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

ABSTRACT

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.

KEYWORDS:

• Ballistic performance
• push-off distance
• jump height
• maximum force
• maximum power

Acknowledgments

The present study was conducted under the supervision of Prof. Slobodan Jaric, who passed away during the writing process of this paper. We wish to thank Prof. Slobodan Jaric for inspiring our past, present and future research work.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially supported by the grants 175037 and 175012 from the Ministry of education, science and technological development of Republic of Serbia, by the University of Granada under a post-doctoral grant (perfeccionamiento de doctores) awarded to AGR, and by the Spanish Ministry of Education, Culture and Sport under a pre-doctoral grant (FPU15/03649) awarded to APC.