There has been increasing interest in using low-load resistance exercise in combination with a reduction in blood flow to promote muscle adaptation. Although few studies have examined the safety of blood flow–restricted (BFR) exercise, the current research on this exercise modality suggests that it is relatively safe.1 Further work is needed to better understand the adverse effects of this exercise modality so that educated risk-to-benefit assessments can be made.
Rhabdomyolysis is the breakdown of muscle tissue that leads to the release of muscle fiber contents (eg, creatine kinase [CK]) into the blood, which are harmful, and can cause damage, to the kidneys. Exertional rhabdomyolysis is a type of rhabdomyolysis resulting from strenuous physical exercise. There has been 1 case of exertional rhabdomyolysis associated with BFR exercise,2 and herein, we report the second.
This case is selected from a total of 79 apparently healthy subjects participating in at least 1 BFR exercise session between the authors' respective laboratories. This case occurred at Ohio University in a 20-year-old healthy man taking no medications/supplements (body mass index: 23.6 kg/m2). The subject's physical activity status was “low active” based on the Lipid Research Clinics Physical Activity Questionnaire. The subject had enrolled in a training study, and before the first exercise session, the subject had completed 2 unremarkable testing sessions involving strength assessments and an MRI. The BFR exercise session consisted of 3 sets of bilateral knee-extension and 3 sets of bilateral elbow-flexion resistance exercises (25% intensity) with the cuff pressure inflated on the exercising limbs to 167 mm Hg (KAATSU Master Mini; KAATSU Global Inc, Huntington Beach, CA). During the first set, the subject was asked to complete 30 repetitions followed by a 30-second recovery, and during the second and third sets, the subject performed repetitions to volitional failure (15 repetitions for both sets with both concentric and eccentric actions; ∼2 s/action). The pressure cuff remained inflated during the rest periods for a total BFR time of ∼ 5 minutes. After the BFR exercise, 3 sets of 15 lumbar-extension exercises were performed at 25% intensity (without BFR) while seated in a MedX Lumbar Extension Dynamometer.
Approximately 48 hours after the first BFR exercise session, the subject reported pain in the thigh region (7.5 on a 0–10 scale) and exhibited difficulty ambulating. He volitionally sought medical treatment where his urine was positive for blood and protein. A blood sample indicated a serum CK activity of 18 022 IU/L. He was diagnosed with exertional rhabdomyolysis and was hospitalized. While hospitalized, the serum CK peaked at 36 000 IU/L and returned to 6000 IU/L on discharge (∼72 hours after the BFR exercise session) (Figure). Renal function, as assessed by creatinine and blood urea nitrogen values, remained within normal ranges during this time.
This is the second case report of BFR exercise causing exertional rhabdomyolysis, which underscores the high metabolic stress that BFR exercise places on skeletal muscle3 and highlights the need for practitioners to gradually progress BFR exercise protocols. Our observation, when coupled with that of Iversen and Rostad,2 raises the question of “does BFR resistance exercise pose a higher risk for exertional rhabdomyolysis in comparison with more traditional, high-intensity resistance exercise?” This question cannot easily be addressed based on empirical data; however, it is our opinion that exertional rhabdomyolysis is a potential side effect of any rigorous and intense exercise program, including—but not limited to—BFR exercise. It is clear that rigorous physical activity, in general, and unaccustomed activity, in particular, can result in exertional rhabdomyolysis.4,5 For instance, ∼25% of individuals have been reported to exhibit serum CK levels >10 000 IU/L after the performance of 50 maximal eccentric contractions of the elbow flexor muscles,6 and other high-intensity exercise programs have resulted in exertional rhabdomyolysis.4,5 There are even some cases of whole-body, high-intensity resistance exercise training programs resulting in exertional rhabdomyolysis with CK values exceeding 200 000 IU/L5 and 2 sets of 25 maximal eccentric actions of the elbow flexors resulting in CK values as high as 40 000 IU/L.7
Our previous work has indicated that a comparable BFR exercise protocol only resulted in mild muscle soreness (2.8 ± 0.3 on a 1–10 visual analog scale).8 Thus, we consider our case unexpected, which indicates that BFR exercise may induce a high degree of muscle damage in only certain individuals. The observation of “high responders” to standardized eccentric exercise protocols has been well described, and recent evidence suggests that exacerbated responses may be associated with specific genotypes.9 However, we do not know whether this case exhibited any of the gene coding patterns associated with exertional muscle damage.
We should note that in thoroughly reviewing the literature, there is only one other report of exertional rhabdomyolysis (not previously mentioned) involving BFR exercise.10 This study surveyed 105 facilities in Japan that reported using BFR exercise in more than 12 000 individuals and reported 1 case of exertional rhabdomyolysis occurring in a clinical orthopedic setting.
There has been some indication that the type of cuff might influence the occurrence of adverse events. In past research, we have used the phrase “blood flow–restricted exercise” to refer to all exercise protocols that involve performing exercise while a pressure cuff of any type is applied to the proximal end of an exercising limb. In the extant literature, there are a number of different devices and approaches used to apply pressure, ranging from standard blood pressure cuffs to electronic cuffs used in surgical procedures, as well as those commercially marketed specifically for BFR exercise. One series of devices that are marketed specifically for BFR exercise is the “KAATSU” equipment (KAATSU Global Inc). We were recently surprised to read a release from KAATSU Global, Inc. stating that “when KAATSU Global was first established, there was a misunderstanding in the marketplace that KAATSU causes rhabdomyolysis. However, this misunderstanding came from a documented case of a Norwegian ice hockey player using the Delfi PTS ii Tourniquet Systems, a modified blood pressure cuff system.” This statement refers to the case study described by Iversen and Rostad.2 It should be noted that our case of rhabdomyolysis occurred using the KAATSU Master Mini. Therefore, in our opinion, there is no conceptual reason to why the physical instrumentation used to perform BFR would alter the risks of exertional rhabdomyolysis per se.
In summary, based on the case described herein, we urge that investigators and practitioners use caution with BFR exercise protocols as they would with any exercise that is expected to result in elevated soreness. It is suggested that all personnel involved with BFR exercise protocols be aware of the potentially serious consequences of muscle damage and exertional rhabdomyolysis and to begin all BFR exercise programs modestly and gradually progress them with time. Practitioners are also urged to recognize early signs of complications with BFR exercise and regularly report serious adverse events to enhance its safety and efficacy.[LINE SEPARATOR]
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