Skeletal Muscle Adaptations to High-Load Resistance Training With Pre-Exercise Blood Flow Restriction.

ABSTRACT: Hammert, WB, Moreno, EN, Martin, CC, Jessee, MB, and Buckner, SL. Skeletal muscle adaptations to high-load resistance training with pre-exercise blood flow restriction. J Strength Cond Res 37(12): 2381-2388, 2023-This study aimed to determine if blood flow restriction (BFR) could augment adaptations to a high-load training protocol that was inadequate for muscle growth. Forty nontrained individuals had each arm assigned to 1 of 3 elbow flexion protocols: (a) high-load resistance training [TRAD; 4 sets to muscular failure at 70% 1 repetition maximum (1RM)], (b) low repetition high-load resistance training with pre-exercise BFR (PreBFR; 4 sets of 3 repetitions at 70% 1RM + 3 min of pre-exercise BFR), and (c) low repetition high-load resistance training (LRTRAD); 4 sets of 3 repetitions at 70% 1RM). Muscle thickness (MT), 1RM strength, and local muscular endurance (LME) of the elbow flexors were measured before and after 8 weeks. An alpha level of 0.05 was used for all comparisons. For the 50% site, MT increased for TRAD (0.211 cm, 95% confidence interval [95% CI]: 0.143-0.280), PreBFR (0.105 cm, 95% CI: 0.034-0.175), and LRTRAD (0.073 cm, 95% CI: 0.000-0.146). The change for TRAD was greater than PreBFR and LRTRAD. For the 60% site, MT increased for TRAD (0.235 cm, 95% CI: 0.153-0.317), PreBFR (0.097 cm, 95% CI: 0.014-0.180), and LRTRAD (0.082 cm, 95% CI: 0.000-0.164). The change for TRAD was greater than PreBFR and LRTRAD. For the 70% site MT increased for TRAD (0.308 cm, 95% CI: 0.247-0.369), PreBFR (0.103 cm, 95% CI: 0.041-0.166), and LRTRAD (0.070 cm, 95% CI: 0.004-0.137). The change for TRAD was greater than PreBFR and LRTRAD. One repetition maximum and LME significantly increased for each condition, with no differences between conditions. Collapsed across conditions 1RM strength increased 2.094 kg (95% CI: 1.771-2.416) and LME increased 7.0 repetitions (95% CI: 5.7-8.3). In conclusion, the application of BFR to low-repetition, high-load training did not enhance the adaptative response.

Unilateral, bilateral, and alternating muscle actions elicit similar muscular responses during low load blood flow restriction exercise.

PURPOSE: Compare acute muscular responses to unilateral, bilateral, and alternating blood flow restriction (BFR) exercise. METHODS: Maximal strength was tested on visit one. On visits 2-4, 2-10 days apart, 19 participants completed 4 sets of knee extensions (30% one-repetition maximum) with BFR (40% arterial occlusion pressure) to momentary failure (inability to lift load) using each muscle action (counterbalanced order). Ultrasound muscle thickness was measured at 60% and 70% of the anterior thigh before (Pre), immediately (Post-0), and 5 min (Post-5) after exercise. Surface electromyography and tissue deoxygenation were measured throughout. Results, presented as means, were analyzed with a three-way (sex by time by condition) Bayesian RMANOVA. RESULTS: There was a time by sex interaction (BFinclusion: 5.489) for left leg 60% muscle thickness (cm). However, changes from Pre to Post-0 (males: 0.39 vs females: 0.26; BF10: 0.839), Post-0 to Post-5 (males: - 0.05 vs females: - 0.06; BF10: 0.456), and Pre to Post-5 (males: 0.34 vs females: 0.20; BF10: 0.935) did not differ across sex. For electromyography (%MVC), there was a sex by condition interaction (BFinclusion: 550.472) with alternating having higher muscle excitation for females (16) than males (9; BF10: 5.097). Tissue deoxygenation (e.g. channel 1, µM) increased more for males (sets 1: 11.17; 2: 2.91; 3: 3.69; 4: 3.38) than females (sets 1: 4.49; 2: 0.24; 3: - 0.10; 4: - 0.06) from beginning to end of sets (all BFinclusion ≥ 4.295e + 7). For repetitions, there was an interaction (BFinclusion: 17.533), with alternating completing more than bilateral and unilateral for set one (100; 56; 50, respectively) and two (34; 16; 18, respectively). CONCLUSION: Alternating, bilateral, and unilateral BFR exercise elicit similar acute muscular responses.

