Considerations For Using Spot Usg To Detect Inadequate Between Running Bout Fluid Intake Volume

Abstract

PURPOSE: No single measure to detect real time hydration status is without limits; however, the validity of using urine specific gravity (USG) has received considerable scrutiny recently. Data used to draw these conclusions potentially suffers from multiple flaws (e.g. samples collected immediately after exercise or when significant sweat loss has not been incurred) in regards to practical application for runners. This study examined the efficacy of USG to detect inadequate beverage fluid consumption between training bouts in a twice-per-day training scenario. METHODS: Data was pooled from multiple studies resulting in 143 total samples. USG of male and female runners was measured 10-14 hours after runs of 60-90 min in temperate to hot environments. Two meals and snacks were provided during the recovery period of each study. Multiple type of beverages were consumed, and all beverage fluid consumption was measured with some samples being taken before and after the second meal. Pearson r was examined for percent of sweat loss that was replaced with fluid from beverages and USG. Inadequate fluid intake detection was deemed to have taken place when <100% of sweat losses were replaced and USG was ≥1.020. Analysis were repeated after removing 80 samples in which participants did not begin their run euhydrated (USG <1.020) and/or lost <3% body mass in sweat. RESULTS: When all samples were included, moderate correlation between fluid replacement percentage and USG (r = -0.50; p < 0.001) was found. Total false diagnosis was detected in 22.4% (n = 32) of samples with 22% of runners replacing <100% of sweat losses exhibiting a USG < 1.020. After removing samples correlation strength increased (r = -0.69). Total false diagnosis was reduced to 12.7% (n = 8), and most importantly error for runners replacing <100% of sweat losses exhibiting a USG < 1.020 was decreased to 15%. CONCLUSIONS: Pre-run spot USG assessment can be used as a practical field assessment to determine if intentional increased recovery fluid intake is warranted when training twice per day, particularly if the first running bout is undertaken in a euhydrated state (USG < 1.020) and significant sweat losses are incurred (3% body mass).