Acute and Chronic Vascular Responses to Blood Flow Restriction in the Upper Body

Blood flow restriction (BFR) with low load exercise increases muscular size and strength. Little is known of vascular adaptations to this training modality, and nothing was known at very low loads. These studies examined cardiovascular responses to high load (70% of one-repetition maximum (1RM)) and very low load (15%1RM) exercise, alone or at two levels of BFR. Study 1: Participants performed unilateral biceps curls using either 15%1RM with no BFR (15/00), 40% of arterial occlusion pressure (AOP) (15/40), or 80%AOP (15/80), or 70%1RM (70/00). Systolic and diastolic blood pressure (SBP, DBP) and blood flow (BF) were measured in the arms during four sets performed to voluntary failure. BF increased in 15/00 (+470.8 (257.6) ml·min-1), 15/40 (325.3 (174.9) ml·min-1), and 70/00 (445.6 (249.3) ml·min-1) following the 2nd set, but not in 15/80. One minute following the 4th set, BF increased in 15/80 (+300.6 (206.4) ml·min-1), with no differences between conditions. SBP rose across all conditions (+10 (11) mmHg), whereas DBP rose in 15/00 (+8 (5) mmHg), 15/40 (+9 (7) mmHg), and 15/80 (+3 (7) mmHg) only. Study 2: Participants trained twice weekly, with one of the four conditions in each arm. Forearm blood flow (FBF), vascular conductance (VC), maximum venous outflow (MVO), venous volume variation (VVV), and venous compliance (CV) were examined before and after training. FBF and VC increased in 15/80 (+0.520 (0.218) ml·min-1·100ml-1; +8.286 (2.66) ml·mmHg-1) and 70/00 (+0.616 (0.212) ml·min-1·100ml-1; +8.595 (2.60) ml·mmHg-1). MVO increased for all conditions at 60 mmHg (+4.020 (1.416) ml·min-1·100ml-1), and for 15/00 (+6.52 (3.02) ml·min-1·100ml-1) and 15/80 (+11.468 (2.965) ml·min-1·100ml-1) at 80 mmHg. VVV increased at 20 mmHg (+0.075 (0.030) %), 40 mmHg (+0.162 (0.069) %), and 80 mmHg (+0.310 (0.103) %) for all conditions, but decreased for 15/00 (-0.632 (0.200) %) at 60 mmHg. CV increased across all conditions following training (+0.003 (0.002) %·mmHg-1). Rating of perceived exertion decreased halfway through training and remained depressed, while discomfort at first decreased at 4 weeks but returned to baseline at 8 weeks. High BFR pressures combined with very low loads result in similar vascular adaptations as high loads with eight weeks of training

Comparison of Vascular Dopplers in Measuring Limb Occlusion Pressure for Blood Flow Restriction Therapy

Topics in Exercise Science and Kinesiology Volume 4: Issue 1, Article 7, 2023. The use of blood flow restriction is becoming more common and requires the use of individualized pressures in order to remain a safe and effective rehabilitation modality. Measuring limb occlusion pressure (LOP) allows the practitioner to set the restriction pressure so that full occlusion does not occur. Objective: Compare a research-grade clinical vascular doppler and a consumer-grade vascular doppler in the measurement of LOP. Design: A randomized crossover design measuring LOP in the upper and lower body. Methods: 20 participants (men=10) visited the laboratory on one occasion. Limb circumference in the arm and thigh was measured. Following 10 min of supine rest, LOP was measured either in the arm, using a 5 cm wide inelastic cuff, or in the leg, using a 10 cm wide inelastic cuff. Measurements were repeated at 5 min intervals until LOP had been measured in both limbs with both dopplers. Results: Bland-Altman analysis showed agreement between the two dopplers in both the upper body (mean bias: 0.6 (-1.3 – 2.4) mmHg) and lower body (mean bias: -1.5 (-4.4 – 1.4) mmHg). Two one-sided tests of equivalence determined that both dopplers measured a statistically equivalent LOP in the upper body (p = .547) and lower body (p = .288). Conclusions: In a healthy, young population, the consumer-grade vascular doppler measured LOP equally as well as the research-grade clinical doppler

The Basics of Training for Muscle Size and Strength: A Brief Review on the Theory

The periodization of resistance exercise is often touted as the most effective strategy for optimizing muscle size and strength adaptations. This narrative persists despite a lack of experimental evidence to demonstrate its superiority. In addition, the general adaptation syndrome, which provides the theoretical framework underlying periodization, does not appear to provide a strong physiological rationale that periodization is necessary. Hans Selye conducted a series of rodent studies which used toxic stressors to facilitate the development of the general adaptation syndrome. To our knowledge, normal exercise in humans has never been shown to produce a general adaptation syndrome. We question whether there is any physiological rationale that a periodized training approach would facilitate greater adaptations compared with nonperiodized approaches employing progressive overload. The purpose of this article is to briefly review currently debated topics within strength and conditioning and provide some practical insight regarding the implications these reevaluations of the literature may have for resistance exercise and periodization. In addition, we provide some suggestions for the continued advancement within the field of strength and conditioning

