The influence of exercise load with and without different levels of blood flow restriction on acute changes in muscle thickness and lactate

The aim of this study was to compare exercise with and without different degrees of blood flow restriction (BFR) on acute changes in muscle thickness (MTH) and whole blood lactate (WBL). Forty participants were assigned to Experiment 1, 2 or 3. Each experiment completed protocols differing by pressure, load and/or volume. MTH and WBL were measured pre and postexercise. The acute changes in MTH appear be maximized at 30% one repetition maximum (1RM) with BFR, although the difference between 20% 1RM and 30% 1RM at the lateral site was small (0·1 versus 0·2 cm, P = 0·09). Increasing the exercise load from 20% to 30% 1RM with BFR produces clear changes in WBL (3·7 versus 5·5 mmol l^?1, P<0·001). The acute changes in MTH and WBL for 30% 1RM in combination with BFR were similar to that observed with 70% 1RM and 20 and 30% to failure, albeit at a lower exercise volume. These findings may have implications for designing future studies as it suggest that exercise load (to a point) may have a greater influence on acute changes in MTH and metabolic accumulation than the applied relative pressure.     

Acute skeletal muscle responses to very low‐load resistance exercise with and without the application of blood 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<0·001] 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.     

Impact of blood flow‐restricted bodyweight exercise on skeletal muscle adaptations

This study ascertains the ability of bodyweight blood flow‐restricted (BFR) exercise training to promote skeletal muscle adaptations of significance for muscle accretion and metabolism. Six healthy young individuals (three males and three females) performed six weeks of bodyweight BFR training. Each session consisted of five sets of sit‐to‐stand BFR exercise to volitional failure with 30‐second inter‐set recovery. Prior to, and at least 72 h after training, muscle biopsies were taken from m. vastus lateralis to assess changes in fibre type‐specific cross‐sectional area (CSA), satellite cell (SC) and myonuclei content and capillarization, as well as mitochondrial protein expression. Furthermore, magnetic resonance imaging was used to assess changes in whole thigh muscle CSA. Finally, isometric knee extensor muscle strength was evaluated. An increase in knee extensor whole muscle CSA was observed at middle and distal localizations after training (3·2% and 3·5%, respectively) (P<0·05), and a trend was observed towards an increase in type I fibre CSA, whereas muscle strength did not increase. Additionally, the number of SCs and myonuclei associated with type I fibres increased by 65·7% and 20%, respectively (P<0·05). No significant changes were observed in measures of muscle capillarization and mitochondrial proteins. In conclusion, six weeks of bodyweight‐based BFR exercise promoted myocellular adaptations related to muscle accretion, but not metabolic properties. Moreover, the study revealed that an appropriate total training volume needs further investigation before recommending bodyweight BFR to patient populations.     

Session rating of perceived exertion following resistance exercise with blood flow restriction

Session ratings of perceived exertion (SRPE) provide a valid and reliable indicator of resistance exercise session intensity. However, there is a lack of studies on the effects of resistance exercise with blood flow restriction (BFR) on SRPE. Thus, the aim of this study is to compare the effects of resistance exercise at high intensity versus low intensity with BFR on internal training load measured by SRPE. Thirteen young (22·2 ± 3·8 years) resistance‐trained men (training experience 3·2 ± 2·4 years) participated in the study protocol. After determining one maximum repetition (1‐RM), the subjects were assigned to two groups in a counterbalanced design (i) high‐intensity exercise (HIE, performed one training session at 80% of 1‐RM) and (ii) low intensity with BFR (BFR, performed an exercise session at 50% of 1‐RM with BFR). During each session, subjects performed three sets of unilateral elbow flexion leading to concentric failure with a 1‐min rest interval between sets. A cuff around the arm, inflated at 110 mmHg, was used continuously for BFR. The SRPE was reported 30 min after the end of the session. The low intensity with BFR showed lower total work (197·13 ± 63·49 versus 300·92 ± 71·81 kg; P = 0·002) and higher SRPE (9 versus 6; P = 0·007) than high‐intensity resistance exercise. The present results indicate that BFR is an important factor to increase internal training load. Future studies should investigate the physiological stress imposed by different training methods rather than just quantify the external training load such as intensity or volume.     

