The effects of caffeine ingestion on firefighter work tolerance




Kellawan, Mikhail

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Anecdotal evidence suggests that caffeine ingestion (mostly in the forms of coffee and tea consumption) is prevalent amongst firefighters and yet there is no data on whether this behaviour should be identified, measured, or monitored. PURPOSE: The purpose of this experiment was to determine the physiological and psychophysical effects of caffeine ingestion during repeated bouts of simulated firefighter work. In a randomized, double blind, crossover design, ten healthy males (age 36 ± 9.8 yr, body mass 88.3 ± 5.7 kg, height 182.78 ± 3.9 cm, approximate caffeine use 492.8 ± 318.2 mg/day) completed three 10 min work bouts (WB) at an intensity one work load below ventilatory threshold wearing full Firefighter personal protective equipment (PPE) and breathing through a self contained breathing apparatus (SCBA) on two different occasions. One hour before exercise each subject ingested either a 6 mg•kg-1 of caffeine (CAFF) or dextrose placebo (PLA), as well as, 500 ml of water. During the work trials, expired gases were sampled for oxygen consumption ( O2), carbon dioxide production ( CO2), respiratory exchange ratio (RER), minute ventilation ( E), respiratory rate (RR), tidal volume (Vt), and total air consumed (AcVE). Core temperature (Tc), heart rate (HR), oxyhemoglobin saturation (% O2 sat), capillarized blood lactate (BLa), rating of perceived exertion (RPE) (10pt Borg), perceived thermal distress (PTD), and sweat loss were also measured. Physiological strain index (PSI) was calculated from HR and Tc values. Tc was significantly higher in all CAFF WB compared to PLA (37.83 ± 0.08 oC vs. 37.61 ±0.12 oC) (p ≤ 0.05). E and Vt were also significantly increased in CAFF whereas, RPE was significantly decreased (p ≤ 0.05). The elevated Tc values caused an increase in calculated PSI in the CAFF condition during exercise (p ≤ 0.01). CAFF increases in E and Vt also increased AcVE. In conclusion, a caffeine induced elevation in Tc caused increased strain as indicated by calculated PSI during repeated work bouts during exercise below ventilatory threshold wearing full PPE and breathing through an SCBA. Elevated Tc in the CAFF condition likely caused increases in E, Vt and AcVE. Thus, caffeine ingestion may have to be monitored in firefighters during work days.



physiology, Caffeine