Limb Occlusion Pressure: A Method to Assess Changes in Systolic Blood Pressure

Although often used as a surrogate, comparisons between traditional blood pressure measurements and limb occlusion assessed via hand-held Doppler have yet to be completed. Using limb occlusion pressure as a method of assessing systolic pressure is of interest to those studying the acute effects of blood flow restriction, where the removal of the cuff may alter the physiological response. Purpose: We sought to determine how changes in limb occlusion pressure track with changes in traditional assessments of blood pressure. Basic Procedures: Limb occlusion pressure measured by hand-held Doppler and blood pressure measured by an automatic blood pressure cuff were assessed at rest and following isometric knee extension (post and 5 minutes post). Main Findings: Each individual had a similar dispersion from the mean value for both the limb occlusion pressure measurement and traditional systolic blood pressure measurement [BF10: 0.33; median (95% credible interval): 0.02 (−6.0, 5.9) %]. In response to lower body isometric exercise, blood pressure changed across time. The difference between measurements was small at immediately post and 5 minutes post. The Bayes factors were in the direction of the null but did not exceed the threshold needed to accept the null hypothesis. However, at 5 minutes post, the differences were within the range of practical equivalence (within ± 4.6%). Principal Conclusions: Our findings suggest that changes in limb occlusion pressure measured by hand-held Doppler track similarly to traditional measurements of brachial systolic blood pressure following isometric knee extension exercise

A narrative review of the effects of blood flow restriction on vascular structure and function

Abstract Blood flow restriction is growing in popularity as a tool for increasing muscular size and strength. Currently, guidelines exist for using blood flow restriction alone and in combination with endurance and resistance exercise. However, only about 1.3 of practitioners familiar with blood flow restriction applications have utilized it for vascular changes, suggesting many of the guidelines are based on skeletal muscle outcomes. Thus, this narrative review is intended to explore the literature available in which blood flow restriction, or a similar application, assess the changes in vascular structure or function. Based on the literature, there is a knowledge gap in how applying blood flow restriction with relative pressures may alter the vasculature when applied alone, with endurance exercise, and with resistance exercise. In many instances, the application of blood flow restriction was not in accordance with the current guidelines, making it difficult to draw definitive conclusions as to how the vascular system would be affected. Additionally, several studies report no change in vascular structure or function, but few studies look at variables for both outcomes. By examining outcomes for both structure and function, investigators would be able to generate recommendations for the use of blood flow restriction to improve vascular structure and/or function in the future

The Impact of Ultrasound Probe Tilt on Muscle Thickness and Echo-Intensity: A Cross-Sectional Study

Introduction/background: To determine the influence of ultrasound probe tilt on reliability and overall changes in muscle thickness and echo-intensity. Materials and Methods: Thirty-six individuals had a total of 15 images taken on both the biceps brachii and tibialis anterior muscles. These images were taken in 2° increments with the probe tilted either upward (U) or downward (D) from perpendicular (0°) to the muscle (U6°, U4°, U2°, 0°, D2°, D4°, and D6°). All images were then saved, stored, and analyzed using Image-J software for echo-intensity and muscle thickness measures. Mean values (2–3 measurements within each probe angle) were compared across each probe angle, and reliability was assessed as if the first measure was taken perpendicular to the muscle, but the second measure was taken with the probe tilted to a different angle (to assume unintentional adjustments in reliability from probe tilt). Results: Tilting the probe as little as 2° produced a significant 4.7%, and 10.5% decrease in echo-intensity of the tibialis anterior and biceps brachii muscles, respectively, while changes in muscle thickness were negligible (\u3c1%) at all probe angles. The reliability for muscle thickness was greater than that of echo-intensity when the probe was held perpendicular at both measurements (∼1% vs 3%), and the impact that probe tilt had on reliability was exacerbated for echo-intensity measurements (max coefficient of variation: 24.5%) compared to muscle thickness (max coefficient of variation: 1.5%). Conclusion: While muscle thickness is less sensitive to ultrasound probe tilt, caution should be taken to ensure minimal probe tilt is present when taking echo-intensity measurements as this will alter mean values and reduce reliability. Echo-intensity values should be interpreted cautiously, particularly when comparing values across technicians/studies where greater alterations in probe tilt is likely

Blood Flow Restriction Augments the Skeletal Muscle Response During Very Low-Load Resistance Exercise to Volitional Failure

