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1.
Front Nutr ; 4: 40, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28868290

RESUMO

BACKGROUND: Low levels of caffeine ingestion do not induce dehydration at rest, while it is not clear if larger doses do have an acute diuretic effect. The aim of the present investigation was to examine the acute effect of low and high levels of caffeine, via coffee, on fluid balance in habitual coffee drinkers (at least one per day) at rest. METHODS: Ten healthy adults (eight males and two females; age: 27 ± 5 years, weight: 89.5 ± 14.8 kg, height: 1.75 ± 0.08 m, and body mass index: 29.1 ± 4.4 kg m-2) ingested 200 mL of water (W), coffee with low caffeine (3 mg kg-1, LCAF), or coffee with high caffeine (6 mg kg-1, HCAF) on three respective separate occasions. All sessions were performed at 09:00 in the morning in a counterbalanced, crossover manner, at least 5 days apart. Subjects remained in the laboratory while urine samples were collected every 60 min for 3 h post ingestion. RESULTS: Absolute caffeine consumption was 269 ± 45 and 537 ± 89 mg for the LCAF and HCAF, respectively. Coffee ingestion at the HCAF trial induced greater diuresis during the 3-h period (613 ± 101 mL, P < 0.05), when compared to W (356 ± 53 mL) and LCAF (316 ± 38 mL). In addition, cumulative urinary osmotic excretion was significantly greater in the HCAF (425 ± 92 mmol, P < 0.05), as compared to the W (249 ± 36 mmol) and LCAF (177 ± 16 mmol) trials. CONCLUSION: The data indicate that caffeine intake of 6 mg kg-1 in the form of coffee can induce an acute diuretic effect, while 3 mg kg-1 do not disturb fluid balance in healthy casual coffee drinking adults at rest.

2.
Nutr Res ; 43: 25-32, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28739050

RESUMO

Epidemiological research has demonstrated that low daily total water intake is associated with increased diagnosis of hyperglycemia. Possible mechanisms for this increase include hormones related to the hypothalamic pituitary axis as well as the renin-angiotensin-aldosterone system (RAAS). Therefore, the hypothesis of the present study was that acute low water intake would result in differential hormonal profiles and thus impaired blood glucose regulation during an oral glucose tolerance test (OGTT) in people with type 2 diabetes mellitus (T2DM). Nine men (53 ± 9 years, 30.0 ± 4.3 m∙kg-2, 32% ± 6% body fat) diagnosed with T2DM completed OGTTs in euhydrated (EUH) and hypohydrated (HYP) states in counterbalanced order. Water restriction led to hypohydration of -1.6% of body weight, with elevated plasma (EUH: 288 ± 4, HYP: 298 ± 6 mOsm·kg-1; P < .05) and urine (EUH: 512 ± 185, HYP: 994 ± 415 mOsm·kg-1; P < .05) osmolality. There was a significant main effect of condition for serum glucose (at time 0 minute 9.5 ± 4.2 vs 10.4 ± 4.4 mmol∙L-1 and at time 120 minutes 19.1 ± 4.8 vs 21.0 ± 4.1 mmol∙L-1 for EUH and HYP, respectively; P < .001) but not insulin (mean difference between EUH and HYP -12.1 ± 44.9 pmol∙L-1, P = .390). An interaction between time and condition was observed for cortisol: decrease from minute 0 to 120 in EUH (-85.3 ± 82.1 nmol∙L-1) vs HYP (-25.0 ± 43.0 nmol∙L-1; P = .017). No differences between conditions were found within RAAS-related hormones. Therefore, we can conclude that 3 days of low total water intake in people with T2DM acutely impairs blood glucose response during an OGTT via cortisol but not RAAS-mediated glucose regulation.


