Η επίδραση των επιπέδων υδάτωσης στην καρδιαγγειακή λειτουργία και στην αθλητική απόδοση

Abstract

Water is the most essential element for life. Fluid and electrolyte balance are critical for the function of all organs and indeed, for maintaining health in general. It is well documented that dehydration provokes unfavorable results in athletic performance and in health in general. Although there is a plethora of studies relating hydration status, prevalence of dehydration and performance in adults, there is a lack of data concerning hydration status and children. One of the main consequences of dehydration is the induced cardiovascular strain. Moreover, endothelial dysfunction is a proven negative indicator of cardiac function; thus, there might be a link between dehydration, endothelial and cardiac function. Lastly, intense scientific interest has been emerged, concerning the mechanisms which affect water consumption and in turn, athletic performance, during exercise under warm environmental conditions. However the results are controversial. The main aims of the present thesis are: (i) To estimate the hydration status of young athletes participating in different sports, (ii) To study the effect of hydration status on endothelial function and consequently cardiovascular function and (iii) To investigate the role of oral/pharyngeal receptors in fluid consumption during exercise in the heat, and if they affect athletic performance. 1st StudyThere is a lack of studies concerning hydration status of young athletes exercising in the heat. PURPOSE: To assess pre-exercise 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 years) during the 2nd day of the camp. Seventy two athletes agreed to be monitored during two more training sessions (3rd and 5th day of the camp) in order 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 out of 107 of the children were hypohydrated (USG≥1.020), prior to practice. The prevalence of dehydration observed was maintained in both days, with 95.8% and 97.2% of the children being dehydrated, after the training sessions in the 3rd and 5th day, respectively. Despite fluid availability, 54 out of the 66 (81.8 %) dehydrated children reduced their body weight (-0.35±0.04 kg) as a response to training, while 74.6% (47 out of the 63) reduced further their body weight (-0.22±0.03 kg) after training in the 5th day. CONCLUSIONS: 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. 2nd StudyPURPOSE: We aimed to evaluate if an intervention program emphasizing in increased fluidintake can improve exercise performance in children exercising in the heat. METHODS: 92young athletes participated in the study (age: 13.8±0.4 yr, weight: 54.9±1.5 kg). 31 (boys:13,girls:18) children served as the control group (CON) and 61 (boys: 30, girls:31) as the intervention (INT). Volunteers had free access to fluids. Hydration was assessed on the basis of first morning urine. A series of field tests were used to evaluate exercise performance. All tests took place outdoors in the morning (Mean ambient temperature = 28°C). After baseline testing, INT attended a lecture on hydration, and urine color charts were mounted in all bathrooms. Additionally, water accessibility was facilitated in training, dining, and resting areas. RESULTS: INT improved significantly hydration status [USG: pre=1.031±0.09, post=1.023±0.012, p<0.05; Urine Osmolality (mOsm/kg water): pre=941±30, post=782±34, p<0.05], while no statistically significant changes were found in the CON [USG pre=1.033±0.011, post=1.032±0.013, p>0.05; Urine Osmolality (mOsm/kg water) 970±38 vs. 961±38 p>0.05]. Performance in an endurance run was improved significantly only in INT (time for 600 m: pre=189±5sec, post=167±4 sec, p<0.05). CONCLUSION: Improving hydration status by ad libitum consumption of water can enhance performance in young children exercising in the heat. 3rd Study PURPOSE: Moderate levels of dehydration provoke numerous unfavorable physiological alterations. We aimed to investigate whether mild dehydration affects endothelium function. METHODS: Ten healthy, physically active but not trained males participated in this crossover study (body weight 80.8±4.3 kg, age 24.3±1.6 y). Endothelium function was estimated by flowmediated dilatation (FMD). In the dehydration trial (DEH), FMD was measured at baseline, and after 24h of dehydration, while in the control trial (CON), FMD was measured at baseline and after 24h of euhydration. Dehydration was induced by combined water-restriction for one day (0.5 L of water only and no other fluids) and a 2h moderate-intensity treadmill exercise (25 min at 70% of maximum heart rate alternating with 5 min rest at 31°C) while in the control trial, body mass loss during the same exercise protocol, was replenished by an equal amount of water. RESULTS: FMD fell from 8.2±1.2% at baseline to 6.0±1.0% at the end of the dehydration phase (p<0.05) while in the control trial, FMD remained practically unaffected [5.6±0.8% to 5.4±1.1%, respectively (p>0.05)]. Dehydration equal to -1.9±0.1% of body weight (p<0.001) decreased plasma volume by 3.5±1.8%. CONCLUSION: Our data suggest that milddehydration induced by moderate exercise and fluid restriction may impair endothelium function, an early marker of subclinical atherosclerosis. 4th Study PURPOSE: We hypothesized that pharyngeal receptor activation through ingestion of a small amount of water could enhance performance better than mouth rinse in dehydrated subjects. METHODS: Ten healthy, trained male cyclists (weight: 78.2±2.2 kg, age: 25.9±1.0 y, body fat: 15.6±1.6 %, VO2 max: 53.8±4.8 ml·kg-1·min-1) completed three time to exhaustion cycling tests at 75% of their maximum power output, after being dehydrated by 2% of their total body weight. Dehydration was induced by a 2 h moderate intensity exercise (70% of maximum heart rate) which included 30-minutes intervals alternating between jogging and cycling in the heat (31°C). All subjects repeated the protocol in random order on three separate occasions: a) mouth rinse with 25 ml of plain water before and every 5 minutes of the trial (MR), b) ingestion of 25 ml of plain water before and every 5 minutes (DR), and c) control (CON) where no fluids were provided. Blood and urine samples were collected at the beginning of the dehydration phase, before the performance test and at the end of the experimental protocol. RESULTS: A significantly greater time to exhaustion was recorded in the DR trial compared to MR and CON (21.9±1.2 min vs. 18.7±1.3 min and 17.7±1.1 min, respectively p<0.05). There were no differences in mean heart rate, maximum lactate concentration, or rating of perceived exertion between the three trials (p>0.05). CONCLUSION: The results demonstrated that even small amount of water ingestion increased exercise time in dehydrated subjects possibly through activation of pharyngeal receptors.

