Physiological responses and concerns regarding syncope of soldiers during State Ceremonial and Public Duties

State Ceremonial and Public Duties (SCPD) expose soldiers to extreme physiological stressors, predisposing to syncope. Despite a high incidence of syncope in military personnel, physiological responses during SCPD are unknown. Data were collected across three ceremonial parades (n = 41; 3 female, age = 24 ± 1 years, duration = 2.5 h). Parades had alternating phases of motionless standing and marching. Pre-parades, baseline cardiovascular parameters (systolic arterial pressure [SAP] and heart rate [HR]), anthropometric measures, urinary sodium, anxiety and parade perspectives were collected. Salivary steroid analyses were performed pre- and post-parade. In thirty participants (n = 10/parade; 2 female) continuous SAP, HR, respiration, postural sway and skin temperature were collected using discrete wearable technology (Astroskin) worn underneath the traditional uniform. During parades, HR and minute ventilation were elevated, with maximum HR reflecting 71 ± 1.5% of age-predicted max. Parade SAP_min was 107 ± 1.8 mmHg (range 88-125 mmHg). During prolonged motionless standing (Stand 2; 63 ± 1mins), 50% of participants experienced reduced SAP that exceeded clinical criteria for orthostatic hypotension. Lower Stand 2 SAP_min was associated with larger leg mass (r = 0.484, p = 0.012), and lower percent body fat (r = 0.523, p = 0.006). Post-parade, salivary cortisol decreased (p < 0.001) while aldosterone increased (p < 0.001). Maximum estimated core temperature was 38.6 ± 0.03 °C, indicating considerable thermal stress, with a "high" physiological stress index of 7.2 ± 0.2. Participants did not fear repercussions for fainting during SCPD, but associated it with profound stigma. This work highlights the utility of wearables in field environments. SCPD represent considerable physiological stress, with marked cardiovascular instability, and substantial thermal, orthostatic, and exercise stress. Use of evidence-based prevention measures could improve syncope outcomes during SCPD.