Daily Axillary Temperature ΔT and Cognitive–Autonomic Patterns in Free-Living Adults: Identification of Stress–Energy Response Phenotypes in an Observational Cohort

Circadian oscillation of body temperature reflects autonomic and mitochondrial regulation orchestrated by the suprachiasmatic nucleus and clock genes (PER, CRY, CLOCK, BMAL1). The Energy Resistance Principle (ERP) proposes that energetic resistance (éR) governs energy transformation in living systems, with excess éR associated with oxidative stress, inflammation, and accelerated aging. This 15-day prospective observational study examined daily axillary temperature oscillation (ΔT = night-minus-morning), a simplified 6-item cognitive-autonomic assessment (MiSBIE Brief-6), morning light exposure, and nighttime screen time as real-world correlates of allostatic load in 16 adults (9 women, 7 men; mean age 58.35 ± 7.8 years), achieving 100% adherence (239 valid daily records). Elevated ΔT (>0°C) was associated with higher composite stress load (CSL; r = 0.52; p < 0.001). K-means clustering (k=3; silhouette=0.75; Gap p<0.001) of 239 daily observations revealed three eco-physiological profiles: Cluster 1 (Low ΔT/High Recovery; n=87 observations) with ΔT=-0.188±0.091°C and MiSBIE-delta=+1.84±0.62; Cluster 2 (Neutral ΔT/Intermediate Recovery; n=98 observations) with ΔT=+0.003±0.067°C and MiSBIE-delta=+1.12±0.51; Cluster 3 (High ΔT/Minimal Recovery; n=54 observations) with ΔT=+0.214±0.104°C and MiSBIE-delta=+0.41±0.68.. Morning light exposure >15 minutes was associated with lower ΔT (β=-0.24°C; p=0.002). MiSBIE Brief-6 predicted 78% of thermal stability variance (R²=0.78; p<0.001). ΔT and MiSBIE Brief-6 capture ecological éR, supporting algorithmic frameworks for early identification of elevated éR aligned with ERP and MiSBIE.