Differential muscle hypertrophy and edema responses between high‐load and low‐load exercise with blood flow restriction

We sought to determine whether early increases in cross‐sectional area (CSA) of different muscles composing the quadriceps with low‐load resistance training with blood flow restriction (LL‐BFR) were mainly driven by muscle hypertrophy or by edema‐induced swelling. We also compared these changes to those promoted by high‐load resistance training (HL‐RT). In a randomized within‐subject design, fifteen healthy, untrained men were submitted to magnetic resonance imaging (MRI) for CSA and edema‐induced muscle swelling assessment (fast spin echo inversion recovery, FSE‐STIR). MRI was performed in LL‐BFR and HL‐RT at baseline (W0) and after 3 weeks (W3), with a further measure after 6 weeks (W6) for HL‐RT. Participants were also assessed at these time points for indirect muscle damage markers (range of motion, ROM; muscle soreness, SOR). CSA significantly increased for all the quadriceps muscles, for both LL‐BFR and HL‐RT at W3 (all P < .05) compared to W0. However, FSE‐STIR was elevated at W3 for all the quadriceps muscles only for HL‐RT (all P < .0001), not LL‐BFR (all P > .05). Significant increases and decreases were shown in SOR and ROM, respectively, for HL‐RT in W3 compared to W0 (both P < .05), while these changes were mitigated at W6 compared to W0 (both P > .05). No significant changes in SOR or ROM were demonstrated for LL‐BFR across the study. Early increases in CSA with LL‐BFR seem to occur without the presence of muscle edema, whereas initial gains obtained by HL‐RT were influenced by muscle edema, in addition to muscle hypertrophy.