The Role of Salt and Glucose Replacement Drinks in the Marathon

Exercise-Associated Hyponatremia in Marathon Runners

Exercise-associated hyponatremia (EAH) was first described as water intoxication by Noakes et al. in 1985 and has become an important topic linked to several pathological conditions. However, despite progressive research, neurological disorders and even deaths due to hyponatremic encephalopathy continue to occur. Therefore, and due to the growing popularity of exercise-associated hyponatremia, this topic is of great importance for marathon runners and all professionals involved in runners' training (e.g., coaches, medical staff, nutritionists, and trainers). The present narrative review sought to evaluate the prevalence of EAH among marathon runners and to identify associated etiological and risk factors. Furthermore, the aim was to derive preventive and therapeutic action plans for marathon runners based on current evidence. The search was conducted on PubMed, Scopus and Google Scholar using a predefined search algorithm by aggregating multiple terms (marathon run; exercise; sport; EAH; electrolyte disorder; fluid balance; dehydration; sodium concentration; hyponatremia). By this criterion, 135 articles were considered for the present study. Our results revealed that a complex interaction of different factors could cause EAH, which can be differentiated into event-related (high temperatures) and person-related (female sex) risk factors. There is variation in the reported prevalence of EAH, and two major studies indicated an incidence ranging from 7 to 15% for symptomatic and asymptomatic EAH. Athletes and coaches must be aware of EAH and its related problems and take appropriate measures for both training and competition. Coaches need to educate their athletes about the early symptoms of EAH to intervene at the earliest possible stage. In addition, individual hydration strategies need to be developed for the daily training routine, ideally in regard to sweat rate and salt losses via sweat. Future studies need to investigate the correlation between the risk factors of EAH and specific subgroups of marathon runners.

Hydration Status, Fluid Intake, Sweat Rate, and Sweat Sodium Concentration in Recreational Tropical Native Runners

AIM

The purpose of this study was to evaluate hydration status, fluid intake, sweat rate, and sweat sodium concentration in recreational tropical native runners.

METHODS

A total of 102 males and 64 females participated in this study. Participants ran at their self-selected pace for 30-100 min. Age, environmental conditions, running profiles, sweat rates, and sweat sodium data were recorded. Differences in age, running duration, distance and pace, and physiological changes between sexes were analysed. A p-value cut-off of 0.05 depicted statistical significance.

RESULTS

Males had lower relative fluid intake (6 ± 6 vs. 8 ± 7 mL·kg-1·h-1, p < 0.05) and greater relative fluid balance deficit (-13 ± 8 mL·kg-1·h-1 vs. -8 ± 7 mL·kg-1·h-1, p < 0.05) than females. Males had higher whole-body sweat rates (1.3 ± 0.5 L·h-1 vs. 0.9 ± 0.3 L·h-1, p < 0.05) than females. Mean rates of sweat sodium loss (54 ± 27 vs. 39 ± 22 mmol·h-1) were higher in males than females (p < 0.05).

CONCLUSIONS

The sweat profile and composition in tropical native runners are similar to reported values in the literature. The current fluid replacement guidelines pertaining to volume and electrolyte replacement are applicable to tropical native runners.

Interindividual variability in sweat electrolyte concentration in marathoners

BACKGROUND

Sodium (Na(+)) intake during exercise aims to replace the Na(+) lost by sweat to avoid electrolyte imbalances, especially in endurance disciplines. However, Na(+) needs can be very different among individuals because of the great inter-individual variability in sweat electrolyte concentration. The aim of this investigation was to determine sweat electrolyte concentration in a large group of marathoners.

METHODS

A total of 157 experienced runners (141 men and 16 women) completed a marathon race (24.4 ± 3.6 °C and 27.7 ± 4.8 % of humidity). During the race, sweat samples were collected by using sweat patches placed on the runners' forearms. Sweat electrolyte concentration was measured by using photoelectric flame photometry.

RESULTS

As a group, sweat Na(+) concentration was 42.9 ± 18.7 mmol·L(-1) (minimal-maximal value = 7.0-95.5 mmol·L(-1)), sweat Cl(-) concentration was 32.2 ± 15.6 mmol·L(-1) (7.3-90.6 mmol·L(-1)) and sweat K(+) concentration was 6.0 ± 0.9 mmol·L(-1) (3.1-8.0 mmol·L(-1)). Women presented lower sweat Na(+) (33.9 ± 12.1 vs 44.0 ± 19.1 mmol·L(-1); P = 0.04) and sweat Cl(-) concentrations (22.9 ± 10.5 vs 33.2 ± 15.8 mmol·L(-1); P = 0.01) than men. A 20 % of individuals presented a sweat Na(+) concentration higher than 60 mmol·L(-1) while this threshold was not surpassed by any female marathoner. Sweat electrolyte concentration did not correlate to sweat rate, age, body characteristics, experience or training. Although there was a significant correlation between sweat Na(+) concentration and running pace (r = 0.18; P = 0.03), this association was weak to interpret that sweat Na(+) concentration increased with running pace.

