Modern day blood flow restriction (BFR) training was discovered in 1966 by Yoshiaki Sato, who called it KAATSU (“added pressure”) training (76). In the 54 years since his discovery, BFR training has been studied in hundreds of published articles and is used by a wide variety of populations—from the injured (29,40) to the physique athlete looking to maximize muscle growth during contest preparation (58).
BFR training involves use of a compressive cuff wrapped around the proximal portion of the limb so as to partially reduce arterial flow and completely restrict venous return (71). As a result, blood pools in the extremity distal to the cuff, altering the local muscular environment. The reduction in blood flow from the applied pressure decreases oxygen delivery, challenging local energy metabolism and reducing the time needed to reach volitional failure during aerobic training and resistance training (RT) compared with similar exercise without restriction (27,28,99). Because of the unique metabolic environment in the limb from the compressive cuff, BFR training is commonly prescribed with loads as light as 20% one repetition maximum (1RM) (71). Low-load RT with BFR can provide similar increases in muscle mass compared with heavier (70+% 1RM) lifting, making it an alternative for physique athletes seeking to maximize muscle growth without additional joint stress (21,53). This article will provide an evidence-based review of current research on the resistance-training benefits of BFR exercise with respect to hypertrophy and draw practical conclusions as to how the strategy can be applied by physique athletes to optimize increases in muscle mass.
BLOOD FLOW RESTRICTION TRAINING MECHANISMS OVERVIEW (HYPERTROPHY FOCUSED)
The mechanisms underlying BFR RT are still contentious but appear to be somewhat modulated by similar processes as free-flow exercise. Skeletal muscle hypertrophy occurs when net protein balance is positive, providing a favorable environment to induce muscle growth (16). Muscle growth appears to be mediated by mechanistic target of rapamycin complex 1 (mTORC1), a molecular nodal point in the anabolic molecular intracellular signaling pathway (36). Sufficient stimulation of skeletal muscle via RT induces post-exercise increases in mTORC1 expression, eventually leading to visible increases in muscle size with continued training (32,63). Both heavy- and light-load training, with and without BFR, performed to volitional failure have shown to induce significant mTORC1 expression and, in longitudinal studies, are reported to produce similar increases in muscle size in various populations (18,20,21,53). However, low-load exercise that is work-matched to BFR (i.e., 30-15-15-15 repetitions) does not appreciably increase mTORC1 levels nor alter mTORC1 downstream protein kinase molecules such as S6 kinase beta-1 (S6K1), and thus, these protocols are inferior in producing appreciable gains in muscle size (32,33), conceivably because the intensity of effort is not sufficiently challenging to evoke a robust hypertrophic stimulus. Finally, administering mTORC1's antagonist, rapamycin, blunts the muscle protein synthesis (MPS) response to BFR exercise, highlighting the importance of this pathway during BFR exercise (36). Thus, it seems that mTORC1 expression is crucial to the long-term hypertrophic response to BFR training regardless of the exact mechanisms that differentiate low-load BFR versus high-load traditional training.
RESISTANCE TRAINING: MECHANISMS UNDERLYING HYPERTROPHY
Current theory proposes 2 primary mechanisms underlying the benefits observed with low-load RT with BFR: metabolite-induced accelerated fatigue and cellular swelling. Both mechanisms have the capacity to create an anabolic environment in the muscle to augment MPS responses to exercise and are discussed in the following subsections.
Metabolite-induced accelerated fatigue describes the phenomena that occur when BFR is applied to an exercising limb. Byproducts of muscular contractions such as lactate, hydrogen ions (H+), ATP, and inorganic phosphates are produced and are unable to exit the limb through the venous system due to the restrictive cuff (56). These metabolites interfere with the excitation–contraction mechanism causing earlier recruitment of type 2 muscle fibers relative to the same exercise being performed in free-flow conditions (22,98). As fatigue accumulates from the metabolic stress, muscle contraction velocity slows and muscle activation increases (85), ultimately stimulating anabolic processes.
Metabolites also stimulate the group III–IV afferents in and around the muscle fiber during contractions to promote increased blood flow to the exercising muscle in an effort to reduce peripheral fatigue accumulation (loss of the muscle fiber's ability to create force) (5). It is theorized that group III–IV afferents can stimulate additional motor unit recruitment through activation of the fusimotor neuron-muscle spindle-motor neuron pathway so as to ensure force remains steady during repeated muscular contractions (34). The group III–IV afferents also have synapses onto the central nervous system (CNS) and are postulated to play a role in subjective increases in perception of effort during exercise (25,70). Higher levels of effort during fatiguing contractions have been thought to correspond with type II muscle fiber recruitment (70). Importantly, when free-flow low-load exercise is performed with and without BFR to failure, both report very high levels of effort and localized muscle pain, likely by the combined effects of the accumulated metabolites stimulating group III–IV afferents and the resultant changes in CNS activation (11,25,95,96).
