Parsing cause from consequence in blood flow restriction training: Insights from integrated human physiology

Blood flow restriction training (BFRT) is a training technique that involves limiting blood flow to active muscles during exercise. BFRT is achieved through the use of an inflatable cuff or tourniquet system wrapping around the proximal portion of a limb to partially or fully restrict limb arterial inflow and impede venous outflow during exercise of that limb. The reduction of blood flow during muscle contraction will result in a hypoxic environment distal to the restriction, where the degree of hypoxia will be determined by the pressure used to cause the restriction as well as the intensity of the muscle contractile activity distal to the restriction. The hypoxic environment induced by blood flow restriction leads to muscle and whole-body physiological adaptations that differ from free-flow exercise alone. The physiological adaptations resulting from BFRT are multiple and varied depending on, among other variables, the restriction protocols used, training modality and intensity (He et al., 2025). BFRT adaptations include a host of local effects in the restricted limb, including muscle growth, muscle strength, vascular adaptations, myokine, immune, and oxidative responses and effects on pain sensitivity, bone remodelling and tendon stiffness (Hjortshoej et al., 2023; Loenneke et al., 2025). Beyond the restricted limb, central effects have also been documented, including unique hormonal responses, cardiovascular effects and systemic effects that may alter orthostatic tolerance and cognitive function (Loenneke et al., 2025). Therefore, there may be a host of local and central adaptations dependent on the BFRT experimental conditions. BFRT protocols of particular interest include contracting limb muscles at low intensities/loads while restricting blood flow frequently and intermittently, with periods of hyperaemia in between bouts of restriction. Although results vary with the specific experimental protocols, BFRT with low-load/intensity resistance exercise simulates similar increases in muscle strength and muscle mass as would be achieved at high-load/intensity resistance training under free-flow conditions. The practicality of being able to train at lower load/intensities and yield similar muscular adaptational advantages to high-load/intensity training has garnered interest from both athletic (Pignanelli et al., 2021) and clinical communities. Thus, BFRT may serve as an alternative or supplement to traditional training to improve athletic performance and offer effective modified training opportunities for special populations and adaptive sport such as for para-athletes with biomechanical or muscular differences. BFRT could also serve athletes as a rehabilitative therapy to accelerate the successful return to sport after injury. The reduced joint stress of lowering the intensity and the load of training by using BFRT makes this strategy ideal for rehabilitation from musculoskeletal injuries, anterior cruciate ligament reconstruction, Achilles tendon repair, etc. Further, BFRT may confer the benefits of high intensity/load resistance exercise to special populations unable to work at high intensities; for example, use in the prevention of sarcopenia in the elderly, or as part of rehabilitative therapy for special patient populations with biomechanical or muscular limitations, degenerative joint disorders, cardiovascular and respiratory diseases and pathologies that result in exercise intolerance. Clearly, there are exciting possibilities for the athletic and clinical benefits of BFRT but the expansion of the utilization of BFRT will necessitate a more complete physiological and mechanistic understanding of the adaptations to determine the utility, safety and efficacy of this training modality. In this issue, Lavigne et al. (2025) significantly add to the understanding of the integrative physiological response and mechanistic adaptations to BFRT during moderate-intensity interval exercise. Lavigne et al. (2025) used an extensive battery of measurements to determine vascular, muscular, metabolic and neural adaptations to 6 weeks of dynamic knee-extensor training, one leg exercising with blood flow restriction and using the contralateral leg as a trained, free-flow control. They measured muscle contractile parameters including peak force, time to peak and half-relaxation time, fatigue, peak power and muscle metabolic respiratory capacity. They assessed central and peripheral fatigue, metaboreflex sensitivity and cardiovascular and respiratory adaptations including heart rate and blood pressure. They assessed vascular function including femoral artery diameter, blood flow, shear rate and vascular conductance, microvascular adaptations via reactive hyperaemia and vascular responses to muscle contraction, endothelial cell function via flow-mediated vasodilatation, and nitric oxide bioavailability via passive leg movement. This suite of assessments showed that BFRT in moderate-intensity interval training resulted in improvements in exercise capacity including an increase in peak power, longer time to task failure, as well as reduced peripheral fatigue development with no effect of BFRT on mitochondrial respiratory capacity. No changes in large vessel adaptation were observed but there were indications of differences in reactive hyperaemia and the vasodilatory response to muscle contraction, indicating local, intramuscular vascular adaptations. Blood pressure and heart rate responses were reduced following BFRT while the metaboreflex sensitivity was unchanged. The integrated interpretation of the results surmises that the attenuated cardiovascular responses were a result of the peripheral adaptations to BFRT, i.e. reduction in accumulation of metabolites due to local contractile and vascular adaptation, which reduced stimulation of the metaboreflex. Thus, the reduced heart rate and blood pressure responses may be tertiary effects resulting from primary changes in skeletal muscle contractile and vascular adaptations and secondary to alterations in metabolite production. Therefore, with moderate-intensity BFRT, peripheral skeletal muscle adaptations can occur while reducing stress on the cardiovascular system without an amplification of neural reflexes. This is the important ‘puzzle-piecing’ needed to understand the primary causal mechanisms of BFRT adaptations and secondary and tertiary integrated consequences that result. With this type of understanding, BFRT protocols could be adjusted in order to amplify specific desired beneficial effect and minimize undesirable deleterious effects depending on the training benefits desired, the patient population being treated and therapeutic results sought. Importantly, this study exemplifies the strength of the human model and integrated systems in order to the decipher the complex interplay between interconnected physiological mechanisms and capture emergent behaviours and complexity. This Perspective joins the chorus of voices in the BFRT field that advocates for a better understanding of the training adaptations to BFRT and advocates for the mechanistic and integrated systems approach that Lavigne et al. (2025) brings to this field. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. None declared. Sole author. C.L.M. is funded by the Natural Sciences and Engineering Research Council of Canada Due to the restrictions on the number of articles that can be cited in a Perspectives article, not all relevant literature has been cited.