Muscle strength is important for normal survival and daily living. It is also considered an important predictor of cardiometabolic risk and is associated with morbidity in adults and older adults (Silventoinen et al., 2009). Studies have identified low grip strength as a potential risk factor for skeletal sarcopenia, functional limitation, and disability (Rantanen et al., 1999; Manini and Clark, 2012); it is also considered a valuable indicator of frailty in older adults (Takahashi et al., 2017). In addition, a meta-analysis study of data from approximately 20,000 men and women associated high levels of upper and lower limb muscle strength with a reduced risk of mortality in adults (García-Hermoso et al., 2018). Another follow-up study over a period of 33 years showed a negative association between muscle strength and all-cause mortality (Stenholm et al., 2014). This correlation was also observed in people with specific diseases, including cardiovascular disease, peripheral arterial disease, cancer, renal failure, chronic occlusive lung disease, and rheumatoid arthritis, and among critically ill patients (Jochem et al., 2019). Therefore, muscle strength can be regarded as a potential predictor of morbidity and mortality risk in the general population (Leon et al., 2005; Peterson and Krishnan, 2015), and it plays a key role in protecting human health.

The American College of Sports Medicine previously suggested that the use of high-load resistance training [(HL-RT, ≥70% 1RM)] is an effective means of promoting muscle strength gain (Garber et al., 2011). However, this training method has drawbacks, with HL-RT exercise increasing the likelihood of sports-related injuries. Furthermore, for patients undergoing rehabilitation, HL-RT exercise is not recommended in the early stages of recovery, as it may increase the risk of reinjury (Hughes et al., 2019). In elderly individuals, the presence of comorbidities, such as coronary heart disease, diabetes, or musculoskeletal injuries, may further complicate the use of HL-RT (Papa et al., 2017). However, low-load exhaustive exercise, while also effective in improving muscle strength, may cause subjective discomfort in older adults and rehabilitating patients. Moreover, prolonged recovery time from fatigue may lead to red blood cell abnormalities, increasing the likelihood of tissue damage or the exacerbation of existing injuries (Brun et al., 1994). Emerging blood flow restriction (BFR) training with low-load resistance training (BFR-RT) techniques can circumvent these problems.

BFR training, also known as KAATSU training or vascular occlusion training, refers to the external compression of the limb during exercise by using a special compression device that causes venous occlusion and partial arterial occlusion to improve the training effect (Sato, 2005; Loenneke et al., 2014). BFR-RT produces a local metabolic crisis via physical compression, which induces the brain to secrete growth hormones to promote anabolism, improve muscle strength, and accelerate tissue repair (Fry et al., 2010). Common practice dictates that more muscle strength gain can be obtained with BFR-RT than with low-load resistance training. However, controversy arises when BFR-RT is compared with HL-RT, which is known as the gold standard for increasing muscle strength. For example, some studies have shown that BFR-RT training can produce muscle strength gain similar to HL-RT (Libardi et al., 2015; Centner et al., 2022; Chang et al., 2022), whereas other studies have shown that BFR-RT training leads to less muscle strength gain than HL-RT (Lixandrao et al., 2018; Sieljacks et al., 2019).

It is necessary to discuss these controversies based on cuff pressure characteristics. A meta-analysis explored the effect of using different occlusion pressure prescriptions (individualized and non-individualized pressures) on muscle strength gain during BFR-RT exercise, results indicated that the BFR-RT group demonstrated lower muscle strength gain than the HL-RT group, even after controlling for the abovementioned factors (Lixandrao et al., 2018). Interestingly, however, Individualized pressure appears to be widely accepted owing to its logical basis, but it does not justify the choice of individualized pressure when setting up a BFR-RT exercise program, and more theoretical support needs to be found for the use of individualized pressure for BFR-RT (Clarkson et al., 2020). Another related meta-analysis (Sinclair et al., 2022) described that the cuff inflation pattern (continuous and intermittent pressure) was not a variable affecting muscle strength gain, but the results of the analysis were limited to two articles, entailed limited guidance value in terms of enhancing muscle strength with BFR-RT interventions that use different cuff inflation patterns. In addition. To our knowledge, no meta-analysis has yet considered the effects of BFR-RT occlusion pressure prescription, cuff inflation mode, and participant characteristics on muscle strength adaptation simultaneously.

