Author(s): SHI, J., AHMAD YUSOF, H., CHE MUHAMED, A.M., Institution: ADVANCED MEDICAL AND DENTAL INSTITUTE, UNIVERSITI SAINS MALAYSIA, Country: MALAYSIA, Abstract-ID: 1597

INTRODUCTION:
Given that previous research has demonstrated that higher air velocity can reduce thermal stress during exercise in hot, dry conditions, it raises the question of whether this observation would hold true in more humid environments, where the evaporative capacity of the environment (Emax) is reduced due to higher absolute humidity, potentially limiting the cooling benefits of increased. The purpose of this study was to examined the effect of a higher air velocity in mitigating thermoregulatory stress under varying vapor pressure conditions.
METHODS:
Twelve trained heat-acclimated males cyclists performed a 60 min of fixed-intensity cycling at 65% VO2peak across a high (HVP: 3.37 kPa) and moderate (2.69 kPa) vapor pressure conditions. The HVP environment was set at 310C and 75% RH. While the MVP was made up of two different conditions of MVP1: 310C and 60% RH, and MVP2: 250C and 85% RH. In each of these three conditions, participants performed trials at two air velocity settings: high velocity (HV: 4.5 m·s−1) and low velocity (LV: 2.8 m·s−1). Thermoregulatory and perceptual responses were recorded during exercise.
RESULTS:
Tre was significantly lower in the HV compared to LV trial within each environmental conditions (HVP: 38.6±0.2 vs 38.4±0.2; P=0.004; MVP1: 38.5±0.2 vs 38.3±0.3; P=0.002; MVP2: 38.5±0.2 vs 38.4±0.2; P=0.007). Comparison between HVP and MVP1 also demonstrated the ability to lower Tre in HV trials (P=0.010). Tsk was significantly lower in the HV as compared with the LV trial in the MVP1 (33.54±0.53 vs 33.95±0.56; P=0.008) and MVP2 (30.78±0.80 vs 31.69±0.39; P=0.006) conditions. However, there was no significant difference in Tsk between HV and LV within the HVP condition (34.10±0.42 vs 34.39±0.52; P=0.061). Forehead sweat rate was significantly lower at HV compared to LV in the MVP1 condition (P = 0.046). However, in HVP conditions, no significant differences were observed in forehead sweat rates between HV and LV (P = 0.131). HR was significantly lower in the HV trial compared to LV in both MVP1 and MVP2 conditions (P = 0.010 and P = 0.021, respectively). Contrary, HR was not significantly (P = 0.970) different between HV and LV trials within the HVP conditions. Air velocity had no effect on perceptual responses of thermal sensation and thermal comfort during the fixed-intensity cycling (both P ≥ 0.057).
CONCLUSION:
This study highlighted that a higher air velocity was less effective in reducing thermoregulatory and circulatory strain in the higher vapor pressure. It was evident that higher air velocity significantly reduced thermal and cardiovascular strain in both MVP1 and MVP2 conditions. These observations are consistent with the earlier report by Saunders et al. (2005). This supports the notion that high humidity presents a formidable barrier to effective heat dissipation.