The relationship between body composition and skin temperature responses during exercise is becoming increasingly relevant in performance science. A new preliminary study published in Frontiers in Sports and Active Living investigated how extracellular water (ECW) and sex differences influence thigh skin temperature before, during and after a vigorous exercise task, assessed through infrared thermography (IRT).

This work provides key insights into when thermography can reliably be used to monitor internal load, recovery, and physiological status in athletes.

Thermography, body composition and the role of extracellular water

Infrared thermography is a non-invasive technique capable of detecting thermal changes associated with muscle metabolism, blood flow and inflammation. However, several physiological factors can influence thermal detection and body composition appears to be one of the most important.

In this study, 102 physically active young adults were evaluated using:

• Bioimpedance analysis (BIA) to assess body composition
• Thermal imaging at baseline, immediately after a 30-s countermovement jump test, and after 5 minutes of rest
• Skinfold measurements, leg dominance, and effort-related variables

The key variable of interest was the extracellular water percentage (ECW%), which reflects cellular hydration. Values above 45% indicate water retention, which may alter tissue behavior and thermal conduction.

Main findings: extracellular water shapes the thermal response

This study provides several important insights for interpreting thermal images in sports settings:

1. Higher water retention = lower baseline thigh temperature

A negative correlation was found between ECW% and baseline thigh skin temperature in both legs (r ≈ −0.26 to −0.27). In practical terms, individuals with higher extracellular water levels have colder skin at rest, likely due to differences in thermal conductivity and perfusion.

2. The typical thermal response to exercise only appears when ECW ≤ 44%

Across the full sample, the authors observed the classic thermal pattern:

• A significant reduction in skin temperature immediately after exercise
• A slight increase during the 5-minute recovery period (+0.12–0.14°C)

However, when dividing participants by ECW level:

• LWR (38–40%) and MWR (41–44%) showed the expected pattern: drop → recovery.
• HWR (>45%) showed an opposite recovery trend and consistently lower temperatures at all time points.

This indicates that water retention modifies or blunts the thermal signal, particularly during short-term recovery. For practitioners, this means that athletes with high ECW may produce thermograms that are harder to interpret reliably.

3. Sex differences: women show lower skin temperatures at all times

The female group consistently displayed lower skin temperature values than the male group, reinforcing known differences in thermoregulation and highlighting the importance of sex-specific interpretation when using IRT.

What does this mean for applied thermography?

The study proposes a clear practical threshold:

For reliable thermal assessment of the thigh during or after exercise, ECW should be < 45%.

When ECW exceeds this value, thermal imaging may:

• Underestimate real blood flow
• Show abnormally low temperatures
• Display inverted heating–cooling patterns during recovery
• Complicate the interpretation of muscle status, fatigue or inflammation

In other words, hydration status and water retention must be considered when using IRT, especially in high-performance environments.

Conclusion

This study demonstrates that extracellular water influences both baseline skin temperature and temperature fluctuations after vigorous exercise. For the first time, a specific reference value (45% ECW) is proposed to help determine when thermography data may or may not be physiologically reliable.

These findings support several practical applications:

• Integrating BIA + thermography for more complete athlete monitoring
• Personalizing the interpretation of thermal patterns based on body composition
• Improving early detection of fatigue, overload or risk factors
• Developing more accurate predictive models in sports performance

As thermography continues to evolve, studies like this one bring us closer to data-driven, individualized monitoring that enhances both performance and athlete health.

Referencias

Amato, A., Petrigna, L., Sortino, M., Amorim, P. R. S., & Musumeci, G. (2025). Water retention influences thigh skin temperature variation post-exercise: preliminary study of bioimpedance analysis and thermography data. Frontiers in Sports and Active Living, 7, 1516570.