It is not clear whether metabolites themselves contribute to an exercise-induced hypertrophic response. Emerging evidence indicates that lactate mediates anabolic processes both in vitro (67,68,92,100) and in vivo (68,92). These results may be attributed at least in part to a lactate-induced inhibition of histone deacetylase activity (49), which serves as a negative regulator of muscle growth. Moreover, the buildup of H+ may facilitate greater type I fiber hypertrophy by impairing calcium binding in type II fibers and thereby placing a greater burden on type I fibers to maintain force output as metabolically taxing exercise continues (35). This may help to explain emerging research showing that low-load BFR elicits preferential hypertrophy of slow-twitch muscle fibers (8,9,43). Further research is warranted to better elucidate mechanistic underpinnings of adaptations achieved with low-load BFR training.
Cell swelling describes the acute increase in muscle thickness that results from accumulation of fluid in a limb due to a lack of venous return (56). Fluid is believed to shift from the plasma into the muscle cell due to osmolality gradient differences (91). Fluid accumulation during and after exercise is believed to be due to decreased oxygen availability, the accumulation of metabolites, and subsequent increases in reactive hyperemia (56,62,104). These factors have been linked to earlier type II muscle fiber recruitment (42,73).
Increases in muscle thickness after exercise have been correlated with long-term muscle hypertrophy in free-flow and BFR exercise (28,44). BFR training has been shown to significantly increase cell swelling over work-matched controls (103) while producing similar levels during exercise to failure (6,15,28,108) and high-load training (3,30,44). Thus, exercise with BFR can produce acute increases in cell swelling that hypothetically can contribute to meaningful long-term changes in muscle size.
Cell swelling is believed to act through stimulation of an intrinsic volume sensor in the muscle fiber that, when stretched, begins the process of MPS (56). When fluid is trapped in the limb during and after exercise, the cytoskeletal matrix becomes stressed, eventually leading to activation of anabolic intracellular signaling pathways (56). It is questionable whether cell swelling alone is anabolic in vivo because recent research investigating a passive cell swelling protocol performed with no exercise failed to increase mTORC1 expression (66). However, long-term passive cell swelling applications have been shown to attenuate or completely prevent disuse atrophy (47,86), lending credence to the notion that cell swelling may provide a low-level hypertrophic stimulus sufficient to maintain neutral net protein balance for a period.
BFR RESEARCH ON ATHLETES, WELL-TRAINED INDIVIDUALS, AND PHYSIQUE COMPETITORS
To date, the research on using BFR with physique athletes is sparse (1 case report). Therefore, this section will cover the relevant research pertaining to optimizing hypertrophy in resistance-trained individuals and professional athletes using BFR training, drawing parallels (when appropriate) to the physique athlete.
To the authors' knowledge, the case report by Loenneke et al. (58) on a 22-year-old competitive male bodybuilder is the only published article using BFR with physique athletes. This case report provides some unique insights into the potential applications and benefits of BFR training in this population, especially during contest preparation. The article describes a 22-year-old male bodybuilder who developed knee pain 2 weeks before his bodybuilding show. The individual reported experiencing a pop in his right knee, and a subsequent MRI revealed an osteochondral fracture; a surgical date was then scheduled after competition. The individual decided to use low-load BFR RT for his legs twice a week for the remainder of his contest preparation instead of withdrawing from the show. His lower-body training routine exclusively comprised pain-free low-load BFR training performed predominantly in a 30-15-15-15 scheme (30 reps on the first set, followed by 3 sets of 15 repetitions) twice weekly, although he did occasionally incorporate failure training (58). The individual ended up placing top 5 in his show and was able to exercise pain-free; he ultimately postponed his scheduled surgical date due to limited loss of functional ability (no pain walking) and lack of perceived loss in thigh hypertrophy (58). A follow-up MRI revealed significant healing of his osteochondral fracture, and with conservative nonsurgical treatment, the individual was able to return to high-load training. This report provides limited evidence that BFR can be successfully used in competitive bodybuilders deep into contest preparation despite the presence of lower extremity injuries that would impede heavy-load training.
There does seem to be a superior benefit to maximizing hypertrophy in recreationally active individuals when combining low-load BFR (30% 1RM) with heavy loads (75% 1RM) in a lifting program. Yasuda et al. (106) observed statistically significant increases of +7.2% muscle cross-sectional area (CSA) of the triceps brachii when combining low-load BFR and heavy lifting compared with +4.4% when performing low-load BFR alone in recreationally active men over a 6-week study period, highlighting the additive effects of both types of training when performed concurrently. However, well-trained athletes may respond differently due to their RT history.
