Blood Flow Restriction (BFR) training, or KAATSU training, has been around for nearly half a century but has recently become a popular mainstream strength training and rehabilitation technique. It was created in Japan in the 1970s by Dr. Yoshiaki Sato and has been controversial since its conception because of the possible side effects of excessive muscle damage and rhabdomyolysis.
The benefits of BFR are widely discussed and documented, however, there is conflicting evidence to support different training protocols used in different populations and environments. It is also little known how much muscle damage is caused by various training techniques when using BFR.
Learning to safely improve strength with BFR therapy
A new systematic review published in PLoS ONE aims to systematically analyze the evidence for the occurrence of muscle damage (changes in muscle damage markers) after resistance training with blood flow restriction sessions.
Methods
The systematic review followed the PRISMA guidelines and was pre-published in PROSPERO and adhered well to their protocol. Studies were eligible for inclusion if they were randomized or non-randomized clinical trials published in English between 1990-2020 that included people between the ages of 18-70 and based on the effect with BFR evaluated the following measures:
DOMs
edema
Inflammatory markers such as CRP
Serum activation of muscle proteins
ROM
Strength
Studies on walking, cycling, reviews, case reports and expert opinions were excluded from the analysis.
MEDLINE, PubMed, WoS, CINAHL, LILACS and SPORTdiscus were selected to search using the descriptors “Resistance Training” OR “Strength Training” AND “Kaatsu” OR “Vascular Occlusion” OR “Blood Flow Restriction”. AND "muscle damage". Two independent reviewers were responsible for the selection of the studies, a third was available if necessary to reach a consensus.
The quality of the studies included in the review was assessed using the Cochrane Risk of Bias Tool 2.0. The ROB tool was developed for the evaluation of randomized studies, but was used within this study for non-randomized studies, which is a clear limitation.
Analysis of the included studies
A total of 21 studies were included in the analysis, which included 353 participants with an unequal distribution of men (n = 301) to women (n = 51). The age of the participants tended to be lower and the mean was between 19 and 27 years. The sample sizes of the studies ranged from 6 to 36, which suggests that it will be difficult to draw firm conclusions from the review as the studies are undervalued.
The included studies are divided into comparison groups:
Ten studies compared resistance training with low stress with BFR with resistance training with high stress.
Nine compared resistance training with BFR with strength training with low stress.
Three-way comparison eccentric to concentric in low-load training with BFR.
Two studies compared high-load resistance training with BFR with high-load resistance training.
From an outcome measure perspective, DOMs reported on a 10 VAS scale or perceived muscle soreness during movement were the most commonly used outcome measures and were used in 14 studies. The second most common was muscle edema (ten studies) in which the cross-sectional area was analyzed using MRI or USS . Muscle strength performance was also used in eight studies using strength performance in a single joint or vertical jump force. Seven studies used ROM before and after training.
Overall, the studies were of poor quality. Across the board, there was inadequate coverage of randomization, with only one study reporting how it randomized participants. Even then, participants were free to choose the training session without knowing the type of training, which doesn't sound like randomization. The blinding was also poor across all studies, so that losses were also reported during the study.
On the positive side, all studies presented clear training protocols, including intensity of% 1RM, sets and repetitions, pressure applied, cuff size, recovery intervals, and pace of execution.
Results and clinical take-home
When considering biochemical markers, none of the studies showed a significant increase in serum CK, LDH or Mb 24 hours after strength training with or without blood flow restriction with low-load training . However, 24 hours after high-stress resistance training with restricted blood flow, there was a significant increase in serum CK levels. However, these results should be treated with caution, as earlier studies identified a delayed increase in CK after moderate exercise training, so that a delayed increase cannot be ruled out even with low-level training.
This is further supported by another study in this review that showed that low-impact BFR training increased CPK, but this contrast could be explained by the populations used in the study, which suggest that factors such as Experience and duration of strength training affect the physiological response to this type of training. Essentially, those who have exercised longer react less sensitively to an increase in CK.
The increase in CK in studies with predetermined sessions was not high enough to cause lasting harm to the individuals. Two people in a study that carried out repetitions to muscle failure achieved CK values that indicate rhabdomyolysis, which has long been a criticism of blood flow training.
Brief summary of the effects of strength training with blood flow restriction on muscle damage:
Low-load training with restricted blood flow is considered to be just as harmful as traditional high-load training
Repetitions to failure when using BFR and high-load training increase the risk of rhabdomyolysis
BFR training reduces the number of repetitions required to achieve muscle failure
Participants took similar DOMs with or without a BFR. true
No difference in edema levels between the groups
BFR accelerates the fatigue level
One of the most important indirect markers for muscle damage that we can use if a prolonged reduction in strength lasts over 24 hours. If this is transferred to the results of this review article, it can be assumed that training with low levels of stress with BFR does not lead to prolonged muscle damage. This is in contrast to training with high repetitions and high volumes with BFR, which leads to prolonged muscle damage, with the most damaging units being BFR with high stress up to and including muscle failure.
The results of the studies indicate a rough equivalence between BFR training with low stress and traditional high stress training. However, the study designs make it impossible to draw firm conclusions about this claim. In addition, the addition of BFR significantly reduces the number of repetitions required to reach failure, which can lead to misinterpretation of exercise volume between two groups. This is supported by the increased CK in some BFR training groups.
DOMs is one of the most widely used measures of muscle damage in any research examining muscle damage, and BFR training is no different. In general, people who participated in any of the studies included in this review experienced similar DOMs due to resistance training with or without restriction of blood flow.
Edema was present in both BFR and traditional training groups and no significant difference was found between them. Post-exercise edema (<1 hour) is common and is likely caused by metabolic build-up. It is not known whether the edema differs between the groups.
In summary, the evidence in this review suggests that the use of blood flow training with high training loads leading to muscle failure leads to significant muscle damage and should be avoided. BFR can also accelerate the extent of fatigue and this should be taken into account in protocols.
The authors of the article summarize the use of BFR nicely:
“It should be emphasized that the amount of muscle damage after a first session of resistance training with BFR appears to be attenuated, which shows a protective load effect from this type of exercise. Therefore, experts can apply the principle of progressive overload when structuring resistance training with BFR programs in a clinical context. "
