Medicine & Science in Sports & Exercise:
G-35 Free Communication/Poster - Heat Stress II: JUNE 5, 2010 7:30 AM - 11:00 AM: ROOM: Hall C
Brown, Peter I. FACSM; McLellan, Tom M. FACSM; Linnane, Denise M.; Wilkinson, David M.; Richmond, Victoria L.; Horner, Fleur E.; Blacker, Sam D.; Rayson, Mark P.
Optimal Performance Limited, Bristol, United Kingdom.
(No disclosure reported)
Emergency Service (ES) personnel wear encapsulating impermeable Personal Protective Equipment (PPE) during specific deployments. In such incidents, sweat rates are high and reductions in body mass (BM) may exceed 1% which can reduce work productivity and increase risk of heat injury. However, there are currently only limited fluid replacement guidelines for ES derived from robust empirical evidence.
PURPOSE: To examine whether low (L; 5 ml·kg-1·h-1) or high (H; 10 ml·kg-1·h-1) rates of water replacement were appropriate in a moderate (18°C) or hot (30°C) environment to prevent fluid losses >1% BM in a reasonable worse case scenario.
METHODS: Thirty two ES personnel were required to perform a range of tasks to simulate a "high" work rate while wearing PPE1, n=12, 60 min, PPE2, n=9, 60 min or PPE3, n=11, 120 min. The first trial was performed at 30°C where the intensity was adjusted to 60-84 % heart rate reserve; this reflects a likely worst case scenario for such deployments. The remaining trials replicated the work and rest patterns of this trial. The total volume of water was consumed prior to exercise for PPE1 since this ensemble incorporated extended duration breathing apparatus (volume: L, 0.41±0.07 l; H, 0.82±0.13 l). For PPE2 (L, 0.40±0.06 l; H, 0.80±0.12 l) and PPE3 (L, 0.86±0.10 l; H, 1.67±0.18 l) water was consumed in five equal volumes during the deployment.
RESULTS: At 30°C, the reduction in BM was greater in L than H for all PPE (p<0.05) (L vs. H, PPE1: -0.83±0.41 % vs. -0.38±0.26 %; PPE2: -1.18±0.61 % vs. -0.71±0.66 % and PPE3: -1.62±0.57 % vs. -0.57±0.72 %) since sweat rates and thermal strain were not different between conditions, and 18 vs. 7 subjects exceeded 1% BM loss in L vs. H, respectively. At 18°C, for PPE1 and PPE2 the reduction in BM was greater in L than H (p<0.05) (L vs. H, PPE1: -0.48±0.16 % vs. 0.06±0.18 % and PPE2: -0.66±0.37 % vs. -0.11±0.33 %). In PPE3, BM loss was -0.18±0.27 % in the L trial, however, in the H trial, BM increased (0.67±0.38 %, p<0.05). For 18°C L maintained body mass losses to <1% for all but 2 subjects.
CONCLUSIONS: The fluid replacement strategies emanating from this study will be used by ES to develop an appropriate hydration strategy for each of the PPE ensembles, adjusted accordingly for the environmental conditions.
This work was funded by the Home Office CBRN Science and Technology Programme.