Optical Technology to assess oxidative responses to relative blood flow restriction pressures in the gastrocnemius muscle 

Raquel Martinez-Reviejo a, Manish Verma b, Umut Karadeniz b, M. Atif Yaqub b, Blai Ferrer-Uris a, Albert Busquets a, Nathan Mbuyamba a, Sjors Arnold a and Turgut Durduran bc 

aInstitut Nacional d’Educació Física de Catalunya (INEFC), Universitat de Barcelona (UB), Spain 

bICFO-Institut de Ciéncies Fotóniques, The Barcelona Institute of Science and Technology, Castelldefels, Barcelona, Spain cInstitució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain 

Introduction 

Training with external blood flow restriction (BFR) has been demonstrated to enhance muscle hypertrophy and strength development, likely through oxidative stress mechanisms. Current evidence-based guidelines recommend applying pressures between 40% and 80% of limb occlusion pressure (LOP) for optimal training adaptations. Vascular occlusion tests (VOT) have been extensively utilized to investigate hemodynamic and oxidative alterations in skeletal muscle tissue under maximal occlusive conditions, where diminished blood perfusion correlates with decreased oxidized hemoglobin (HbO₂) and increased reduced hemoglobin (HHb) levels. However, the physiological mechanisms and adaptive responses to partial vascular restriction using sub-maximal relative pressures remain poorly characterized. Optical devices based on infrared light are a non-invasive and harmless technology that could allow researchers and professionals to know these mechanisms and responses better.   The present study aims to quantify real-time alterations in blood flow dynamics and oxygen availability induced at the microcirculatory level by different relative pressure applications using infrared technology. 

Methods 

Twenty-three volunteers (29.9±5.6 years; 11 females) participated in a single-session experimental protocol. LOP was determined for each participant. Four VOTs were randomly conducted on the right leg, applying relative pressures of 40%, 60%, 80%, and 100% of LOP. Medial gastrocnemius hemodynamics were monitored during standardized 5-minute occlusion periods using an integrated measurement system combining time-resolved near-infrared spectroscopy (TR-NIRS) and diffuse correlation spectroscopy (DCS). After signal filtering and treatment, minute-by-minute mean values were computed during the 5-minute occlusion periods, for each pressure and signal. A General Linear Mixed Model was implemented to evaluate HbO₂, HHb, tissue oxygen saturation (StO₂), and blood flow index (BFI) dynamics across time and pressure conditions while accounting for repeated measurements and individual variability. 

Results 

Statistical analysis revealed distinct microcirculatory responses across pressure conditions. HbO₂ exhibited sustained increases under submaximal occlusion pressures (40%, 60%, 80% LOP) while decreasing under maximal occlusion (100% LOP), with peak accumulation observed during minutes 4-5 at 60% and 80% LOP. HHb concentrations increased significantly across all conditions, with maximal values at 80% and 100% LOP and lowest values at 40% LOP. StO₂ demonstrated significant progressive reduction across all conditions, with maximal occlusion producing the most pronounced deoxygenation. Among submaximal restrictions, 80% LOP yielded significantly lower StO₂ than both 40% and 60% LOP. BFI analysis confirmed significantly greater flow restriction at 100% LOP compared to all submaximal pressure conditions, with the most substantial BFI reduction occurring between minutes 1-2 of occlusion. 

Conclusions 

These findings demonstrate that submaximal occlusion pressures of 60% and 80% LOP generate optimal microcirculatory responses for BFR applications, producing significant HHb accumulation while maintaining sufficient tissue perfusion and achieving highest HbO₂ values. Significant differences between these pressure conditions only emerge after 5 minutes of sustained occlusion. Conversely, pressures of 40% LOP might result in incomplete arterial and venous occlusions, seen by a lower accumulation of HbO2 and HHb at minutes 4 and 5, and might be sub-optimal for BFR application purposes. The disparity in the responses between submaximal and maximal restriction underscores the critical importance of individualized LOP determination when implementing BFR interventions. 

References 

Martin PM, Bart RM, Ashley RL, et al. An Overview of Blood Flow Restriction Physiology and Clinical Considerations. Curr Sports Med Rep 2022; 21: 123–128. 

Pearson SJ, Hussain SR. A review on the mechanisms of blood-flow restriction resistance training-induced muscle hypertrophy. Sports Med 2015; 45: 187–200. 

Patterson SD, Hughes L, Warmington S, et al. Blood Flow Restriction Exercise: Considerations of Methodology, Application, and Safety. Front Physiol 2019; 10: 533. [4] Perrey S, Quaresima V, Ferrari M. Muscle Oximetry in Sports Science: An Updated Systematic Review. Sports Med 2024; 54: 975–996 

Funding 

The project was funded by private foundations (CELLEX, La Marato TV3, La Caixa), Generalitat de 

Catalunya (AGAUR, CERCA, SGR-2017, 2017SGR/741, INNOVADORS, RIS3CAT), Spanish government (PHOTOMETABO, ExLe-Brain-DCD PID2020-120453RB-I00, Severo Ochoa, LUX4MED), Agencia Estatal de Investigación (SCOSWEAR, SCOSDET, SafeICP, PHOTOMETABO, PID2019-106481RBC31/10.13039/501100011033), European Union (VASCOVID, LASERLAB), NIH, Instituto de Salud Carlos III (ISCIII) (LiteMuscle, DTS22/00023) co-financed with European Funds (FEDER).