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Assessment of loaded squat jump height with a free-weight barbell and Smith machine

comparison of the take-off velocity and flight time procedures

Pérez-Castilla, Alejandro1; McMahon, John J.2; Comfort, Paul2; García-Ramos, Amador1

The Journal of Strength & Conditioning Research: July 31, 2017 - Volume Publish Ahead of Print - Issue - p
doi: 10.1519/JSC.0000000000002166
Original Research: PDF Only

The aims of this study were to compare the reliability and magnitude of jump height between the two standard procedures of analysing force platform data to estimate jump height (take-off velocity [TOV] and flight time [FT]) in the loaded squat jump (SJ) exercise performed with a free-weight barbell and in a Smith machine. Twenty-three collegiate men (age 23.1 ± 3.2 years, body mass 74.7 ± 7.3 kg, height 177.1 ± 7.0 cm) were tested twice for each SJ type (free-weight barbell and Smith machine) with 17, 30, 45, 60, and 75 kg loads. No substantial differences in reliability were observed between the TOV (Coefficient of variation [CV]: 9.88%; Intraclass correlation coefficient [ICC]: 0.82) and FT (CV: 8.68%; ICC: 0.88) procedures (CV ratio: 1.14), while the Smith SJ (CV: 7.74%; ICC: 0.87) revealed a higher reliability than the free-weight SJ (CV: 9.88%; ICC: 0.81) (CV ratio: 1.28). The TOV procedure provided higher magnitudes of jump height than the FT procedure for the loaded Smith machine SJ (systematic bias: 2.64 cm; P<0.05), while no significant differences between the TOV and FT procedures were observed in the free-weight SJ exercise (systematic bias: 0.26 cm; P>0.05). Heteroscedasticity of the errors was observed for the Smith machine SJ (r2: 0.177) with increasing differences in favour of the TOV procedure for the trials with lower jump height (i.e. higher external loads). Based on these results the use of a Smith machine in conjunction with the FT more accurately determine jump height during the loaded SJ.

1 Department of Physical Education and Sport, Faculty of Sport Sciences, University of Granada, Granada, Spain.

2 Directorate of Sport, Exercise and Physiotherapy, University of Salford, Salford, UK

Corresponding author: Amador García-Ramos, Faculty of Sport Sciences, University of Granada, Ctra. Alfacar, s/n, 18011, Granada (Spain), Phone: (+34) 677815348, Fax: (+34) 958244369, E-mail:

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