Karen Sharwood

Weight changes, medical complications, and performance during an Ironman triathlon

Background: Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss. Objectives: To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses. Methods: Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race. Results: Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups. Conclusions: Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.

Obesity and overweight in South African primary school children—the Health of the Nation Study

Objectives. To determine the prevalence of overweight and obesity in a sample of South African children aged 6–13 years. Design. Random sampling of schools within each provincial and socio-economic category. Setting. Primary school children from 5 South African provinces. Subjects. 10 195 (5 611 male and 4 584 female) primary school children. Outcome measure. Height and weight were measured and body mass index (BMI) (weight (kg)/height (m)2) was calculated for each grouping (age x gender x ethnic group). Cut-off points for BMI defining obese and overweight for gender and age (6–13 years) were calculated in accordance with international standards. Results. There were significant differences in height and mass between the different ethnic groups and genders. This trend was not evident for the BMI values. The prevalence of obesity within the sample was 3.2% for boys and 4.9% for girls, whereas overweight prevalence was 14.0% for boys and 17.9% for girls. When the contribution of each ethnic group was adjusted to the demographics of South Africa these values were only slightly different. The prevalence of obesity and overweight among boys was 2.4% and 10.9% respectively, while obese and overweight girls comprised 4.8% and 17.5%, respectively. Conclusions. South African children show trends of obesity and overweight, similar to values in developed countries about 10 years ago. Intervention strategies to combat an increasingly sedentary lifestyle may need to be developed for the South African context.

Weight changes, sodium levels, and performance in the South African Ironman Triathlon.

ObjectiveTo establish relationships between body weight changes and serum sodium during and after an Ironman Triathlon, and postrace fluid status and rectal temperature, including the incidence of hyponatremia. DesignDescriptive research. SettingThe 2000 South African Ironman Triathlon, in which each athlete swam 3.8 km, cycled 180 km, and ran 42.2 km. ParticipantsAll entrants in the race were invited to participate in the study. MethodsAthletes were weighed at registration, immediately prerace, immediately postrace, and 12 hours later. Blood samples were drawn at registration and immediately postrace. Rectal temperatures were measured postrace. ResultsStarting body weight was significantly related to total finishing time (r = 0.27) and to cycling (r = 0.20) and running (r = 0.28) time. Body weight decreased significantly (p < 0.0001) during the race and had not returned to prerace values 12 hours later (p < 0.0001). Percentage change in body weight was unrelated to postrace rectal temperatures and inversely related to the postrace serum sodium concentrations (r = −0.45). Postrace serum sodium concentrations fell within a normal distribution (141.8 ± 3.1 mmol.L−1, mean ± SD) and were negatively correlated to overall triathlon time (r = −0.22). Three sodium values (0.6%) were below 135 mmol.L−1. Percentage change in body weight was unrelated to time in the marathon leg. ConclusionsPercentage change in body weight was linearly related to postrace serum sodium concentrations but unrelated to postrace rectal temperature or performance in the marathon. There was no evidence that in this study, more severe levels of weight loss or dehydration were related to either higher body temperatures or impaired performance.

Oral salt supplementation during ultradistance exercise.

ObjectiveThe objective of this study was to determine whether sodium supplementation 1) influences changes in body weight, serum sodium [Na], and plasma volume (PV), and 2) prevents hyponatremia in Ironman triathletes. SettingThe study was carried out at the South African Ironman triathlon. ParticipantsThirty-eight athletes competing in the triathlon were given salt tablets to ingest during the race. Data collected from these athletes [salt intake group (SI)] were compared with data from athletes not given salt [no salt group (NS)]. InterventionsSalt tablets were given to the SI group to provide approximately 700 mg/h of sodium. Main Outcome MeasurementsSerum sodium, hemoglobin, and hematocrit were measured at race registration and after the race. Weights were measured before and after the race. Members of SI were retrospectively matched to subjects in NS for 1) weight change and 2) pre-race [Na]. ResultsThe SI group developed a 3.3-kg weight loss (p < 0.0001) and significantly increased their [Na] (&Dgr;[Na] 1.52 mmol/L; p = 0.005). When matched for weight change during the race, SI increased their [Na] compared with NS (mean 1.52 versus 0.04 mmol/L), but this did not reach statistical significance (p = 0.08). When matched for pre-race [Na], SI had a significantly smaller percent body weight loss than NS (−4.3% versus −5.1%; p = 0.04). There was no significant difference in the increase of [Na] in both groups (1.57 versus 0.84 mmol/L). PV increased equally in both groups. None of the subjects finished the race with [Na] < 135 mmol/L. ConclusionsSodium ingestion was associated with a decrease in the extent of weight loss during the race. There was no evidence that sodium ingestion significantly influenced changes in [Na] or PV more than fluid replacement alone in the Ironman triathletes in this study. Sodium supplementation was not necessary to prevent the development of hyponatremia in these athletes who lost weight, indicating that they had only partially replaced their fluid and other losses during the Ironman triathlon.

