Abstract Purpose: To analyze the effects of water intake on heart rate variability (HRV) during and after exercise. Methods: Thirty-one young males performed three different procedures: I) a maximal exercise test to determine the load for the protocols; II) the control protocol (CP); III) the experimental protocol (EP). The protocols comprised 10 minutes at rest, 90 minutes of treadmill exercise (60% of VO2 peak), and 60 minutes of recovery. No rehydration beverage consumption was allowed during the CP. During the EP, the participants were given water every 15 minutes, being that the amount of water to be ingested by each volunteer was divided over the time of exercise and recovery. For the analysis of HRV data, time and frequency domain indices were investigated in the following moments (M): M1 (5 minutes final of rest), M2 (25-30 minutes of exercise), M3 (55-60 minutes of exercise), M4 (85-90 minutes of exercise), M5 (5-10 minutes of recovery), M6 (15-20 minutes of recovery), M7 (25-30 minutes of recovery), M8 (40-45 minutes of recovery), and M9 (55-60 minutes of recovery). Results: There was no statistically significant difference between the groups that were examined during the exercise. HRV values for the CP and EP at the end of the exercise period were as follows SDNN (5.95±1.89 vs 6.89±2.11); RMSSD (3.29±0.78 vs 3.39±0.95); HF [nu] (24.06±14.26 vs 19.10±11.94); LF [nu] (75.93±14.26 vs 80.89±11.94); HF [ms2] (0.90±1.16 vs 0.94±0.89); LF [ms2] (4.65±5.94 vs 5.35±5.09); and LF/HF ratio (4.64±3.15 vs 6.95±5.57). HRV values for the CP and the EP at the end of the recovery period were as follows: SDNN (39.63±19.63 vs 49.95±17.79); RMSSD (21.63±15.55 vs 36.43±22.73); HF [ms2] (285.51±392.27 vs 699.29±699.66); LF [nu] (74.55±13.25 vs 61.19±19.27); and HF [nu] (25.44±13.25 vs 38.8±19.27). Conclusion: The hydration with water was not enough to significantly influence the linear HRV indices during exercise; however, it promoted faster recovery of these variables after exercise.

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.

BACKGROUND: The replacement required of water waste is recognized and established in an international consensus. However, the influence of the replacement in cardiorespiratory parameters, especially when administered during and after physical activity, remains poorly understood. OBJECTIVE: To analyze the effects of fluid replacement in heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), partial oxygen saturation (SpO2) and respiratory rate (f) of the youngsters during and after a long-term exercise. METHODS: 31 individuals (21.55 ± 1.89 years old) performed three visits in the laboratory (48 hours among them), at first an incremental test was applied to determine the load used during subsequent visits. In the last two, called control protocol (CP) and the experimental protocol (EP), the subjects were undergone to a 10 min of supine rest, 90 min of treadmill exercise (60% of VO2peak) and 60 min of supine rest. The difference between the protocols is that in the EP there was the intake isotonic solution and the CP there wasn't hydration. The parameters HR, SBP, DBP, SpO2 and f were measured at the end of the rest, in 30, 60 and 90 minutes of the activity, except the f parameter, and at 1, 3, 5, 7, 10, 20, 30, 40, 50 and 60 minute post-exercise. Student t test or Mann-Whitney, and ANOVA repeated measures or Friedman test followed by post hoc tests, were applied (p < 0.05). RESULTS: the intake isotonic solution provided SBP and DBP maintenance and smaller increment in HR during the exercise; promoted faster return of HR and kept SpO2, SBP (from the 5th minute) and f (from the 30th min) during recovery. CONCLUSION: the hydration protocol influenced the cardiorespiratory parameters for youngsters during and after submaximal physical exercise of constant intensity and long duration.