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 (<1%) 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.

Acute cardiovascular response to unilateral, bilateral, and alternating resistance exercise with blood flow restriction.

AIM: Blood flow restriction (BFR) exercise is a common alternative to traditional high-load resistance exercise used to increase muscle size and strength. Some populations utilizing BFR at a low load may wish to limit their cardiovascular response to exercise. Different contraction patterns may attenuate the cardiovascular response, but this has not been compared using BFR. PURPOSE: To compare the cardiovascular response to unilateral (UNI), bilateral (BIL), and alternating (ALT) BFR exercise contraction patterns. METHODS: Twenty healthy participants performed four sets (30 s rest) of knee extensions to failure, using 30% one-repetition maximum, 40% arterial occlusion pressure, and each of the three contraction patterns (on different days, at the same time of day, separated by 2-10 days, randomized). Cardiovascular responses, presented as pre- to post-exercise mean changes (SD), were measured using pulse wave analysis and analyzed with Bayesian RMANOVA. RESULTS: ALT caused greater changes in: aortic systolic [ΔmmHg: ALT = 21(8); UNI = 13(11); BIL = 15(8); BF10 = 29.599], diastolic [ΔmmHg: ALT = 13(8); UNI = 7(11); BIL = 8(8); BF10 = 5.175], and mean arterial [ΔmmHg: ALT = 19(8); UNI = 11(11); BIL = 13(7); BF10 = 48.637] blood pressures. Aortic [ΔmmHg bpm: ALT = 4945(2340); UNI = 3294(1408); BIL = 3428 (1461); BF10 = 113.659] and brachial [ΔmmHg bpm: ALT = 6134(2761); UNI = 4300(1709); BIL = 4487(1701); BF10 = 31.845] rate pressure products, as well as heart rate [Δbpm: ALT = 26(14); UNI = 19(8); BIL = 19(11); BF10 = 5.829] were greatest with ALT. Augmentation index [Δ%: UNI = -6(13); BIL = - 7(11); ALT = - 5(16); BF10 = 0.155] and wave reflection magnitude [Δ%: UNI = - 5(9); BIL = - 4(7); ALT = - 4(7); BF10 = 0.150] were not different. CONCLUSION: Those at risk of a cardiovascular event may choose unilateral or bilateral BFR exercise over alternating until further work determines the degree to which it can be tolerated.

Validity of the Handheld Doppler to Determine Lower-Limb Blood Flow Restriction Pressure for Exercise Protocols.

Laurentino, GC, Loenneke, JP, Mouser, JG, Buckner, SL, Counts, BR, Dankel, SJ, Jessee, MB, Mattocks, KT, Iared, W, Tavares, LD, Teixeira, EL, and Tricoli, V. Validity of the handheld Doppler to determine lower-limb blood flow restriction pressure for exercise protocols. J Strength Cond Res 34(9): 2693-2696, 2020-Handheld (HH) Doppler is frequently used for determining the arterial occlusion pressure during blood flow restriction exercises; however, it is unknown whether the blood flow is occluded when the auscultatory signal is no longer present. The purpose of this study was to assess the validity between the HH Doppler and the Doppler ultrasound (US) measurements for determining the arterial occlusion pressure in healthy men. Thirty-five participants underwent 2 arterial occlusion pressure measurements. In the first measure, a pressure cuff (17.5 cm wide) was placed at the most proximal region of the thigh and the pulse of posterior tibial artery was detected using an HH Doppler probe. The cuff was inflated until the auscultatory pulse was no longer detected. After 10 minutes of rest, the procedure was repeated with the Doppler US probe placed on the superficial femoral artery. The cuff was inflated up to the point at which the femoral arterial blood flow was interrupted. The point at which the auscultatory pulse and blood flow were no longer detected was deemed the arterial occlusion pressure. There were no significant differences in arterial occlusion pressure level between the HH Doppler and the Doppler US (133 [±18] vs. 135 [±17] mm Hg, p = 0.168). There was a significant correlation (r = 0.938, p = 0.168), reasonable agreement, and a total error of the estimate of 6.0 mm Hg between measurements. Arterial occlusion pressure level determined by the HH Doppler and the Doppler US was similar, providing evidence that the HH Doppler is a valid and practical method.

