Magnitude and reliability of mechanical outputs obtained during loaded squat jumps performed from different knee angles

This study aimed to explore the effect of the knee angle and loading condition on the magnitude and reliability of squat jump (SJ) performance variables. Thirteen male sport sciences students performed in a random order 4 SJ types (knee angle of 80o [SJ80], 90o [SJ90], 100o [SJ100], and self-preferred [SJ(pref)]) against 3 external loads. The push-off distance (HpO), jump height (Hmax), maximum force (Fmax) and maximum power (Pmax) were obtained from force platform recordings. The HpO during the SJ(pref) (43.4 +/- 6.4 cm) was always between SJ90 (44.3 +/- 4.8 cm) and SJ100 (40.5 +/- 4.2 cm). The magnitudes of Hmax, Fmax and Pmax were comparable or higher during the SJ(pref). The increase of the knee angle was associated with larger values of Fmax and Pmax, but no significant differences were observed for Hmax. An acceptable reliability was observed for HpO (coefficient of variation [CV]<= 5.09% and intraclass correlation coefficient [ICC]>= 0.78), Hmax (CV <= 6.06% and ICC >= 0.84), Fmax (CV <= 3.25% and ICC >= 0.96) and Pmax (CV <= 2.93% and ICC >= 0.96). Reliability did not systematically differ between the 4 SJ types. In conclusion, the higher magnitudes and comparable reliability of the performance variables obtained during the SJ(pref) support its use for testing lower-body ballistic performance against different loads.