Therefore, the objectives of our study were threefold. Firstly, we aimed to examine the adaptation of muscle strength in individuals undergoing BFR-RT compared to those undergoing HL-RT. Secondly, we aimed to analyze the impact of occlusion pressure prescription and cuff inflation pattern on the adaptation of muscle strength. Lastly, we sought to investigate the cuff pressure characteristics that are suitable for promoting muscle strength adaptation in diverse participants.

The systematic review was performed according to the latest guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Page et al., 2021). This study was also registered with PROSPERO (CRD42022364934).

The main purpose of this meta-analysis was to compare the effects of BFR-RT on muscle strength in healthy adults. The included studies reported the effects of BFR-RT (20%–40% 1RM) on muscle strength in healthy adults and compared these with HL-RT (70%–90% 1RM) methods without BFR. The comprehensive results showed that BFR-RT produced less muscle strength gain than HL-RT, which is consistent with the results of previous studies (Lixandrao et al., 2018). Subgroup analysis of the occlusion pressure prescription showed that the BFR-RT group applying individualized pressure produced muscle strength gain comparable to the HL-RT group. Furthermore, the BFR-RT group applying incremental pressure produced muscle strength gain similar to HL-RT, whereas the BFR-RT group applying absolute pressure achieved less muscle strength gain than the HL-RT group. Subgroup analysis of the cuff pattern of inflation showed that the BFR-RT group with intermittent pressure achieved muscle strength gain comparable to that of the HL-RT group, whereas the BFR-RT group with continuous pressure achieved less muscle strength gain than the HL-RT group. Our findings also suggest that better muscle strength gain could be achieved by both “individualized pressure + intermittent pressure” and “incremental pressure + intermittent pressure” in the BFR-RT exercise protocol.

Muscle strength forms the basis for all activities in the human body. Some studies have highlighted the importance of muscle strength for specific motor skills and reduced injury rates (Suchomel et al., 2016). In the elderly population, higher muscle strength in the lower limbs is positively associated with cognitive function (Frith and Loprinzi, 2018), helps to prevent falls, and can lead to increased levels of physical activity (Trombetti et al., 2016). In the adult population, muscle strength and risk factors are negatively associated in terms of metabolic traits, higher muscle strength can reduce this relevance (Fraser et al., 2016). For special populations, muscle strength is a key factor in promoting mobility, cardiovascular capacity, and performance in daily activities (Obrusnikova et al., 2022). Researchers previously thought that the best approach for improving muscle strength is to perform HL-RT; however, as time progressed, increasing evidence showed that BFR-RT can also effectively improve muscle strength (Takarada et al., 2000; Brandner et al., 2019; Chang et al., 2022). Interestingly, many studies have focused their research objectives on comparing the differences in muscle strength gain via BFR-RT and the without vascular occlusion resistance exercise, but the effects of some characteristics of BFR-RT itself on muscle strength gain are generally ignored.

Cuff pressure characteristics are a key factor in establishing a BFR-RT exercise protocol. The choice of prescription regarding cuff occlusion pressure has also evolved, and the initial approach was to implement BFR-RT cuff pressures over arbitrary absolute pressure (Takarada et al., 2000). With the evolution of BFR-RT, the concept of initial absolute pressure became less popular. Some scholars eventually chose to gradually increase pressure during training (Karabulut et al., 2010; Bemben et al., 2022), whereas other researchers chose individualized cuff pressure based on arterial occlusion pressure (Laurentino et al., 2012; Centner et al., 2023). The rationale for the choice of incremental pressure is multifaceted, with some scholars proposing that incremental cuff pressure increases the level of perceived effort in participants (Yasuda et al., 2014b; Yasuda et al., 2015); meanwhile, others proposed that incremental pressure can help participants to better adapt to the occlusion stimulus during the initial phase of training (Junior et al., 2019a; Junior et al., 2019b). The rationale for selecting individualized pressure is that individualized pressure motion prescriptions are more accurate than broad occlusion pressure motion prescriptions when applying cuff pressure during BFR-RT exercise, with individualized prescriptions accounting for device variations (e.g., different cuff widths) when setting the same absolute pressure, thus addressing the limitations caused by this variability (Mouser et al., 2018). Overall, BFR-RT interventions using different cuff pressure characteristics affected perceived effort and adaptation to occlusive stimuli but failed to demonstrate a positive effect on muscle strength adaptation.

