Quantitative muscle MRI analysis of morphological changes induced by blood flow restriction training – a prospective pilot study

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Introduction Low-load blood flow restriction (BFR) resistance training is an innovative training method with equivalent increases in strength as traditional high-load resistance training. While immediate physiological changes have been described, biomarkers for BFR resistance training induced muscle morphology changes are needed to assess its effect mechanisms and safety in healthy and various patient populations. The aim of this pilot study is to identify quantitative magnetic resonance imaging (qMRI) biomarkers of BFR resistance training. Methods A prospective pilot study with 3 participants was conducted. Each participant received a 5-week knee extension training program, including 3 sessions per week. One leg was trained with BFR (60% limb occlusion pressure) using 6 sets until muscle failure at 40% of the repetition maximum (RM). The other leg was trained without BFR with 3 sets at 15RM. At baseline and at the end of the training program, qMRI of a 15 cm section of the thighs was acquired, including T2 mapping, DIXON, and diffusion-weighted imaging to assess oedematous tissue alterations, intramuscular fat fraction, and muscle architecture, respectively. QMRITools was used to process qMRI data. Results The volume-equated mean mechanical training load was 16676±2289 kg for the BFR and 16913±2775 kg for the non-BFR leg. Change from baseline in water T2 relaxation time (BFR: 0.33 ms [0.5%], non-BFR: 0.34 ms [0.9%]) and fat fraction (BFR: 0.09% [4%], non-BFR: -0.19% [–7%]) were within the measurement error. An increase in muscle volume (BFR: 421 ccm [31%], non-BFR: 430 ccm [30%]) and a decrease in fractional anisotropy (BFR: -0.01 [–5%], non-BFR: -0.008 [4%]) with stable mean diffusivity (BFR: -0.0004x10-3 mm2/s [–0.03%], non-BFR: -0.01x10-3 mm2/s [-0.8%]) and radial diffusivity (BFR: 0.005x10-3 mm2/s [0.4%], non-BFR: -0.003x10-3 mm2/s [0.2%]) were observed. Conclusion The BFR and non-BFR leg showed similar signs of hypertrophy in the M. quadriceps femoris without inflammatory processes, indicating a safe use of BFR resistance training in future studies and rehabilitation programs, as it achieves these results with lower individual joint loads. To evaluate the effect mechanisms of BFR resistance training, a sham-BFR group will be included in the full study. Adaptions to patients with hereditary or inflammatory neuromuscular disorders need to be evaluated carefully. Publication History Article published online: 24 November 2025 © 2025. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany

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