# Calculating Vertical Jump Height Using Video

The vertical jump is one of the best tests of an athlete's power output. Its is an integral part of many track and field disciplines as well as ball sports such as basketball and volleyball. This article will explain how to measure vertical jump height using recorded video.

This is one of many methods available for measuring vertical jump height - see the discussion and list of available methods.

Measuring vertical jump height using video is possible because jump height is a function of the time between take-off and landing (hang time). Using video, one can determine the hang time by subtracting the timestamp of the takeoff from the timestamp of the landing. Then, once hang time is known, the jump height is calculated using the following function:

Vertical Jump height = 0.5 x 9.81 m/s2 x (hang time / 2 )2

## Physics of the vertical jump

To understand the formula above we have to take a look at the physics of a vertical jump. To reach a maximum jump height an athlete tries to vertically accelerate his body as fast as possible. Once the jumper leaves the ground it is not possible to further increase velocity and therefore jump height is predetermined at this point.

Starting with the takeoff, the acceleration of earth gravity will slow down the movement of the jumper until velocity reaches zero at the peak of the jump. After that, the downward motion will be accelerated by gravity until landing. Therefore a vertical jump consists of two phases, the ascending phase and the descending phase.

It can be shown that both of these phases take the same time, with the peak of the jump happening at exactly the midpoint of hang time. The following graph shows the plane of flight of an athlete:

Graph: Plane of flight of a vertical jump

The graph shows that the downward movement of the jump takes half of the overall time of the jump and velocity at the peak of the jump is zero. Therefore it is easiest to calculate the jump height by identifying the distance travelled by a physical body which is accelerated by earth gravity for a time which is equal to half the measured hang time:

distance travelled = initial velocity * time + ½ acceleration * time2

==> 0 + ½ * 9.81 m/s2 (hang time / 2)2

(* with 9.81 m/s2 being the earth acceleration which is almost constant on the earth surface)

## How to ensure accurate analysis

To ensure accuracy of the video analysis one has to bear in mind:

• The jumper should not land with bent knees as this would artificially increase hang time and therefore bias the results.
• The frame rate (amount of unique pictures per second) of the video should be as high as possible to ensure a precise measurement of hang time.

This post is a guest article by www.whatsmyvertical.com. This web page offers a video tool to assess the height of any given video-recorded jump.

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