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The effects of hydration changes on neuromuscular function in athletes
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O impacto da desidratação na função neuromuscular (FNM) tem recebido pouca atenção científica, e o resultado dos estudos são inconsistentes. Além disso, permanecem questões metodológicas quanto à abordagem mais eficaz para avaliar o estado de hidratação em atletas. Esta questão é particularmente relevante para atletas subhidratados, que frequentemente apresentam baixo consumo de água e alterações crónicas nos indicadores mais comumente utilizados para determinar o estado de hidratação. Esta dissertação inclui sete artigos. O primeiro estudo é uma revisão sistemática dos estudos sobre os efeitos da desidratação aguda na FNM em indivíduos saudáveis. A revisão adotou uma abordagem inovadora, examinando diferentes níveis do sistema nervoso (supraspinal, espinal e periférico) e a função contrátil. Os resultados revelam uma considerável variabilidade nos métodos para induzir a desidratação, na duração dos estudos, nos testes de FNM e nas características dos participantes. Consequentemente, o segundo estudo fornece uma descrição detalhada do projeto "H2OAthletes", que visa compreender os efeitos das alterações do estado de hidratação na FNM em atletas. O objetivo de publicar este protocolo é apoiar a obtenção de conclusões robustas dos estudos relacionados com este projeto, minimizar o viés de publicação e melhorar a reprodutibilidade. A revisão sistemática também destacou que as inconsistências entre os estudos podem, em parte, ser atribuídas ao facto de que os efeitos da desidratação são frequentemente exacerbados pela fadiga induzida pelo exercício ou pela exposição ao calor. Além disso, há uma necessidade de uma representação mais adequada da população atlética, particularmente das mulheres, e de métodos mais robustos de avaliação da hidratação em estudos desta natureza. Neste sentido, o terceiro estudo teve como objetivo investigar os efeitos de desidratação com corrida a 80-90% do primeiro limiar ventilatório (VT1), combinada com exposição controlada ao calor, em atletas de ambos os sexos. A desidratação foi avaliada pela perda de massa corporal (PMC), parâmetros salivares e séricos. A desidratação não afetou os músculos não recrutados pelo protocolo de desidratação, mas reduziu a força máxima nos membros X inferiores em ambos os sexos. Embora tenha alterado a ativação muscular rápida, a diminuição na produção de força rápida está provavelmente relacionada com a redução da força máxima. A desidratação também afetou a resistência à fadiga, com adaptações específicas da função neuromuscular. O quarto estudo explorou a água corporal total (ACT), água intracelular (AIC) e água extracelular (AEC) utilizando técnicas de diluição, bem como o estado de hidratação medido pela gravidade específica da urina (GEU) e hidratação da massa livre de gordura em atletas subhidratados e euhidratados. Verificou-se que não havia diferenças significativas entre os compartimentos hídricos. No entanto, a GEU foi significativamente mais elevada em atletas com menor ingestão de água. Estes resultados sugerem que os atletas subhidratados podem manter o equilíbrio hídrico, mas potencialmente comprometem a saúde renal. Além disso, os resultados sugerem imprecisões nos indicadores urinários para avaliar a hidratação. Este estudo sublinha a necessidade de uma investigação mais aprofundada sobre a abordagem ideal para avaliar o estado de hidratação em atletas. Neste contexto, o quinto estudo analisou biomarcadores pré e pós-desidratação, incluindo osmolalidade salivar, sérica e urinária, GEU, cor da urina, arginina vasopressina e sódio sérico, bem como a sensação de sede em atletas subhidratados, usando a PMC como referência. Constatou-se que a osmolalidade salivar, sérica e o sódio sérico são métodos eficazes para avaliar a desidratação em atletas. Finalmente, a necessidade contínua de métodos não invasivos, precisos e rentáveis para avaliar o estado de hidratação em tempo real é amplamente reconhecida. Os estudos 6 (transversal) e 7 (longitudinal) compararam o papel preditivo dos parâmetros brutos da análise de impedância bioelétrica (BIA) em série e em paralelo para prever a ACT, AIC e AEC. Ambos os estudos destacam o uso da reatância e capacitância em paralelo como uma alternativa às medições convencionais em série, identificando-os como indicadores válidos do volume celular. Em suma, esta dissertação contribui substancialmente para a compreensão dos efeitos das alterações do estado de hidratação na FNM e clarifica as abordagens para avaliar o estado de hidratação em atletas .