Effects of low‐intensity resistance exercise with blood flow restriction on coagulation system in healthy subjects

Recent studies have demonstrated that even a low‐intensity resistance exercise can effectively induce muscle hypertrophy and strength increase when combined with moderate blood flow restriction (BFR) into the exercising muscle. Although serious side effects of low‐intensity resistance exercise with BFR have not been reported, a concern of thrombosis has been suggested, because this type of exercise is performed with restricted venous blood flow and pooling of blood in extremities. Thus, the purpose of this study was to investigate the effects of low‐intensity resistance exercise with BFR on coagulation system in healthy subjects. Ten healthy men (25·1 ± 2·8 year) performed four sets of leg press exercises with and without BFR (150–160 mmHg) at an intensity of 30% of one‐repetition maximum (1RM). In each exercise session, one set with 30 repetitions was followed by three sets with 15 repetitions. Blood samples were taken before, and 10 min, 1, 4 and 24 h after the exercise. Prothrombin fragment 1 + 2 (PTF) and thrombin–antithrombin III complex (TAT) were measured as markers of thrombin generation, whereas D‐dimer and fibrin degradation product (FDP) were measured as markers of intravascular clot formation. Changes in plasma volume (PV) were calculated from haemoglobin and hematocrit values. PV reduction was significantly greater after the exercise with BFR than without (P<0·05). However, neither markers of thrombin generation nor intravascular clot formation increased after the exercises. These results suggest that low‐intensity resistance exercise with BFR does not activate coagulation system in healthy subjects.     

Perceptual effects and efficacy of intermittent or continuous blood flow restriction resistance training

Blood flow restriction (BFR) exercise may be an alternative form of resistance training; however, a side of effect of BFR resistance exercise is acute muscle pain. Typically, BFR exercise studies restrict blood flow with a cuff continuously during the exercise bout, including rest periods. However, others have used intermittent BFR where the cuff is inflated only during sets. We performed two studies to compare intermittent and continuous BFR exercise. In study one, eleven subjects randomly proceeded through three treatments of unilateral leg extensions to failure: (i) continuous BFR, (ii) intermittent BFR and (iii) control (exercise without BFR). Pain measurements were taken immediately after each set. In study two, subjects (n = 32) underwent a 5‐week resistance training programme after random assignment to one of the three conditions. Lean mass and strength were assessed at baseline and after training. Continuous BFR resulted in significantly greater pain than intermittent BFR or control. Both BFR conditions resulted in significantly fewer repetitions to failure than control. This suggests that an acute bout of intermittent BFR exercise may produce as much muscle fatigue as an acute bout of continuous BFR exercise, but with less pain. With training, maximal knee extension (P = 0·033) and maximum knee flexion (P = 0·007) strength increased among all groups. There were no significant differences between groups in strength or lean mass. These results suggest that short‐term low‐load resistance training increases muscle strength to a similar extent as low‐load resistance training without BFR.     

