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Med Sci Sports Exerc. 2019 Nov 1. doi: 10.1249/MSS.0000000000002197. [Epub ahead of print]

A Joint Power Approach to Define Countermovement Jump Phases Using Force Platforms.

Author information

1
Department of Kinesiology & Sport Management, Texas Tech University, Lubbock, TX.
2
Department of Exercise Science and Pre-Health Professions, Creighton University, Omaha, NE.
3
School of Health Studies, The University of Memphis, Memphis, TN.

Abstract

Conflicting methodologies are used to define certain countermovement vertical jump (CMVJ) phases, which limits identification of performance-enhancing factors (e.g., rate of force development).

PURPOSE:

We (a) utilized a joint power approach to define CMVJ phases that accurately describe body weight unloading (i.e., unweighting) and eccentric (i.e., braking) actions, which were combined with the robustly-defined concentric (i.e., propulsion) phase, and (b) determined whether the phases can be identified using only ground reaction force (GRF) data.

METHODS:

Twenty-one men performed eight maximal CMVJs while kinematic and GRF data were obtained. Hip, knee, and ankle joint powers were calculated using inverse dynamics. The net sum of the joint powers (JPSUM) was calculated to define phases by the preeminence of negative (i.e., net eccentric actions) or positive (i.e., net concentric actions) power where appropriate. Unloading, eccentric, and concentric phases were identified using JPSUM and linked to GRF and center of mass (COM) velocity features.

RESULTS:

Bland & Altman plots of the bias and 95% confidence intervals for the limits of agreement (LOA), intra-class correlation coefficients (ICC), and coefficients of variation (CV) indicated precise agreement for detecting the unloading (bias: 0.060 s; LOA: -0.110 to 0.229 s) and eccentric (bias: 0.012 s; LOA: -0.010 to 0.040 s) phases with moderate (ICC: 0.578; CV: 40.72%) and excellent (ICC: 0.993; CV: 2.18%) reliability, respectively. The eccentric phase should be divided into yielding (eccentric actions while accelerating downward) and braking (eccentric actions while decelerating downward) sub-phases for detailed assessments.

CONCLUSION:

CMVJ phases defined by combining joint and COM mechanics can be detected using only force platform data, enabling functionally relevant CMVJ assessments using instrumentation commonly available to practitioners.

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