CONCLUSIONS

The inter-individual variability in sweat electrolyte concentration was not explained by any individual characteristics except for individual running pace and sex. An important portion (20 %) of marathoners might need special sodium intake recommendations due to their high sweat salt losses.

Sweat sodium loss influences serum sodium concentration in a marathon

The aim of this investigation was to determine the influence of sweat electrolyte concentration on body water and electrolyte homeostasis during a marathon. Fifty-one runners completed a marathon race in a warm and dry environment (24.4 ± 3.6 °C). Runners were classified as low-salt sweaters (n = 21; <30 mmol/L of sweat Na⁺ concentration), typical sweaters (n = 20; ≥30 and <60 mmol/L of sweat Na⁺ concentration), and salty sweaters (n = 10; ≥60 mmol/L of sweat Na⁺ concentration). Before and after the race, body mass and a sample of venous blood were obtained. During the race, sweat samples were collected by using sweat patches, and fluid and electrolyte intake were recorded by using self-reported questionnaires. Low-salt, typical and salty sweaters presented similar sweat rates (0.93 ± 0.2, 0.92 ± 0.29, 0.99 ± 0.21 L/h, respectively), body mass changes (-3.0 ± 1.0, -3.3 ± 1.0, -3.2 ± 0.8%), total Na⁺ intake (12.7 ± 8.1, 11.5 ± 9.7, 14.5 ± 16.6 mmol), and fluid intake (1.3 ± 0.8, 1.2 ± 0.8, 1.2 ± 0.6 L) during the race. However, salty sweaters presented lower post-race serum Na⁺ concentration (140.8 ± 1.3 vs 142.5 ± 1.1, 142.4 ± 1.4 mmol/L; P < 0.01) and serum osmolality (297 ± 6 vs 299 ± 5, 301 ± 6 mOsm/kg; P < 0.05) than low-salt and typical sweaters. Sweat electrolyte concentration could influence post-race serum electrolyte concentration in the marathon. However, even the saltiest sweaters did not develop exercise-associated hyponatremia or associated symptoms.

The effects of ingestion of sugarcane juice and commercial sports drinks on cycling performance of athletes in comparison to plain water

PURPOSE

Sugarcane juice (ScJ) is a natural drink popular in most tropical Asian regions. However, research on its effect in enhancing sports performance is limited. The present investigation was to study the effect of sugarcane juice on exercise metabolism and sport performance of athletes in comparison to a commercially available sports drinks.

METHODS

Fifteen male athletes (18-25 yrs) were asked to cycle until volitional exhaustion at 70% VO2 max on three different trials viz. plain water (PW), sports drink (SpD) and ScJ. In each trial 3ml/kg/BW of 6 % of carbohydrate (CHO) fluid was given at every 20 min interval of exercise and a blood sample was taken to measure the hematological parameters. During recovery 200 ml of 9% CHO fluid was given and blood sample was drawn at 5, 10, 15 min of recovery.

RESULTS

Ingestion of sugarcane juice showed significant increase (P<0.05) in blood glucose levels during and after exercise compared to SpD and PW. However, no significant difference was found between PW, SpD and ScJ for total exercise time, heart rate, blood lactate and plasma volume.

CONCLUSION

ScJ may be equally effective as SpD and PW during exercise in a comfortable environment (<30°C) and a more effective rehydration drink than SpD and PW in post exercise as it enhances muscle glycogen resynthesis.

A scientific nutrition strategy improves time trial performance by ≈6% when compared with a self-chosen nutrition strategy in trained cyclists: a randomized cross-over study

We investigated whether an athlete’s self-chosen nutrition strategy (A), compared with a scientifically determined one (S), led to an improved endurance performance in a laboratory time trial after an endurance exercise. S consisted of about 1000 mL·h–1 fluid, in portions of 250 mL every 15 min, 0.5 g sodium·L–1, 60 g glucose·h–1, 30 g fructose·h–1, and 5 mg caffeine·kg body mass–1. Eighteen endurance-trained cyclists (16 male; 2 female) were tested using a randomized crossover-design at intervals of 2 weeks, following either A or S. After a warm-up, a maximal oxygen uptake test was performed. Following a 30-min break, a 2.5-h endurance exercise on a bicycle ergometer was carried out at 70% maximal oxygen uptake. After 5 min of rest, a time trial of 64.37 km (40 miles) was completed. The ingested nutrition was recorded every 15 min. In S, the athletes completed the time trial faster (128 vs. 136 min; p ≤ 0.001) and with a significantly higher power output (212 vs. 184 W; p ≤ 0.001). The intake of fluid, energy (carbohydrate-, mono-, and disaccharide), and sodium was significantly higher in S compared with A (p ≤ 0.001) during the endurance exercise. In the time trial, only sodium intake was significantly higher in S (p ≤ 0.001). We concluded that a time trial performance after a 2.5-h endurance exercise in a laboratory setting was significantly improved following a scientific nutrition strategy.

