Abstract
sess 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. Methods:In 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. Results:Of 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, R4p<0.001;R2p< 0.05) and glomerular filtration rate (p< 0.001) increased, and body mass decreased in all races (p<0.05).Δbody mass was inversely related to the number of kilometers achieved (p<0.001)in R2 where better ultra-MTBers tended to lose more weight.Δbody mass (p< 0.001) and %Δbody 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 + ]. Conclusions:The 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
similarly ultra-runners in R3 (p< 0.05) where finishers with more kilometres had lower post-race plasma [Na + ]. Conclusions:The 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. Keywords:24-hour race, Multi-stage race, Fluid intake, Body mass, Sodium * Correspondence:beat.knechtle@hispeed.ch † Equal contributors 2 Institute of General Practise and for Health Services Research, University of Zurich, Zurich, Switzerland 5 Facharzt FMH für Allgemeinmedizin, Gesundheitszentrum St. Gallen, Vadianstrasse 26, 9001 St. Gallen, Switzerland Full list of author information is available at the end of the article © 2014 Chlíbková et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Chlíbkováet al. Journal of the International Society of Sports Nutrition2014,11:3 http://www.jissn.com/content/11/1/3
Background Hydration status and its role in endurance performance is an important topic in exercise physiology. Recent studies investigated the changes in hydration status and the devel- opment of exercise-associated hyponatremia (EAH) in ultra-distance running races [1-15], in triathlon races [16-20], in mountain bike (MTB) multi-stage races [21-24], in single ultra-distance road cycling races [8,25,26], and in single ultra-distance MTB races [8,27,28]. However, 24- hour races have been investigated to a lesser extent [29-36]. Prior to 2010 there had been only one published study [9] investigating the prevalence of EAH in a single- stage ultra-marathon held in Europe. Excessive fluid consumption leading to weight gain is thought to be the principal cause of reduced plasma [Na + ] and previous studies in ultra-endurance events have shown an association between fluid intake, changes in body mass and plasma [Na + ] [16,29,37-40]. However, in some studies a significant relationship between post-race plasma [Na + ] and losses in body mass was reported [11,41]. EAH is most commonly found in athletes compet- ing in ultra-endurance events and it is defined as plasma [Na + ] < 135 mmol/l [39]. Signs and symptoms of EAH include nausea, vomiting, confusion, headache, seizures, pulmonary and cerebral oedema (hyponatremic encephal- opathy), and possibly death [39]. Risk factors for EAH in- clude low race pace, prolonged exercise with duration of more than four hours, female gender, a low body mass, pre-exercise hyperhydration, the use of non-steroidal anti- inflammatory drugs (NSAIDs), non-elite status, and ex- tremely hot or cold environment [12,20,39,40]. Aside from the excessive fluid consumption associated with a high fluid availability and a sustained intake, EAH occurs due to an increased retention of fluid brought on by non-osmotic secretion of arginine vasopressin [12,42,43], elevated sweat sodium loss, the inability to mobilise ex- changeable internal sodium stores, an inappropriate inacti- vation of osmotically-activesodium,metabolicwater production, and an impaired renal blood flow or glomeru- lar filtration [11,40]. Previous data on regular distance marathons have shown the prevalence of this fluid and electrolyte dis- order to be at 22% [39]. However, in general, in ultra- endurance athletes, the prevalence of