Assuntos
Glicemia/metabolismo , Diabetes Mellitus Tipo 2/sangue , Ingestão de Líquidos , Adulto , Biomarcadores/sangue , Índice de Massa Corporal , Peso Corporal , Teste de Tolerância a Glucose , Humanos , Hidrocortisona/sangue , Insulina/sangue , Masculino , Pessoa de Meia-Idade , Estado de Hidratação do Organismo , Concentração Osmolar , Projetos Piloto , Sistema Renina-Angiotensina
3.
Med Sci Sports Exerc ; 49(7): 1494, 2017 07.
Artigo em Inglês | MEDLINE | ID: mdl-28622202
4.
Med Sci Sports Exerc ; 49(6): 1244-1251, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-28079705

RESUMO

Drinking ad libitum during exercise often leads to dehydration ranging from -1% to -3% of body weight. PURPOSE: This article aimed to study the effect of a prescribed hydration protocol matching fluid losses on a simulated 30-km criterium-like cycling performance in the heat (31.6°C ± 0.5°C). METHODS: Ten elite heat-acclimatized male endurance cyclists (30 ± 5 yr, 76.5 ± 7.2 kg, 1.81 ± 0.07 m, V˙O2peak = 61.3 ± 5.2 mL·min·kg, body fat = 10.5% ± 3.3%, Powermax = 392 ± 33 W) performed three sets of criterium-like cycling, which consisted of a 5-km cycling at 50% power max followed by a 5-km cycling all out at 3% grade (total 30 km). Participants rode the course on two separate occasions and in a counterbalanced order, during either ad libitum drinking (AD; drink water as much as they wished) or prescribed drinking (PD; drink water every 1 km to much fluid losses). To design the fluid intake during PD, participants performed a familiarization trial to calculate fluid losses. RESULTS: After the exercise protocol, the cyclist dehydrated by -0.5% ± 0.3% and -1.8% ± 0.7% of their body weight for the PD and AD trial, respectively. The mean cycling speed for the third bout of the 5-km hill cycling was greater in the PD trial (30.2 ± 2.4 km·h) compared with the AD trial (28.8 ± 2.6 km·h) by 5.1% ± 4.8% (P < 0.05). Gastrointestinal, mean skin, and mean body temperatures immediately after the last hill climbing were greater in the AD compared with the PD trial (P < 0.05). Overall, sweat sensitivity during the three climbing bouts was lower in the AD (15.6 ± 5.7 g·W·m) compared with the PD trial (22.8 ± 3.4 g·W·m, P < 0.05). CONCLUSION: The data suggested that PD to match fluid losses during exercise in the heat provided a performance advantage because of lower thermoregulatory strain and greater sweating responses.


Assuntos
Desempenho Atlético/fisiologia , Ciclismo/fisiologia , Ingestão de Líquidos , Temperatura Alta , Resistência Física/fisiologia , Adulto , Pressão Sanguínea/fisiologia , Peso Corporal/fisiologia , Desidratação/prevenção & controle , Frequência Cardíaca/fisiologia , Humanos , Ácido Láctico/sangue , Masculino , Percepção , Esforço Físico/fisiologia , Sudorese , Sede/fisiologia
5.
J Strength Cond Res ; 30(3): 621-5, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26907836

RESUMO

Swimming, either competitively or leisurely, is a unique activity that involves prolonged exercise while immersed in stable water temperatures. This environment could have an influence on the hydration status of swimmers independently of fluid balance. Forty-six healthy adolescent swimmers (26 males and 20 females; 12.8 ± 2.3 years; 50.6 ± 13.4 kg) were studied during a typical training session in an indoor swimming pool. First morning, prepractice and postpractice urine samples were tested for osmolality and specific gravity, whereas all athletes consumed fluids ad libitum. Sixty-seven percent of the athletes were hypohydrated (urine osmolality [Uosm] ≥700 mmol·kg(-1)) based on their first morning urine sample, which increased to 78% immediately before training. During the 2-hour swimming practice, the minimal sweat loss (0.39 ± 0.27 L) combined with ad libitum fluid availability resulted in unchanged body weight (0.1 ± 0.3 kg). Additionally, thirst was similar (before practice: 46 ± 26, after practice: 55 ± 33 mm on a 100-mm visual analog scale) at pretraining and posttraining time points (p > 0.05). Interestingly, postpractice Uosm was reduced significantly compared with the prepractice value (630 vs. 828 mmol·kg(-1); p = 0.001), without any significant change in body weight (0.1 ± 0.3 kg; p > 0.05). In conclusion, the present data indicated that more than two-thirds of the young swimmers appeared in their practice suboptimally hydrated. Although no changes in body mass were observed during the swimming practice, the decrease in urine hydration markers after swimming might less accurately reflect hydration state.


