INTRODUCTION: Heated garments can attenuate the drop in muscle temperature often observed during `heat loss windows` prior to competition (1). However, these garments traditionally use wire heater elements, which are limited by an inability to generate heat uniformly. A printed graphene-based solution enables more uniform heating over larger areas and avoids local hot spots (2). This study aimed to quantify the technical performance of garments containing graphene-based heaters, and the effects of the use of these garments on lower-body peak power output (PPO) following a simulated post-warm up `heat loss window`. METHODS: Firstly, in off-person testing, the graphene-based garments were hung inside out whilst images of the heater panels were captured using a thermal imaging camera. Time to reach target temperature, mean temperature, battery life, and rate of temperature decline over battery life were quantified. These were compared to two wire heater-based commercially available garments. Secondly, the graphene-based garments were worn by six participants resting in a controlled 20°C environment for 15-min to assess the effects on body surface temperature using thermal imaging immediately after their removal. Finally, nine participants completed a standardised cycling warm-up, followed by 30-min passive rest in cold (5°C) and temperate (20°C) environments with the graphene-based garment heating either enabled or disabled (i.e. four trials in total). PPO during counter-movement jumps was assessed at various times pre and post warm-up. RESULTS: In the off-person testing, the trousers and jacket took 4.4-min and 10.6-min to reach target temperature, respectively. The mean temperature across all panels was 47.0°C (trousers) and 42.7°C (jacket). On full power, the batteries lasted for 2.49-h (trousers) and 3.22-h (jacket), with a temperature decline of 0.6 and 1.2°C/h, respectively. When activated, the garments led to an increase in body surface temperature in all heated regions after just 15-min. Post warm-up, compared to an inactivated worn garment, the activated garments significantly increased skin temperature, thermal comfort and thermal sensation in both cold and temperate conditions (all p < 0.05). Core temperature was raised but not significantly at any measured timepoint. When the garments were activated, PPO was 57 W (1.6%) to 145 W (3.9%) greater in the 30-min post warm-up, and this difference was significant in the cold environment after 30-min. CONCLUSION: Graphene-based heaters integrated into competition-ready garments provided greater heat output than commercial wire-heater garments. The graphene-based garments increased body surface and skin temperature, and attenuated the reduction in PPO during the 30-min post warm-up. Further consideration of garment control and design could improve the practicality and performance further.
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