Day-to-day variability and method agreement of sweat sodium concentration during pilocarpine iontophoresis and exercise.

purposeSweat sodium testing is increasingly used to estimate electrolyte losses during exercise; however, the reliability of sweat sodium assessment and the influence of methodological factors remain unclear. We evaluated the day-to-day variability and agreement between common sweat induction, collection, and analytical approaches, including pilocarpine iontophoresis and exercise-induced sweating.

methodsTwenty physically active adults (10 males 33 ± 11 y, 10 females 33 ± 10 y) completed two experimental trials separated by 48 h. Local sweat was induced at rest using pilocarpine iontophoresis. Participants then performed 60 min of treadmill running or cycling in 27 °C, 50% relative humidity, during which sweat was collected. Sweat sodium concentration was then analyzed and agreement between measurements was evaluated using Bland-Altman analysis.

resultsDay-to-day variability was good, with coefficients of variation of 13.8% for iontophoresis, 14.9% for exercise-derived Macroduct samples, and 9.9% for patch-based collection. Iontophoresis-derived sweat sodium concentrations were higher than exercise-derived values (42.0 ± 9.3 vs. 33.5 ± 11.0 mmol·L

conclusionSweat sodium concentration exhibits moderate day-to-day variability under controlled laboratory conditions. Exercise-derived values were lower than those obtained via pilocarpine iontophoresis, with iontophoresis overestimating sweat sodium by ~ 8.5mmol·L