest weight loss have been shown to lower type 2 diabetes risk by up to 58% in high-risk populations. Most benefits of PA on diabetes management are realized through acute and chronic improvements in insulin action, accomplished with both aerobic and resistance training. The benefits of physical training are discussed, along with recommendations for varying activities, PA-associated blood glucose management, diabetes prevention, gestational diabetes mellitus, and safe and effective practices for PA with diabetes-related complications.

Energy and macronutrient requirements for physical fitness in exercising subjects

Optimal nutritional intakes are critical for health- and skill-related physical fitness. This review details the effect of energy restriction and supplementation on physical fitness, discusses the optimal chronic macronutrient intakes for physical fitness in exercising subjects and finally overviews the impact of short-term intakes of carbohydrate and protein, before, during and after exercise, on physical fitness of athletes. The present standings highlight that it is essential that health care givers personalize nutritional advice to meet the specific needs of exercising individuals while applying the described recommendations. It reminds the difficulty of providing straight nutritional recommendations for physical fitness on the basis of evidence-based medicine.

Energy balance during two days of continuous stationary cycling

This study examined the capabilities of an ultraendurance athlete to self-regulate their diet during an attempt on the record for the longest period of stationary cycling. The attempt required the athlete to complete at least 20 km/hr, with a 15 minute break allowed every eight hours. Laboratory tests determined a heart rate-oxygen consumption regression equation enabling calculation of energy expenditure from heart rate during the attempt. Energy intake was determined by a non-weighed dietary record collected at the time of consumption. The athlete completed 46.7 hours, covering 1126 km, at a speed of 24 +/- 1.6 km/hr. He expended 14486 kcal and consumed 11098 kcal resulting in an energy deficit (-3290 kcal) and a weight loss (-0.55 kg). The carbohydrate (42 +/- 32 g/hr), water (422 +/- 441 ml/hr), and sodium (306 +/- 465 mg/hr) intake were all below current recommendations. The athlete was unable to self-regulate his diet or exercise intensity to prevent a negative energy balance.

Glycogen resynthesis and exercise performance with the addition of fenugreek extract (4-hydroxyisoleucine) to post-exercise carbohydrate feeding

The purpose of this study was to determine the effect of adding fenugreek extract (FG) to post-exercise carbohydrate feeding on glycogen resynthesis and subsequent exercise performance in normoglycemic male endurance athletes. A muscle biopsy sample was obtained from the vastus lateralis from subjects prior to exercise for 5 h at 50% of peak cycling power (52.1 +/- 3.3% of VO(2) peak). A second muscle biopsy sample was obtained immediately after exercise. Immediately after and 2 h after the second biopsy subjects ingested either an oral dose of dextrose (GLU) (1.8 g x kg BW(-1)) or GLU with FG containing 1.99 +/- 0.20 mg x kg(-1) 4-hydroxyisoleucine (GLU + FG) in a randomized, cross-over, double blind design. At 4 h post-exercise a third biopsy was taken and subjects received a standardised meal along with FG or a placebo capsule. At 15 h post-exercise subjects underwent their final muscle biopsy before completing a simulated 40 km cycling time trial. There was no difference in muscle glycogen at any time between GLU and GLU + FG. Additionally, 40 km time trial performance was similar for average power output (221 +/- 28 vs. 213 +/- 16 watts) and for time to completion (69.7 +/- 3.7 vs. 70.5 +/- 2.2 min) for the GLU and GLU + FG, respectively. Despite earlier data to the contrary, the present results do not support an effect of fenugreek supplementation on glycogen resynthesis, even though this may have been the result of differences in experimental protocol.

Gender differences in carbohydrate metabolism and carbohydrate loading

Prior to endurance competition, many endurance athletes participate in a carbohydrate loading regimen in order to help delay the onset of fatigue. The "classic" regimen generally includes an intense glycogen depleting training period of approximately two days followed by a glycogen loading period for 3–4 days, ingesting approximately 60–70% of total energy intake as carbohydrates, while the newer method does not consist of an intense glycogen depletion protocol. However, recent evidence has indicated that glycogen loading does not occur in the same manner for males and females, thus affecting performance. The scope of this literature review will include a brief description of the role of estradiol in relation to metabolism and gender differences seen in carbohydrate metabolism and loading.

