Feasibility of the 2-point method to determine the load−velocity relationship variables during the countermovement jump exercise

Purpose: This study aimed to examine the reliability and validity of load−velocity (L–V) relationship variables obtained through the 2-point method using different load combinations and velocity variables. Methods: Twenty men performed 2 identical sessions consisting of 2 countermovement jumps against 4 external loads (20 kg, 40 kg, 60 kg, and 80 kg) and a heavy squat against a load linked to a mean velocity (MV) of 0.55 m/s (load_0.55). The L–V relationship variables (load-axis intercept (L₀), velocity-axis intercept (v₀), and area under the L–V relationship line (A_line)) were obtained using 3 velocity variables (MV, mean propulsive velocity (MPV), and peak velocity) by the multiple-point method including (20–40–60–80–load_0.55) and excluding (20–40–60–80) the heavy squat, as well as from their respective 2-point methods (20–load_0.55 and 20–80). Results: The L–V relationship variables were obtained with an acceptable reliability (coefficient of variation (CV) ≤ 7.30%; intra-class correlation coefficient ≥ 0.63). The reliability of L₀ and v₀ was comparable for both methods (CV_ratio (calculated as higher value/lower value): 1.11–1.12), but the multiple-point method provided A_line with a greater reliability (CV_ratio = 1.26). The use of a heavy squat provided the L–V relationship variables with a comparable or higher reliability than the use of a heavy countermovement jump load (CV_ratio: 1.06–1.19). The peak velocity provided the load–velocity relationship variables with the greatest reliability (CV_ratio: 1.15–1.86) followed by the MV (CV_ratio: 1.07–1.18), and finally the MPV. The 2-point methods only revealed an acceptable validity for the MV and MPV (effect size ≤ 0.19; Pearson's product-moment correlation coefficient ≥ 0.96; Lin's concordance correlation coefficient ≥ 0.94). Conclusion: The 2-point method obtained from a heavy squat load and MV or MPV is a quick, safe, and reliable procedure to evaluate the lower-body maximal neuromuscular capacities through the L–V relationship.