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- ItemNo hyponatremia despite continuous plasma sodium decline in female runners during a seven stage ultramarathon(Nature Portfolio, 2025-04-03) Chlíbková, Daniela; Filipenská, Marina; Knechtle, Beat; Rauter, Samo; Trnka, Martin; Weiss, Katja; Rosemann, ThomasThe role of sodium supplements and sex in the occurrence of exercise-associated hyponatremia (EAH) remains controversial. This study investigated hydration status in ultrarunners (19 males and 9 females) who completed seven marathons over seven consecutive days. Due to the limited number of female participants, no statistical comparison between sexes was performed. Plasma sodium concentration ([Na+]) and multiple hydration markers were assessed before, during, and after the race. Reported sodium supplement consumption showed no association with plasma [Na+]. An overall decline in plasma [Na+] was observed in females (regression slope = -1.278, p=0.02) across the event, whereas no significant change was detected in males (slope = -0.325, p=0.57). Additionally, no significant associations were found between plasma [Na+] and other monitored variables, including sodium supplement intake, pre-race hydration strategy, body mass, total body water, plasma osmolality, hematocrit, hemoglobin, urine specific gravity, urinary [Na+], thirst rating, or fluid intake reported pre-, during, and post-stage. No cases of symptomatic or asymptomatic hyponatremia were identified, suggesting that total fluid and sodium intake were adequate to maintain fluid-electrolyte balance and prevent EAH in both sexes.
- ItemKinematic and neuromuscular responses to different visual focus conditions in stand-up paddleboarding(PeerJ, 2025-04-23) Freitas, Joo Diogo; Conceiço, Ana; Šťastný, Jan; Morais, Jorge E.; Marques, Diogo L.; Louro, Hugo; Marinho, Daniel Almeida; Neiva, Henrique P.Purpose: This study analyzed the kinematics and muscle activity during the stand-up paddleboarding (SUP) under different visual focus points in three conditions: i) eyes on the board nose, ii) looking at the turn buoy, and iii) free choice. Methods: Fourteen male paddleboarders (24.2 +/- 7.1 years) performed three trials covering 65 m, and the electromyographic (EMG) activation patterns and kinematic parameters in four cycle strokes for the left and right sides were analyzed. Surface EMG of the upper trapezius, biceps brachii, triceps brachii, tibialis anterior, and gastrocnemius medialis were recorded. The data were processed according to the percentage of maximum voluntary contraction (%MVC). Speed, stroke frequency (SF), stroke length, and stroke index (SI) were analyzed. Results: The speed, SF, and SI (p < 0.01, eta 2 >= 0.42) showed significant variance between conditions, with the free condition achieving the highest speed (1.20 +/- 0.21 m/s), SF (0.65 +/- 0.13 Hz) and SI (2.25 +/- 0.67 m2/s). This condition showed greater neuromuscular activity, particularly in the triceps brachii during both the left (42.25 +/- 18.76 %MVC) and right recoveries (32.93 +/- 16.06 %MVC). During the pull phase, the free choice presented higher biceps brachii activity (8.51 +/- 2.80 %MVC) compared to the eyes on the board nose (6.22 +/- 2.41 %MVC; p < 0.01), while showing lower activity in the triceps brachii (10.02 +/- 4.50 %MVC vs. 16.52 +/- 8.45 %MVC; p < 0.01) and tibialis anterior (12.24 +/- 7.70 %MVC vs. 17.09 +/- 7.73 %MVC; p < 0.01) compared to looking at the turn buoy. Conclusion: These results suggest that a free visual focus allows paddleboarders to enhance their kinematics and muscle activation, highlighting the significance of visual focus strategies in improving both competitive and recreational SUP performance.
