Author(s): CONTINI, L., AMENDOLA, C., NABACINO, M., RE, R., CONTINI, D., SPINELLI, L., D’ANTONA, G., TORRICELLI, A., Institution: POLITECNICO DI MILANO, Country: ITALY, Abstract-ID: 1139

INTRODUCTION:
Designing personalized training programs based on quantitative physiological measurements is central to optimizing athletic performance. In this context, non-invasive optical methods for monitoring muscle oxygenation, metabolism, and post-exercise recovery, such as Time-Domain Near-Infrared Spectroscopy (TD-NIRS) and Diffuse Correlation Spectroscopy (DCS), provide useful information on training-induced changes.
METHODS:
Sixteen competitive sprinters (age: 24±2; 6 females, 10 males) underwent a vascular occlusion test (VOT) on the dominant leg before and after two exercise sessions: low intensity (LI) and high intensity (HI). TD-NIRS was acquired at 100 ms integration time to derive tissue oxygen saturation (StO₂), while DCS was acquired at 2 s integration time to quantify changes in muscle blood flow index (BFI) [1]. A source-detector distance of 2.5 cm was used. The desaturation slope (DeO2) was computed in the 30-90 s interval after occlusion onset, and the hyperemic area was computed as the area under the curve (AUC) from the cuff release to recovery of baseline values for both StO2 and BFI, using a polynomial fitting of the response to improve robustness.
RESULTS:
As expected, DeO2 increased after both training sessions, reflecting a condition of higher metabolic rate for the muscle [2]. In particular, post-training DeO₂ was significantly higher after HI (−11.8±7.1%/min) compared to LI (−7.8±4.8%/min; p=0.014), indicating faster oxygen depletion under higher metabolic demand. AUC values for both StO₂ and BFI showed no significant difference between LI and HI, consistent with the expected absence of a training-load-dependent modulation of vascular reactivity. Sex-related differences revealed a higher muscle oxygen consumption rate in men than in women, as demonstrated by higher post-training DeO₂ (−13.0±4.8 vs −3.2±0.8 %/min; p<0.001). Consistently, greater post-occlusive oxygenation was observed in men, reflected by higher StO₂ AUC values (p=0.010), likely associated with differences in capillary density and oxidative metabolism. Similar results were obtained before the sessions, indicating sex-specific muscle characteristics rather than training-induced adaptations. In contrast, comparable baseline StO₂ and BFI AUC values indicated similar resting oxygenation and post-occlusive blood flow responses despite sex-related differences in oxygen metabolism.
CONCLUSION:
Combining TD-NIRS and DCS enables multiparametric characterization of muscle hemodynamics. The observed increase in DeO₂ reflects elevated metabolic rate after training, with stronger effects for HI sessions, consistent with higher muscular stress and recovery demand. Our results support that non-invasive optical methods, which provide real-time, quantitative measurements, may be suitable for longitudinal monitoring in athletes.

[1] Nabacino et al. Sensors, 2024.
[2] Tuesta et al. Biology, 2022.