Effects of aerobic fitness on hypohydration-induced physiological strain and exercise impairment

Cardiovascular drift and cerebral and muscle tissue oxygenation during prolonged cycling at different pedalling cadences

We hypothesized that a faster cycling cadence could exaggerate cardiovascular drift and affect muscle and cerebral blood volume and oxygenation. Twelve healthy males (mean age, 23.4 ± 3.8 years) performed cycle ergometry for 90 min on 2 separate occasions, with pedalling frequencies of 40 and 80 r·min–1, at individual workloads corresponding to 60% of their peak oxygen consumption. The main measured variables were heart rate, ventilation, cardiac output, electromyographic activity of the vastus lateralis, and regional muscle and cerebral blood volume and oxygenation. Cardiovascular drift developed at both cadences, but it was more pronounced at the faster than at the slower cadence, as indicated by the drop in cardiac output by 1.0 ± 0.2 L·min–1, the decline in stroke volume by 9 ± 3 mL·beat–1, and the increase in heart rate by 9 ± 1 beats·min–1 at 80 r·min–1. At the faster cadence, minute ventilation was higher by 5.0 ± 0.5 L·min–1, and end-tidal CO2 pressure was lower by 2.0 ± 0.1 torr. Although higher electromyographic activity in the vastus lateralis was recorded at 80 r·min–1, muscle blood volume did not increase at this cadence, as it did at 40 r·min–1. In addition, muscle oxygenation was no different between cadences. In contrast, cerebral regional blood volume and oxygenation at 80 r·min–1 were not as high as at 40 r·min–1 (p < 0.05). Faster cycling cadence exaggerates cardiovascular drift and seems to influence muscle and cerebral blood volume and cerebral oxygenation, without muscle oxygenation being radically affected.

Hydration and performance during Ramadan

In the absence of any food or fluid intake during the hours of daylight during the month of Ramadan, a progressive loss of body water will occur over the course of each day, though these losses can be completely replaced each night. Large body water deficits will impair both physical and cognitive performance. The point at which water loss will begin to affect performance is not well defined, but it may be as little as 1-2% of body mass. For resting individuals in a temperate environment, the water loss that occurs during a day without food or fluid will typically amount to about 1% of body mass by the time of sunset. This small loss of body water is unlikely to have a major adverse effect on any aspect of physical or cognitive performance. Larger body water losses will occur, however, in hot weather or if exercise is undertaken. Performance in events lasting about 1 hour or longer may be impaired in the absence of fluid intake during the event. In weight-category sports, there may be difficulties due to the impossibility of restoring body water content between the weigh-in and competition, and athletes will require alternative strategies. Where more than one competition or training session takes place in a single day and where substantial fluid losses are incurred, recovery will be impaired by the absence of fluid intake.

Efeitos da reposição hidroeletrolítica sobre parâmetros cardiorrespiratórios em exercício e recuperação

INTRODUÇÃO: a necessidade de reposição ao máximo das perdas hídricas tornou-se estabelecida e difundida nos consensos internacionais. Entretanto, permanece pouco compreendida a influência da reposição quando administrada, igualmente, durante e após o exercício sobre parâmetros cardiorrespiratórios. OBJETIVO: analisar os efeitos da reposição hidroeletrolítica na frequência cardíaca (FC), pressão arterial sistólica (PAS), pressão arterial diastólica (PAD), saturação parcial de oxigênio (SpO2) e frequência respiratória (f) de jovens durante e após um exercício de longa duração. MÉTODOS: 31 jovens (21,55 ± 1,89 anos) realizaram três visitas ao laboratório (intervalo de 48 horas entre elas), sendo na primeira aplicado um teste incremental, para determinação da carga utilizada nas visitas seguintes, e nas duas últimas, denominadas protocolo controle (PC) e protocolo experimental (PE), os sujeitos foram submetidos a 10 min de repouso supino, 90 min de exercício em esteira ergométrica (60% do VO2pico) e 60 min de repouso supino. No PC não houve hidratação e no PE houve ingestão de solução isotônica. Os parâmetros FC, PAS, PAD, SpO2 e f foram mensurados no final do repouso; nos minutos 30, 60 e 90 do exercício, com exceção da f; e nos minutos 1, 3, 5, 7, 10, 20, 30, 40, 50 e 60 pós-exercício. Foi aplicado o teste t de Student ou teste de Mann-Whitney e ANOVA para medidas repetidas ou teste de Friedman seguidos de testes post hoc, com p < 0,05. RESULTADOS: a solução hidroeletrolítica proporcionou manutenção da PAS e da PAD, e menor incremento da FC durante o exercício; e promoveu retorno mais rápido da FC e conservou PAD, SpO2, PAS (a partir do 5º min) e f (a partir do 30º min) no período de recuperação. CONCLUSÃO: o protocolo de hidratação influenciou parâmetros cardiorrespiratórios de jovens durante e após a realização de atividade física submáxima de intensidade constante e longa duração.