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

Area of Science:

• Biomechanics
• Human Movement Analysis
• Sports Science

Background:

• Standardized definitions for countermovement vertical jump (CMVJ) phases are lacking, hindering the identification of key performance-enhancing factors like rate of force development.
• Existing methodologies for defining CMVJ phases are inconsistent, limiting detailed analysis of jump mechanics.

Purpose of the Study:

• To define countermovement vertical jump (CMVJ) phases using a joint power approach, specifically identifying body weight unloading and eccentric (braking) actions.
• To determine if these defined CMVJ phases can be reliably identified using only ground reaction force (GRF) data.

Main Methods:

• Utilized a joint power approach, calculating hip, knee, and ankle joint powers from inverse dynamics and joint angular velocities.
• Defined CMVJ phases (unloading, eccentric, concentric) based on the net sum of joint powers (JPSUM) and linked them to GRF and center of mass velocity.
• Obtained kinematic and GRF data from 21 male participants performing maximal CMVJs.

Main Results:

• The unloading and eccentric phases of the CMVJ were precisely identified using the JPSUM method.
• Reliability for detecting the unloading phase was moderate (ICC, 0.578), while the eccentric phase showed excellent reliability (ICC, 0.993).
• The eccentric phase can be further divided into yielding and braking subphases for more detailed analysis.

Conclusions:

• Countermovement vertical jump (CMVJ) phases, defined by integrating joint and center of mass mechanics, are detectable using solely force platform (GRF) data.
• This approach enables functionally relevant CMVJ assessments with commonly available equipment for practitioners.
• The proposed method offers a reliable and practical way to analyze CMVJ mechanics and identify performance-enhancing factors.