Jeremy P. Loenneke

Influence of relative blood flow restriction pressure on muscle activation and muscle adaptation.

Introduction: The aim of this study was to investigate the acute and chronic skeletal muscle response to differing levels of blood flow restriction (BFR) pressure. Methods: Fourteen participants completed elbow flexion exercise with pressures from 40% to 90% of arterial occlusion. Pre/post torque measurements and electromyographic (EMG) amplitude of each set were quantified for each condition. This was followed by a separate 8‐week training study of the effect of high (90% arterial occlusion) and low (40% arterial occlusion) pressure on muscle size and function. Results: For the acute study, decreases in torque were similar between pressures [–15.5 (5.9) Nm, Pu2009=u20090.344]. For amplitude of the first 3 and last 3 reps there was a time effect. After training, increases in muscle size (10%), peak isotonic strength (18%), peak isokinetic torque (180°/su2009=u200923%, 60°/su2009=u200911%), and muscular endurance (62%) changed similarly between pressures. Conclusion: We suggest that higher relative pressures may not be necessary when exercising under BFR. Muscle Nerve 53: 438–445, 2016

Muscular adaptations to fatiguing exercise with and without blood flow restriction.

The purpose of this study was to determine the muscular adaptations to low‐load resistance training performed to fatigue with and without blood flow restriction (BFR). Middle‐aged (42–62 years) men (n = 12) and women (n = 6) completed 18 sessions of unilateral knee extensor resistance training to volitional fatigue over 6 weeks. One limb trained under BFR, and the contralateral limb trained without BFR [free flow (FF)]. Before and after the training, measures of anterior and lateral quadriceps muscle thickness (MTh), strength, power and endurance were assessed on each limb. The total exercise training volume was significantly greater for the FF limb compared with the BFR limb (P<0·001). Anterior quadriceps thickness and muscle function increased following the training in each limb with no differences between limbs. Lateral quadriceps MTh increased significantly more (P<0·05) in the limb trained under BFR (BFR: 3·50 ± 0·61 to 3·67 ± 0·62 cm; FF: 3·49 ± 0·73 to 3·56 ± 0·70 cm). Low‐load resistance training to volitional fatigue both with and without BFR is viable options for improving muscle function in middle‐aged individuals. However, BFR enhanced the hypertrophic effect of low‐load training and reduced the volume of exercise needed to elicit increases in muscle function.

Effects of exercise with and without different degrees of blood flow restriction on torque and muscle activation.

An unresolved question in resistance training combined with blood flow restriction (BFR) is what percentage of estimated arterial occlusion pressure provides the most robust acute muscular response.

Blood flow restriction in the upper and lower limbs is predicted by limb circumference and systolic blood pressure

PurposeTo determine what factors should be accounted for when setting the blood flow restriction (BFR) cuff pressure for the upper and lower body.MethodsOne hundred and seventy one participants visited the laboratory for one testing session. Arm circumference, muscle (MTH) and fat (FTH) thickness were measured on the upper arm. Next, brachial systolic (SBP) and diastolic (DBP) blood pressure measurements were taken in the supine position. Upper body arterial occlusion was then determined using a Doppler probe. Following this, thigh circumference and lower body arterial occlusion were determined. Models of hierarchical linear regression were used to determine the greatest predictor of arterial occlusion in the upper and lower body. Two models were employed in the upper body, a Field (arm size) and a Laboratory model (arm composition).ResultsThe Laboratory model explained 58xa0% of the variance in arterial occlusion with SBP (βxa0=xa00.512, partxa0=xa00.255), MTH (βxa0=xa00.363, partxa0=xa00.233), and FTH (βxa0=xa00.248, partxa0=xa00.213) contributing similarly to explained variance. The Field model explained 60xa0% of the variance in arterial occlusion with arm circumference explaining the greatest amount (βxa0=xa00.419, partxa0=xa00.314) compared to SBP (βxa0=xa00.394, partxa0=xa00.266) and DBP (βxa0=xa00.147, partxa0=xa00.125). For the lower body model the third block explained 49xa0% of the variance in arterial occlusion with thigh circumference (βxa0=xa00.579, partxa0=xa00.570) and SBP (βxa0=xa00.281, partxa0=xa00.231) being significant predictors.ConclusionsOur findings indicate that arm circumference and SBP should be taken into account when determining BFR cuff pressures. In addition, we confirmed our previous study that thigh circumference is the greatest predictor of arterial occlusion in the lower body.