Previous research has shown that a 24-week routine consisting of heavy elbow flexion exercise in competitive male and female bodybuilders did not substantially increase muscle CSA of the elbow flexors (4). It is important to note that although the sample size was small (n = 10), half of the participants (3 males and 2 females) reported using anabolic steroids concurrently throughout the program. Therefore, it seems that a single-mode approach (heavy lifting—6RM to 10RM) typical of bodybuilding programs may not be able to increase hypertrophy to a significant extent after a period (5.5+ years training experience on average in the bodybuilders in the aforementioned study), even with the use of anabolic agents. Multimode approaches using a combination of lower and higher repetition schemes such as during low-load BFR training (i.e., 30-15-15-15) could theoretically increase muscle size over low-repetition training alone (i.e., heavy training in the 6–10RM range) due to stimulation of the spectrum of muscle fiber types, although this hypothesis remains somewhat speculative.
BFR training may be an appealing modality to integrate into the resistance exercise programs of physique athletes due to the unique metabolic stress it provides to the musculoskeletal system when training with lighter loads and intensities not typical of bodybuilding routines (69). The metabolic stress produced from BFR exercise may expose muscle fibers (particularly type I fibers) to new recruitment demands not obtained from traditional heavy-load training and thus provide a way to further augment muscle hypertrophy in highly trained athletes. Indeed, this has been shown in national-level powerlifters undergoing two 1-week training blocks of BFR over 6.5 weeks using 30% 1RM during front squats compared with the non-BFR group performing the same exercise at 60–85% 1RM (8). Vastus lateralis hypertrophy increased +7.7% in the BFR group versus 0% in the non-BFR group, with gains primarily attributed to increases in CSA of type I muscle fibers. This study provides intriguing evidence that the addition of BFR can augment the hypertrophic response in highly trained athletes.
Several other studies provide additional support for the combined use of high-load training and low-load BFR training in athletes and well-trained individuals, although the results on hypertrophy are not always consistent (Table 1). Most studies incorporating BFR into their training used the strategy as a low-load supplement to heavy-load training (59,60,77,102), while others used BFR with heavy loads (70% of 1RM) (19) or performed the same exercises but substituted BFR at lighter intensities (8). The majority of the research using concurrent training show significant improvements in muscle strength relative to the non-BFR training groups (19,60,102) with some showing concurrent improvements in muscle hypertrophy (8,60,102), and yet, others showing no effect of BFR training on strength or hypertrophy (77). Methodological and/or participant characteristics may explain the variance in outcomes between studies. It seems that when groups are volume-equated, the results are mixed. Three studies show either no difference in hypertrophy between groups (59,60) or no changes at all (77), while one study shows superior hypertrophy of the BFR group over the volume-matched control (102).
Table 1 -
Relevant studies on athletes and resistance-trained individuals using concurrent BFR and high load
||Variables of interest
|Yamanaka et al. (102)
||32 Division IA Collegiate Football Players (min 5-y RT experience); ∼19.2 y
Strength: BP and SQ 1RM
Hypertrophy: CM measures of upper and lower chest and arm girth, thigh girth
|30-20-20-20 repetitions of BP and SQ after regular HLT with or without BFR
|Luebbers et al. (60)
||62 Division II Collegiate Football Players (avg. 7.1-y RT experience); ∼20 y
Strength: BP and SQ 1RM
Hypertrophy: CM measures of arm, leg, chest girth
|4 Groups: 30-20-20-20 repetitions of BP and SQ after regular HLT with or without low-load BFR or low-load training; 1 group did not perform BP or SQ but performed BFR
||2×/wk per body region
|Scott et al. (77)
||21 Semiprofessional Male Australian Football Players (avg. 1.6× BW SQ); ∼19.8 y
Strength: 3RM BS
Hypertrophy: VL architecture
|30-15-15-15 repetitions after regular HLT with or without BFR
||3×/wk (except for week 5–2×/week)
|Cook et al. (19)
||20 Semiprofessional Male Rugby Players (min 2-y RT experience); ∼21 y
Strength: 1RM BP and BS
||5 × 5 repetitions were performed with PU, BP and SQ
|Bjornsen et al. (8)
||19 National Level Powerlifters (16 men, 3 women) (avg. ∼5 y of RT experience)
Strength: 1RM FS or MVIC knee extension
Hypertrophy: Muscle fiber analysis on VL, MT of VL, VM, RF, VI
|Failure-15-12-Failure FS repetitions with or without BFR in addition to regular HLT; CON group performed 60–85% 1RM FS
||5× FS/wk × 2 wk
|Lowery et al. (59)
||20 Resistance-Trained Collegiate Males (min 1 y of RT experience); ∼23 yo
Hypertrophy: BB MT measurements
||3 × 30 repetitions with BFR
3 × 15 repetitions with HLT
Groups performed same program for 8 wk but with and without BFR (4 wk each) and then switched
||30% 1RM BFR; 60% 1RM HLT
||BFR application type
||BFR pressure applied
||BFR between rest periods?