The purpose of this study was to compare the acute muscular response with resistance exercise between the following conditions [labeled (% one-repetition maximum/% arterial occlusion pressure)]: high-load (70/0), very low-load (15/0), very low-load with moderate (15/40), and high (15/80) blood flow restriction pressures. Twenty-three participants completed four sets of unilateral knee extension to failure (up to 90 repetitions) with each condition, one condition per leg, each day. Muscle thickness and maximal voluntary contraction (MVC) were measured before (Pre), immediately after (Post-0), and 15 min after (Post-15) exercise and electromyography (EMG) amplitude during exercise. Pre to Post-0 muscle thickness changes in cm [95% CI] were greater with 15/40 [0.57 (0.41, 0.73)] and 15/80 [0.49 (0.35, 0.62)] compared to 70/0 [0.33 (0.25, 0.40)]. Pre to Post-0 MVC changes in Nm [95% CI] were higher with 15/40 [−127.0 (−162.1, −91.9)] and 15/80 [−133.6 (−162.8, −104.4)] compared to 70/0 [−48.4 (−70.1, −26.6)] and 15/0 [−98.4 (−121.9, −74.9)], which were also different. Over the first three repetitions, EMG increased across sets, whereas in the last three repetitions it did not. EMG was also different between conditions and was generally greater during 70/0. Repetitions decreased across sets reaching the lowest for 70/0, and for very low loads decreased with increased pressure. In trained participants exercising to failure, lower load and the application of restriction pressure augment changes in muscle thickness and torque. The EMG amplitude was augmented by load. Training studies should compare these conditions, as the results herein suggest some muscular adaptations may differ

Acute Hemodynamic Changes Following High Load and Very Low Load Lower Body Resistance Exercise With and Without the Restriction of Blood Flow

Objective: To examine the acute changes in blood flow and blood pressure of very low load knee extensor exercise (15% one repetition maximum (1RM)) with and without different levels of applied pressure to determine how these effects might differ from high load exercise. We also sought to examine if this differed between men and women. Approach: A total of 90 participants (45 men, 45 women) were randomized into a very low load condition with no restriction 15/0, (n  =  21), a very low load condition with 40% arterial occlusion pressure (15/40, n  =  23), a very low load condition with 80% arterial occlusion pressure (15/80, n  =  22), and a traditional high load condition (70/0, n  =  24). Pre-post change in blood flow and blood pressure were compared across conditions. Evidence for or against the null hypothesis was quantified using Bayes factors (BF10). Main results: For blood flow, there was no evidence that the changes were different across conditions (BF10: 0.902). However, only the very low load free flow condition (15/0) had evidence to suggest a change (mean, (standard deviation)) from baseline (5.3 (9.1) ml · min−1; BF10: 3.687). Systolic pressure increased ~17 mmHg for the 15/0, 15/40, and 70/0 conditions, with no change in the 15/80 condition. There was no effect of sex for any variable. Significance: There was substantial variability in our blood flow measurements, making conclusions difficult for this variable. Of note, the blood pressure response was not augmented by blood flow restriction. The hemodynamic changes were also similar between sexes, indicating that men and women were not changing differently

Acute Skeletal Muscle Responses to Very Low-Load Resistance Exercise With and Without the Application of Blod Flow Restriction in the Upper Body

The purpose was to examine the acute skeletal muscle response to high load exercise and low‐load exercise with and without different levels of applied pressure (BFR). A total of 22 participants completed the following four conditions: elbow flexion exercise to failure using a traditional high load [70% 1RM, (7000)], low load [15% 1RM,(1500)], low load with moderate BFR [15%1RM+40%BFR(1540)] or low load with greater BFR [15% 1RM+80%BFR(1580)]. Torque and muscle thickness were measured prior to, immediately post, and 15 min postexercise. Muscle electromyography (EMG) amplitude was measured throughout. Immediately following exercise, the 7000 condition had lower muscle thickness [4·2(1·0)cm] compared to the 1500 [4·4 (1·1)cm], 1540 [4·4(1·1)cm] and 1580 [4·5(1·0)cm] conditions. This continued 15 min post. Immediately following exercise, torque was lower in the 1500 [31·8 (20) Nm], 1540 [28·3(16·9) Nm, P\u3c0·001] and 1580 [29·5 (17) Nm] conditions compared to the 7000 condition [40 (19) Nm]. Fifteen minutes post, 1500 and 1540 conditions demonstrated lower torque compared to the 7000 condition. For the last three repetitions percentage EMG was greater in the 7000 compared to the 1580 condition. Very low‐load exercise (with or without BFR) appears to result in greater acute muscle swelling and greater muscular fatigue compared to high load exercise