A method to standardize the blood flow restriction pressure by an elastic cuff.

Blood flow restriction training using a practical (non-pneumatic) elastic cuff has recently increased in popularity. However, a criticism of this method is that the pressure applied and the amount of blood flow restriction induced is unknown. The aim was to quantify blood flow following the application of an elastic cuff and compare that to what is observed using a more traditional pressurized nylon cuff. Thirty-five young participants (16 men and 19 women) visited the laboratory once for testing. In a randomized order (one condition per arm), an elastic cuff (5 cm wide) was applied to one arm and blood flow was measured following the cuff being pulled to two distinct lengths; 10% and 20% of the resting length based on arm circumference. The other arm would follow a similar protocol but use a pressurized nylon cuff (5 cm wide) and be inflated to 40% and 80% of the individuals resting arterial occlusion pressure. There was a main effect of pressure for blood flow with it decreasing in a pressure-dependent manner (High < Low, P < 0.001). The mean difference (95% CI) in blood flow between cuffs was -5.9 (-18.9, 7.0) % for the lower pressure and -4.0 (-13.2, 5.1) % for the higher pressure. When the relative changes for each cuff were separated by sex, there were no differences in the changes from Pre (P ≥ 0.509). The application of a pressure relative to the initial belt length, which is largely dependent upon arm circumference, appears to provide one method to standardize the practical blood flow restriction pressure for future research.

Central cardiovascular hemodynamic response to unilateral handgrip exercise with blood flow restriction.

AIM: Exercise training with blood flow restriction (BFR) increases muscle size and strength. However, there is limited investigation into the effects of BFR on cardiovascular health, particularly central hemodynamic load. PURPOSE: To determine the effects of BFR exercise on central hemodynamic load (heart rate-HR, central pressures, arterial wave reflection, and aortic stiffness). METHODS: Fifteen males (age = 25 ± 2 years; BMI = 27 ± 2 kg/m2, handgrip max voluntary contraction-MVC = 50 ± 2 kg) underwent 5-min bouts (counter-balanced, 10 min rest between) of rhythmic unilateral handgrip (1 s squeeze, 2 s relax) performed with a moderate-load (60% MVC) with and without BFR (i.e., 71 ± 5% arterial inflow flow reduction, assessed via Doppler ultrasound), and also with a low-load (40% MVC) with BFR. Outcomes included HR, central mean arterial pressure (cMAP), arterial wave reflection (augmentation index, AIx; wave reflection magnitude, RM%), aortic arterial stiffness (pulse wave velocity, aPWV), and peripheral (vastus lateralis) microcirculatory response (tissue saturation index, TSI%). RESULTS: HR increased above baseline and time control for all handgrip bouts, but was similar between the moderate load with and without BFR conditions (moderate-load with BFR = + 9 ± 2; moderate-load without BFR = + 8 ± 2 bpm, p < 0.001). A similar finding was noted for central pressure (e.g., moderate load with BFR, cMAP = + 14 ± 1 mmHg, p < 0.001). No change occurred for RM% or AIx (p > 0.05) for any testing stage. TSI% increased during the moderate-load conditions (p = 0.01), and aPWV increased above baseline following moderate-load handgrip with BFR only (p = 0.012). CONCLUSIONS: Combined with BFR, moderate load handgrip training with BFR does not significantly augment central hemodynamic load during handgrip exercise in young healthy men.