||Outcomes? (only BFR reported)
|Yamanaka et al. (102)
||N/A—2-inch overlap on KW
Strength: +7.0% BP 1RM and +8.0% BS 1RM
Hypertrophy: +3% in upper and lower chest girth
|Luebbers et al. (60)
||N/A—3-inch overlap on KW
Strength: No differences in increases in BP 1RM between groups (+2.7–8.69 kg) but differences in BS (+24.87 kg versus 5.97–14.13 kg) 1RM
Hypertrophy: No differences observed in increases in arm or thigh measures between groups; chest girth did not increase in any group
|Scott et al. (77)
||N/A—“7/10 perceived tightness”
Strength: No differences in increases in SQ 3RM between groups (+12.3–12.5%)
Hypertrophy: No changes in VL architecture for any group
|Cook et al. (19)
||180 mm Hg during PU, BP and SQ
Strength: +1.4% and +2.0% in BP and BS 1RM in BFR group compared with CON
|Bjornsen et al. (8)
||∼120 mm Hg
Strength: No group differences in MVIC KE (+9.4 Nm in BFR versus −1.8 Nm in CON pre to post) or 1RM FS (+4.1 kg in BFR versus +5.9 kg in CON pre to post)
Hypertrophy: Type 1 fibers CSA increased more in BFR (974 versus 13 µm2) with no differences in Type 2 fiber CSA between groups. CSA of VL increased in BFR versus CON (+1.64 versus 0.12 cm2) and similar trends observed in RF and VM but not VI.
|Lowery et al. (59)
||“6–7/10 perceived tightness”
||No difference between HLT-BFR and BFR-HLT groups in BB hypertrophy (pooled means 3.66 ± 0.06 cm to 4.11 ± 0.07 cm)
BFR = blood flow restriction; BP = bench press; BW = bodyweight; CM = circumferential; CSA = cross-sectional area; FS = front squat; HLT = high-load training; KW = knee wraps; LOP = limb occlusion pressure; MT = muscle thickness; MVIC = maximum voluntary isometric contraction; PN = pneumatic; PU = pull-ups; RM = repetition maximum; RF = rectus femoris muscle; RT = resistance training; SQ = back squat; VI = vastus intermedius muscle; VL = vastus lateralis muscle; VM = vastus medialis muscle; YO = years old.
Taking the aforementioned information into consideration, the research tends to show that the addition of low-load BFR training to a high-intensity training program increases muscle hypertrophy in resistance-trained participants over periods of 4–7 weeks compared with similar routines performed without BFR, although more research is needed to optimize RT exercise prescription to maximize hypertrophic potential in mixed training (i.e., heavy and light load) approaches.
Some evidence suggests that BFR may enhance the satellite cell (SC) response to RT, thereby augmenting long-term hypertrophic adaptations; an outcome that would be of considerable benefit to the physique athlete, particularly those close to maximizing their genetic capacity for muscle development. It has been proposed that each myonuclei controls the production of proteins for a finite volume of cytoplasm (the “myonuclear domain theory”), and beyond this theoretical “ceiling,” additional nuclei must be derived from SCs to realize further increases in muscle mass (72). The molecular underpinnings of how SCs are recruited to assist in muscle building are beyond the scope of this article, but in short—a damaging bout of exercise activates a quiescent SC from the basal lamina of the muscle fiber to proliferate, differentiate, and ultimately fuse to the muscle fiber, donating nuclei and helping with repair and growth processes (90,110).
Given emerging research showing that hypoxia potentiates the RT-induced myogenic response (13), it can be speculated that BFR may be an effective strategy to promote increases in SC content. Indeed, a 3-week, high frequency BFR training program was shown to increase SC proliferation over work-matched low-load free-flow exercise (65). The findings led the authors to speculate that perhaps interspersing short blocks of low-load BFR training into traditional RT programs might enhance hypertrophic long-term adaptations. However, the fact that the control performed work-matched sets raises that prospect that differences between conditions may have been due to differences in proximity to failure. Other studies have reported no changes in SC/myonuclei concentrations after 6 or 12 weeks of BFR training to failure (at 30% 1RM) compared with nonfailure high-intensity training (70%+ 1RM) (26,80). It thus remains equivocal whether BFR is a viable strategy to increase SC content in physique athletes; further research is needed to draw evidence-based conclusions on the topic.
