Quantifying hydration-related measures and their association with wearable-derived ergonomic risk in warehouse workers.

INTRODUCTION: Warehouse workers may experience prolonged heat exposure and sweat loss, which can influence fatigue and movement patterns related to ergonomic risk. However, evidence in this occupational group remains limited. Therefore, we aimed to quantify acute (pre- and post-shift) and across-week (Days 1-4) changes in urine specific gravity (USG) and explore the associations between hydration-related measures (Δ urine color, sweat rate, and total fluid intake), wearable-derived ergonomic risk metrics, and self-reported fatigue. METHODS: A total of 25 employees at a Florida beverage bottling facility completed pre- and post-shift urine sampling over four workdays, recorded total fluid intake, and self-reported fatigue/energy. Sweat volume, sweat rate, sweat sodium concentration, and ergonomic risk metrics were measured on Days 2-4 using wearable devices. Linear mixed-effects models were used to assess USG changes by time point and day. Multiple linear regression was used to examine the associations between predictors (Δ urine color, sweat rate, and total fluid intake) and ergonomic risk outcomes and pre-to-post-shift changes in fatigue/energy. RESULTS: USG increased from pre- to post-shift (p = 0.03), with no significant effect of day across the workweek (p = 0.58). Change in urine color was significantly associated with the injury risk score (p = 0.03), total elevated risk movement count (p < 0.01), and mild-risk movement count (p < 0.01). Sweat rate was a significant predictor of changes in physical fatigue from pre- to post-shift (p = 0.03). Night-shift workers demonstrated higher activity scores and sweat sodium loss than morning-shift workers (p < 0.01). CONCLUSION: Workers frequently presented with concentrated urine both pre- and post-shift, and a greater within-shift worsening of urine color was associated with a higher occurrence of certain wearable-derived ergonomic risk movements.