The impact of dehydration on neuromuscular function (NMF) has received limited attention, and existing studies present inconsistent results. Furthermore, methodological issues remain regarding the most effective approach to assessing hydration in athletes. This issue is particularly relevant for underhydrated athletes, who often exhibit low water intake and chronic alterations in the indicators used to determine hydration. This dissertation includes seven articles. The first study is a systematic review of the effects of acute dehydration on NMF in healthy individuals. The review adopted an innovative approach by examining different nervous system levels (supraspinal, spinal, and peripheral) and contractile function. The results reveal considerable variability in methods for inducing dehydration, study durations, NMF tests, and participants’ characteristics. Consequently, the second study provides a detailed description of the "H2OAthletes" project that aims to understand the effects of hydration changes on NMF in athletes. The purpose of publishing this protocol is to support drawing robust conclusions from studies related to this project, minimize publication bias, and enhance reproducibility. The systematic review also highlighted that inconsistencies between studies may, in part, be attributed to the fact that the effects of dehydration are often exacerbated by exerciseinduced fatigue or heat exposure. Additionally, there needs to be more evidence of adequate representation of the athletic population, particularly women, and more robust hydration assessment methods are required in studies of this nature. In this sense, the third study aimed to investigate the effects of a running dehydration at 80-90% of the first ventilatory threshold (VT1) combined with controlled heat exposure in athletes of both sexes. The dehydration was assessed by body mass loss (BML), salivary and serum parameters. Dehydration did not impact non-recruited muscles but reduced maximal strength in the lower limbs for both sexes. While it impaired rapid muscle activation, the decline in rapid force production likely stems from reduced maximal strength. Dehydration also affected fatigue resistance during sustained isometric contractions, with specific neuromuscular adaptations after dehydration. The fourth VIII study explored total body water (TBW), intracellular (ICW), and extracellular water (ECW) using dilution techniques, as well as hydration status measured by urine specific gravity (USG) and fat-free mass hydration in underhydrated and euhydrated athletes. It was found that there were no significant differences between water compartments. However, USG was significantly higher in athletes with lower water intake. These results suggest that underhydrated athletes may maintain fluid balance but potentially compromise renal health. Additionally, the results may indicate inaccuracies in urinary indicators for assessing hydration. This study underscores the need for a more thorough investigation into the optimal approach for assessing hydration in athletes. In this context, the fifth study analyzed pre- and postdehydration biomarkers, including salivary, serum, and urinary osmolality, USG, urine color, arginine vasopressin, and serum sodium, as well as thirst sensation in underhydrated athletes, using body mass loss as a reference. It was found that salivary, serum osmolality, and serum sodium are effective methods for assessing dehydration in athletes. Finally, the ongoing need for non-invasive, accurate, and cost-effective methods to assess hydration status in real time is well recognized. Studies six (cross-sectional) and seven (longitudinal) compared the predictive role of raw bioelectrical impedance analysis (BIA) parameters in series and in parallel for predicting TBW, ICW, and ECW. Both studies highlight the use of parallel reactance and capacitance as an alternative to conventional series measurements, identifying them as valid indicators of cellular volume. This dissertation substantially contributes to understanding the effects of hydration status changes on NMF and clarifies approaches for assessing hydration in athletes.
The impact of dehydration on neuromuscular function (NMF) has received limited attention, and existing studies present inconsistent results. Furthermore, methodological issues remain regarding the most effective approach to assessing hydration in athletes. This issue is particularly relevant for underhydrated athletes, who often exhibit low water intake and chronic alterations in the indicators used to determine hydration. This dissertation includes seven articles. The first study is a systematic review of the effects of acute dehydration on NMF in healthy individuals. The review adopted an innovative approach by examining different nervous system levels (supraspinal, spinal, and peripheral) and contractile function. The results reveal considerable variability in methods for inducing dehydration, study durations, NMF tests, and participants’ characteristics. Consequently, the second study provides a detailed description of the "H2OAthletes" project that aims to understand the effects of hydration changes on NMF in athletes. The purpose of publishing this protocol is to support drawing robust conclusions from studies related to this project, minimize publication bias, and enhance reproducibility. The systematic review also highlighted that inconsistencies between studies may, in part, be attributed to the fact that the effects of dehydration are often exacerbated by exerciseinduced fatigue or heat exposure. Additionally, there needs to be more evidence of adequate representation of the athletic population, particularly women, and more robust hydration assessment methods are required in studies of this nature. In this sense, the third study aimed to investigate the effects of a running dehydration at 80-90% of the first ventilatory threshold (VT1) combined with controlled heat exposure in athletes of both sexes. The dehydration was assessed by body mass loss (BML), salivary and serum parameters. Dehydration did not impact non-recruited muscles but reduced maximal strength in the lower limbs for both sexes. While it impaired rapid muscle activation, the decline in rapid force production likely stems from reduced maximal strength. Dehydration also affected fatigue resistance during sustained isometric contractions, with specific neuromuscular adaptations after dehydration. The fourth VIII study explored total body water (TBW), intracellular (ICW), and extracellular water (ECW) using dilution techniques, as well as hydration status measured by urine specific gravity (USG) and fat-free mass hydration in underhydrated and euhydrated athletes. It was found that there were no significant differences between water compartments. However, USG was significantly higher in athletes with lower water intake. These results suggest that underhydrated athletes may maintain fluid balance but potentially compromise renal health. Additionally, the results may indicate inaccuracies in urinary indicators for assessing hydration. This study underscores the need for a more thorough investigation into the optimal approach for assessing hydration in athletes. In this context, the fifth study analyzed pre- and postdehydration biomarkers, including salivary, serum, and urinary osmolality, USG, urine color, arginine vasopressin, and serum sodium, as well as thirst sensation in underhydrated athletes, using body mass loss as a reference. It was found that salivary, serum osmolality, and serum sodium are effective methods for assessing dehydration in athletes. Finally, the ongoing need for non-invasive, accurate, and cost-effective methods to assess hydration status in real time is well recognized. Studies six (cross-sectional) and seven (longitudinal) compared the predictive role of raw bioelectrical impedance analysis (BIA) parameters in series and in parallel for predicting TBW, ICW, and ECW. Both studies highlight the use of parallel reactance and capacitance as an alternative to conventional series measurements, identifying them as valid indicators of cellular volume. This dissertation substantially contributes to understanding the effects of hydration status changes on NMF and clarifies approaches for assessing hydration in athletes.
Descrição
Palavras-chave
Atletas Desidratação Estado de hidratação Subhidratação Produção de força Athletes Dehydration Force production Hydration Status Underhydration