loss, the inability to mobilise ex- changeable internal sodium stores, an inappropriate inacti- vation of osmotically-activesodium,metabolicwater production, and an impaired renal blood flow or glomeru- lar filtration [11,40]. Previous data on regular distance marathons have shown the prevalence of this fluid and electrolyte dis- order to be at 22% [39]. However, in general, in ultra- endurance athletes, the prevalence of EAH should not exceed 10% [30], although there have been variable re- sults in studies investigating the prevalence of EAH in ultra-marathons and other ultra-endurance events. Knechtle et al. reported that the prevalence of EAH was no higher in ultra-endurance athletes compared with existing reports on marathoners and Ironman triathletes [8], while studies of a single-stage mountain ultra- marathoner race [10], a 1,600-km multi-stage race [13] in Australia and a European 24-hour race showed no cases of EAH [10,30]. Conversely, in a recent study of 45 male ultra-marathoners in a 161-km ultra-marathon held in the USA, 51.2% of the finishers presented with EAH [7]. The longer nature of the 161-km ultra-marathon coupled with the prolonged period spent on the trail were assumed to be the main reasons for the increased preva- lence of EAH, though when the data for five consecutive years were combined, the prevalence of EAH was shown to be 15.1% and positively related to ambient temperature [11]. In another study, 8% of mountain ultra-marathoners competing in a 7-stage race (350 km) in Switzerland devel- oped EAH [8], while mild asymptomatic EAH was found to occur in 4% of the volunteer ultra-endurance mountain runners in New Zealand [9]. Studies investigating fluid intake and electrolyte metabol- ism balance have also been conducted in mountain ultra- endurance bike races. Studies of a single stage MTB race held in Switzerland [27,28] and multi-stage races in South Africa, the Alps (i.e.Germany, Austria, Switzerland and Italy) [21,22]. Similarly, no case of EAH was found in 65 ultra-endurance road cyclists competing in a 720-km ultra- cycling marathon in Switzerland [25]. On the contrary, 50% of the participants in an Alaskan cold weather race presented symptoms of EAH upon finishing the race [24]. Knechtle et
and multi-stage races in South Africa, the Alps (i.e.Germany, Austria, Switzerland and Italy) [21,22]. Similarly, no case of EAH was found in 65 ultra-endurance road cyclists competing in a 720-km ultra- cycling marathon in Switzerland [25]. On the contrary, 50% of the participants in an Alaskan cold weather race presented symptoms of EAH upon finishing the race [24]. Knechtle et al. described for 200 athletes competing in different disciplines in Switzerland that 12 finishers (6%) developed EAH [8]. The prevalence of EAH was 13% in swimmers, 10.7% for road cyclists, 8% for both ultra- marathoners and mountain ultra-marathoners and no case in mountain bikers. Regarding different disciplines, EAH was higher in running [1,3,4,6-12,38,39,44,45] compared to cycling [8,22,25,27,28]. However, according to recent findings the comparison of cyclists and runners is prob- lematic because there are fewer studies of bike races [8]. There is a dearth of data on the prevalence of EAH in races held in Europe. Therefore, the aim of the current study was to investigate a series of ultra-endurance races held in the Czech Republic. Twenty-four-hour races held in different disciplines such as cycling and running are an ideal occasion to compare a prevalence of EAH between ultra-cyclists and ultra-runners. We intended to assess the prevalence of EAH in ultra-MTBers and ultra-runners in 24-hour races as single ultra-marathons and nearly non- stop performances without defined breaks with a specific load, and in a multi-stage race with an intermittent load with possibility of regeneration. We hypothesized an in- creased fluid intake during a 24-hour race for both cyclists and runners due to the large amount of fluids available at the refreshment stations in every lap. Since a slow running [31] or a slow cycling pace were considered as a main risk factor for fluid overload and development of EAH [21,25,29,38] we hypothesized that the prevalence of EAH would be higher in 24-hour races compared to a MTB stage race because there is a possibility of excessive drink- ing behavior and the duration of exercise is nearly Chlíbkováet al. Journal of the International Society of Sports Nutrition2014,11:3 Page 2 of 17
