The prevalence of exercise-associated hyponatremia in 24-hour ultra-mountain bikers, 24-hour ultra-runners and multi-stage ultra-mountain bikers in the Czech Republic

Abstract

BackgroundTo assess the prevalence of exercise-associated hyponatremia (EAH) in two 24-hour mountain bike (MTB) (R1,R2), one 24-hour running (R3) and one multi-stage MTB (R4) races held in the Czech Republic in a cluster of four cross-sectional studies.MethodsIn 27 ultra-mountain bikers (ultra-MTBers), 12 ultra-runners, and 14 multi-stage MTBers, fluid intake, changes (Δ) in body mass, hematocrit, plasma volume, plasma [Na+], plasma [K+], plasma osmolality, urine [Na+], urine [K+], urine specific gravity, urine osmolality, K+/Na+ ratio in urine, transtubular potassium gradient and glomerular filtration rate were measured and calculated. The use of non-steroidal anti-inflammatory drugs and symptoms of EAH were recorded using post-race questionnaires.ResultsOf the 53 finishers, three (5.7%) developed post-race EAH, thereof one (3.7%) ultra-MTBer, one (8.3%) ultra-runner and one (7.1%) multi-stage MTBer. Plasma [Na+] decreased significantly (p < 0.001) only in R4. Urine osmolality (R1, R3, R4 p < 0.001; R2 p < 0.05) and glomerular filtration rate (p < 0.001) increased, and body mass decreased in all races (p < 0.05). Δ body mass was inversely related to the number of kilometers achieved (p < 0.001) in R2 where better ultra-MTBers tended to lose more weight. Δ body mass (p < 0.001) and %Δ body mass (p = 0.05) were positively related to lower post-race plasma [Na+] in R3 that was associated with increased loss in body mass. Fluid intake was positively related to race performance in R1 and R2 (R1: p = 0.04; R2: p = 0.01) where ultra-MTBers in R1 and R2 who drank more finished ahead of those who drank less. Post-race plasma [Na+] was negatively associated with race performance in ultra-MTBers in R2 (p < 0.05), similarly ultra-runners in R3 (p < 0.05) where finishers with more kilometres had lower post-race plasma [Na+].ConclusionsThe prevalence of EAH in the Czech Republic was no higher compared to existing reports on ultra-endurance athletes in other countries. Lower plasma [Na+] and development of EAH may be attributed to overdrinking, a pituitary secretion of vasopressin, an impaired mobilization of osmotically inactive sodium stores, and/or an inappropriate inactivation of osmotically active sodium.

Pre-race characteristics and race performance in hyponatremic and normonatremic finishers of Czech ultra-races

“…In summary, the primary etiology and pathophysiological mechanism underlying EAH in the present ultra-endurance athletes group was presumably overconsumption of hypotonic fluids in likely combination with non-osmotic arginin vasopressin secretion as we stated in our previous studies (Chlíbková et al, 2014;Chlíbková et al, 2015;Chlíbková et al, 2016).…”

“…The ultrarunners had to run 66 laps of a 1,500 m circuit. Other details of the races are provided elsewhere (Chlíbková et al, 2014).…”

“…Recently, it was reported that in 2012/2013 11.5% of 113 ultra-endurance athletes from a number of different sports developed post-race hyponatremia (Chlíbková et al, 2015). This was an increase from previous research on this population in the Czech Republic in 2012 (5.7% of the 53 finishers) (Chlíbková, Knechtle, Rosemann, Žákovská, & Tomášková, 2014). It is important to examine the risk factors for EAH (Bennett et al, 2013;Hew-Butler et al, 2015;.…”

“…It is important to examine the risk factors for EAH (Bennett et al, 2013;Hew-Butler et al, 2015;. Risk factors such as overdrinking water, sport drinks, and other hypotonic beverages; weight gain during race, race fluid intake of finishers and pre and during a race habits were investigated in detail in our recent publications (Chlíbková et al, 2015;Chlíbková et al, 2014;Chlíbková, Rosemann, Posch, Matoušek, & Knechtle, 2016). Little is known; however, about selected pre-race characteristics and risk factors such as training experience, gender, age, pre-race BMI and race performance between those ultra-athletes developing EAH and those not developing EAH.…”

Ultramarathon Running: Medical Issues

“…In ultra-marathons held in Switzerland, Europe, the prevalence of exerciseassociated hyponatremia was between 0% and 8% [66,67,69]. Also in ultra-marathoners competing in the Czech Republic, Europe, the prevalence of exercise-associated hyponatremia was low [70].…”