The effects of resistance exercise with and without different degrees of blood-flow restriction on perceptual responses

Abstract The aim was to compare exercise with and without different degrees of blood-flow restriction on perceived exertion (RPE) and discomfort. Participants were assigned to Experiment 1, 2, or 3. Each completed protocols differing by pressure, load, and/or volume. RPE and discomfort were taken before and after each set. For pressure and RPE, the 20% one repetition maximum (1RM) blood-flow restriction conditions were affected by increasing the pressure from 40% to 50% blood-flow restriction (~12 vs. ~14). This did not appear to happen within the 30% 1RM blood-flow restriction conditions or the higher pressures in the 20% 1RM conditions. The similar RPE between 20% and 30% 1RM to failure was expected given both were to failure. For discomfort, ratings were primarily affected by load at the lowest pressure. Increasing pressure to 50% blood-flow restriction increased discomfort at 20% 1RM (~2.6 vs. ~4). There was a further increase when increasing to 60% blood-flow restriction (~4 vs. ~4.8). The high-load condition had the lowest discomfort, while ratings were highest with 20% 1RM to failure. In conclusion, exercise with blood-flow restriction does not appear to augment the perceptual response observed with low-load exercise to failure.

Cycle training induces muscle hypertrophy and strength gain: strategies and mechanisms

Cycle training is widely performed as a major part of any exercise program seeking to improve aerobic capacity and cardiovascular health. However, the effect of cycle training on muscle size and strength gain still requires further insight, even though it is known that professional cyclists display larger muscle size compared to controls. Therefore, the purpose of this review is to discuss the effects of cycle training on muscle size and strength of the lower extremity and the possible mechanisms for increasing muscle size with cycle training. It is plausible that cycle training requires a longer period to significantly increase muscle size compared to typical resistance training due to a much slower hypertrophy rate. Cycle training induces muscle hypertrophy similarly between young and older age groups, while strength gain seems to favor older adults, which suggests that the probability for improving in muscle quality appears to be higher in older adults compared to young adults. For young adults, higher-intensity intermittent cycling may be required to achieve strength gains. It also appears that muscle hypertrophy induced by cycle training results from the positive changes in muscle protein net balance.

Validity of ultrasound prediction equations for total and regional muscularity in middle-aged and older men and women

To test the validity of published equations, 79 Caucasian adults (40 men and 39 women) aged 50-78 y had muscle thickness (MT) measured by ultrasound at nine sites of the body. Fat-free mass (FFM), lean soft tissue mass (LM) and total muscle mass (TMM) were estimated from MT using equations previously published in the literature. Appendicular LM (aLM) was estimated using dual-energy X-ray absorptiometry (DXA) and this method served as the reference criterion. There were strong correlations (range r = 0.85-0.94) between DXA-derived aLM and estimated FFM, leg LM or TMM. Total error between DXA-derived aLM and TMM (∼2 kg) was lower compared with the three other selected equations (6-10 kg). A Bland-Altman plot revealed that there was no systematic bias between aLM and TMM; however, the other three equations included systematic error. Our results suggest that an ultrasound equation for TMM is appropriate and useful for evaluating skeletal muscle mass in the body.