Nutritional considerations in triathlon

Triathlon combines three disciplines (swimming, cycling and running) and competitions last between 1 hour 50 minutes (Olympic distance) and 14 hours (Ironman distance). Independent of the distance, dehydration and carbohydrate (CHO) depletion are the most likely causes of fatigue in triathlon, whereas gastrointestinal (GI) problems, hyperthermia and hyponatraemia are potentially health threatening, especially in longer events. Although glycogen supercompensation may be beneficial for triathlon performance (even Olympic distance), this does not necessarily have to be achieved by the traditional supercompensation protocol. More recently, studies have revealed ways to increase muscle glycogen concentrations to very high levels with minimal modifications in diet and training. During competition, cycling provides the best opportunity to ingest fluids. The optimum CHO concentration seems to be in the range of 5-8% and triathletes should aim to achieve a CHO intake of 60-70 g/hour. Triathletes should attempt to limit body mass losses to 1% of body mass. In all cases, a drink should contain sodium (30-50 mmol/L) for optimal absorption and prevention of hyponatraemia.Post-exercise rehydration is best achieved by consuming beverages that have a high sodium content (>60 mmol/L) in a volume equivalent to 150% of body mass loss. GI problems occur frequently, especially in long-distance triathlon. Problems seem related to the intake of highly concentrated carbohydrate solutions, or hyperosmotic drinks, and the intake of fibre, fat and protein. Endotoxaemia has been suggested as an explanation for some of the GI problems, but this has not been confirmed by recent research. Although mild endotoxaemia may occur after an Ironman-distance triathlon, this does not seem to be related to the incidence of GI problems. Hyponatraemia has occasionally been reported, especially among slow competitors in triathlons and probably arises due to loss of sodium in sweat coupled with very high intakes (8-10 L) of water or other low-sodium drinks.

Training Principles and Issues for Ultra-endurance Athletes

Ultra-endurance competition is defined as events that exceed than 6 hours in duration. The longer events rely on long-term preparation, sufficient nutrition, accommodation of environmental stressors, and psychologic toughness. Successful ultra-endurance performance is characterized by the ability to sustain a higher absolute speed for a given distance than other competitors. This can be achieved through a periodized training plan and by following key principles of training. Periodization is an organization of training into large, medium and small training blocks which are referred to as macro-, meso-, and microcycles, respectively. When the sequencing of training is correctly applied, athletes can achieve a high state of competition readiness and during the months of hard training, avoid the overtraining syndrome. A plan is executed in accordance with the following principles of training: all-around development, overload, specificity, individualization, consistent training, and structural tolerance. Training relies heavily on the athlete's tolerance to repetitive strain. Today's ultra-endurance athlete must also follow appropriate nutritional practices in order to recover and prepare for daily training and remain injury free and healthy. Rehydration after exercise, together with the timing and method of increased food intake to cope with heavy training, are essential for optimal performance. Furthermore, the treatment of soft tissue after training or racing is necessary to control inflammation.

Nutritional concerns for the child and adolescent competitor

With exercise for sports competition in children and adolescents, acute nutrient needs will change. Fluid intake to ensure the replacement of water and minerals (electrolytes) lost in sweat is important. Energy needs also increase because of the elevated energy expenditure with physical activity. Arguably carbohydrate is the recommended source of training needs, although research has yet to be done to show performance benefits in young athletes on a high-carbohydrate diet. In the majority of sports, an increased intake of food naturally occurs to accommodate the day-to-day nutrient needs of young athletes, and unlike non-athlete, young competitors typically come closer to meeting their requirements for micronutrients. Nonetheless, certain athletic groups may be at risk for shortfalls in their diet. Compared to athletes in team sports, participants in weight-control sports may be at greater risk of failing to meet requirements for energy, protein, and some micronutrients. Endurance athletes, particularly female distance runners, may have intake deficits for the minerals iron and calcium. Acute issues such as heat illness and chronic concerns that include impaired growth and development, and the risk of injuries that include stress fractures may be an outcome of inadequate nutrition during physical training.

Cerebral perturbations provoked by prolonged exercise

This review addresses cerebral metabolic and neurohumoral alterations during prolonged exercise in humans with special focus on associations with fatigue. Global energy turnover in the brain is unaltered by the transition from rest to moderately intense exercise, apparently because exercise-induced activation of some brain regions including cortical motor areas is compensated for by reduced activity in other regions of the brain. However, strenuous exercise is associated with cerebral metabolic and neurohumoral alterations that may relate to central fatigue. Fatigue should be acknowledged as a complex phenomenon influenced by both peripheral and central factors. However, failure to drive the motorneurons adequately as a consequence of neurophysiological alterations seems to play a dominant role under some circumstances. During exercise with hyperthermia excessive accumulation of heat in the brain due to impeded heat removal by the cerebral circulation may elevate the brain temperature to >40 degrees C and impair the ability to sustain maximal motor activation. Also, when prolonged exercise results in hypoglycaemia, perceived exertion increases at the same time as the cerebral glucose uptake becomes low, and centrally mediated fatigue appears to arise as the cerebral energy turnover becomes restricted by the availability of substrates for the brain. Changes in serotonergic activity, inhibitory feed-back from the exercising muscles, elevated ammonia levels, and alterations in regional dopaminergic activity may also contribute to the impaired voluntary activation of the motorneurons after prolonged and strenuous exercise. Furthermore, central fatigue may involve depletion of cerebral glycogen stores, as signified by the observation that following exhaustive exercise the cerebral glucose uptake increases out of proportion to that of oxygen. In summary, prolonged exercise may induce homeostatic disturbances within the central nervous system (CNS) that subsequently attenuates motor activation. Therefore, strenuous exercise is a challenge not only to the cardiorespiratory and locomotive systems but also to the brain.

