Effect of Blood Flow Restriction on Tissue Oxygenation during Knee Extension

PURPOSE: Time-Resolved Near Infrared Spectroscopy (TR-NIRS) was used to quantify tissue oxy- and deoxy-hemoglobin concentrations ([HbO(2)], [HbR]), and O(2) saturation (stO(2)) in the oblique fibers of the vastus medialis muscle (VMO) and brain prefrontal cortex (PFC) during knee extension with and without blood flow restriction (BFR). METHODS: Six young healthy males performed three sets of knee extensions on a dynamometer (50% 1 RM), separated by 90 sec rest periods, in three conditions: 1) until fatigue without BFR (Fatigue); 2) until fatigue with BFR (100 mm Hg cuff constriction around thigh, BFR); 3) same number of repetitions from condition 2, without BFR (Matched). Each condition was performed on a separate visit. RESULTS: BFR was associated with higher VMO [HbR] (rest 1: 57.8 μM BFR vs. 35.0 μM Matched, p < 0.0001) and a significantly lower stO(2) during recovery periods between sets (7.5 – 11.2 % lower than non-BFR conditions for rest 1 and 2, p < 0.0001). Using a piecewise linear spline method, a spike in [HbR] was observed before the onset of HbR clearance during recovery, causing HbR clearance to begin at a higher concentration (BFR: 81 μM vs. Matched: 62 μM, p = 0.029). [HbO(2)] kinetics during recovery were also affected by BFR, with longer duration (BFR: 51 s, Matched: 31 s, p = 0.047) but lower rate of increase (BFR: 58 μM/min, Matched: 89 μM/min, p = 0.004) during recovery. In the PFC, BFR was associated with increased [HbR], diminished increase in [HbO(2)], and higher subjective exertion. CONCLUSIONS: These findings yield insight into possible physiological mechanisms of BFR, and suggest a role of TR-NIRS in monitoring and optimization of BFR exercise on an individual basis

The influence of participant characteristics on the relationship between cuff pressure and level of blood flow restriction

This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons. org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Purpose: Previous investigations to establish factors influencing the blood flow restriction (BFR) stimulus have determined cuff pressures required for complete arterial occlusion, which does not reflect the partial restriction prescribed for this training technique. This study aimed to establish characteristics that should be accounted for when prescribing cuff pressures required for partial BFR. Methods: Fifty participants were subjected to incremental blood flow restriction of the upper and lower limbs by proximal pneumatic cuff inflation. Popliteal and brachial artery diameter, blood velocity and blood flow was assessed with Doppler ultrasound. Height, body mass, limb circumference, muscle–bone cross-sectional area, adipose thickness (AT) and arterial blood pressure were measured and used in different models of hierarchical linear regression to predict the pressure at which 60 % BFR (partial occlusion) occurred. Results: Combined analysis revealed a difference in cuff pressures required to elicit 60 % BFR in the popliteal (111 ± 12 mmHg) and brachial arteries (101 ± 12 mmHg). MAP (r = 0.58) and AT (r = −0.45) were the largest independent determinants of lower and upper body partial occlusion pressures. However, greater variance was explained by upper and lower limb regression models composed of DBP and BMI (48 %), and arm AT and DBP (30 %), respectively. Conclusion: Limb circumference has limited impact on the cuff pressure required for partial blood flow restriction which is in contrast to its recognised relationship with complete arterial occlusion. The majority of the variance in partial occlusion pressure remains unexplained by the predictor variables assessed in the present study