Morphological and functional relationships with ultrasound measured muscle thickness of the lower extremity: a brief review:

Ultrasound is a potential method for assessing muscle size of the extremity and trunk. In a large muscle, however, a single image from portable ultrasound measures only muscle thickness (MT), not anatomical muscle cross-sectional area (CSA) or muscle volume (MV). Thus, it is important to know whether MT is related to anatomical CSA and MV in an individual muscle of the extremity and trunk. In this review, we summarize previously published articles in the lower extremity demonstrating the relationships between ultrasound MT and muscle CSA or MV as measured by magnetic resonance imaging and computed tomography scans. The relationship between MT and isometric and isokinetic joint performance is also reviewed. A linear relationship is observed between MT and muscle CSA or MV in the quadriceps, adductor, tibialis anterior, and triceps surae muscles. Intrarater correlation coefficients range from 0.90 to 0.99, except for one study. It would appear that anterior upper-thigh MT, mid-thigh MT and posterior thigh MT are the best predictors for evaluating adductor, quadriceps, and hamstrings muscle size, respectively. Despite a limited number of studies, anterior as well as posterior lower leg MT appear to reflect muscle CSA and MV of the lower leg muscles. Based on previous studies, ultrasound measured anterior thigh MT may be a valuable predictor of knee extension strength. Nevertheless, more studies are needed to clarify the relationship between lower extremity function and MT.

Effects of detraining after blood flow-restricted low-intensity concentric or eccentric training on muscle size and strength.

We investigated the effects of 6xa0weeks of detraining on muscle size and strength in young men who had previously participated in 6xa0weeks (3xa0days/week) of 30xa0% of concentric one-repetition maximal (1-RM) dumbbell curl training [one arm: concentric blood flow restricted (BFR) exercise (CON-BFR); the other arm: eccentric BFR exercise (ECC-BFR)]. MRI-measured muscle cross-sectional area (CSA) at 10xa0cm above the elbow joint increased from pre to post (pxa0<xa00.01), and the muscle CSA following detraining remained greater than pre (pxa0<xa00.01) but was similar to that observed at post. Maximal voluntary contraction (MVC) increased from pre to post (pxa0<xa00.05), and the MVC following detraining remained greater than pre (pxa0<xa00.05) but was similar to that observed at post. The ECC-BFR did not produce any changes across time. Increased muscle strength following 6xa0weeks of CON-BFR was well preserved at 6xa0weeks of detraining, which may be primarily related to muscle hypertrophy.

Effects of age on arterial stiffness and central blood pressure after an acute bout of resistance exercise

PurposeTo investigate the influence of age on arterial stiffness and blood pressure after performing a resistance exercise bout.MethodsRecreationally active men were separated into young (YG, nxa0=xa012, 26.5xa0±xa03.3 years), middle (MG, nxa0=xa014, 49.4xa0±xa05.7 years), and old (OG, nxa0=xa010, 67.4xa0±xa06.3 years)-aged groups. In a randomized cross-over design, participants performed control and exercise conditions with at least 3xa0days separating conditions. The exercise condition consisted of leg press, chest press, knee flexion, lat pulldown and knee extension atxa0~65xa0% one-repetition maximum for three sets of 10 repetitions. Brachial and central blood pressures, augmented pressure, augmentation index, central and peripheral pulse wave velocities were measured prior to each condition and starting at 5xa0min post-exercise.ResultsBrachial systolic blood pressure (SBP) significantly increased similarly after exercise for all age groups (YG, 8xa0±xa08xa0mmHg; MG, 5xa0±xa05xa0mmHg; OG, 5xa0±xa06xa0mmHg; pxa0<xa00.05). However, central SBP did not significantly increase for any age group after exercise. Augmentation index significantly increased after exercise only in the YG (11xa0±xa08xa0%, pxa0<xa00.05). Central pulse wave velocity did not significantly increase in any age group after exercise when compared to the control condition.ConclusionsWhen performing a whole body moderate resistance exercise bout, acute changes in arterial stiffness and blood pressure appear to be minimally affected by age.