Perceptual changes to progressive resistance training with and without blood flow restriction.

The purpose was to examine changes in the perceptual responses to lifting a very low load (15% one repetition maximum (1RM)) with and without (15/0) different pressures [40% (15/40) and 80% (15/80) arterial occlusion pressure] and compare that to traditional high load (70/0) resistance exercise. Ratings of perceived exertion (RPE) and discomfort were measured following each set of exercise. In addition, resting arterial occlusion pressure was measured prior to exercise. Assessments were made in training sessions 1, 9, and 16 for the upper and lower body. Data are presented as means and 95% CI. There were changes in RPE in the upper body with condition 15/40 [-2.1 (-3.4, -0.850)] and 15/80 [-2.4 (-3.6, -1.1)] decreasing by the end of training. In the lower body, RPE decreased in condition 15/40 [-1.4 (-2.3, -0.431)] by the end of the training study. There was a main effect of time in the upper body with all conditions decreasing discomfort. In the lower body, all conditions decreased except for 15/80. For arterial occlusion pressure, there were differences across time in the 15/40 condition and the 15/80 condition in the upper body. Repeated exposure to blood flow restriction may dampen the perceptual responses over time.

Skeletal muscle mass in human athletes: What is the upper limit?

OBJECTIVES: To examine the amount of absolute and relative skeletal muscle mass (SM) in large sized athletes to investigate the potential upper limit of whole body muscle mass accumulation in the human body. METHODS: Ninety-five large-sized male athletes and 48 recreationally active males (control) had muscle thickness measured by ultrasound at nine sites on the anterior and posterior aspects of the body. SM was estimated from an ultrasound-derived prediction equation. Body density was estimated by hydrostatic weighing technique, and then body fat percentage and fat-free mass (FFM) were calculated. We used the SM index and FFM index to adjust for the influence of standing height (ie, divided by height squared). RESULTS: Ten of the athletes had more than 100 kg of FFM, including the largest who had 120.2 kg, while seven of the athletes had more than 50 kg of SM, including the largest who had 59.3 kg. FFM index and SM index were higher in athletes compared to controls and the percentage differences between the two groups were 44% and 56%, respectively. The FFM index increased linearly up to 90 kg of body mass, and then the values leveled off in those of increasing body mass. Similarly, the SM index increased in a parabolic fashion reaching a plateau (approximately 17 kg/m2 ) beyond 120 kg body mass. CONCLUSIONS: SM index may be a valuable indicator for determining skeletal muscle mass in athletes. A SM index of approximately 17 kg/m2 may serve as the potential upper limit in humans.

Moderately heavy exercise produces lower cardiovascular, RPE, and discomfort compared to lower load exercise with and without blood flow restriction.

PURPOSE: To determine the acute cardiovascular and perceptual responses of low-load exercise with or without blood flow restriction and compare those responses to that of moderately heavy exercise. METHODS: Twenty-two participants completed unilateral elbow flexion exercise with a moderately heavy-load- [70% one-repetition maximum (1RM); 70/0] and with three low-load conditions (15% 1RM) in combination with 0% (15/0), 40%, (15/40) and 80% (15/80) arterial occlusion pressure. Participants exercised until failure (or until 90 repetitions per set). The cardiovascular response (arterial occlusion) was measured pre and post exercise and the perceptual responses [ratings of perceived exertion (RPE) and discomfort] were determined before and after each set of exercise. RESULTS: For arterial occlusion pressure, the lower-load conditions had greater change from pre to post compared to 70/00 (e.g., 15/80: 44 vs. 70/0: 34 mmHg). RPE was highest across the sets for the 15/80 condition with the other conditions having similar RPE (e.g., set 4: median rating of 17.2 for 15/80 vs. ~ 15.5 for other conditions). Ratings of discomfort were also greatest for the 15/80 condition (15/80 > 15/40 > 15/0 > 70/0). Exercise volume within the 15/0 and 15/40 conditions were similar but were significantly greater than that observed with the 15/80 and 70/0 conditions. CONCLUSION: Low-load exercise to volitional failure results in a greater cardiovascular response to that of moderately heavy-load exercise. When high pressure is applied to low load exercise, there is a reduction in exercise volume but an elevated perceptual response that may be an important consideration when applying this stimulus in practice.

