Infrared Thermography (IRT) has become a key non-invasive tool for the functional assessment of soft tissues and physiological monitoring, especially in the fields of sports medicine and health sciences. However, traditional interpretation has been based primarily on two strategies with inherent limitations:

• Contralateral Comparison: Assumes thermal symmetry between homologous regions of the healthy body (1). Although useful, this method is purely intra-regional and does not provide information about the thermal behavior of a region relative to its adjacent anatomical areas.
• Absolute Temperature Values: Describes regional thermal normality (2). This approach disregards the significant influence of technical and environmental factors on skin temperature, assuming that the value reflects only the local physiological state.

A recent study, based on the retrospective analysis of the extensive anonymized ThermoHuman® database (comprising over 25,000 upper body thermograms and over 100,000 lower body thermograms), has addressed these limitations by proposing an alternative approach: the analysis of interregional thermal relationships (3).

The main objective was to establish systematic patterns of temperature distribution across different anatomical regions, culminating in the creation of a thermal gradient scale. This framework provides a reference model that contextualizes spatial thermal responses.

Key Study Findings:

• Proximal-to-Distal Gradient: A progressive decrease in temperature from proximal to distal regions was confirmed in both sexes. This pattern has been correlated with the physiological need to preserve central vital organs. The most abrupt changes were recorded between the forearm and wrist and between the leg and ankle.
• Sex Differences: Male subjects consistently exhibited higher mean skin temperatures than female subjects in most regions, with differences ranging from +0.09 to +1.64°C. The greatest disparities were observed in the lower back and adductors. Conversely, wrists showed slightly higher temperatures in women. These findings are consistent with previous literature that attributes differences in thermal distribution to the distribution of adipose tissue and regional blood perfusion (2).
• Regional Variability: Greater variability (Standard Deviation, SD) was observed in distal regions, such as the wrist and ankle. This variability reinforces the need for standardized protocols to mitigate the susceptibility of these areas to environmental and positional factors.

The main contribution of this study is the incorporation of the thermal gradient scale for individual interpretation. Visualizing thermal measurements in relation to population norms differentiated by sex allows for contextualized interpretation and improves the detection of physiological or clinical deviations. Identification of Focal Dysfunction:

• A localized deviation in a single Region of Interest (ROI) that significantly exceeds the reference range (e.g., two standard deviations) suggests possible regional dysfunction (inflammation, vascular alteration).
• Detection of Systemic Influences: If all regions show a consistent shift in the same direction along the gradient, the variation is more likely due to environmental or systemic factors.
• Longitudinal Monitoring: The thermal gradient approach facilitates the monitoring of patients or athletes over time, as alterations in proximal-to-distal ratios can be an early indicator of functional changes.

In conclusion, this normative framework, derived from massive data analysis, reinforces the clinical utility of IRT, transforming it into a more objective, reproducible, and individualized assessment tool.

References

1. Vardasca, R., Ring, E. F. J., Plassmann, P., & Jones, C. D. (2012). Thermal symmetry of the upper and lower extremities in healthy subjects.
2. Marins JC, Fernandes AA, Cano SP, Moreira DG, da Silva FS, Costa CM, Fernandez-Cuevas I, Sillero-Quintana M. Thermal body patterns for healthy Brazilian adults (male and female). J Therm Biol. 2014 May;42:1-8. doi: 10.1016/j.jtherbio.2014.02.020. Epub 2014 Mar 7. PMID: 24802142.
3. Escamilla-Galindo V et al. 2025. Beyond Symmetry: Defining Normative Inter-Regional Patterns in Infrared Thermography