Table 2 summarizes some of the important considerations to make when applying BFR before training.
Table 2 -
Considerations for the practical application of BFR
|Practical (knee wraps) using a perceived “7/10” tightness versus pneumatic (tourniquet) using limb occlusion pressure (LOP)a
||Pneumatic using LOP
||Although KW have shown efficacy in a number of studies (8,60,102), they do not allow the individual to obtain a standardized pressure from session to session (7). Bell et al. (2019) showed that when individuals were asked to pump the cuff pressure in the arms and legs to a “7/10” tightness once each day over 3 d, it resulted in overestimation/underestimation of LOP in the arms by 25% and legs by 20%. This suggests that setting pressures relative to LOP may provide a more standardized stimulus.
|Cuff width—narrow or wide (5–17 cm)
||Depends—both are acceptable if using %LOP
||All different cuff widths have been shown to have efficacy (71), but narrow cuffs require higher pressures to obtain LOP, potentially increasing risk to underlying neurovasculature (55). However, use of wider cuffs may attenuate hypertrophy underneath the restriction site (26), although setting to individualized LOP may mitigate that chance (51). Narrow cuffs have also been shown to be more comfortable compared with wider cuffs when set to the same relative LOP (83).
||Safety concerns for a nerve injury arise with external compression directly over vulnerable regions at the elbow (ulnar nerve) or knee (common fibular nerve) tractions the nerve and increases risk of demyelination with muscular contractions. The neurovasculature is more protected closer to the trunk due to increased soft tissue; so application is best suited proximally.
|Maximum no. of cuffs at one time
||2 (2 upper body or 2 lower body)
||Although there is no research comparing the acute or chronic safety of BFR applied to 4 limbs simultaneously, bilateral BFR has been shown to increase heart rate to compensate for loss of stroke volume during exercise, increasing rate pressure productb threefold compared with free-flow exercise (74). In individuals exercising with more than 2 cuffs on simultaneously, it may unnecessarily increase risk of adverse cardiovascular events and is therefore not recommended.
|Body position and LOP
||Determine LOP in the position (standing/sitting/supine) of the exercise
||LOP has been shown to vary based on the position of testing (38,78). Underestimating or overestimating LOP may decrease effectiveness of nonfailure BFR exercise or safety (71).
|Determining LOP (frequency)
||Once every 4–8 wk
||LOP has not shown to change significantly in healthy individuals over the course of 8 wk (61).
LOP = limb occlusion pressure, is determined either with an automatic BFR device or manually with an external Doppler and a pneumatic cuff. LOP is preferably determined in the position of the exercise, where the individual is relaxed, and an external Doppler is positioned at the level of the radial or posterior tibial artery. The cuff is gradually inflated until there is no audible sound heard from the Doppler. The cuff is gradually deflated, and the first sound heard is the individual's LOP. Recent research also supports the use of a pulse oximeter in the upper but not lower extremities (111
bRPP = rate pressure product is calculated by the equation, “RPP = heart rate × systolic blood pressure” and is a measure of the workload on the heart.
BFR = blood flow restriction.
Researchers use a number of different BFR methodologies in the laboratory setting that makes translating research into practical recommendations challenging for the physique athlete. Practical recommendations for the physique athlete must take into consideration BFR cuff safety, cost, and potential benefits with chronic use.
Research studies typically use cuffs that are pneumatic or nonpneumatic. Pneumatic cuffs fill up with air by external means (either manually through a pump or automatically through a computer system or wireless device) and apply the pressure to the limb by increasing the amount of air within the bladder of the cuff. Nonpneumatic cuffs, such as elastic knee wraps, apply pressure to the limb through increased tension on the band or strap provided by the user. Although both types of applications have shown to improve muscle mass in the research (59,60,79,102), there exists some conflicting evidence on the potential safety of nonpneumatic applications (i.e., knee wraps). Commonly recommended application of nonpneumatic cuffs involve tightening knee wraps to a perceived tightness of 6–7 (on a scale where “where “10” is maximal discomfort”) to achieve adequate occlusion pressure (59,77). However, some studies suggest that individuals have difficulty achieving a standardized restrictive stimulus on a session-to-session basis, overestimating or underestimating applied pressures by as much as 25% (7). This may contribute to situations where individuals are exercising under full limb occlusion, increasing the risk of adverse events even in healthy individuals. Furthermore, if the applied pressure is too low, the local metabolic environment is not significantly altered thus rendering the addition of the cuffs ineffective at accelerating fatigue accumulation at light loads (42,73).