A critical review of the current evidence examining whether resistance training improves time trial performance.

A number of reviews have concluded that resistance training is beneficial for improving sports performance despite the inclusion of studies which do not actually measure a performance outcome (i.e. a timed trial). The purpose of this review was to examine only those studies which would allow us to infer the benefits of resistance training on improving time trial performance. Of the nine studies meeting all inclusion criteria only three demonstrated an additive effect of adding resistance training to the current activity-specific training being performed. These three studies demonstrated improvements in either 5 or 10 km time trial among recreationally skilled athletes (i.e. non-elite level time). Previous reviews have included studies which did not include: (1) performance outcomes; (2) control groups; and/or (3) equal volumes of activity-specific exercise among the resistance training and control groups. Presently, there is little evidence that adding resistance exercise to a sport-specific training program will augment time trial performance. While it is difficult to perform such long-term studies assessing the effects of resistance training among time trial athletes, the statement that resistance training is efficacious for improving time trial performance should be tempered until sufficient evidence is presented to support such claims.

The Application of Blood Flow Restriction: Lessons From the Laboratory.

Blood flow restriction by itself or in combination with exercise has been shown to produce beneficial adaptations to skeletal muscle. These adaptations have been observed across a range of populations, and this technique has become an attractive possibility for use in rehabilitation. Although there are concerns that applying blood flow restriction during exercise makes exercise inherently more dangerous, these concerns appear largely unfounded. Nevertheless, we have advocated that practitioners could minimize many of the risks associated with blood flow-restricted exercise by accounting for methodological factors, such as cuff width, cuff type, and the individual to which blood flow restriction is being applied. The purpose of this article is to provide an overview of these methodological factors and provide evidence-based recommendations for how to apply blood flow restriction. We also provide some discussion on how blood flow restriction may serve as an effective treatment in a clinical setting.

What does individual strength say about resistance training status?

The point at which an individual becomes resistance "trained" is not well defined in the literature. Some studies have defined training status as having engaged in consistent resistance training activities for a given period of time, whereas others base inclusion criteria on strength levels alone, or levels of strength in combination with training age/time. If the primary focus of a study is to examine adaptations in individuals with high levels of strength, then it may be appropriate to exclude the individuals who do not meet strength requirements. However, given the heterogeneity of the strength response to resistance training, strength cannot separate those who are "trained" from those who are "untrained." We suggest that, when determining resistance training status, training age (time) and the modality of training (specificity) should be the primary criteria considered. Muscle Nerve 55: 455-457, 2017.

Muscle growth: To infinity and beyond?

Strength increases following training are thought to be influenced first by neural adaptions and second by large contributions from muscle growth. This is based largely on the idea that muscle growth is a slow process and that a plateau in muscle growth would substantially hinder long-term increases in strength. This Review examines the literature to determine the time course of skeletal muscle growth in the upper and lower body and to determine whether and when muscle growth plateaus. Studies were included if they had at least 3 muscle size time points, involved participants 18 years or older, and used a resistance training protocol. Muscle growth occurs sooner than had once been hypothesized, and this adaptation is specific to the muscle group. Furthermore, the available studies indicate that the muscle growth response will plateau, and additional growth is not likely to occur appreciably beyond this initial plateau. However, the current study durations are a limitation. Muscle Nerve 56: 1022-1030, 2017.

Do metabolites that are produced during resistance exercise enhance muscle hypertrophy?

