Muscular activation, as well as neuromuscular fatigue, varies as a function of relative BFR intensity. Therefore, the individual determination of vascular restriction levels is crucial before engaging in BFR exercise.

Blood flow restrictive (BFR) exercise elicits a localized hypoxic environment compatible with greater metabolic stress. We intended to compare the acute changes in muscle microvascular oxygenation following low-intensity knee extension exercise, combined with different levels of BFR. Thirteen active young men (age: 23.8 ± 5.4 years) were tested for unilateral knee extension exercise (30 + 15 + 15 + 15 reps at 20% one repetition maximum) on four different conditions: no-BFR (NOBFR), 40, 60, and 80% of arterial occlusion pressure (AOP). Deoxyhemoglobin+myoglobin concentration Deoxy[Hb+Mb], total hemoglobin [T(H+Mb)] and tissue oxygen saturation [TOI] were measured on the vastus lateralis muscle using near-infrared spectroscopy (NIMO, Nirox srl, Brescia, Italy). The magnitude of change in Deoxy[Hb+Mb]during exercise was similar between 60 and 80% AOP. Overall, compared to that seen during 60 and 80% AOP, NOBFR as well as 40% AOP resulted in a lower magnitude of change in Deoxy[Hb+Mb] ( p < 0.05). While the oxygen extraction decreased during each inter-set resting interval in NOBFR and 40% AOP, this was not the case for 60 or 80% AOP. Additionally, TOI values obtained during recovery from each set of exercise were similarly affected by all conditions. Finally, our data also show that, when performed at higher restrictive values (60 and 80%), BFR exercise increases total Deoxy[Hb+Mb] extraction ( p < 0.05). Taken together, we provide evidence that BFR is effective for increasing deoxygenation and reducing tissue oxygenation during low-intensity exercise. We also showed that when using low loads, a relative pressure above 40% of the AOP at rest is required to elicit changes in microvascular oxygenation compared with the same exercise with unrestricted conditions.

Fatela, P, Reis, JF, Mendonca, GV, Freitas, T, Valamatos, MJ, Avela, J, and Mil-Homens, P. Acute neuromuscular adaptations in response to low-intensity blood flow restricted exercise and high-intensity resistance exercise: are there any differences? J Strength Cond Res 32(4): 902-910, 2018-Numerous studies have reported similar neuromuscular adaptations between low-intensity (LI) blood-flow restricted exercise (BFRE) and high-intensity (HI) resistance training. Unfortunately, none of these experimental designs individualized blood flow restriction (BFR) levels to each participant. Thus, their findings are difficult to interpret. We aimed at comparing the acute effects of LI BFR (80% of absolute vascular occlusion pressure) with LI non-BFR and HI training on muscle torque, activation, and neuromuscular fatigue. Ten men (23.8 ± 5.4 years) exercised at 20 and 75% of 1 repetition maximum with and without BFR (for LI). Blood flow restriction pressure was determined individually using resting blood-flow measurements. Torque was determined during maximal voluntary contractions (MVCs) at pre-exercise and postexercise time points. Surface electromyographic activity (root mean square [RMS] and median frequency [MF]) was recorded for the rectus femoris (RF) and vastus medialis (VM) muscles, before and after each session of training, during isometric contractions at 20% MVC. Torque decreased post-HI and LI BFR (-9.5 and -7.8%, respectively; p < 0.01), but not after LI non-BFR. The MF was reduced following HI training in the VM and the RF muscles (-5.3 and -12.5%, respectively; p ≤ 0.05). Conversely, the impact of LI BFR on reducing MF was limited to the RF muscle (-10.7%, p ≤ 0.05). Finally, when compared to all other conditions, RMS values were consistently higher during submaximal contractions performed after HI training (p ≤ 0.05). Thus, we conclude that, despite enhancing the acute magnitude of muscular activation and fatigue, LI BFR exercise exerts a less profound impact on neuromuscular function than HI resistance training.

We aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action potential amplitudes (MUAP). Force decrement was only seen after LI BFR exercise (–20.5%; p<0.05). LI BFR exercise also induced greater decrements in the linear slope coefficient of the regression lines between motor unit recruitment threshold and firing rate (BFR: –165.1±120.4 vs. non-BFR: –44.4±33.1%, p<0.05). Finally, there was a notable shift towards higher values of firing rate and MUAP amplitude post-LI BFR exercise. Taken together, our data indicate that LI BFR exercise increases the activity of motor units with higher MUAP amplitude. They also indicate that motor units with similar MUAP amplitudes become activated at higher firing rates post-LI BFR exercise.