Keeping cool and calm in the heat: The development of evidence-based recovery strategies for optimised performance and safety in operational firefighters

This experiment will be a randomised control cross over trial. Participants will visit UTS Moore Park climate chamber on four separate occasions separated by at least one week. Participants will perform one of three separate conditions during each visit (control and two recovery protocols [basic and advanced cooling]) plus a familiarisation visit. Protocol The performance task will be representative of parts of structural, rescue and bushfire fire-fighting as these were the most demanding (physically and mentally) and hottest perceived tasks found in previous research, the most demanding critical task simulations highlighted in physical aptitude testing (PAT) previous research (Taylor et al. 2015a, Taylor et al., 2015b, Groeller et al. 2015, Fullagar et al., 2015) and will overall reflect current FRNSW operational procedures (e.g. firefighters are trained and familiar with these tasks and loads). Overall, this task will last approximately 20 minutes in total to replicate an average breathing apparatus wear which firefighters perform in the field. Firefighters will wear duty wear (standard undergarments), full personal protective clothing (PPC), breathing apparatus (BA), helmet and radio (total weight ~20 kg) as per normal FRNSW procedures. Task will involve: Stressful firefighter task in the heat 2 min warm up walk on treadmill (5 km/h, no incline) Loaded carry walk (5 km/h level; 26 kg black rock jerry can [water] using preferred hand; 1 min) Step up task on blocks off treadmill (replicate stair climb [structural]; set cadence and step up w/ 17.5 kg load [water blue cap]; 4 min) Car rescue task with tool. This task involves static hold of a 19.5 kg tool at three differing levels —knee, waist, and eye level (approx. duration 2 min 40 sec [rescue]) Bushfire replicated task – alternating minute on treadmill and minute off with battle rope whips/bands/hose (replicate bush walk/hose pull [bushfire]; 5 km/h at 3.5%; 10 min in total) The climate chamber will be set and matched to mean max temperature and humidity for summer in the Sydney region to replicate likely firefighter conditions (~30-32oC, 60% humidity) and a normobaric (750 mmHg) environment. The simulated task will then be repeated (40 min in total [2 BA wears]; SOG, Incident Ground Rehabilitation FRNSW)), with mandatory “rehabilitation/recovery” periods in between each task as per standard firefighting and SOG procedures. Here, three separate conditions will be undertaken (control and two recovery protocols; each 20 minutes) outside the climate chamber in the UTS physiological laboratory. The conditions are: CONTROL: Passive, seated rest with top layer of PPC/BA removed + 7 g·kg-1 BW (e.g. ~600 ml for an 85 kg person; Ihsan et al. 2010) ambient water [sealed bottle; 20oC; which contains a dissolved hypotonic solution (150 mOsmol·L-1) (Aqualyte, Point Health Pty Ltd., Australia)]. RECOVER-BASIC (R1): Remove top and bottom layer of clothing as per control + fans + CoolaTM chairs w/ ambient water [20oC] + wet towels [to be placed on head/upper back/neck; pulled from ambient water buckets; 20oC]) + 7 g·kg-1 BW cold water ingestion [sealed bottle from fridge; 13-15oC, which contains a dissolved hypotonic solution (150 mOsmol·L-1) (Aqualyte, Point Health Pty Ltd., Australia)] Example timeline: TASK 1 – R1 – TASK 2 – R1 RECOVER-ADVANCED (R2): Remove top and bottom layer of clothing as per control + misting/cooling fans + CoolaTM chairs w/ iced water [13-15oC] + ice packs/towels [to be placed on head/upper back/neck; pulled from iced water buckets; 10-12oC] + ice slushy ingestion [7 g·kg-1 BW of crushed ice slush drink (–1 °C; Caress 1, CAB S.p.A, Italy), which contains a dissolved hypotonic solution (150 mOsmol·L-1) (Aqualyte, Point Health Pty Ltd., Australia)). That is, there will be 20 minutes of pre-baseline measures, a 20 minute task, a 20 min recovery protocol, a 20 min task and a 20 min recovery protocol followed by post-measures. Four ESSA accredited exercise scientists will be supervising, and there will always be one of these personnel who is first aid trained. The experiment will be completed individually, with instruction and recording completed by the support personnel. There will be a minimum of a 5 day washout between sessions and a maximum of two weeks. The familiarisation will be a guided simulation of the activities to be undertaken during the assessment sessions but with actual completion of all performance measures. Primary outcome measures will include: • Pre-post nude body mass (kg) • Core temperature (BodyCap core temperature pills, ToC). Core-temperature pills will be ingested at least 6-8 h before exercise. Core temperature will be recorded continuously (1-minute intervals) using a wireless data logger worn by the participants. • Heart rate (Polar Systems; HR; beats per min) monitored continually through the protocol through a HR belt • Blood pressure (Hg; automatic cuff; Omron) • Rating of perceived exertion (RPE; arbitrary units) • Grip strength (Handgrip dynamometer; N) • Proprioception/balance (Balance Error Scoring System (BESS); score) • Validated perceptual scales (thermal sensation, fatigue, task performance) • Thermal sensation scale prior to and after performance. Thermal sensation will be evaluated using a subjective scale from 1 (extremely cold) to 13 (extremely hot), modified after Gagge et al. (1967), where the end points have been extended to enable a better resolution of thermal sensation. Participants will be asked: “How does the temperature of your body feel?”. Thermal discomfort will be assessed using a second scale (1= comfortable to 5= extremely uncomfortable), also modified after Gagge et al. (1967), and participants will respond to the question: “How comfortable do you feel with the temperature of your body?” • Perceptual fatigue (1= no fatigue, 10 = fully fatigued; (Neuberger 2003) • Task performance (Likert; 1 = extremely poor, 10 = extremely good) • Gastrointestinal comfort (Likert 1 = no symptoms, 100 = extreme symptoms; Costa et al 2016) • Perceptual-cognitive and -motor tasks • Multiple object tracking task (sustained selective attention; task developed using the MOT paradigm, Pylyshyn & Storm, 1988) where participants are required to track a subset of identical items designated as target items, while all items move randomly and independently. • Precued reaction time task. Finally, a precued reaction time paradigm (Beavan et al., 2019; Barela et al., 2019) will be used to assess firefighters ability to use or suppress congruent and incongruent information that is presented as a brief precue.