risk factor for fluid overload and development of EAH [21,25,29,38] we hypothesized that the prevalence of EAH would be higher in 24-hour races compared to a MTB stage race because there is a possibility of excessive drink- ing behavior and the duration of exercise is nearly Chlíbkováet al. Journal of the International Society of Sports Nutrition2014,11:3 Page 2 of 17 http://www.jissn.com/content/11/1/3
24 hours. Regarding recent studies, we hypothesized that the prevalence of EAH would be higher in runners com- pared to cyclists. Finally, it was hypothesized, that body mass loss in all races would have no influence on race per- formance [18,38,46,47]. In cases of fluid overload, we would expect post-race an increase in body mass [39] and a decrease in plasma [Na + ] [12,39,48]. Methods Ethics Research within the projectproceeded in accordance with the law (No. 96/2001 Coll. M. S. on Human Rights and Bio- medicine and Act No. 101/2000 Coll. Privacy) and the study was approved by the local institutional ethics committee. Subjects (a cluster of four races) Data were collected during four ultra-endurance races in the Czech Republic, were derived from four observational, cross-sectional studies and comprised athletes (i.e.ultra- MTBers, ultra-runners, and mountain bikers) partici- pating in the‚Czech Championship 24-hour MTB race‘ in Jihlava city (R1), in the‚Bike Race Marathon Rohozec 24 hours‘in Liberec city (R2), in the‚Sri Chinmoy Self- Transcendence Marathon 24-hour race‘in Kladno city (R3) and in the Trilogy Mountain Bike Stage Race‘in Teplice nad Metují (R4) (see Tables 1 and 2). Race participants were notified of the study approximately three months before the race start via an e-mail and were in- formed about the planned investigation with indication that participation was voluntary. Those who volunteered were instructed to keep a training diary until the start of the race. The training three months before the race, (i.e.number and duration of training units, training distance in kilometers and hours pre-race experience) were recorded. A total of 58 athletes, thirteen recreational ultra- MTBers from 91 participants in solo category (R1), seventeen ultra-MTBers from 116 participants in solo category (R2), thirteen ultra-runners from 48 partici- pants in solo category (R3) and fifteen MTBers from 206 participants (R4), all originating from the Czech Repub- lic, agreed to participate (Table 2). Races (R1,R2,R3,R4) The first measurement was performed at the‚Czech Championship 24-hour MTB race‘in Jihlava (R1), the race with the highest number of participants from the series of 24-hour MTB races held in the Czech Republic. The ultra-MTBers started at
category (R3) and fifteen MTBers from 206 participants (R4), all originating from the Czech Repub- lic, agreed to participate (Table 2). Races (R1,R2,R3,R4) The first measurement was performed at the‚Czech Championship 24-hour MTB race‘in Jihlava (R1), the race with the highest number of participants from the series of 24-hour MTB races held in the Czech Republic. The ultra-MTBers started at 12:00 on May 19 th 2012 and finished at 12:00 on May 20 th 2012. The course was comprised of a 9.5 km single-track with an elevation of 220 m. A single aid station, located at the start/finish area was provided by the organizer where a variety of food and beverages such as hypotonic sports drinks, tea, soup, caffenaited drinks, water, fruit, vegetables, energy bars, bread, soup, sausages, cheese, bread, chocolate and biscuits were available. The ultra-MTBers could also use their own supplies in their pitstops. The maximum temperature was +30°C, the minimum temperature was +6°C during the night on some places of the route and the average temperature was +18 (6)°C. No precipitation was recorded and relative humidity was at 43 (12)% over the duration of the race. The largest and the oldest (18 th edition) 24-hour cyc- ling race in the Czech Republic with the longest trad- ition‚the, Bike Race Marathon Rohozec‘in Liberec (R2), took place from June 