Infrared thermography of the quadriceps during early passive recovery (0-6 min) after incremental exercise in professional female volleyball athletes

Background: Infrared thermography (IRT) is increasingly applied to monitor muscle temperature during recovery, offering insight into thermoregulatory and vascular responses after exercise. However, evidence linking early post-exercise skin temperature changes with systemic markers such as oxygen uptake and lactate remains limited. Objective: To analyze the early passive recovery behavior of quadriceps skin temperature (0-6 min) after a progressive exercise test in trained female volleyball athletes and examine its association with aerobic capacity and blood lactate. Methods: Twenty professional female volleyball players completed a progressive treadmill test until volitional fatigue. Skin temperature of the rectus femoris and vastus lateralis was measured via IRT immediately after exercise cessation (minute 0) and during minutes 1-6 of passive recovery. Aerobic capacity (VO₂peak) was assessed through breath-by-breath gas analysis, and blood lactate was obtained at rest, immediately post-exercise, and at 3 min of recovery. Temperature change (ΔT) and thermal slope (C.min-1) were calculated. Pearson correlations and multiple regression models were applied. Results: Minimal skin temperature change occurred within the first 6 min of recovery. Both muscle regions exhibited high coherence in thermal responses (ΔT and slope correlations r = .76-.91, ps < .001). Neither VO₂peak nor lactate levels significantly predicted thermal behavior (all ps > .05). Early cooling patterns appeared primarily regulated by autonomic vascular adjustments rather than aerobic fitness or lactate kinetics. Conclusions: In professional female volleyball players, quadriceps skin temperature remains relatively stable during early passive recovery after incremental exercise, and this response is unrelated to aerobic capacity or lactate removal. Early post-exercise IRT reflects local vasomotor regulation, suggesting that longer monitoring windows and multimodal physiological assessments are needed for a comprehensive evaluation of recovery.