The dipsomania of great distance: water intoxication in an Ironman triathlete

Of 371 athletes (62% of all finishers) whose weights were measured before and after the 226 km South African Ironman Triathlon, the athlete who gained the most weight (3.6 kg) during the race was the only competitor to develop symptomatic hyponatraemia. During recovery, he excreted an excess of 4.6 litres of urine. This case report again confirms that symptomatic hyponatraemia is caused by considerable fluid overload independent of appreciable NaCl losses. Hence prevention of the condition requires that athletes be warned not to drink excessively large volumes of fluid (dipsomania) during very prolonged exercise. This case report also shows that there is a delayed diuresis in this condition and that it is not caused by renal failure.

Sodium supplementation is not required to maintain serum sodium concentrations during an Ironman triathlon

Context: Critical assessment of recommendations that athletes consume additional sodium during athletic events. Objective: To evaluate if sodium supplementation is necessary to maintain serum sodium concentrations during prolonged endurance activity and prevent the development of hyponatraemia. Design: Prospective randomised trial of athletes receiving sodium (620 mg table salt), placebo (596 mg starch), or no supplementation during a triathlon. The sodium and placebo tablets were taken ad libitum, with the suggested range of 1–4 per hour. Setting: The 2001 Cape Town Ironman triathlon (3.8 km swim, 180 km cycle, 42.2 km run). Subjects: A total of 413 triathletes completing the Ironman race. Main outcome measures: Sodium supplementation was not necessary to maintain serum sodium concentrations in athletes completing an Ironman triathlon nor required to prevent hyponatraemia from occurring in athletes who did not ingest supplemental sodium during the race. Results: Subjects in the sodium supplementation group ingested an additional 3.6 (2.0) g (156 (88) mmol) sodium during the race (all values are mean (SD)). There were no significant differences between the sodium, placebo, and no supplementation groups with regard to age, finishing time, serum sodium concentration before and after the race, weight before the race, weight change during the race, and rectal temperature, systolic and diastolic blood pressure after the race. The sodium supplementation group consumed 14.7 (8.3) tablets, and the placebo group took 15.8 (10.1) tablets (p  =  0.55; NS). Conclusions: Ad libitum sodium supplementation was not necessary to preserve serum sodium concentrations in athletes competing for about 12 hours in an Ironman triathlon. The Institute of Medicine’s recommended daily adequate intake of sodium (1.5 g/65 mmol) seems sufficient for a healthy person without further need to supplement during athletic activity.

Left ventricular wall segment motion after ultra-endurance exercise in humans assessed by myocardial speckle tracking

AIMS Assessment of the left ventricular responses to prolonged exercise has been limited by technology available to assess cardiac tissue movement. Recently developed strain and strain rate imaging provide the unique opportunity to assess tissue deformation in all planes of motion. METHODS AND RESULTS Nineteen runners (mean+/-SD age; 41+/-9 years) were assessed prior to and within 60 min (34+/-10 min) of race finish (Comrades Marathon, 89 km). Standard echocardiography assessed ejection fraction and the ratio of early to atrial (E/A) peak transmitral blood flow velocities. Myocardial speckle tracking determined segmental strain as well as systolic and diastolic strain rates in radial, circumferential, and longitudinal planes. Cardiac troponin T (cTnT) assessed cardiomyocyte insult. Ejection fraction (71+/-5 to 64+/-6%) and E/A (1.47+/-0.35 to 1.25+/-0.30) were reduced (P<0.05). Peak strain and peak systolic and diastolic strain rates were altered post-race in circumferential (e.g. peak strain reduced from 21.3+/-2.4 to 17.3+/-3.2%, P<0.05) and radial planes. Some individual heterogeneity was observed between segments and planes of motion. A post-race elevation in cTnT (range 0.013-0.272 microg/L) in 5/12 runners did not differentiate changes in LV function. CONCLUSION Completion of the Comrades Marathon resulted in a depression in ejection fraction, E/A, as well as radial and circumferential strain and strain rates. Group data, however, masked some heterogeneity in cardiac function.

Maintenance of plasma volume and serum sodium concentration despite body weight loss in ironman triathletes.

