Physiological stress responses to a live-fire training evolution in career structural firefighters.

OBJECTIVE: This study assessed firefighters' physiological stress response to a live fire training evolution (LFTE). METHODS: Seventy-six (n = 76) firefighters completed an LFTE. Salivary samples were collected pre-, immediately post, and 30-min post-LFTE and analyzed for α-amylase (AA), cortisol (CORT), and secretory immunoglobulin-A (SIgA). RESULTS: Concentrations of AA, CORT, and SIgA were elevated immediately post LFTE versus pre (p < 0.0001) and 30-min post (p < 0.0001). Cohen's d effect size comparing pre and immediately-post means were 0.83, 0.77, and 0.61 for AA, CORT, and SIgA, and were 0.54, 0.44, and 0.69 for AA, CORT, and SIgA, comparing immediately-post and 30-min post respectively. CONCLUSIONS: These data demonstrate the stress response and activation of the hypothalamic-pituitary-adrenal/sympathetic-adreno-medullar axis and immune system immediately after real-world firefighting operations. Future work is needed to understand the impact of elevated stress biomarkers on firefighter performance and disease risk.

Stress response to virtual reality based active shooter training: Impact of caffeine consumption.

Participation in a virtual reality based active shooter training drill (VR-ASD) has been shown to increase biomarkers of stress; however, the impact of caffeine consumption on this response has not been studied. Caffeine ingestion has been shown to have favorable effects on physical and cognitive performance among athletic and tactical occupations alike. This study examined the impact of caffeine ingestion on subjective and physiological markers of stress in response to a mental stress task (MST) which involved participation in a VR-ASD and cognitive challenge consisting of mental arithmetic and a Stroop challenge. Fifty-three subjects were randomly assigned either caffeine (n = 26) or placebo (n = 27) prior to being exposed to the MST. Saliva samples, heart rate (HR), and state-anxiety inventory (SAI) scales, were collected before and after exposure to the MST. Saliva was analyzed for α-amylase (sAA), secretory IgA (SIgA), and cortisol (sCORT) concentrations. The MST resulted in significant increases in sAA, SIgA, HR, and SAI. Immediately post MST, sAA concentrations were significantly higher following the caffeine treatment compared to placebo. These data demonstrate that caffeine consumption results in significantly greater sAA concentrations post MST. This study was pre-registered as a clinical trial ("Impact of supplements on stress markers": NCT05592561).

Slow Breathing Reduces Biomarkers of Stress in Response to a Virtual Reality Active Shooter Training Drill.

Tactical occupations regularly encounter life-threatening situations while on duty. Although these occupations are often trained to utilize slow breathing (SB) during intense stress, there is no evidence supporting the effects on markers of stress in response to a virtual reality active shooter training drill (VR-ASD). The purpose of the study was to determine the impact of acute SB on biomarkers of stress in response to a VR-ASD. Seventy-nine (n = 79) subjects performed either slow breathing method 1 (SB1), slow breathing method 2 (SB2), or normal breathing (control) for five minutes, both pre- and post-VR-ASD. Saliva samples were analyzed for stress markers, including α-amylase (sAA) and secretory immunoglobulin-A (SIgA). Both methods of SB resulted in significantly lower sAA concentrations at 5 (p < 0.001) and 30 min post-VR-ASD (SB1: p = 0.008; SB2: p < 0.001) compared to the control. In the control condition, the sAA concentrations were significantly elevated 5 min post-VR-ASD (p < 0.001) but did not change across time in SB1 or SB2 (p > 0.05). Thus, both SB1 and SB2 reduced the sAA response and resulted in lower concentrations post-VR-ASD. This study was pre-registered as a clinical trial ("Impact of Breathing Interventions on Stress Markers"; NCT05825846).