Reliability of the two-point method applied in field conditions and its validity in estimating the one-repetition maximum using the load–velocity relationship of the free-weight back squat

In most studies examining the reliability and validity of the load-velocity relationship (LVR) determined with the two-point method, a pair of points derived from a previously applied protocol involving multiple loads is selected to compute the relationship (multipoint method-MP). While testing only two loads (two-point applied in field conditions-2P_FC) allows for a reliable free-weight back squat LVR determination, it is not known whether the average optimal minimum velocity threshold enables accurate one-repetition maximum (1RM) estimations. LVRs based on the 2P_FC were compared to those obtained with the MP, in 18 participants. Reliability of LD0 (load at zero velocity), slope, V0 (velocity at zero load), and Aline (area under the line) determined with the 2P_FC was assessed with intraclass correlation coefficients (ICCs) and coefficients of variation (CVs). Absolute percent errors of estimation were compared between MP and 2P_FC. Agreement between actual and predicted 1RM was assessed with Bland-Altman plots. LVR parameters were similar between profiling methods. The 2P_FC showed acceptable reliability (CVs < 10% and ICCs > 0.70). The absolute percent error of estimation was lower with the 2P_FC (6.7% and 4.6%, for MP and_. 2P_FC respectively). Coaches can determine the LVR of their athletes and further estimate their 1RM relying on the average optimal MVT (with small error < 5%). This can be done by simply measuring mean concentric velocity in response to a practical protocol of two loads. However, caution is advised, as this method may misestimate the 1RM by 14 kg in some individual cases.