Objective:To examine the relationship between body weight, plasma volume, and serum sodium concentration ([Na+]) during prolonged endurance exercise. Design:Observational field study. Settings:2000 South African Ironman Triathlon. Participants:181 male triathletes competing in an Ironman triathlon. Main Outcome Measures:Body weight, plasma volume, and serum ([Na+]) change from pre- to postrace. Results:Significant body weight loss occurred (−4.9 ± 1.7%; P < 0.0001), while both plasma volume (1.0 ± 11.2%; P = 0.4: NS) and serum [Na+] (0.6 ± 2.4%; P < 0.001) increased from pre- to postrace. Blood volume (−0.6 ± 6.6%) and red cell volume (−2.6 ± 5.5%; P < 0.001) decreased in conjunction with the body weight loss. There was a strong correlation between blood and plasma volume change, both as a percentage, and absolute change in fluid volume (r = 0.9; P < 0.001). Body weight change was positively correlated with plasma volume change (r = −0.4; P < 0.001), but inversely correlated with serum [Na+] change (r = −0.4; P < 0.001). Plasma volume change was not significantly correlated with serum [Na+] change (r = 0.0; NS). Serum [Na+] change was inversely correlated with both percentage of red cell volume change (r = −0.2; P < 0.05) and percentage body weight change (r = −0.4; P < 0.001). Conclusion:Plasma volume and serum [Na+] were maintained in male Ironman triathletes, despite significant (5%) body weight loss during the course of the race. Body weight was not an accurate “absolute” surrogate of fluid balance homeostasis during prolonged endurance exercise. Clinicians should be warned against viewing these three regulatory parameters as interchangeable during an Ironman triathlon.

Dysnatremia predicts a delayed recovery in collapsed ultramarathon runners.

Objective:To assess (1) the incidence of dysnatremia in collapsed runners presenting to the medical tent of the 89-km Comrades Marathon and whether dysnatremia influences time to discharge, and (2) whether intravenous fluids could restore serum sodium concentration ([Na+]) to 140 mM faster than could the administration of oral fluids. Design:Prospective randomized controlled trial. Setting:2005 Comrades Marathon. Participants:One hundred thirty-three collapsed runners and 31 control-group runners. Interventions:Collapsed runners presenting to the medical tent at the finish of the 2005 Comrades Marathon were randomized into an intravenous or oral fluid administration group, with the type and amount of fluid administered dictated by initial [Na+]. Main Outcome Measures:Time to discharge, serum [Na+]. Results:Forty-five percent of collapsed runners were hypernatremic, 2% were hyponatremic, and 53% were normonatremic. Normonatremic runners spent significantly less time in the medical tent (80 ± 31 minutes) compared with hypernatremic (102 ± 36 minutes) and hyponatremic (146 ± 122 minutes) runners. Intravenous fluid therapy produced larger but nonsignificant reductions in [Na+] than oral therapy (−2.1 ± 3.1 versus −0.7 ± 1.8 mM); however, 45% of runners assigned to the oral fluid group could not tolerate oral rehydration. Conclusions:A slight majority of collapsed runners were normonatremic and spent significantly less time in the medical tent compared with hyper- and hyponatremic athletes. Initial rates of correction of hypernatremia were similar with intravenous and oral hypotonic fluid therapy. Clinicians should be advised that intravenous fluid resuscitation may best benefit hypernatremic collapsed runners who are intolerant to oral fluid ingestion.

Changes in muscle power and neuromuscular efficiency after a 40-minute downhill run in veteran long distance runners.

ObjectiveTo establish whether there was a relationship between the total accumulated distances of racing in veteran runners and the neuromuscular efficiency of the quadriceps muscles before and after a downhill run. SettingUniversity of Cape Town, Sports Science Institute of South Africa. ParticipantsTwenty male veteran long distance runners (45–50 years of age) with a range of training (1,300 km to 111,280 km) and racing (0 km to 9,737 km) experience. InterventionA 40-minute downhill run (−10% decline) on a treadmill, at a speed corresponding to 70% of the subjects peak treadmill running speed. Main Outcome MeasuresThe difference between integrated electromyography (IEMG)/mean force over a 5 s maximal voluntary isometric contraction before and after the downhill run was calculated as the delta (&Dgr;) neuromuscular efficiency. This was related to the total kilometers trained, current training distance, total kilometers raced, and number of races > 56 km. The difference in drop jump height before and after the downhill run was measured as well as changes in heart rate throughout the run. ResultsThere was a significant curvilinear relationship between the &Dgr; neuromuscular efficiency and total kilometers raced (R2 = 0.53, p < 0.05), and a significant inverse relationship between &Dgr; neuromuscular efficiency and the number of races > 56 km (r = −0.50, p < 0.05). Drop jump height decreased after the downhill run, and heart rate increased during the run. ConclusionsRunners who have raced an accumulated distance of > 5,000 km show a significant dissociation in the &Dgr; neuromuscular efficiency after a downhill run, compared with less experienced runners. Although possible causes for the dissociation are discussed, further research is needed.