Assuntos
Desidratação/urina , Condicionamento Físico Humano/fisiologia , Natação/fisiologia , Equilíbrio Hidroeletrolítico , Adolescente , Peso Corporal , Criança , Ingestão de Líquidos , Feminino , Humanos , Masculino , Concentração Osmolar , Gravidade Específica , Sudorese , Sede
7.
J Athl Train ; 48(6): 741-7, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23952038

RESUMO

CONTEXT: Hydration has been shown to be an important factor in performance; however, the effects of mild dehydration during intense cycling are not clear. OBJECTIVE: To determine the influence of mild dehydration on cycling performance during an outdoor climbing trial in the heat (ambient temperature = 29.0°C ± 2.2°C). DESIGN: Crossover study. SETTING: Outdoor. PATIENTS OR OTHER PARTICIPANTS: Ten well-trained, male endurance cyclists (age = 28 ± 5 years, height = 182 ± 0.4 cm, mass = 73 ± 4 kg, maximal oxygen uptake = 56 ± 9 mL·min(-1)·kg(-1), body fat = 23% ± 2%, maximal power = 354 ± 48 W). INTERVENTION(S): Participants completed 1 hour of steady-state cycling with or without drinking to achieve the desired pre-exercise hydration level before 5-km hill-climbing cycling. Participants started the 5-km ride either euhydrated (EUH) or dehydrated by -1% of body mass (DEH). MAIN OUTCOME MEASURE(S): Performance time, core temperature, sweat rate, sweat sensitivity, and rating of perceived exertion (RPE). RESULTS: Participants completed the 5-km ride 5.8% faster in the EUH (16.6 ± 2.3 minutes) than DEH (17.6 ± 2.9 minutes) trial (t1 = 10.221, P = .001). Postexercise body mass was -1.4% ± 0.3% for the EUH trial and -2.2% ± 0.2% for the DEH trial (t1 = 191.384, P < .001). Core temperature after the climb was greater during the DEH (39.2°C ± 0.3°C) than EUH (38.8°C ± 0.2°C) trial (t1 = 8.04, P = .005). Sweat rate was lower during the DEH (0.44 ± 0.16 mg·m(-2)·s(-1)) than EUH (0.51 ± 0.16 mg·m(-2)·s(-1)) trial (t8 = 2.703, P = .03). Sweat sensitivity was lower during the DEH (72.6 ± 32 g·°C(-1)·min(-1)) than EUH (102.6 ± 54.2 g·°C(-1)·min(-1)) trial (t8 = 3.072, P = .02). Lastly, RPE after the exercise performance test was higher for the DEH (19.0 ± 1.0) than EUH (17.0 ± 1.0) participants (t9 = -3.36, P = .008). CONCLUSIONS: We found mild dehydration decreased cycling performance during a 5-km outdoor hill course, probably due to greater heat strain and greater perceived intensity.


Assuntos
Desempenho Atlético/fisiologia , Ciclismo/fisiologia , Desidratação , Teste de Esforço/métodos , Adulto , Índice de Massa Corporal , Temperatura Corporal , Estudos Cross-Over , Ingestão de Líquidos , Febre , Frequência Cardíaca , Temperatura Alta , Humanos , Masculino , Oxigênio/metabolismo , Resistência Física/fisiologia , Esforço Físico/fisiologia , Sudorese
8.
Med Sci Sports Exerc ; 45(9): 1782-9, 2013 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-23470313