Recently, some studies have investigated alternative methods for standardizing cuff pressure with the use of practical BFR. Abe et al. (2) determined that pulling elastic cuffs to 10–20% of initial length achieved similar reductions in brachial artery blood flow as that of a pressurized nylon cuff inflated to 40 and 80% of resting arterial occlusion pressure, respectively. Similarly, Thiebaud et al. (89) reported that elastic knee wraps, either stretched by 2 inches or to a length of ∼85% of thigh circumference, provided a valid alternative to pneumatically inflated cuffs. It should be noted that these studies used specially designed elastic cuffs that allow for precise determination of the magnitude of stretch; this is a more difficult task with standard elastic wraps, rendering their practical utility somewhat limited.
Ideally, pneumatic devices are recommended in the gym setting because they are able to provide a more consistent restrictive stimulus for BFR application, minimizing safety risk despite the higher cost to the consumer. Newer technology has been recently released for consumer purchase that removes some of the previous barriers of using pneumatic cuffs in the gym setting. These cuffs can determine individualized subocclusive pressures without use of an external Doppler (the current gold standard in clinical application). The wireless nature of these devices also makes them more “gym-friendly” than clinical models that are tethered, expanding their ability for widespread gym use. That said, practical BFR using elastic knee wraps remains a valid option for promoting an anabolic stimulus. Individuals choosing to use this option should do so with caution and reduce restrictive pressures if any numbness, tingling, or excessive bruising underneath the restriction zone occurs.
PRACTICAL RECOMMENDATIONS FOR INTEGRATING BLOOD FLOW RESTRICTION RESISTANCE TRAINING
Implementing BFR into the RT program for physique athletes requires some basic programming considerations. Shown in Table 3 are some general programming guidelines to maximize hypertrophic potential with BFR training based on the current research.
Table 3 -
Evidence-based practical recommendations for BFR resistance training
|Programming variables to consider
||2–3×/wk for >3 wk, 1–2×/d <3 wk
||BFR training can be performed chronically 2–3×/wk in combination with HLT or used to “shock” the musculoskeletal system for a short period (<3 wk) for 1–2×/d in the absence of HLT (like during a deload week) (71). Of note, despite the low-load nature of BFR, 1–2×/d is very stressful and likely requires considerable recovery (10 d) to observe benefits (9)
|In nonfailure exercise, metabolic stress is shown to increase with higher pressures and in the legs, 40% LOP produces a similar metabolic environment as free-flow exercise (42,73). However, in the arms, 40% LOP produces similar outcomes as 90% LOP (23).
|No. of exercises per session
||Most studies use either 1 exercise (i.e., leg extension); some use 2 exercises per muscle group performing a multijoint and single-joint variation (i.e., leg press/leg extension) (21).
||30-15-15-15 or failure training × multiple sets
||Both routines show efficacy in numerous studies, but failure training tends to increase recovery time (97). Failure may be needed to maximally fatigue target muscle groups, especially in advanced trainees.
|Maximum wear time
||Recommended to reduce risk of adverse events. Deflate after every 1–2 exercises and wait at least 1 min before reinflating (71).
||Loads greater than 50% 1RM do not seem to augment the benefits of BFR exercise (50). Loads less than 20% provide suboptimal outcomes with respect to hypertrophy (14).
||1–2 s concentric/eccentric
||Lifting tempo should be between 1 and 2 s because most research have used these numbers (71).
||Shorter rest periods augment metabolic stress to a greater degree than longer rest periods (150 s) (54).
|Continuous (CON) or intermittent application (deflated during rest)b
||CON application shows superior metabolic stress (84) and muscle fatigue (107) despite similar levels of perceptual effort during exercise (31). Of note, when BFR is removed (or not applied) during the rest periods, tissue oxygen levels tend to recover, reducing metabolic stress (73).
|Before or after HLT?
||After, unless no HLT performed (deloads)
||After HLT, as maximizing hypertrophy likely needs a combination of high mechanical and metabolic stress, which could be sacrificed long term if BFR is performed before HLT due to acute fatigue response with BFR exercise (69).
|Multijoint or single-joint exercises?
||Both types have shown to increase hypertrophy, but single-joint exercises likely superior to drive growth to muscles distal to the cuff due to higher local fatigue tolerance (41).
|Exercise order in BFR—multijoint or single-joint?
||Either, although single-joint may stress muscles distal to the cuff to a greater degree
||Both have shown to be effective, but likely excessive fatigue accumulation during single-joint movements may impede completion of multijoint exercise performance.
aLOP = limb occlusion pressure is the minimum pressure needed to completely restrict both arterial and venous flow to the limb. Exercise is performed at a percentage of this value.
bCON = continuous application describes when the BFR cuff is left inflated throughout the duration of the exercise versus deflated during the rest periods.
