Optimal two-point loading strategy for accurate leg press force-velocity assessment

Accurate assessment of an individual force-velocity (F-V) profile is essential for prescribing targeted resistance training; however, F-V outcomes depend strongly on the testing method used. This study examined the concurrent validity of the F-V relationship in a horizontal leg press exercise by comparing two-point methods, which use pairs of different loads relative to body weight, with a multiple-point method using a wider range of loads. Sixteen men (mean ± SD, age: 20.0 ± 1.4 years, height: 172.4 ± 6.3 cm, body mass: 69.2 ± 7.6 kg) performed maximal-effort horizontal dynamic leg press actions on a device equipped with pneumatic artificial muscles (ddrobotec®, Switzerland) against eleven external loads (100%-300% of body weight [BW] in 20% increments). The F-V relationship was obtained using 10 two-point methods that paired a 100% BW load with each of the additional loads (120%-300% BW) and also from all points. The F-V relationship parameters were compared between the two-point methods and the multiple-point method, and their correlations were analyzed. The results showed that the F-V relationship obtained from the four two-point methods with wider load differences (100% and 240%, 100% and 260%, 100% and 280%, and 100% and 300% BW) was nearly perfectly correlated with that by the multiple-point method (r = 0.906 to 0.993). The concurrent validity of the F-V relationship parameters obtained from the two-point methods tended to decrease when using loads that were closer together (e.g., 100% and 120% BW) than loads with a larger difference (e.g., 100% and 240% BW). These findings indicate that, on a horizontal leg press with pneumatic artificial muscles, a two-point method based on sufficiently distinct loads can provide an accurate estimate of the F-V relationship and may be a practical alternative to comprehensive multi-load testing.