Time under tension decreased with blood flow-restricted exercise

Objectives: Exercise to failure results in similar muscle protein synthesis responses, independent of intensity. However, low‐intensity exercise likely requires more time under tension and those with injuries may be incapable of sustaining the mechanical stress to reach failure. Design: The purpose was to determine whether elastic knee wraps (KW) provide a stimulus to decrease time under tension and overall volume of work while maintaining a similar level of metabolic stress. Methods: Thirteen healthy subjects participated in a randomized crossover study consisting of three trials. The first determined 1 repetition maximum (1RM) on the bilateral leg extension. Subjects were then assigned to a blood flow restriction (BFR) or control (CON) group. After trial 2, subjects crossed over to the opposite trial. KW were placed around the thigh of each leg during BFR. Leg extensions were completed at 30% 1RM until failure. Whole blood lactate (WBL) was taken pre‐, post‐, and 3 and 5 min postexercise. Heart rate (HR) was measured before, following the first and second sets, and 3 and 5 min postexercise. Results: This study found KW provide a BFR stimulus allowing failure to occur sooner with similar metabolic stress postreperfusion. There were no differences in HR at any time point. Conclusions: These results may benefit populations that cannot sustain the mechanical stress of high‐intensity exercise or low‐intensity exercise that requires a longer sustained time under tension.     

The acute hemodynamic effects of blood flow restriction in the absence of exercise

The purpose was to investigate the acute effects of blood flow restriction (BFR) on arterial and venous hemodynamic parameters. Nine participants completed a 10‐min time control (resting condition) and then a lower body BFR protocol. The protocol was five, 5‐min bouts of restrictive cuff inflation with 3‐min of deflation between each bout. The pressure was set relative to each individual's thigh circumference. There were no significant differences between resting and BFR conditions for blood pressure or wave reflection. There was, however, a significant decrease in venous compliance and maximal venous outflow following BFR. Acute BFR with pressures relative to thigh circumference does not result in acute changes in blood pressure or wave reflection. There is, however, an acute decrease in venous compliance and maximal venous outflow, the significance of which is currently unknown. These results suggest that an acute BFR protocol affects venous but not arterial hemodynamics.     

Postexercise blood flow restriction does not enhance muscle hypertrophy induced by multiple‐set high‐load resistance exercise

To test the applicability of postexercise blood flow restriction (PEBFR) in practical training programmes, we investigated whether PEBFR enhances muscle hypertrophy induced by multiple‐set high‐load resistance exercise (RE). Seven men completed an eight‐week RE programme for knee extensor muscles. Employing a within‐subject design, one leg was subjected to RE + PEBFR, whereas contralateral leg to RE only. On each exercise session, participants performed three sets of unilateral knee extension exercise at approximately 70% of their one‐repetition maximum for RE leg first, and then performed three sets for RE + PEBFR leg. Immediately after completion of the third set, the proximal portion of the RE + PEBFR leg was compressed with an air‐pressure cuff for 5 min at a pressure ranging from 100 to 150 mmHg. If participants could perform 10 repetitions for three sets in two consecutive exercise sessions, the work load was increased by 5% at the next exercise session. Muscle thickness and strength of knee extensor muscles were measured before and after the eight‐week training period and after the subsequent eight‐week detraining period. There was a main effect of time but no condition × time interaction or main effect of condition for muscle thickness and strength. Both muscle thickness and strength increased after the training period independent of the condition. This result suggests that PEBFR would not be an effective training method at least in an early phase of adaptation to high‐load resistance exercise.     

血流量限制结合低强度抗阻训练对下肢骨科术后肌肉功能的影响

目的:探索血流量限制结合低强度抗阻训练对下肢骨科术后肌肉功能的影响.方法:选取下肢骨科术后4～12周患者39例,随机将患者分为观察组19例和对照组20例.2组患者均接受为期4周的康复训练,对照组根据渐进抗阻原则进行肌力训练,观察组使用血流量限制结合低强度抗阻肌力训练.等速伸膝峰力矩、超声下股四头肌肌肉形态、肢体围度、静...     

The acute muscular response to blood flow‐restricted exercise with very low relative pressure

To investigate the acute responses to blood flow‐restricted (BFR) exercise across low, moderate and high relative pressures. Muscle thickness, maximal voluntary contraction (MVC) and electromyography (EMG) amplitude were assessed following exercise with six different BFR pressures: 0%, 10%, 20%, 30%, 50% and 90% of arterial occlusion pressure (AOP). There were differences between each time point within each condition for muscle thickness, which increased postexercise [+0·47 (0·40, 0·54) cm] and then trended towards baseline. For MVC, higher pressures resulted in greater decrements than lower pressures [e.g. 10% AOP: ?20·7 (?15·5, ?25·8) Nm versus 90% AOP: ?24 (?19·1, ?28·9) Nm] postexercise. EMG amplitude increased from the first three repetitions to the last three repetitions within each set. When using a common BFR protocol with 30% 1RM, applying BFR does not seem to augment acute responses over that of exercise alone when exercise is taken to failure.     