This meta-analysis analyzed the effect of cuff pressure characteristics on muscle strength gain. For the first time, cuff occlusion pressure prescriptions were divided into individualized, incremental, and absolute pressures for subgroup analysis. The application of individualized pressure in BFR-RT leads to muscle strength gain that is comparable to that in HL-RT. This result differs from the meta-analysis of Lixandrao et al., 2018; the heterogeneity observed in studies may be attributed to the number of included articles. In this meta-analysis, the individualized pressure in the included articles ranged between 40% and 80% limb occlusion pressure. Lixandrão et al., 2015 implemented personalized occlusion pressures of 40% and 80%, along with exercise loads of 20% and 40% of 1RM, the results of this study indicated that higher occlusion pressures yielded greater benefits for muscle strength when exercise loads were lower, whereas exercise load played a more significant role when higher exercise load were implemented. Letieri et al., 2018 implemented a personalized occlusion pressure of 80% and an exercise load ranging from 20% to 30% of 1RM over a span of 16 weeks. The participants completed a total of 48 training sessions during this period, notably, during the initial 2 weeks of the study, three sets of each exercise were executed (30, 15, 15), while in subsequent sessions, four sets were performed (15, 15, 15, 15), this discrepancy in the number of sets may lead to a more rigorous exercise stimulus at a lower pre-exercise load. In addition, in the included articles applying 50% arterial occlusion pressure, the BFR-RT intervention yielded similar muscle strength adaptations as HL-RT. Regarding incremental and absolute pressures, a recent review examined the effect of BFR-RT cuff pressure characteristics on cardiovascular metrics (Cerqueira et al., 2021). Although the significance of cardiovascular metrics in BFR-RT interventions is important, no conclusions were given regarding whether incremental or absolute pressure could be better applied in BFR-RT. In the current study, we approached this research gap from the perspective of muscle strength gain. Of the articles included in this review, five articles applied incremental pressures with pressure increases of 40, 60, and 80 mmHg, with cuff pressures ranging from 80 mm Hg to 240 mmHg, with a mean pressure of approximately 158 mmHg, and reported cuff widths ranging from 3 to 5 cm; and five articles applied absolute pressures with cuff pressures ranging from 50 mm Hg to 187.5 mmHg, with reported cuff widths ranging from 6 to 14 cm. The results of this meta-analysis showed that the BFR-RT group applied with incremental pressure showed comparable muscle strength gain to the HL-RT group. The finding differed for the BFR-RT group applied with absolute pressure.

Moreover, subgroup analysis of the cuff pattern of inflation showed that the muscle strength gain of the BFR-RT group applied with intermittent pressure was comparable to that of the HL-RT group. By contrast, the muscle strength gain of the BFR-RT group applied with continuous pressure was less apparent than that of the HL-RT group. We explained the reasons for the differences in outcomes between subgroups in the following three ways. Regarding the cause of fatigue, BFR-RT may produce higher levels of discomfort and a higher rate of perceived exertion than HL-RT without blood flow occlusion; the subjects may have manifested significant intolerance to the BFR-RT exercise regimen (Bell et al., 2018; Soligon et al., 2018; Dankel et al., 2019). The rate of perceived exertion after exercise was lower in the BFR-RT group applied with intermittent pressure; this phenomenon was not observed in the BFR-RT group applied with continuous pressure (Corvino et al., 2017). This finding may be explained by the BFR-RT applied with continuous pressure leading to an immediate onset of physiological and metabolic stress, causing increased fatigue and decreased exercise performance (Wernbom et al., 2009; Loenneke et al., 2012), suggesting greater discomfort (Neto et al., 2018; Wilk et al., 2018; Okita et al., 2019) compared with the BFR-RT group applied with intermittent pressure. From an energy supply perspective, the phosphocreatine concentration gradually decreases in BFR-RT applied with continuous pressure because of blood flow occlusion; by contrast, the release of vascular occlusion and subsequent restoration of phosphocreatine concentration through the phosphocreatine shuttle system occurs in BFR-RT applied with intermittent pressure (Suga et al., 2012; Guimarães-Ferreira, 2014; Okita et al., 2019), prompting replenishment of stored adenosine triphosphate and an increase in muscle tissue energy status (Guimarães-Ferreira, 2014). From a body metabolism perspective, BFR-RT applied with intermittent pressure provides better perfusion, venous return, and shorter occlusion times compared with BFR-RT applied with continuous pressure, with the former further preventing anaerobic respiratory byproducts from pooling and accumulating in the body, further resulting in lower levels of expected metabolic disturbances (Pearson and Hussain, 2015; Teixeira et al., 2018; Okita et al., 2019).