Effects of carbohydrates-BCAAs-caffeine ingestion on performance and neuromuscular function during a 2-h treadmill run: a randomized, double-blind, cross-over placebo-controlled study

BACKGROUND

Carbohydrates (CHOs), branched-chain amino acids (BCAAs) and caffeine are known to improve running performance. However, no information is available on the effects of a combination of these ingredients on performance and neuromuscular function during running.

METHODS

The present study was designed as a randomized double-blind cross-over placebo-controlled trial. Thirteen trained adult males completed two protocols, each including two conditions: placebo (PLA) and Sports Drink (SPD: CHOs 68.6 g.L-1, BCAAs 4 g.L-1, caffeine 75 mg.L-1). Protocol 1 consisted of an all-out 2 h treadmill run. Total distance run and glycemia were measured. In protocol 2, subjects exercised for 2 h at 95% of their lowest average speeds recorded during protocol 1 (whatever the condition). Glycemia, blood lactate concentration and neuromuscular function were determined immediately before and after exercise. Oxygen consumption (V˙O2), heart rate (HR) and rate of perceived exertion (RPE) were recorded during the exercise. Total fluids ingested were 2 L whatever the protocols and conditions.

RESULTS

Compared to PLA, ingestion of SPD increased running performance (p = 0.01), maintained glycemia and attenuated central fatigue (p = 0.04), an index of peripheral fatigue (p = 0.04) and RPE (p = 0.006). Maximal voluntary contraction, V˙O2, and HR did not differ between the two conditions.

CONCLUSIONS

This study showed that ingestion of a combination of CHOs, BCAAs and caffeine increased performance by about 2% during a 2-h treadmill run. The results of neuromuscular function were contrasted: no clear cut effects of SPD were observed.

TRIAL REGISTRATION

ClinicalTrials.gov, http://www.clinicaltrials.gov, NCT00799630.

Risk of hypothermia in a new Olympic event: the 10-km marathon swim

INTRODUCTION

There are no available data addressing the potential clinical risks of open-water swimming competitions.

OBJECTIVE

Address the risks of hypothermia and hypoglycemia during a 10-km open-water swimming competition in order to alert physicians to the potential dangers of this recently-introduced Olympic event.

METHODS

This was an observational cross-sectional study, conducted during a 10-km open-water event (water temperature 21 degrees C). The highest ranked elite open-water swimmers in Brazil (7 men, 5 women; ages 21+/-7 years old) were submitted to anthropometrical measurements on the day before competition. All but one athlete took maltodextrine ad libitum during the competition. Core temperature and capillary glycemia data were obtained before and immediately after the race.

RESULTS

Most athletes (83%) finished the race with mild to moderate hypothermia (core temperature <35 degrees C). The body temperature drop was more pronounced in female athletes (4.2+/-0.7 degrees C vs. male: 2.7+/-0.8 degrees C; p=0.040). When data from the athlete who did not take maltodextrine was excluded, capillary glycemia increased among athletes (pre 86.6+/-8.9 mg/dL; post 105.5+/-26.9 mg/dL; p=0.014). Time to complete the race was inversely related to pre- competition body temperature in men (r=-0.802; p=0.030), while it was inversely correlated with the change in capillary glycemia in women (r=-0.898; p=0.038).

CONCLUSION

Hypothermia may occur during open-water swimming events even in elite athletes competing in relatively warm water. Thus, core temperature must be a chief concern of any physician during an open-water swim event. Capillary glycemia may have positive effects on performance. Further studies that include more athletes in a controlled setting are warranted.

Nutrigenomics and personalized nutrition: science and concept

Diet and genomes interact. Nutrition has the most important life-long environmental impact on human health. While nutrigenetics addresses how an individual’s genetic makeup predisposes for dietary susceptibility, nutrigenomics asks how nutrition influences the expression of the genome. Nutrigenomics builds on the three omics disciplines transcriptomics, proteomics and metabolomics. They are a prerequisite for nutritional systems biology, the understanding of the interaction between food components and diet with cells, organs and the whole body. Personalized nutrition is a conceptual analog to personalized medicine. While there are food products available that address requirements or preferences of specific consumer groups, these products are based on empirical consumer science rather than on nutrigenomics and nutrigenetics. The latter two build the science foundation for understanding human variability in preferences, requirements and responses to diet, and may become the future tools for consumer assessment motivated by personalized nutritional counseling for health maintenance and disease prevention.