Human tibialis anterior contractile responses following fatiguing exercise with and without β-adrenoceptor blockade

The effects of oral propranolol (2 × 80 mg/day) on the contractile responses to twitch and tetanic electrical stimulation were examined in the tibialis anterior (TA) muscle of seven healthy young males. The TA muscle was fatigued by four forms of repeated isometric contractions: (1) maximal voluntary contractions (MVC), (2) MVC with circulation occluded, (3) electrically evoked contractions with 20 Hz supramaximal voltage stimulation and (4) electrically evoked contractions with circulation occluded. Each contraction was sustained for 10 s with 5 s recovery. Duration of exercise was 10 min for intact circulation and 4 min for circulatory occlusion. Pre-exercise, both the twitch contraction time and the 1/2 relaxation time were significantly (P<0·05) longer with β-blockade than placebo, β-blockade did not affect torque output during tetanic stimulation or MVC. Immediately post-exercise, the peak twitch torque was reduced in all β-blocked and placebo conditions except electrically induced exercise with intact circulation. The 1/2 relaxation time was significantly lengthened by repeated MVC with circulation intact; β-blockade caused a greater lengthening than placebo (P<0·05). The tetanic torque was reduced immediately post-exercise at each of 10, 20, 50 and 100 Hz for both β-blockade and placebo for each form of exercise. There were no significant β-blockade effects. Torque output at 10 Hz was still reduced up to 10 min post-exercise. In contrast, 100 Hz torque output recovered by 5 min post-exercise. The changes in tetanic responses were qualitatively similar with intact circulation and with circulatory occlusion. In the tibialis anterior muscle, the effects of fatiguing exercise are not accentuated by β-blockade. These data in the TA are notably different from those in the triceps surae, where greater fatigue has been shown with β-blockade.     

Muscular activity of the shoulder and neck region during sustained and intermittent exercise

Sustained isometric contractions of the neck and shoulder muscles in laboratory conditions are often assumed to be representative of muscular load in occupational tasks. The present study aims to investigate whether differences can be found between these contractions and those in intermittent tasks. Ten subjects performed forward flexions of the right arm during three tests to the limit of endurance: (1) a sustained contraction; (2) an intermittent contraction with a cycle time of 10 s and a duty cycle of 0·7; and (3) the same intermittent contraction with the possibility of changing the shoulder angle during relaxation. Muscular activities of the upper trapezius, deltoid pars anterior and medialis and infraspinatus were registered using surface electromyography, and changes in the signal were quantified by root mean square (RMS) and mean power frequency (MPF) values. During the continuous test, highly significant changes in both parameters were found for the four muscles. Significant changes were found during both intermittent conditions, although to a lesser degree than in the continuous test. Significant differences between the regression coefficients of the sustained test and the two intermittent tests were found on all occasions: for RMS and MPF of the four muscles. Significant differences were also found regarding the intermittent tests. The test in which no variation in limb position was allowed during relaxation caused a more pronounced MPF decrease for the trapezius (P≤0·01), which was confirmed by the subjective scores of perceived exertion and a higher RMS increase (P≤0·01) for the middle part of the deltoid. The intermittent condition with changes in shoulder angle showed more MPF decrease for the deltoid, significant for the middle part (P≤0·05), not significant for the anterior part and a larger RMS increase for infraspinatus (P≤0·05). It can be concluded that the latter condition represents more the trapezius and deltoid activity as in occupational tasks.