BFR = blood flow restriction; HLT = high-load training (70+% 1RM); RM = repetition maximum.
Physique athletes can program BFR RT to increase muscle hypertrophy in a number of ways. The most practical way to include BFR RT into a program would be to add on 1–2 exercises per target muscle group at the end of a heavy-load training session to preferentially stress muscle fibers that may not be sufficiently stressed at higher loading intensities (i.e., type I fibers) (8,69). The combination of heavy-load and low-load BFR in a single training session provides both metabolic and mechanical stress to the muscle, which have been hypothesized to positively contribute to maximal increases in hypertrophy (69). Studies have also shown that the additional volume provided by nonfailure BFR RT (i.e., 30-15-15-15) does not negatively impact recovery from training (57,87,88). However, incorporating multiple sets of failure training may prolong recovery and increase delayed-onset muscle soreness, especially during unaccustomed bouts of exercise (28,93). This may reduce weekly training frequency and lead to suboptimal hypertrophy over time. Despite the potential for increased recovery time performing failure routines, physique athletes may require this approach occasionally to maximize long-term hypertrophy, especially if type I fiber hypertrophic potential is limited by chronic training with heavier loading protocols (8,9).
The best evidence-based approach seemingly would be to program multiple sets (2–4) of failure training periodically, most likely in exercise sessions where there are scheduled rest days afterward, so as to not provide a performance decrement to subsequent lifting sessions. Since unaccustomed failure training tends to increase recovery time, failure training should be performed after an initial acclimation period (2–4 weeks, 2–3×/week) of BFR RT has been completed. BFR failure training also is more perceptually demanding than high-load training despite significantly less overall volume, making it challenging to continually perform in practice (94). Finally, single-joint exercises (i.e., leg extensions and biceps curls) tend to be able to drive more localized fatigue to the muscles compared with compound exercises (i.e., squats and bent-over rows), so these should be prioritized in training when heavy-load variations of the same type of exercise are used concurrently in the lifting session (41).
Another unique application for BFR RT could be during a planned deload phase or when a competitor is deep in contest preparation, and the likelihood of musculoskeletal injury theoretically increases. Two recent studies polling elite physique athletes reported that 40+% of respondents train through musculoskeletal pain (81,82). Short blocks (1–2 weeks) of BFR RT could reduce the stress on the joints of the elbows and knees while providing similar hypertrophic benefits as heavier training (71). There also is evidence to suggest a significant hypoalgesic effect during and after BFR (45), which may last up to 24 hours (39). This may enable the physique athlete to continue training despite injuries that would otherwise hinder training intensity (58). Taken together, low-load BFR RT could help physique athletes maintain their physique during periods of relative deloading while also decreasing pain during and after exercise. Figure 1 displays the potential applications for BFR during an RT program for a physique athlete.
BFR RT exercise (20–50% 1RM) seems to elicit similar benefits in muscle hypertrophy when directly compared with moderate-load (70% 1RM) and heavy-load (80% 1RM) protocols (21,46). However, heavy-load RT may confer additional neuromuscular and musculoskeletal benefits including greater increases in dynamic strength measures (i.e., 1RM), central activation (a measure of neural drive to the muscle), and greater muscle retention during periods of detraining (12,109), which may be of relevance to those aspiring to maximize muscle development over the long term. Thus, it is recommended that BFR never completely replace heavy-load RT in a long-term periodized program in physique athletes.
There seems to be a difference in responses between men and women with respect to submaximal BFR exercise tolerance. Women have been shown to have greater submaximal endurance at lower loads (20–40% 1RM) than men (48,101). Accordingly, women physique athletes may need either additional loads and/or repetitions to achieve a similar hypertrophic stimulus as men using lower load, nonfailure BFR protocols.
From a loading standpoint, there likely exists a floor beneath which optimal hypertrophy can occur during BFR training. Buckner et al. (14) randomized participants into 1 of 4 groups: 70% 1RM without BFR, 15% 1RM without BFR, and 15% 1RM with 40 and 80% limb occlusion pressure (LOP). Each participant performed up to 4 sets of elbow flexion exercise to volitional failure (or 90 repetitions) twice a week for 8 weeks. Results showed nonhomogenous increases in muscle growth of the elbow flexors in the 15% conditions irrespective of BFR, with lesser absolute increases in hypertrophy compared with the 70% 1RM condition. Therefore, it seems that metabolite-induced fatigue and cell swelling act to augment the hypertrophic response to BFR RT in response to external loads above 15% 1RM, but not lower. When integrating BFR RT into exercise prescriptions, loads corresponding to at least 20% 1RM should be used to ensure maximal benefit in work-matched or failure exercise protocols.
