Altered water vapor and evaporation during exercise in a cold weather garment layering system

Water vapor accumulation within a garment layering system during exercise in the cold may alter evaporative heat loss. The objective of this study was to investigate the impact of altered water vapor accumulation within a garment layering system during cold weather exercise. Subjects (N=10) exercised on a treadmill for 45 min (70% VO 2max ) while wearing a wind impermeable (air permeability: .02 m 3 /min/m 2 ) running jacket with (open) and without (closed) open mesh fabric (air permeability: 39 m 3 /min/m 2 ) panels placed at the chest (120 cm 2 ), sides (120 cm 2 ), and back (120 cm 2 ). Jackets were worn over a standard polyester t‐shirt. Average (front and back) water vapor pressure (P w ) was calculated from humidity (%) and air temperature under the running jacket (between t‐shirt and jacket). Whole body temperature (T wb ), total sweat loss, and evaporation of sweat were also determined. Average P w in the running jacket was 13.1±0.4 and 10.4±0.3 mmHg for the closed and open jacket conditions, respectively. The decreased P w enhanced evaporation in the open (84±2%) compared to the closed jacket condition (79±2%; P <0.05), without a statistical difference in sweat loss (closed: 654±56 vs. open: 642±55 g) or T wb (closed: 36.6±0.1 vs. open: 36.4±0.2 °C). Results suggest a ~3 mmHg reduction in P w in running jackets enhances sweat evaporation without a significant reduction in whole body temperature. Research support from Nike Inc.