Beyond the Comfort Zone: Elevation, Temperature, Fatigue and Pain Perception

This study provides a comprehensive evaluation of the effects of environmental stressors and physical exertion on human nociceptive processing across multiple ecologically relevant conditions. Using a repeated-measures design, participants (N = 45) completed up to five controlled laboratory (thermoclimatic chamber) sessions (baseline, simulated altitude at 4200 m asl, heat at +42 °C, cold at −10 °C, and exertion). Participants were tested by using electrical stimuli. Linear mixed-effects models with participant-level random intercepts, alongside estimated marginal means and bootstrap derived effect sizes, enabled robust characterization of within-subject differences. Thermal stress emerged as the strongest modulator of nociception. Heat exposure significantly elevated sensory and pain thresholds compared with all other conditions, whereas tolerance thresholds peaked during cold exposure, yielding the largest observed effects. Altitude consistently produced the lowest thresholds across all modalities. These contrasts were confirmed statistically in the mixed-effects models, and effect-size analyses indicated substantial within-subject differences between the thermal extremes. By integrating three distinct nociceptive modalities and extreme environment simulations, this work offers novel and informative insights into how environmental stressors shape pain processing. The discovery of opposing thermal effects on sensory/pain versus tolerance thresholds—within the same cohort and design—reveals modality-specific patterns not previously documented and suggests that hypoxia may further modulate these responses.