Robert S. Thiebaud

Effects of Blood Flow Restricted Low-Intensity Concentric or Eccentric Training on Muscle Size and Strength

We investigated the acute and chronic effects of low-intensity concentric or eccentric resistance training with blood flow restriction (BFR) on muscle size and strength. Ten young men performed 30% of concentric one repetition maximal dumbbell curl exercise (four sets, total 75 reps) 3 days/week for 6 weeks. One arm was randomly chosen for concentric BFR (CON-BFR) exercise only and the other arm performed eccentric BFR (ECC-BFR) exercise only at the same exercise load. During the exercise session, iEMG for biceps brachii muscles increased progressively during CON-BFR, which was greater (p<0.05) than that of the ECC-BFR. Immediately after the exercise, muscle thickness (MTH) of the elbow flexors acutely increased (p<0.01) with both CON-BFR and ECC-BFR, but was greater with CON-BFR (11.7%) (p<0.01) than ECC-BFR (3.9%) at 10-cm above the elbow joint. Following 6-weeks of training, MRI-measured muscle cross-sectional area (CSA) at 10-cm position and mid-upper arm (12.0% and 10.6%, respectively) as well as muscle volume (12.5%) of the elbow flexors were increased (p<0.01) with CON-BFR. Increases in muscle CSA and volume were lower in ECC-BFR (5.1%, 0.8% and 2.9%, respectively) than in the CON-BFR and only muscle CSA at 10-cm position increased significantly (p<0.05) after the training. Maximal voluntary isometric strength of elbow flexors was increased (p<0.05) in CON-BFR (8.6%), but not in ECC (3.8%). These results suggest that CON-BFR training leads to pronounced acute changes in muscle size, an index of muscle cell swelling, the response to which may be an important factor for promoting muscle hypertrophy with BFR resistance training.

Exercise intensity and muscle hypertrophy in blood flow–restricted limbs and non‐restricted muscles: a brief review

Although evidence for high‐intensity resistance training–induced muscle hypertrophy has accumulated over the last several decades, the basic concept of the training can be traced back to ancient Greece: Milo of Croton lifted a bull‐calf daily until it was fully grown, which would be known today as progressive overload. Now, in the 21st century, different types of training are being tested and studied, such as low‐intensity exercise combined with arterial as well as venous blood flow restriction (BFR) to/from the working muscles. Because BFR training requires the use of a cuff that is placed at the proximal ends of the arms and/or legs, the BFR is only applicable to limb muscles. Consequently, most previous BFR training studies have focused on the physiological adaptations of BFR limb muscles. Muscle adaptations in non‐BFR muscles of the hip and trunk are lesser known. Recent studies that have reported both limb and trunk muscle adaptations following BFR exercise training suggest that low‐intensity (20–30% of 1RM) resistance training combined with BFR elicits muscle hypertrophy in both BFR limb and non‐BFR muscles. However, the combination of leg muscle BFR with walk training elicits muscle hypertrophy only in the BFR leg muscles. In contrast to resistance exercise with BFR, the exercise intensity may be too low during BFR walk training to cause muscle hypertrophy in the non‐BFR gluteus maximus and other trunk muscles. Other mechanisms including hypoxia, local and systemic growth factors and muscle cell swelling may also potentially affect the hypertrophic response of non‐BFR muscles to BFR resistance exercise.

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, P = 0.344]. 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°/s = 23%, 60°/s = 11%), 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

Cardiovascular and perceptual responses to blood‐flow‐restricted resistance exercise with differing restrictive cuffs

The purpose of this study was to determine (i) the cardiovascular responses to acute blood‐flow‐restricted (BFR) resistance exercise and (ii) the influence of applied BFR cuff type on the cardiovascular and perceptual responses.

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.