9 th 2012 to June 10 th 2012. The course was comprised of a12.6 km track with an eleva- tion of 250 m. The track surface consisted of paved and unpaved roads and paths. There was one aid sta- tion located at the start and finish with food and bever- ages similar to those mentioned above. The maximum temperature was +23°C, the minimum temperature was +6°C during the night and the average temperature was +15 (4)°C. Over the duration of the race, 3 (1.5) mm of precipitation was recorded and relative humid- ity varied from 44% till 98%. The‚Sri Chinmoy Self-transcendence Running Marathon 24- hour race‘(R3) took place from July 21 st 2012 to July 22 nd 2012 in Kladno. We chose this race because it was the largest 24-hour
the average temperature was +15 (4)°C. Over the duration of the race, 3 (1.5) mm of precipitation was recorded and relative humid- ity varied from 44% till 98%. The‚Sri Chinmoy Self-transcendence Running Marathon 24- hour race‘(R3) took place from July 21 st 2012 to July 22 nd 2012 in Kladno. We chose this race because it was the largest 24-hour running race in the Czech Republic with the highest number of participants and we also wanted to compare ultra-runners with ultra-MTBers. The lap was 1 km, situated around an athletic stadium on asphalt with 1 m rise. The athletes could consume food and beverages ad libitumfrom a buffet provided by the organizer with warm and cool food like apples, ananas, oranges, dried fruit, potatoes, rice, cookies,bread, pasta, porridge, soup, water, tea, isotonic drinks, fruit juices, cola, broth, and coffee. Runners could place their own camping tables and chairs with personal belongings, food and drinks in a Table 1 Description of races, Nr–number of race, TR–temperature range, AT–average temperature, AH–average relative humidity, weather, P–precipitation, F - finishers, prevalence of EAH (R1,R2,R3,R4) Nr Type of race TR (°C) AT (°C) AH (%) Weather P (mm) F Prevalence of EAH R1 24-h MTB race 6 –30 18 (6) 43 (1) Sun — 12 0 (0%) R2 24-h MTB race 6 –23 15 (4) 72 (2) Clouds 3 (2) 15 1 (6.7%) R3 24-h running race 10 –18 12 (3) 62 (3) Rain 15(5) 12 1 (8.3%) R4 Multi-stage race 22 –33 26 (7) 55 (9) Sun — 14 1 (7.1%) Chlíbkováet al. Journal of the International Society of Sports Nutrition2014,11:3 Page 3 of 17 http://www.jissn.com/content/11/1/3
designated area. The maximum temperature was +18°C, the minimum temperature was +10°C, and the average temperature was +12 (3)°C. On average 15 (5) mm of pre- cipitation was recorded and relative humidity changed from 58 till 94% over the duration of the race. The‚Trilogy Mountain Bike Stage Race‘(R4), the first MTB stage race held in the Czech Republic, took place from July 4 th 2012 till July 8 th 2012 in Teplice nad Metují. This four day race consisted of a prologue and three stages, each of which had a completely different character. We chose this race to compare 24-hour races with a stage race. The difficulty of this race was similar to other stage MTB races in Europe. The prologue cov- ered 3 km with 300 m difference in elevation, Stage 1 covered 66 km with 2,200 m of altitude to climb, Stage 2 was 63 km in length with 2,300 m difference in elevation and Stage 3 was 78.8 km with 3,593 m. Stage routes were characterized by a large number of individual trails which only interrupted by a necessary minimum of road sections. Aid stations located along the routes offered beverages such as hypotonic sports drinks, tea, soup, caffenaited drinks, water, fruit, vegetables, energy bars, bread, soup, sausages, cheese, bread, chocolate and bis- cuits. During the prologue the average temperature was +32 (1)°C and relative humidity was 55 (2)% over the duration of the race. At Stage 1 the maximum tempera- ture was +33°C, the minimum +22°C, the average temperature was +27 (7)°C and relative humidity chan- ged from 80% at the start till 48% at the end of the race. At Stage 2 the maximum temperature was +30°C, the minimum +22°C, the average temperature +25 (3)°C and relative humidity changed from 83% till 60% over the dur- ation of the race. At Stage 3 the maximum temperature was +31°C, the minimum +19°C, the average temperature was +25 (2)°C and relative humidity changed from 85% till 37% over the duration of the race. Procedures and calculations The procedures of pre- and post-race measurements were identical. At first,