RESUMO

INTRODUCTION: Hypohydration exceeding 2% of body mass decreases exercise performance. However, the effects of mild hypohydration (<2%) are not clear. PURPOSE: The aim of this study was to determine the effects of mild hypohydration on cycling performance during a simulated-hill circuit course in a warm environment (32.5°C ± 0.5°C). METHODS: Ten trained male cyclists (age, 30 ± 7 yr; mass, 78.4 ± 9.5 kg; height, 1.80 ± 0.01 m; V˙O2max, 52.4 ± 3.3 mL·min·kg; and Powermax, 355 ± 29 W) performed a cycling circuit three times on a laboratory ergometer consisting of 5 km at 50% of maximum power output and 5 km at an all-out pace, followed by a 5-min rest every 5 km. Subjects started the performance test either euhydrated (EUH) or hypohydrated (HYP), by 0% ± 0% and -1.0% ± 0.1% of body mass, respectively. RESULTS: Mean speed at the first, second, and third 5-km simulated-hill cycling was higher in the EUH (28.1 ± 3.1, 27.7 ± 3, and 27.0 ± 3.6 km·h) than that in the HYP trial (27.0 ± 2.9, 26.1 ± 3.7, and 25.9 ± 3.6 km·h) (P < 0.05). Mean power output at the first, second, and third 5-km simulated-hill cycling was greater in the EUH (284 ± 55, 266 ± 53, and 254 ± 58 W) than that in the HYP trial (272 ± 56, 250 ± 61, and 240 ± 57 W) (P < 0.05). Gastrointestinal temperature at the end of the first, second, and third 5-km simulated-hill cycling was greater in the HYP (38.3°C ± 0.4°C, 38.4°C ± 0.2°C, and 38.6°C ± 0.2°C) than that in the EUH trial (38.1°C ± 0.3°C, 38.1°C ± 0.3, and 38.3°C ± 0.3°C) (P < 0.05). Overall, sweat sensitivity during the circuit course was greater in the EUH (115 ± 58 g·°C·min) versus HYP trial (67 ± 19 g·°C·min) (P < 0.05). Furthermore, RPE and heart rate were similar and near maximal between trials (P > 0.05). CONCLUSION: The data showed that mild hypohydration decreased cycling performance, possible by inducing greater thermal and cardiovascular strain.


Assuntos
Desempenho Atlético/fisiologia , Ciclismo/fisiologia , Desidratação/fisiopatologia , Esforço Físico/fisiologia , Adulto , Temperatura Corporal , Teste de Esforço , Frequência Cardíaca , Temperatura Alta , Humanos , Masculino , Sudorese , Sede , Adulto Jovem
9.
Int J Sport Nutr Exerc Metab ; 23(3): 245-51, 2013 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-23166200

RESUMO

UNLABELLED: There is a lack of studies concerning hydration status of young athletes exercising in the heat. PURPOSE: To assess preexercise hydration status in young soccer players during a summer sports camp and to evaluate body- water balance after soccer training sessions. METHODS: Initial hydration status was assessed in 107 young male soccer players (age 11-16 yr) during the 2nd day of the camp. Seventy-two athletes agreed to be monitored during 2 more training sessions (3rd and 5th days of the camp) to calculate dehydration via changes in body weight, while water drinking was allowed ad libitum. Hydration status was assessed via urine specific gravity (USG), urine color, and changes in total body weight. Mean environmental temperature and humidity were 27.2 ± 2 °C and 57% ± 9%, respectively. RESULTS: According to USG values, 95 of 107 of the players were hypohydrated (USG ≥ 1.020) before practice. The prevalence of dehydration observed was maintained on both days, with 95.8% and 97.2% of the players being dehydrated after the training sessions on the 3rd and 5th days, respectively. Despite fluid availability, 54 of the 66 (81.8%) dehydrated players reduced their body weight (-0.35 ± 0.04 kg) as a response to training, while 74.6% (47 out of the 63) further reduced their body weight (-0.22 ± 0.03 kg) after training on the 5th day. CONCLUSION: Approximately 90% of the young soccer players who began exercising under warm weather conditions were hypohydrated, while drinking ad libitum during practice did not prevent further dehydration in already dehydrated players.


Assuntos
Atletas , Desidratação/prevenção & controle , Ingestão de Líquidos/fisiologia , Futebol/fisiologia , Adolescente , Peso Corporal , Criança , Temperatura Alta , Humanos , Umidade , Modelos Lineares , Masculino , Prevalência , Estações do Ano , Manejo de Espécimes , Inquéritos e Questionários , Equilíbrio Hidroeletrolítico/fisiologia
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