Vertical Jump WK7

Introduction

  • Vertical jump, specifically the countermovement jump (CMJ), is a common method for assessing neuromuscular capacity.

  • CMJ is easy to control, requires minimal familiarization, and provides information about neuromuscular and stretch-shortening cycle (SSC) function.

  • The chapter focuses on factors to consider for valid and reliable CMJ results.

Equipment

  • Factors influencing equipment choice: data interests, equipment access, and required speed of information.

  • "Gold standard" is the force platform but field-based methods are also available.

Force Platform

  • Measures ground reaction force (GRF) using strain gauges or piezoelectric sensors based on Newton’s Law of Reaction.

  • Measures GRF in three directions (vertical, anterior-posterior, and medio-lateral); vertical GRF is typically the main interest for CMJ.

  • Portable force platforms are validated against in-ground platforms.

  • Considerations for force platform setup:

    • Flat surface

    • Proper cable connection

    • Software connectivity

    • Calibration

    • Suitable sample frequency and duration

    • Zeroing

  • A minimum sample frequency of 1000 Hz is recommended.

Field-Based Equipment

  • Alternative equipment to force platforms are categorized by their method of quantifying CMJ performance (jump height).

  • Practitioners should be aware of the limitations of using jump height alone.

Protocols

  • Protocols influence collected data and CMJ performance data quality.

  • Key factors to control:

    • Arm swing

    • Body position before command

    • Verbal instructions

    • Landing position

  • Multiple trials reduce random errors.

Arm Swing

  • Arm swing has minimal effect on CMJ variable reliability.

  • CMJ height is generally higher with arm swing due to increased lower extremity work.

  • Unless there's a specific rationale (e.g., for volleyball athletes), avoid arm swing to improve data reliability.

Starting Position

  • Stand upright, arms akimbo or holding a dowel, feet hip-shoulder width apart.

  • Remain still for at least 1 second before jumping when collecting force-time data.

  • With a linear position transducer (LPT), "zero" COM take-off height in a fully plantar flexed position before adopting the starting position.

Countermovement Technique

  • Considerations: movement speed and depth (displacement).

  • Encourage preferred countermovement depth for reliability and quantification of natural jump strategy.

  • Athletes should perform the countermovement as quickly as possible to initiate the SSC.

Jump Technique

  • The jump phase should be performed as fast as possible, aiming for maximal jump height to increase COM velocity at take-off.

Landing Position

  • When using field-based equipment, athletes should avoid flexing hips, knees, and ankles during the flight phase and at touchdown.

  • Instruct athletes to