The Effect of Initial Knee Angle on Concentric-Only Squat Jump Performance

Abstract

For young physically active adult men, the use of a self-selected depth in the SJ results in optimal performance and has only a trivial difference to a constrained knee angle of either 90° or 100°.

Knowledge of results during vertical jump testing: an effective method to increase the performance but not the consistency of vertical jumps

“…The magnitude of the mechanical variables was reported to be similar or higher when selecting self-preferred knee angles compared to a standardised knee angle for both SJs and CMJs. Indeed, it has been reported that both SJ and CMJ performance is affected by the position at the beginning of the propulsion phase (Gheller et al, 2015;McBride et al, 2010;Mitchell et al, 2017;Petronijevic et al, 2018). For example, Gheller et al (2015) and Janicijevic et al (2019) observed higher values of peak power, but not peak force, for the SJ pref compared to the SJ90.…”

“…The initial position has been commonly standardised at a fixed knee angle of 90º (Duthie et al, 2002;Impellizzeri et al, 2007;Skurvydas et al, 2000). However, recent studies have suggested that a self-preferred starting position can be reliably used to simplify the vertical jump testing procedure (Janicijevic et al, 2019;Mitchell et al, 2017;Petronijevic et al, 2018). Of note is that participants only receive one instruction when they self-select the initial knee angle (e.g., 'jump as high as possible'), but two instructions when the initial position is standardised (e.g., 'meet a 90º knee angle' and 'jump as high as possible').…”

“…Of note is that participants only receive one instruction when they self-select the initial knee angle (e.g., 'jump as high as possible'), but two instructions when the initial position is standardised (e.g., 'meet a 90º knee angle' and 'jump as high as possible'). Most of the studies that have compared the standardised and self-preferred initial positions have used the SJ since it is easier to strictly control the initial knee angle (Argus & Chapman, 2014;Janicijevic et al, 2019;Mitchell et al, 2017;Petronijevic et al, 2018). For example, Janicijevic et al (2019) showed that the mechanical outputs (i.e., maximal jump height [Hmax], peak power [Pmax] and peak force [Fmax]) can be obtained with a comparable or higher magnitude and reliability when the SJ is performed from the self-preferred knee angle (SJ pref ) compared to the SJ performed from a fixed initial knee angle (e.g., SJ from a 90º knee angle; SJ90).…”

The prediction of swim start performance based on squat jump force-time characteristics

“…Participants started in an upright standing position with their hands on their hips. They were then instructed to adopt a squat position using a self-selected depth that was held for 3 s before they attempted to jump as high as possible (Mitchell et al, 2017). A self-selected squat depth was chosen as it has been reported to produce the greatest jump height and higher peak force outputs in comparison to measured squat depths (Kirby et al, 2011).…”

Peer Review #1 of "The prediction of swim start performance based on squat jump force-time characteristics (v0.1)"

“…Participants started in an upright standing position with their hands on their hips. They were then instructed to adopt a squat position using a self-selected depth that was held for 3 seconds before they attempted to jump as high as possible (Mitchell et al 2017). A self-selected squat depth was chosen as it has been reported to produce the greatest jump height and higher peak force outputs in comparison to measured squat depths (Kirby et al 2011).…”