Cardiorespiratory Strain During Inclined Treadmill Walking in a Hot-Dry Environment Whilst Wearing Weighted-Clothing

Abstract

The nature and scale of equipment that must be carried by emergency and security services during operations together with the need to afford personal protection from potential hazards adds weight to the body. Added weight risks increasing the metabolic demand (MD) thereby limiting the time that can be sustained on duty. Whilst strategies to mitigate MD tend to reduce the mass of equipment and clothing there is a need to understand the effect of the distribution of the load on the body. During walking gait Knapik et al 2004 reported that the rise in oxygen cost for a given mass was lowest when loads were placed closest to the body's centre of mass (CoM). However, tight-fitting loads around the chest were found to restrict breathing and increase heat strain by comparison with carrying the load on the back. PURPOSE: To compare the cardiorespiratory strain (CrS) of a standard treadmill task for 4 garments where increased load was maintained close to the CoM. METHODS: Seven healthy, heat-acclimatised, male volunteers (mean (1 sd) age 21.3 (3.5) years; body mass (BM) 76.0 (8.8) kg; height 1.79 (0.08) m) participated in this ethics approved study. Participants (PPs) conducted a standard motor-driven treadmill test (TT) (walking for 120 min (speed: 5.3 km.h−1; incline: 4.0%) in a climate-controlled laboratory (CL) (38.0°C dry-bulb temperature, 30% relative humidity) while fluids were consumed ad libitum) on 4 consecutive days. PPs wore Standard Operational Clothing (SOC: underwear, British Army combat clothing, socks, boots and webbing) weighing 10.1 (0.2) kg. One of 4 (A to D) garments (A: 5.2 kg; B: 9.2 kg; C: 8.6 kg; D: 7.9 kg) was fitted to the torso of PPs prior to each TT. Garments were matched for moisture vapour permeability. Loads within each garment were evenly distributed. The order in which PPs wore each garment was randomised. Douglas bags were used to assess VO2 and VE within the CL prior to- and at 30 min intervals throughout TT. Aural temperature (Tau) was monitored to ensure the safety of PPs. Statistical evaluation was by paired T-test with α = 0.05. RESULTS: Despite Tau remaining within safe limits only 4 PPs completed 120 min of TT, 6 completed 90 min whilst all 7 completed 60 min. Differences in VO2 (mean (1sd) ml.min−1.kg(BM)−1: A 25.2 (1.9); B 26.3 (2.4); C 28.9 (4.8): D 24.8 (3.6)) and VE ((L. min−1) A 42.5 (6.6); B 44.7 (9.2); C 45.8 (14.1); D 40.9 (7.3)) between garments were not statistically significant (p>0.05). CONCLUSIONS: Although the small sample size cannot substantiate generalisations of the results these data suggest that strategies to mitigate CrS of carrying loads on the body must consider how the load is distributed.