Does blood flow restriction result in skeletal muscle damage? A critical review of available evidence

Blood flow restriction (BFR) alone or in combination with exercise has been shown to result in muscle hypertrophy and strength gain across a variety of populations. Although there are numerous studies in the literature showing beneficial muscular effects following the application of BFR, questions have been raised over whether BFR may lead to or even increase the incidence of muscle damage. The purpose of this review is to examine the proposed mechanisms behind muscle damage and critically review the available BFR literature. The available evidence does not support the hypothesis that BFR in combination with low‐intensity exercise increases the incidence of muscle damage. Instead, the available literature suggests that minimal to no muscle damage is occurring with this type of exercise. This conclusion is drawn from the following observations: (a) no prolonged decrements in muscle function; (b) no prolonged muscle swelling; (c) muscle soreness ratings similar to a submaximal low load control; and (d) no elevation in blood biomarkers of muscle damage.

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 pressure recommendations: a tale of two cuffs.

Blood flow restriction (BFR) alone or in combination with exercise has been shown to result in favorable effects on skeletal muscle function and morphology (Loenneke et al., 2012a). BFR is a stimulus commonly applied with specialized pressure cuffs placed at the top of a limb which are inflated to a set pressure throughout exercise. The pressure applied should be high enough to occlude venous return from the muscle but low enough to maintain arterial inflow into the muscle. Throughout the literature several different methods are applied with respect to setting the BFR pressure, however, many of these appear methodologically flawed. The purpose of the current manuscript is to discuss the importance of setting BFR cuff pressure based on appropriate factors. This manuscript will focus on applying pressures to the lower limbs because the majority of the data has been collected on the lower body.

Effects of low-intensity concentric and eccentric exercise combined with blood flow restriction on indices of exercise-induced muscle damage.

UNLABELLED Low-intensity blood-flow restriction (BFR) resistance training significantly increases strength and muscle size, but some studies report it produces exercise-induced muscle damage (EIMD) in the lower body after exercise to failure. PURPOSE To investigate the effects of a pre-set number of repetitions of upper body concentric and eccentric exercise when combined with BFR on changes in EIMD. METHODS Ten young men had arms randomly assigned to either concentric BFR (CON-BFR) or eccentric BFR (ECC-BFR) dumbbell curl exercise (30% one-repetition maximum (1-RM), 1 set of 30 repetitions followed by 3 sets of 15 repetitions). Maximal isometric voluntary contraction force (MVC), muscle thickness (MTH), circumference, range of motion (ROM), ratings of perceived exertion (RPE), and muscle soreness were measured before, immediately after, and daily for 4 days post-exercise. RESULTS MVC decreased by 36% for CON-BFR and 12% for ECC-BFR immediately after exercise but was not changed 1-4 days post-exercise (p > 0.05). Only CON-BFR had significant changes in MTH and circumference immediately after exercise (p < 0.05). Muscle soreness was observed in the ECC-BFR arm at 1 and 2 days after exercise. CONCLUSIONS Low-intensity ECC-BFR produces significant muscle soreness at 24 h but neither ECC-BFR nor CON-BFR exercise produces significant changes in multiple indices of EIMD.

Blood flow restriction: an evidence based progressive model (Review).

To remain independent and healthy, an important factor to consider is the maintenance of skeletal muscle mass. Inactivity leads to measurable changes in muscle and bone, reduces exercise capacity, impairs the immune system, and decreases the sensitivity to insulin. Therefore, maintaining physical activity is of great importance for skeletal muscle health. One form of structured physical activity is resistance training. Generally speaking, one needs to lift weights at approximately 70% of their one repetition maximum (1RM) to have noticeable increases in muscle size and strength. Although numerous positive effects are observed from heavy resistance training, some at risk populations (e.g. elderly, rehabilitating patients, etc.) might be advised not to perform high-load resistance training and may be limited to performance of low-load resistance exercise. A technique which applies pressure cuffs to the limbs causing blood flow restriction (BFR) has been shown to attenuate atrophy and when combined with low intensity exercise has resulted in an increase in both muscle size and strength across different age groups. We have provided an evidence based model of progression from bed rest to higher load resistance training, based largely on BFR literature concentrating on more at risk populations, to highlight a possible path to recovery.