and relative humidity changed from 83% till 60% over the dur- ation of the race. At Stage 3 the maximum temperature was +31°C, the minimum +19°C, the average temperature was +25 (2)°C and relative humidity changed from 85% till 37% over the duration of the race. Procedures and calculations The procedures of pre- and post-race measurements were identical. At first, pre-race anthropometry of the subjects was assessed. Athletes were measured after voiding their urinary bladder. Body mass was measured using a cali- brated commercial scale (Tanita BC-351, Tanita corpor- ation of America, Inc.) to the nearest 0.1 kg. Subjects were barefoot and generally clothed in cycling attire for both the pre- and post-race measurements. Body height was de- termined using a stadiometer (Harpenden Stadiometer, Baty International Ltd) to the nearest 0.01 m. Body mass index was calculated using body mass and body height. Blood samples were drawn from an antecubital vein. Standardization of the sitting position prior to blood col- lection was respected since postural changes can influence blood volume and concentration of hematocrit. One Sar- stedt S-Monovette (plasma gel, 7.5 ml) for chemical and one Sarstedt S-Monovette (EDTA, 2.7 ml) for hemato- logical analysis were cooled and sent to the laboratory and were analysed within 6 hours. Blood samples were ob- tained to determine pre- and post-race hematocrit, plasma [Na + ], plasma [K + ], and plasma osmolality. Hematocrit was determined using Sysmex XE 2100 (Sysmex Corpor- ation, Japan), plasma [Na + ] and plasma [K + ]weredeter- mined using biochemical analyzer Modula SWA, Modul P + ISE (Hitachi High Technologies Corporation, Japan, Roche Diagnostic), and plasma osmolality was determined using Arkray Osmotation (Arkray Factory, Inc., Japan). Samples of urine were collected in one Sarstedt monovett Table 2 Age, anthropometry, training, pre-race experience, and race performance of subjects (R1,R2,R3,R4), n = 53 Race 1 n = 12 Race 2 n = 15 Race 3 n = 12 Race 4 n = 14 Type of race 24-h MTB race 24-h MTB race 24-hour RUN race Stage MTB race Age, y 40.3 (9.1) 36.8 (6.4) 38.3 (7.7) 38.0 (6.1) Body
Age, anthropometry, training, pre-race experience, and race performance of subjects (R1,R2,R3,R4), n = 53 Race 1 n = 12 Race 2 n = 15 Race 3 n = 12 Race 4 n = 14 Type of race 24-h MTB race 24-h MTB race 24-hour RUN race Stage MTB race Age, y 40.3 (9.1) 36.8 (6.4) 38.3 (7.7) 38.0 (6.1) Body mass, kg 75.2 (12.9) 72.1 (11.0) 66.3 (8.8) 75.3 (8.2) Body height, m 178.1 (11.6) 176.7 (9.5) 174.8 (10.9) 176.6 (5.5) BMI, kg/m 2 23.5 (2.0) 23.0 (1.9) 21.7 (1.2) 24.1 (2.0) Years as active cyclist or runner 10.3 (5.7) 8.6 (6.2) 9.8 (7.2) 11.4 (8.0) Number of finished ultra-marathons 9.3 (7.2) 8.3 (7.3) 15.7 (19.3) 5.6 (6.6) Total training hours weekly, h 12.3 (7.0) 12.1 (3.2) 10.6 (4.2) 10.7 (5.0) Training cycle or run hours weekly, h 11.6 (6.2) 11.4 (3.2) 8.2 (3.4) 9.6 (3.9) Training intensity, b/min 139.2 (6.7) 140.0 (9.3) 141.3 (18.8) 131.4 (12.3) Cases of EAH, absolute 01 1 1 Prevalence of EAH, % 0 6.7 8.3 7.1 Results are presented as mean (SD). EAH = exercise-associated hyponatremia. R1: ,Czech Championship 24-hour MTB race‘in Jihlava city, 24-hour MTB race, R2: Bike Race Marathon Rohozec 24 hours‘in Liberec city, 24-hour MTB race, R3: Sri Chinmoy Self-transcendence Marathon 24-h race‘in Kladno city, 24-hour RUN race, R4: Trilogy Mountain Bike Stage Race‘in Teplice nad Metují, multi-stage MTB race (prolog: 3 km with 300 m difference in elevation, Stage 1: 66 km with 2,200 m, Stage 2: 63 km with 2,300 m and Stage 3: 78.8 km with 3,593 m). Chlíbkováet al. Journal of the International Society of Sports Nutrition2014,11:3 Page 4 of 17 http://www.jissn.com/content/11/1/3
Description
Study investigates EAH prevalence in ultra-endurance athletes during 24-hour races.