- ItemExercise-Associated Hyponatremia in Endurance and Ultra-Endurance Performance-Aspects of Sex, Race Location, Ambient Temperature, Sports Discipline, and Length of Performance: A Narrative Review.(MDPI, 2019-08-26) Knechtle, Beat; Chlíbková, Daniela; Papadopoulou, Sousana; Mantzorou, Maria; Rosemann, Thomas; Nikolaidis, Pantelis T.Exercise-associated hyponatremia (EAH) is defined as a plasma sodium concentration of <135 mmol/L during or after endurance and ultra-endurance performance and was first described by Timothy Noakes when observed in ultra-marathoners competing in the Comrades Marathon in South Africa in the mid-1980s. It is well-established that a decrease in plasma sodium concentration <135 mmol/L occurs with excessive fluid intake. Clinically, a mild hyponatremia will lead to no or very unspecific symptoms. A pronounced hyponatremia (<120 mmol/L) will lead to central nervous symptoms due to cerebral edema, and respiratory failure can lead to death when plasma sodium concentration reaches values of <110-115 mmol/L. The objective of this narrative review is to present new findings about the aspects of sex, race location, sports discipline, and length of performance. The prevalence of EAH depends on the duration of an endurance performance (i.e., low in marathon running, high to very high in ultra-marathon running), the sports discipline (i.e., rather rare in cycling, more frequent in running and triathlon, and very frequent in swimming), sex (i.e., increased in women with several reported deaths), the ambient temperature (i.e., very high in hot temperatures) and the country where competition takes place (i.e., very common in the USA, very little in Europe, practically never in Africa, Asia, and Oceania). A possible explanation for the increased prevalence of EAH in women could be the so-called Varon-Ayus syndrome with severe hyponatremia, lung and cerebral edema, which was first observed in marathon runners. Regarding the race location, races in Europe seemed to be held under rather moderate conditions whereas races held in the USA were often performed under thermally stressing conditions (i.e., greater heat or greater cold).
- ItemChanges in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers(BioMed Central, 2014-03-24) Chlíbková, DanielaThe effects of running and cycling on changes in hydration status and body composition during a 24-hour race have been described previously, but data for 24-hour ultra-mountain bikers are missing. The present study investigated changes in foot volume, body composition, and hydration status in male and female 24-hour ultra-mountain bikers.
- ItemThe Effect of a 100-km Ultra-Marathon under Freezing Conditions on Selected Immunological and Hematological Parameters(FRONTIERS MEDIA SA, 2017-09-12) Žákovská, Alena; Knechtle, Beat; Chlíbková, Daniela; Miličková, Marie; Rosemann, Thomas; Nikolaidis, Pantelis T.Although moderate exercise is beneficial for the human body and its immune system, exhaustive ultra-endurance performance in cold conditions might be harmful. The aim of this study was to examine the effect of a 100-km ultra-marathon under cold conditions (temperatures from -1 degrees C to + 1 degrees C) on selected immunological, biochemical and hematological parameters. Participants were 15 runners (12 men and three women, age 40.3 +/- 9.7 years, body mass 67.3 +/- 9.0 kg and body height 1.74 +/- 0.10 m, mean +/- standard deviation). Leukocytes increased (p < 0.01) and, particularly, the number of leucocytes doubled in seven out of 15 athletes. Immature neutrophils, mature neutrophils and monocytes increased (p < 0.02), whereas lymphocytes and eosinophils did not change. IgG increased (p < 0.02), but IgA and IgM remained unchanged. Platelets increased (p < 0.01), whereas red blood cells, hematocrit and hemoglobin did not change. lactate dehydrogenase (LDH) and creatine kinase (CK) increased (p < 0.01), but alanine aminotransferase (ALT) did not change. There was an association between the markers of the acute inflammation of the organism (i.e., neutrophils, immature neutrophils, platelets, and monocytes) and the markers of muscle damage (i.e., CK, platelets, and LDH). There were no relationships among all the markers in relation to upper respiratory tract infections and liver damage. The highest change was noted in the increase of the number of immature neutrophils (1,019.2%) and CK levels (1,077.6%). In summary, this is the first study investigating immunological, hematological and biochemical parameters and showing that running a 100-km ultra-marathon under cold conditions leads to changes in several immunological, biochemical and hematological parameters indicating a severe stress on the body associated with increasing susceptibility to the development of infections.