Explaining the Variance in Repetitions-In-Reserve After Low-Load Blood Flow Restricted Resistance Exercise.

Davids, CJ, Vasiljevic, I, Katsifolis, A, Suppiah, H, James, LP, and Scott, BR. Explaining the variance in repetitions-in-reserve after low-load blood flow restricted resistance exercise. J Strength Cond Res XX(X): 000-000, 2025-Low-load resistance exercise with blood flow restriction (LL-BFR) is prescribed using standardized protocols (e.g., 30, 15, 15, 15 repetitions at 20-40% 1-repetition maximum). However, considerable variance exists in proximity to muscular failure under these guidelines, potentially affecting the adaptive stimulus. This study aimed to evaluate the variability in LL-BFR performance and identify factors influencing this variance. In addition, the accuracy of a subjective autoregulation strategy was evaluated during LL-BFR. Twenty recreationally active adults (12 men, 8 women) completed a leg press LL-BFR protocol, a local muscular endurance (LME) task, and conditioned pain modulation (CPM) assessments. Results revealed significant interindividual differences in the number of additional repetitions completed beyond the prescribed 15 repetitions in the final set of LL-BFR (19 ± 12, range 4-47). Local muscular endurance capacity (r = 0.63, p = 0.003) and relative CPM response (r = 0.50, p = 0.026) were key predictors of this variance, explaining 56% of the variability. In addition, subjects tended to underestimate repetitions-in-reserve (RIR) during LL-BFR (RIR error: 12 ± 11), reducing the accuracy of subjective autoregulation strategies. These findings suggest that higher LME and greater pain modulation capacity allow individuals to complete more repetitions before failure, resulting in a heterogeneous stimulus when using fixed LL-BFR protocols. Practitioners should consider LME and pain modulation when prescribing LL-BFR and may need to adjust loads or repetitions to ensure proximity to failure. Autoregulation using RIR should be applied cautiously, with predictions made closer to task failure for accuracy.