Evaluation of local quadriceps action response patterns during cycling using a multimodal NIRS and thermal imaging protocol: a pilot study

Abstract

This study aimed to develop and evaluate a comprehensive physiological testing protocol for cyclists that integrates thermal imaging and near-infrared spectroscopy during standardized incremental exercise. Eight trained male cyclists performed a standardized incremental cycling test under controlled conditions. After a 10-minute warm-up (1.0 W·kg⁻¹), workload increased by 0.5 W·kg⁻¹ every 3 minutes until voluntary exhaustion, followed by a 10-minute cool-down. Muscle oxygen saturation (SmO₂) of the rectus femoris was continuously recorded bilaterally using wearable near-infrared spectroscopy (Moxy Monitor), and thermal imaging of selected quadriceps muscles was conducted with a FLIR T1020 camera. Heart rate was monitored continuously. Measurements were performed after a 25-minute acclimatization period under standardized environmental conditions. No statistically significant differences in normalized skin temperature (Tsk) or normalized SmO₂ were observed across exercise phases after Bonferroni correction (p = 0.012). A significant positive correlation was found between exercise-induced changes in normalized Tsk and SmO₂ (ΔEX: Spearman’s r = 0.89, p << 0.017). No significant correlation was observed during the warm-up (ΔWU: r = 0.02) or recovery (ΔCD: r = 0.14) phases. Due to the small sample size (n = 8), correlations were interpreted descriptively as indicative of a physiological connection rather than causal relationships. Increasing exercise intensity was associated with concurrent alterations in muscle oxygenation and Tsk, reflecting integrated hemodynamic and metabolic responses. The combined IRT–NIRS protocol demonstrated methodological feasibility and may provide a valid framework for multidimensional assessment of muscular responses, warranting further validation in larger cohorts.