Validity of a Linear Velocity Transducer for Testing Maximum Vertical Jumps

in Journal of Applied Biomechanics
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This study aimed to examine the validity of mechanical variables obtained by a linear velocity transducer from the unconstrained and constrained squat jump (SJ). Twenty-three men were tested on the unconstrained SJ and the SJ constrained by a Smith machine. Maximum values of force, velocity, and power were simultaneously recorded both by a linear velocity transducer attached to a bar of mass of 17, 30, 45, 60, and 75 kg and by a force plate. Linear velocity transducer generally overestimated the outcomes measured as compared to the force plate, particularly in unconstrained SJ. Bland-Altman plots revealed that heteroscedasticity of errors was mainly observed for velocity variables (r 2 = .26–.58) where the differences were negatively associated with the load magnitude. However, exceptionally high correlations were observed between the same outcomes recorded with the 2 methods in both unconstrained (median r = .89 [.71–.95]) and constrained SJ (r = .90 [.65–.95]). Although the systematic and proportional bias needs to be acknowledged, the high correlations between the variables obtained by 2 methods suggest that the linear velocity transducer could provide valid values of the force, velocity, and power outputs from both unconstrained and constrained SJ.

Pérez-Castilla, Feriche, Padial, and García-Ramos are with the Department of Physical Education and Sport, Faculty of Sport Sciences, University of Granada, Granada, Spain. Jaric is with the Department of Kinesiology and Applied Physiology & Biomechanics and Movement Science Graduate Program, University of Delaware, Newark, DE. García-Ramos is also with the Faculty of Education, Catholic University of the Most Holy Conception, Concepción, Chile.

Address author correspondence to Amador García-Ramos at amagr@ugr.es.
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