Table 2

Comparisons of sodium and fluid balance measured during the recovery period after exercise demonstrating race characteristics and biochemical differences between fluid overload hyponatraemia (Irving et al,123 Speedy et al141 and Speedy et al140) versus suspected hypovolaemic hyponatraemia (Owen et al139)

VariableIrving et al (1991)Speedy et al (2000)Speedy et al (2000: 2 cases)Owen et al (2014)
Number of EAH participants (classification)8 (symptomatic)7 (symptomatic)2 (asymptomatic)26 (asymptomatic)
Peak race temperature (°C)NR212133
Mean exercise duration (h)<11 (mean NR)1213/12 (case 1/case 2)22
Monitored recovery time (h)1611.611.7/131
Presenting U[Na+] (mmol/L)NR17* (41 controls†)NR15 pre-trial (22.3 post-trial)
Presenting BUN (mg/dL)15.5 pretrial (9.8 post-trial)NRNR31 (pre-trial and post-trial)
Body sodium retained‡ (mean value)48%−84 mmol (0 mmol controls†)34%/0%96%
Excess fluid excreted§ (mL)+2953+1670 (−441 controls†)+1500/+2500+20
Presenting serum [Na+] (mean±SD)
Body weight change (post-race—pre-race) (%)NRNR+0.9/+2.5−2.4±3.1
  • *All but one of these seven athletes with EAH were released from the hospital with hyponatraemia.

  • †EAH data compared with control group of normonatraemic triathletes partaking in the same event.

  • ‡This represents the total amount of sodium retained by the body and expressed as a percentage of the total amount of sodium that was administered during the monitored recovery period (sodium deficit/sodium given). In Speedy et al,141 this was expressed as a positive or negative amount (mmol) of sodium administered so that a negative value reflected the amount of sodium retained by the body (U[Na+] output minus Na+ input).

  • §This represents the amount of fluid excreted (urine volume) during the recovery period compared with the amount of fluid that was administered during the recovery period.

  • BUN, blood urea nitrogen; EAH, exercise-associated hyponatraemia; NR, not reported in the manuscript.