Το νερό είναι το πιο σημαντικό συστατικό στη ζωή. Η διατήρηση της υδατικής και ηλεκτρολυτικής ομοιόστασης είναι μείζονος σημασίας για την εύρυθμη λειτουργία του οργανισμού. Η μείωση των επιπέδων υδάτωσης επιφέρει αποδεδειγμένα αρνητικά αποτελέσματα στην υγεία και στην αθλητική απόδοση. Παρόλο που υπάρχουν πολλές μελέτες οι οποίες να εξετάζουν τα επίπεδα υδάτωσης, την επικράτηση της αφυδάτωσης και την αθλητική απόδοση σε ενήλικες, λίγα επιστημονικά δεδομένα υπάρχουν για τη σχέση μεταξύ επιπέδων υδάτωσης και παιδιών. Μία από τις πιο σοβαρές επιπτώσεις της αφυδάτωσης είναι και η επιβάρυνση της καρδιαγγειακής λειτουργίας. Η δυσλειτουργία του ενδοθηλίου παράλληλα, έχει αποδειχτεί ότι επιβαρύνει σημαντικά την καρδιαγγειακή λειτουργία, και συνεπώς, είναι πιθανό να υπάρχει κάποιος μηχανισμός ο οποίος να συνδέει τα μειωμένα επίπεδα υδάτωσης, την ενδοθηλιακή και την καρδιαγγειακή λειτουργία. Τέλος, έντονο επιστημονικό ενδιαφέρον εμφανίζει τα τελευταία χρόνια η μελέτη των μηχανισμών με τους οποίους η πρόσληψη υγρών επηρεάζει την αθλητική απόδοση στη ζέστη. Τα αποτελέσματα ωστόσο, είναι αντικρουόμενα. Συνοψίζοντας τα προαναφερθέντα και λαμβάνοντας υπόψη τα ερευνητικά κενά που υπάρχουν, οι στόχοι της παρούσας διατριβής είναι οι εξής: (i) Να αξιολογηθούν τα επίπεδα υδάτωσης σε νεαρούς αθλητές διαφόρων αθλημάτων, (ii) Να μελετηθεί η επίδραση των επιπέδων υδάτωσης στη λειτουργία του ενδοθηλίου και κατ’ επέκταση στην καρδιαγγειακή λειτουργία (iii) Να προσδιοριστεί η δράση των στοματοφαρυγγικών υποδοχέων στην επίδραση της πρόσληψης υγρών κατά τη διάρκεια της άσκησης και στην αθλητική απόδοση.