Carbohydrate supplementation and exercise-induced changes in T-lymphocyte function

Carbohydrate (CHO) ingestion during exercise has been shown to reduce perturbations in immune cell numbers and function, possibly through a reduction in the cortisol response to exercise. We have previously observed that exercise decreases T-lymphocyte responses to mitogen via an increase in cell death of both CD4 and CD8 T lymphocytes (Green KJ and Rowbottom DG. J Appl Physiol. 95: 57-63, 2003). This study tested the hypothesis that CHO ingestion rather than placebo (Pl) would result in an attenuation of the cortisol response to exercise and a reduction of the exercise-associated alterations in cell death. Six well-trained cyclists completed two exercise trials consisting of 2.5 h of cycling at 85% of individual ventilatory threshold. In a random order, trials were completed under either CHO (6% CHO solution, 3.2 g CHO/kg body wt total) or Pl conditions. Blood samples were collected before exercise, midexercise (after 60 min of exercise), immediately after exercise, and after 60 min of recovery. T-lymphocyte responses to mitogen were determined by using carboxyfluorescein diacetate succinimidyl ester fluorescent cell division tracking and expansion rates, and cell death rates were calculated for each sample as well as mitosis rates for each cell generation. Cellular expansion of T lymphocytes was decreased after exercise in Pl only. The reduction in cellular expansion was related to an increase in cell death of both CD4 and CD8 cells in culture rather than a decrease in the ability of cells to undergo mitosis. CHO ingestion compared with Pl was associated with no reductions in cellular expansion or increases in cell death. CHO ingestion during exercise acted to reduce the impairment of T-lymphocyte function by decreasing cell death within mitogen-stimulated cell cultures; however, the mechanism of action appears to be independent of cortisol.

Nutritional aspects in ultra-endurance exercise

PURPOSE OF REVIEW

Despite much current debate regarding central and peripheral neural mechanisms which may be responsible for the onset of fatigue during prolonged exercise, maintenance of nutritional and hydration status remains critical for successful participation in ultra-endurance exercise. This review focuses on substrate and fluid homeostasis during ultra-endurance exercise and the use of nutritional supplementation both as ergogenic aid and to attenuate exercise-induced immunosuppression.

RECENT FINDINGS

Current evidence continues to support mandatory high carbohydrate intakes (1). before the event to maximize muscle glycogen stores, (2). during the event to prevent hypoglycaemia and (3). after the event to optimize post-event repletion of endogenous carbohydrate stores. No consistent performance benefit has yet been shown following a high-fat diet. Greater utilization of intrafascicular triglyceride stores appears to account for additional fat utilization in females. Recent trends towards excessive fluid intake have resulted in frequent reports of hyponatraemic hyperhydration in ultra-distance athletes, with greater incidence in women than in men. Carbohydrate supplementation during the event attenuates immunosuppressive hormonal and cytokine responses to ultra-endurance exercise, but may impair vitamin C absorption, while the ergogenic value of caffeine supplementation in ultra-endurance performance is currently being questioned.

SUMMARY

Meeting macronutrient and fluid intake demands remains an important priority for ultra-endurance athletes. Yet these athletes are reported to present with a high incidence of disordered eating patterns during periods of training, and excessive fluid replacement strategies have resulted in an increased incidence of water intoxication with resultant central nervous system dysfunction.

A Framework for Understanding the Training Process Leading to Elite Performance

The development of performance in competition is achieved through a training process that is designed to induce automation of motor skills and enhance structural and metabolic functions. Training also promotes self-confidence and a tolerance for higher training levels and competition. In general, there are two broad categories of athletes that perform at the highest level: (i) the genetically talented (the thoroughbred); and (ii) those with a highly developed work ethic (the workhorse) with a system of training guiding their effort. The dynamics of training involve the manipulation of the training load through the variables: intensity, duration and frequency. In addition, sport activities are a combination of strength, speed and endurance executed in a coordinated and efficient manner with the development of sport-specific characteristics. Short- and long-term planning (periodisation) requires alternating periods of training load with recovery for avoiding excessive fatigue that may lead to overtraining. Overtraining is long-lasting performance incompetence due to an imbalance of training load, competition, non-training stressors and recovery. Furthermore, annual plans are normally constructed in macro-, meso- and microcycles around the competitive phases with the objective of improving performance for a peak at a predetermined time. Finally, at competition time, optimal performance requires a healthy body, and integration of not only the physiological elements but also the psychological, technical and tactical components.