An observed benefit to BFR RT in untrained or injured populations when performing multijoint exercises such as the back squat or bench press involves additional hypertrophy of the proximal muscle groups (i.e., gluteals and pectorals) (1,10,105). However, the gains in hypertrophy are variable and tend to be greater with individuals who are more deconditioned (10,105). In the physique athlete who can tolerate additional loading (70+% 1RM), BFR may not provide enough of a hypertrophic stimulus to the muscles proximal to the cuff to warrant its inclusion in a training program. This is attributed to decreased muscle activation secondary to reduced training loads (especially during nonfailure, multijoint exercise) (1). It is recommended that muscles proximal to the cuff be directly trained with heavier loads without BFR to maximize hypertrophy of these muscles.
Figure 1 highlights the gradual introduction of BFR RT into a heavy-load RT program over 12 weeks. Although applied pressure is not specified, research has shown that a wide variety of pressures can be used to improve muscle hypertrophy at various loads (52). However, it seems that when using lighter loads closer to 20% 1RM, higher relative pressures (50% LOP in the arms and 80% LOP in the legs) may be needed to maximize muscle gains (52). In nonfailure routines (i.e., 30-15-15-15), metabolic responses (i.e., rise in lactate and muscle deoxygenation) seem to be augmented in a pressure-dependent manner above 40% LOP (80% > 60% > 40% = low load-free flow) (42). Conversely, higher relative pressures (i.e., 50% LOP in the arms and 80% LOP in the legs) may not be required at loads approaching 50% 1RM because the intramuscular pressure may be high enough from the contraction itself to produce occlusion during the exercise bout (37,50,75). There also seems to be no additional acute or chronic benefit for adding BFR to heavy loading as the muscle activation is already high (50,64). Finally, although BFR has been shown to be relatively safe and promote benefits in both muscle and connective tissue (17) despite the low loads, not much is known about effects from long-term continuous (16+ weeks) application. Therefore, a periodic removal of BFR from the RT program is advised to minimize the risk of potential chronic adverse events currently unknown.
Table 4 provides BFR evidence-based progression guidelines for the use of BFR training with athletes and bodybuilders. The same principles of intensifying strength training may apply to BFR at lower loads (i.e., drop sets, compound sets, etc.), but potential benefits over traditional approaches without BFR warrant further research.
Table 4 -
Possible ways to progress BFR resistance training
||Range of motion
||Partial range of motion
Bilateral (i.e., squats)
|Avoid lengthening two-joint muscles (i.e., calf raises on the floor versus off step)
Lower pressure (40% arms, 60–70% legs)
Lower %1RM (20–35% 1RM)
||Full range of motion
Long-lever exercises (i.e., Straight leg raise flexion)
Single-leg biased (i.e., lunge)
Single-leg dynamic (i.e., walking lunge)
|Intensification techniques (drop sets, compound sets, etc.)
Full 2-joint muscle excursions (straight leg calf raise off step into full dorsiflexion)
|Failure (2–4 sets)
Higher pressure (50% arms/80% legs)
Higher % 1RM (35–50% 1RM)
BFR = blood flow restriction; RM = repetition maximum.
SUMMARY AND CONCLUSIONS
BFR RT seems to be a novel way to enhance muscle hypertrophy in physique athletes, especially when used in conjunction with heavy-load RT. Although the benefits of BFR AT are less conclusive, the strategy does modestly increase EE, cell swelling, and (in some modes of exercise) metabolic stress compared with work-matched free-flow exercise, all of which can be beneficial to the physique athlete by either aiding in maintaining/producing a caloric deficit or by creating an anabolic environment to aid in muscle growth. Both of these applications may be used in tandem to maximize the hypertrophic potential of a combined exercise session, but caution is warranted with long-term continuous use.
Despite the fact that BFR generally has been shown to be safe to use in healthy resistance-trained adults, not much is known about the long-term effects (16+ weeks) on vascular function, especially during RT where intramuscular pressures from muscle contractions may excessively stress the structure of the arteriovenous system (i.e., stiffness/compliance etc) (24). Therefore, it is strongly advised to schedule a programmed 4-week period where BFR is completely removed from training to account for any potential as-yet-undetermined adverse events.
With respect to the physique athlete, there are numerous avenues for future research that could help elucidate the effectiveness of BFR within this population. There are currently no studies comparing heavy-load RT to heavy-load RT plus low-load BFR RT in highly trained physique athletes nor are there any studies showing the effectiveness of low-load BFR RT in maintaining lean body mass during contest preparation.
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