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OBJECTIVE: To review the technical aspects of body composition assessment by dual-energy X-ray absorptiometry (DXA) and other methods based on the most recent scientific evidence. MATERIALS AND METHODS: This Official Position is a result of efforts by the Scientific Committee of the Brazilian Association of Bone Assessment and Metabolism (Associação Brasileira de Avaliação Óssea e Osteometabolismo, ABRASSO) and health care professionals with expertise in body composition assessment who were invited to contribute to the preparation of this document. The authors searched current databases for relevant publications. In this first part of the Official Position, the authors discuss the different methods and parameters used for body composition assessment, general principles of DXA, and aspects of the acquisition and analysis of DXA scans. CONCLUSION: Considering aspects of accuracy, precision, cost, duration, and ability to evaluate all three compartments, DXA is considered the gold-standard method for body composition assessment, particularly for the evaluation of fat mass. In order to ensure reliable, adequate, and reproducible DXA reports, great attention is required regarding quality control procedures, preparation, removal of external artifacts, imaging acquisition, and data analysis and interpretation.

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The focus of this review is the effects of creatine supplementation with or without exercise on glucose metabolism. A comprehensive examination of the past 16 years of study within the field provided a distillation of key data. Both in animal and human studies, creatine supplementation together with exercise training demonstrated greater beneficial effects on glucose metabolism; creatine supplementation itself demonstrated positive results in only a few of the studies. In the animal studies, the effects of creatine supplementation on glucose metabolism were even more distinct, and caution is needed in extrapolating these data to different species, especially to humans. Regarding human studies, considering the samples characteristics, the findings cannot be extrapolated to patients who have poorer glycemic control, are older, are on a different pharmacological treatment (e.g., exogenous insulin therapy) or are physically inactive. Thus, creatine supplementation is a possible nutritional therapy adjuvant with hypoglycemic effects, particularly when used in conjunction with exercise.

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Durante anos, pesquisadores inseridos na área de fisiologia do exercício apontaram para o lactato como o principal causador da fadiga durante exercícios de alta intensidade. Hoje, por outro lado, já existem diversos estudos demonstrando que o lactato per se não possui qualquer efeito sobre a fadiga neste tipo de exercício, mas que a acidose muscular, ocasionada pelo acúmulo de íons hidrogênio no interior da célula muscular, seria o fator limitante para o desempenho físico durante exercícios físicos de alta intensidade. Assim, estratégias com o objetivo de atenuar a queda do pH intramuscular, como a suplementação de beta-alanina e bicarbonato de sódio, têm se destacado no cenário esportivo. Embora anteriormente destacado como vilão durante esforços intensos, a suplementação de lactato vem recebendo especial atenção em anos recentes. A suplementação com este composto teoricamente pode aumentar os níveis sanguíneos de pH e bicarbonato, aumentando a capacidade de tamponamento extracelular, e por consequência, o desempenho físico. A suplementação com lactato também pode aumentar os níveis sanguíneos deste composto, aumentando sua disponibilidade como substrato para a gliconeogênese. Assim, estudos tem surgido com o intuito de avaliar a eficácia do lactato como tamponante e como substrato energético. Os poucos estudos até agora conduzidos, entretanto, não nos permitem atestar a eficácia ergogênica desta estratégia nutricional. A falta de estudos dose-resposta sobre as variáveis sanguíneas que caracterizam o mecanismo de ação do lactato, bem como de aplicação de testes físicos com baixo coeficiente de variação e boa validade externa exemplificam a necessidade de mais estudos investigando a eficácia ergogênica desta estratégia nutricional.

For years, researchers from the exercise physiology field pointed to lactate as the main cause of fatigue during high-intensity exercises. Today, however, there are several studies demonstrating that lactate per se does not have any effect on fatigue during this type of exercise, but muscle acidosis occasioned by hydrogen ions accumulation inside the muscle cell would be the limiting factor for performance during high-intensity exercises. Therefore strategies aiming to attenuate the decrease of intramuscular pH levels, like beta-alanine and sodium bicarbonate supplementation, have been prominent in the sports scenario. Although previously highlighted as a villain during high-intensity exercises, lactate supplementation has received special attention in recent years. Supplementation with this compound can theoretically increase blood pH and bicarbonate levels, increasing the extracellular buffering capacity, and hence, performance. Lactate supplementation can also increase lactate blood levels, increasing its availability as a substrate for gluconeogenesis. Thus, studies have arisen aiming to assess the effectiveness of lactate as a buffering agent and as an energy substrate. The few studies so far conducted, however, do not allow us to attest the ergogenic effectiveness of this nutritional strategy. The lack of dose-response studies on blood variables that characterize lactate mechanism of action, as well as the application of physical tests with a low coefficient of variation and good external validity exemplifies the need for further studies investigating the ergogenic effectiveness of this nutritional strategy.

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