Individual load-velocity relationship “in situ”: a novel approach for the characterization of muscle function and 1 R.M. estimation.

Purpose The “traditional” load-velocity(L-V) relationship profiling and 1 R.M. estimation require multiple loads, which limits their applicability. We tested the feasibility and validity of an alternative "in situ" L-V profiling method using lifting velocities of simulated training sessions. Method We retrospectively analyzed a publicly available dataset on 51 resistance-trained individuals who performed: direct 1 R.M. measures, “traditional” L-V profiling test, and simulated training sessions during which “in situ” individual weight and velocity were recorded. Theoretical maximal load (L ₀ ), movement velocity (V ₀ ), regression slope (LV _slope ), goodness of fit (R ² ), and estimation of 1 R.M. were computed and compared between “traditional” and “in situ” methods. Both 1RM predictions were compared vs the directly measured 1RM. Results 1 R.M. and V _1RM mean values were 128 ± 37.6 kg and 0.35 ± 0.08 m•s ^− 1 , respectively. L ₀ , V ₀ , LV _slope , R ² , and 1 R.M. estimations were not different (p > 0.05) between L-V profiling methods. Moreover, both estimates of 1R.M. showed no significant difference (p > 0.05), extremely high correlation (r ≥ 0.97), and not significant bias ( _trad L-V, bias = 1.7 kg, precision = 9.7kg, p > 0.05; _{in situ} L-V, bias = 0.7 kg, precision = 7.6kg, p > 0.05; ) vs the directly measured 1R.M.. Conclusions In adult recreational lifters, the “in situ” L-V profiling is a feasible and valid method for the characterization of muscle function; it represents a safe and time-efficient alternative to “traditional” L-V profiling and direct 1 R.M. determination in the free weight barbell back squat exercise.