Many reviews conclude that metabolites play an important role with respect to muscle hypertrophy during resistance exercise, but their actual physiologic contribution remains unknown. Some have suggested that metabolites may work independently of muscle contraction, while others have suggested that metabolites may play a secondary role in their ability to augment muscle activation via inducing fatigue. Interestingly, the studies used as support for an anabolic role of metabolites use protocols that are not actually designed to test the importance of metabolites independent of muscle contraction. While there is some evidence in vitro that metabolites may induce muscle hypertrophy, the only study attempting to answer this question in humans found no added benefit of pooling metabolites within the muscle post-exercise. As load-induced muscle hypertrophy is thought to work via mechanotransduction (as opposed to being metabolically driven), it seems likely that metabolites simply augment muscle activation and cause the mechanotransduction cascade in a larger proportion of muscle fibers, thereby producing greater muscle growth. A sufficient time under tension also appears necessary, as measurable muscle growth is not observed after repeated maximal testing. Based on current evidence, it is our opinion that metabolites produced during resistance exercise do not have anabolic properties per se, but may be anabolic in their ability to augment muscle activation. Future studies are needed to compare protocols which produce similar levels of muscle activation, but differ in the magnitude of metabolites produced, or duration in which the exercised muscles are exposed to metabolites.

Post-exercise blood flow restriction attenuates hyperemia similarly in males and females.

PURPOSE: Our laboratory recently demonstrated that post-exercise blood flow restriction attenuated muscle hypertrophy only in females, which we hypothesized may be due to alterations in post-exercise blood flow. The aim of this study is to test our previous hypothesis that sex differences in blood flow would exist when employing the same protocol. METHODS: Twenty-two untrained individuals (12 females; 10 males) performed two exercise sessions, each involving one set of elbow flexion exercise to volitional failure on the right arm. The experimental condition had blood flow restriction applied for a 3 min post-exercise period, whereas the control condition did not. Blood flow was measured using an ultrasound at the brachial artery and was taken 1 and 4 min post-exercise. This corresponded to 1 min post inflation and 1 min post deflation in the experimental condition. RESULTS: There were no differences in the alterations in blood flow between the control and experimental conditions when examined across sex. Increases in blood flow [mean (standard deviation)] were as follows: males 1 min [control 764 (577) %; experimental 113 (108) %], males 4 min [control 346 (313) %; experimental 449 (371) %], females 1 min [control 558 (367) %; experimental 87 (105) %], and females 4 min [control 191 (183) %; experimental 328 (223) %]. CONCLUSION: It does not appear that the sex-specific attenuation of muscle hypertrophy we observed previously can be attributed to different alterations in post-exercise blood flow. Future studies may wish to replicate our previous training study, or examine alternative mechanisms which may be sex specific.

A tale of three cuffs: the hemodynamics of blood flow restriction.

INTRODUCTION: The blood flow response to relative levels of blood flow restriction (BFR) across varying cuff widths is not well documented. With the variety of cuff widths and pressures reported in the literature, the effects of different cuffs and pressures on blood flow require investigation. PURPOSE: To measure blood pressure using three commonly used BFR cuffs, examine possible venous/arterial restriction pressures, and measure hemodynamic responses to relative levels of BFR using these same cuffs. METHODS: 43 participants (Experiment 1, brachial artery blood pressure assessed) and 38 participants (Experiment 2, brachial artery blood flow assessed using ultrasound, cuff placed at proximal portion of arm) volunteered for this study. RESULTS: Blood pressure measurement was higher in the 5 cm cuff than in the 10 and 12 cm cuffs. Sub-diastolic relative pressures appear to occur predominantly at <60% of arterial occlusion pressure (AOP). Blood flow under relative levels of restriction decreases in a non-linear fashion, with minimal differences between cuffs [resting: 50.3 (44.2) ml min-1; 10% AOP: 42.0 (36.8); 20%: 33.6 (28.6); 30%: 23.6 (20.4); 40%: 17.1 (15.9); 50%: 12.5 (9.4); 60%: 11.5 (8.1); 70%: 11.4 (7.0); 80%: 10.3 (6.3); 90%: 7.9 (4.8); 100%: 1.5 (2.9)]. Peak blood velocity remains relatively constant until higher levels (>70% of AOP) are surpassed. Calculated mean shear rate decreases in a similar fashion as blood flow. CONCLUSIONS: Under relative levels of restriction, pressures from 40 to 90% of AOP appear to decrease blood flow to a similar degree in these three cuffs. Relative pressures appear to elicit a similar blood flow stimulus when accounting for cuff width and participant characteristics.