Furthermore, when age was considered, we found that in the elderly population, all BFR-RT exercise protocols applying different cuff pressure characteristics achieved similar muscle strength gains to HL-RT; whereas in the younger population, only two exercise protocols applying intermittent and individualized pressures achieved similar muscle strength gains to HL-RT. However, the number of included articles is small and conclusions should be drawn with caution. To provide clinical staff with more accurate BFR-RT exercise protocols, we used 3D models as an aid in investigating the combined effects of occlusion pressure prescription and cuff pattern of inflation on muscle strength gain. The results showed that the two BFR-RT exercise protocols “individualized pressure + intermittent pressure” and “incremental pressure + intermittent pressure” produced better adaptations for muscle strength gain. This finding illustrates the need to consider cuff pressure characteristics when setting up BFR-RT exercise prescriptions for healthy adults.

While focusing on the many benefits of BFR training, it is also important to consider the safety and adherence rates of the subjects.BFR training has some inherent safety concerns, as it essentially pressurizes the limb, resulting in decreased arterial blood inflow and venous blood pooling, This can result in the occurrence of ischemia and hypoxia within the body (Yasuda et al., 2010), while the inadequate elimination of lactic acid and other metabolites generated during this process is observed (Yasuda et al., 2014a; Teixeira et al., 2018). Furthermore, it has been shown that 23 min of BFR-RT training under sustained stress conditions, even with moderate exercise, can lead to muscle damage (Wernbom et al., 2020; Wernbom et al., 2021). However, Nakajima et al.'s questionnaire survey of 12,600 individuals who had experienced BFR training found that the most common side effects of BFR were subcutaneous hemorrhage and temporary numbness, but that this response diminished and disappeared as the cuff was released and training progressed (Nakajima et al., 2006). Therefore, from the point of view of safety and compliance, the BFR-RT with intermittent compression and the BFR with incremental pressure protocols may be a good choice for physical training. This is because with intermittent pressurization, subjects can release the cuff pressure restriction during rest breaks between sets, and electronic compression devices can be easily deflated and inflated during rest breaks without interfering with the training process; intermittent pressurization is also a viable option for people with low tolerance for ischemic pain and discomfort, and can improve adherence ineffective this population (Davids et al., 2021); and incremental pressurization can allow the subject to have a process of adapting to the pressure during training (i.e., cuff pressure can be slowly increased), which would be safer for participants and have a more positive attitude toward subsequent training. Coupled with the fact that our findings also suggest that intermittent pressurized BFR and incremental pressurized BFR exercise interventions have positive muscle strength growth adaptations, we recommend the use of intermittent pressurized incremental pressurized BFR-RT exercise regimens for long-term BFR-RT training, which appears to improve subject safety and compliance rates as well as better training outcomes.

First, the vast majority of the population included in this study was inexperienced in training, which provides limited guidance for those undergoing resistance training. Second, there is a lack of research on young female experimenters, and future research could focus on this population. Thirdly, the duration of the training period spanned a considerable timeframe ranging from 4 to 16 weeks, potentially influencing the observed results. Finally, considering multiple outcomes from the same study in a meta-analysis may also partially affect the homogeneity of results.

Our findings indicate that, in general, HL-RT produces greater muscle strength gains than BF-RT. However, upon further analysis, we observed that BFR-RT can yield similar muscle strength gains to HL-RT when considering specific cuff pressure characteristics, such as individualized pressure, incremental pressure, and intermittent pressure BFR-RT exercise protocols. Additionally, our results indicate that the combination of “individualized pressure + intermittent pressure” and “incremental pressure + intermittent pressure” BFR-RT exercise protocols display a tendency towards enhanced muscle strength gains. Overall, cuff pressure characteristics should be given more attention when setting up BFR-RT exercise protocols. It is important to note that age affects subgroup outcomes, indicating that the age factor should also be considered when considering the cuff pressure characteristics of the BFR-RT.