Gender differences in carbohydrate loading are related to energy intake

We demonstrated that female endurance athletes did not increase their muscle glycogen concentration after an increase in the dietary carbohydrate intake (58 --> 74%), whereas men did (Tarnopolsky MA, SA Atkinson, SM Phillips, and JD McDougall, J Appl Physiol 78: 1360-1368, 1995). This may have been related to a lower energy or carbohydrate intake by the women or due to an inherent gender difference in glycogen storage capacity. We examined whether well-trained men (n = 6) and women (n = 6) increased muscle glycogen concentration after an increase in both the relative (58 --> 75%) and absolute energy and carbohydrate intake and whether potential gender differences were related to muscle hexokinase enzyme activity. Subjects were randomly allocated to three diets [Hab, habitual; CHO, high carbohydrate (75%); and CHO + E, extra energy + CHO ( upward arrow~34%)] for a 4-day period before a muscle biopsy for analysis of total and pro- and macroglycogen and hexokinase activity. Total glycogen concentration was higher for the men on the CHO and CHO + E trials compared with Hab (P < 0.05), whereas women increased only on the CHO + E trial compared with Hab (P < 0.05). There were no gender differences in the proportion of pro- and macroglycogen or hexokinase activity. A low energy intake may explain the previously reported lower capacity for women to glycogen load compared with men.

Energy and macronutrient intakes of elite figure skaters

OBJECTIVES

Dietary guidelines for athletes emphasize complex carbohydrates. This study examined dietary intakes of elite figure skaters relative to current recommendations in sports nutrition.

PARTICIPANTS

Subjects were male (n=80) and female (n=81) figure skaters taking part in a series of training camps held in Colorado between 1988 and 1995. Mean age was 18 years for men and 16 years for women.

DESIGN

Measures of height, weight, and skinfold thickness were used to calculate body mass index and percent body fat. Blood samples were drawn for analysis of nutritional status. Energy and nutrient intakes were based on 3-day food records.

STATISTICAL ANALYSES

Multivariate regression model and correlation analyses used the SPSS for Windows program.

RESULTS

Values of body mass index and percent body fat were similar to those obtained for elite athletes in other studies. Plasma chemistries were in the normal range. Energy intakes (2,329 kcal/day for men and 1,545 kcal/day for women) were below recommended values for sex and age. The skaters derived approximately 50% of their daily energy from sugars and fat. Sugars alone accounted for 25% of daily energy intakes--the skaters consumed between 100 g (women) and 142 g of sugars per day. Sugar and fat intakes, when expressed as percent of daily energy, were inversely linked, providing evidence of a fat-sugar seesaw. Higher-energy diets were higher in fat but lower in carbohydrate and protein.

APPLICATIONS

High consumption of sugars and fat by elite athletes was not associated with overweight or excess body fat. Although recommended diets are usually built around complex carbohydrates, dietetics professionals can address the increased energy needs of elite athletes by recommending energy-dense foods. Sugars and fats are efficient sources of energy per unit volume.

Gender differences in metabolism; nutrition and supplements

For many decades researchers did not consider that there were any differences between the genders in the metabolic response to exercise. As a result, nutritional recommendations and exercise training prescriptions have not considered the potential for gender specific responses. More recently, we and others have demonstrated that females oxidize proportionately more lipid and less carbohydrate during endurance exercise as compared to males. The oxidation of amino acids is similarly lower in females as compared to males during exercise. These gender differences are partially mediated by a higher estrogen concentration in females. Specific areas where there are gender differences in nutritional/supplement recommendations include carbohydrate (CHO) nutrition, protein requirements and creatine (CRM) supplementation. We have shown that females do not carbohydrate load in response to an increase in dietary carbohydrate when expressed as a percentage of total energy intake (i.e., 55-75%), however if they consume >8 g CHOxkg(-1)xd(-1), they show similar increases as compared to males. Top sport male and female athletes require somewhat more dietary protein as compared to sedentary persons. The maximal increase is approximately 100% for elite male athletes and approximately 50-60% for elite female athletes. Fortunately, most athletes habitually consume this level of protein intake. We have recently demonstrated that females show a lesser increase in lean body mass following acute CRM loading as compared to males. Females also did not show reductions in protein breakdown in response to CRM loading, whereas males did. In the future I expect that there will be further research from which gender specific nutritional/supplement recommendations can be made.