Reliability And Validity Of The MX3 Portable Sweat Sodium Analyser During Exercise In Warm Conditions

PURPOSE: Accurately measuring sweat sodium concentration ([Na+]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na+]. This study aimed to assess the validity and reliability of the MX3 hydration testing system. METHODS: Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected using absorbent patches placed at three measurement sites being the left ventral forearm, the upper back, and the right thigh. The samples were then analysed for sweat [Na+] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample. RESULTS: The mean difference between duplicate measurements was 0.1 mmoL·L-1 (95% limits of agreement (LoA): -9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L-1. When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of -1.9 mmoL·L-1 (95% LoA: -18.2, 14.5). The CV was 9.8% and the standard error of the estimate was 8.0 mmoL·L-1. CONCLUSION: In summary, the MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement with, and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity.