The study of peripheral microcirculation and skin temperature has established itself as a foundational pillar in assessing internal workload and recovery processes within sports science. Following physical exertion, the body undergoes blood flow redistribution and prolonged vasodilation that can persist for several hours. Understanding these mechanisms is crucial for accurately interpreting physiological adaptations and optimizing athlete recovery strategies.

A recent study published in Frontiers in Physiology (Priego-Quesada et al., 2026) evaluated lower-limb skin perfusion responses five hours after an aerobic running session under heat stress, combining Laser Doppler Perfusion Imaging (LDPI) and Infrared Thermography (IRT). The findings deliver practical, high-value insights for non-invasive physiological monitoring.

The methodological challenge of peripheral perfusion

Assessing skin blood perfusion has historically been constrained by methodological limitations. Classical techniques, such as single-point contact Laser Doppler Flowmetry (LDF), sample an excessively small volume (typically under 1 mm³), compromising the spatial representativeness of the data. To address this issue, LDPI technology enables two-dimensional, contactless scanning over broader tissue areas, converting frequency shifts of moving erythrocytes into quantifiable color maps.

However, the primary drawback of LDPI systems remains the scan time required for each region of interest (ROI). In elite performance and clinical research settings, minimizing assessment times is a top priority. Consequently, the research team led by Dr. Jose I. Priego-Quesada sought to evaluate the circulatory response and identify which lower-limb anatomical regions most accurately reflect the prolonged physiological impact of exercise.

Experimental design and key variables

The study evaluated 22 participants, divided evenly into an exercise group (EG)—who completed a 50-minute continuous run at moderate intensity outdoors in temperatures between 28°C and 31°C—and a control group (CG) that remained at rest.

Assessments took place across two distinct time points: baseline (Pre) and exactly five hours post-exercise (Post). The five-hour window was specifically chosen to isolate prolonged physiological responses and avoid overlap with immediate, acute thermoregulatory reactions. Alongside tissue perfusion (moorLDI2) and skin temperature (Flir E54), continuous monitoring was conducted for heart rate, heart rate variability (HRV), and core body temperature estimated via body heat-flux sensors.

Key findings: the anterior thigh as the preferred indicator

Statistical analysis revealed significant variations between the exercise group and the control group across specific anatomical regions:

• Selective increase in the anterior thigh: The exercise group exhibited a significantly higher increase in skin perfusion compared to the control group in the anterior thigh (large effect size, ES = 1.0), anterior lower leg (ES = 0.3), and posterior thigh (ES = 0.5).
• Response in the posterior lower leg: The calf region showed marked perfusion increases in both groups, with no significant differences between them. This indicates that while the calf is highly sensitive to local circadian rhythms and general heat dissipation, it is less specific for isolating the direct impact of training loads.
• Predictive model for thermal stress: Multiple linear regression analysis demonstrated that higher skin blood perfusion increases correlate directly with three specific factors: higher peak core body temperature during exercise, greater fluctuations in baseline core temperature at rest, and concomitant variations in skin temperature.

Physiological mechanisms and practical applications

The notable response observed in the anterior thigh stems from the high metabolic demand and mechanical activation of the quadriceps femoris muscle complex during running. This workload generates metabolic heat production that demands compensatory vasodilation.

Evaluated five hours post-exercise, this response is driven not by immediate thermoregulatory needs, but by secondary adaptive processes—including sustained endothelium-dependent vasodilation, local micro-inflammatory tissue repair mechanisms, and a prolonged increase in nitric oxide bioavailability within the microvasculature.

From a practical perspective in professional sports application and infrared thermography, these findings carry two major implications:

1. Data acquisition efficiency: To streamline evaluation times in elite sport or clinical settings using thermal or circulatory mapping systems, the anterior thigh should be prioritized as the primary region for monitoring post-run cumulative fatigue.
2. Independence from global autonomic variables: The study demonstrated that systemic metrics—such as heart rate or HRV indices (RMSSD, HF)—do not correlate directly with local perfusion at the five-hour mark. This reinforces the need for targeted local assessment tools, such as athlete thermal profiling, to accurately capture the peripheral metabolic state of target tissues.

Conclusion

The integration of optical and thermal technologies confirms that exercise-induced stress in warm environments causes measurable microcirculatory alterations hours after activity ceases. The anterior thigh stands out as the optimal anatomical window for monitoring this physiological response, enabling practitioners to achieve more precise and efficient tracking of tissue recovery states.

References

• Priego-Quesada, J. I., Rebollar-Cuenca, E., Galindo-González, C., Sendra-Pérez, C., Hermo-Argibay, A., & Cibrián Ortiz de Anda, R. M. (2026). Laser Doppler mapping of lower limb skin perfusion before and 5 h after exercise in warm conditions. Frontiers in Physiology, 17, 1830186.