Differentiating swelling and hypertrophy through indirect assessment of muscle damage in untrained men following repeated bouts of resistance exercise.

PURPOSE: To examine the swelling response and other markers of muscle damage throughout the early portions of a training program (Experiment 1). We also determined if a "swollen" muscle could swell further following additional exercise (Experiment 2). METHODS: Nine males performed four sets of biceps curls (or time-matched rest on control arm) at 70% of their one-repetition maximum three times over 8 days. Muscle thickness and torque were measured before and after exercise as well as on the days in between. Soreness was measured at the beginning of each day (Experiment 1). On the final day (Experiment 2), participants performed two bouts of exercise, followed by additional measures of muscle thickness. RESULTS: Following three bouts of exercise, muscle thickness was elevated over baseline (mean of visit 9 pre to visit 2 pre, 95% CI) at the 50% [0.21 (0.07, 0.34) cm], 60% [0.21 (0.02, 0.39) cm], and 70% [0.21 (0.06, 0.36) cm] sites. However, differences from a non-exercise control were only observed immediately following bouts of exercise (indicative of acute swelling). Torque was lower at every time point following the first bout of exercise and remained suppressed relative to pre at visit 9 [-6.1 (-11.7, -0.47 Nm] in the experimental arm. Experiment 2 found that a swollen muscle could not appreciably swell more. CONCLUSION: Resting levels of muscle thickness do not appear to change beyond what occurs following the first naïve bout of exercise. Also, the acute swelling response may be used to differentiate swelling from muscle growth.

The Cardiovascular and Perceptual Response to Very Low Load Blood Flow Restricted Exercise.

This study sought to compare cardiovascular and perceptual responses to blood flow restriction (BFR) exercise using various pressure and load combinations. Fourteen participants completed four sets of BFR elbow flexion using 10, 15 and 20% 1RM with 40 and 80% arterial occlusion pressure (AOP). AOP was measured before and after exercise. Perceived exertion (RPE) and discomfort were assessed before exercise and after each set. Data presented as mean (95% CI), except for RPE and discomfort: 25th, 50th, 75th percentiles. AOP increased post-exercise (p<0.001) with larger magnitudes seen when increasing load and pressure (p<0.001) [e. g., 10/40 ΔAOP: 21 (10, 32) mmHg vs. 20/80 ΔAOP: 62 (45, 78) mmHg], which also augmented RPE (p<0.001) [e. g., 4th set 10/40: (7, 8.5, 12) vs. 4th set 20/80: (12.75, 15.5, 17.25)] and discomfort (p<0.001) [e. g., 4th set 10/40: (0.75, 2, 4.25) vs. 4th set 20/80: (4.25, 6, 8,)]. Volume increased via greater loads (p<0.001), and participants only reached failure during 20% 1RM conditions [20/40: 74 (74, 75) repetitions; 20/80: 71 (68, 75) repetitions]. When performing BFR exercise with very low loads the magnitudes of the cardiovascular and perceptual responses are augmented by increasing the load and by applying a higher relative pressure.

The problem Of muscle hypertrophy: Revisited.

In this paper we revisit a topic originally discussed in 1955, namely the lack of direct evidence that muscle hypertrophy from exercise plays an important role in increasing strength. To this day, long-term adaptations in strength are thought to be primarily contingent on changes in muscle size. Given this assumption, there has been considerable attention placed on programs designed to allow for maximization of both muscle size and strength. However, the conclusion that a change in muscle size affects a change in strength is surprisingly based on little evidence. We suggest that these changes may be completely separate phenomena based on: (1) the weak correlation between the change in muscle size and the change in muscle strength after training; (2) the loss of muscle mass with detraining, yet a maintenance of muscle strength; and (3) the similar muscle growth between low-load and high-load resistance training, yet divergent results in strength. Muscle Nerve 54: 1012-1014, 2016.