Measuring Michael Jordan's 1987 Slam Dunk Contest Vertical Leap

Comparing the vertical leap of past winners of the slam dunk contest would give us great insight into who really has the best dunk. So time for a Video Analysis of Sports Vertical Leap Dunk Off.

Last week we discussed how we could use broadcast footage of the slam dunk contests to measure the vertical leap of each player during the dunk. We looked at Vince Carter's 2000 Slam Dunk Contest win and estimated that his vertical leap was about 37.6 inches. see Measuring Vertical Leap at a NBA Slam Dunk Contest

The above story was picked up by Patrick at givemetherock.com, who said "I would love to see how other dunks measure up".

The original plan for last weeks article was to use video of Michael Jordan's dunk from the free throw line in his 1987 Slam Dunk contest win. However Carter's dunk from 2000 gave us a better example. To measure the vertical leap from broadcast footage of the slam dunk contest we needed one view and image from the video that contained 4 elements. 1. A full view of the player, 2. a view of the underside of the backboard, 3. the basketball rim and 4. the floor below the backboard. All 4 of these features need to be in the image.

GiveMeTheRock.com want to see how other dunks measure up so I went back to YouTube to try and find better footage of Jordan in 1987.

Although the dunk from the free throw line is iconic, it may not be the dunk in which Jordan obtained his maximum vertical leap, because for this dunk he needed to cover the distance from the free throw line to the basket and therefore height was less important. During the same slam dunk contest though, Jordan completes a sideways dunk which scores him a perfect score of 50.

This dunk required Jordan to get higher to complete, so lets use this one to compare his vertical leap to Vince Carter's 37.6 inch leap in 2000.

Here is the video. Jordan's sideways dunk can be seen at about 1:59 for his highest point and the dunk from the free throw line can be seen later on.



Assuming his highest point is at 1:59 in the video, we take a snap shot and then use our known measurements. This time we do not need to use the width of the backboard because we have a side on view that allows us to measure the distance from the rim to the ground:

1. Height of the rim is 120 inches above the ground.
2. Michael Jordan is listed at 6 foot 6 inches or 78 inches.
3. Hip height of a standard man is approximately 53% of his total height. Therefore Jordan's hip height is about 41.3 inches.

These measures are ideal for making a comparison between Carter's vertical leap and Jordan's. The fact that they are of the same height, 6 foot 6 inches, allows us to ignore any height advantage. As an example Nate Robinson needs to have a higher vertical leap than Dwight Howard to make a dunk, for the simple reason that he is much shorter. In our comparison both players are the same height and therefore they both require the same vertical leap to make the dunk. In a slam dunk contest it is not only about making the dunk and this is why we are interested in comparing their vertical leaps during the dunk.

Lets look at the image at 1:59 and the measures we can make.

Because it is difficult to make out the backboard we chose to use the height of the rim above the floor for our scale measure. We know this height is 10 feet or 120 inches. We draw the blue line down from the rim to the floor and give it the scale we desire 120 inches.

Now we can measure how high Jordan's hips are above the ground. This measure at 83.88 inches (yellow line). Subtract Jordan's standing hip height of 41.3 inches from this measure of his hip height at the top of the dunk and we get an amazing 42.6 inches or 6 inches (half a foot) higher than Carter's hip height in the 2000 slam dunk contest.

Of course the different angles of the cameras and footage and the differences in how the vertical leap measurements were made (not using the backboard for scaling in this image but using it for Vince Carter's dunk) means that inaccuracies will still exist. However a quick look through the literature and some past studies of Jordan at his best suggest that he could regularly jump 42 inches during a one handed dunk.

We will therefore assume our measure of Jordan's 1987 dunk to be a good estimate and based on the 2000 video footage of Carter's dunk we will assume that our measure of 37.6 inches is a good estimate of vertical leap for his dunk.

There is no doubt then that Jordan wins this video analysis of sports dunk off. Anyone think they have footage of a dunk with a vertical leap that can top Jordan's?

Measuring Vertical Leap at a NBA Slam Dunk Contest

The Slam Dunk contest at the NBA All Star event is usually spectacular. Dwight Howard flying with his Superman cape is a great highlight. Slam dunks are all about getting up high and we want to know how high they jump?

Recently a reader of this website asked whether he could measure the vertical leap of winners of past slam dunk contests from NBA footage of the event, including Michael Jordan's leap from the free throw line in 1987. Unfortunately in a basketball broadcast the camera and usually cameras are often moving, panning or zooming to catch the best view of the player, particularly during a dunk. Analyzing the vertical leap from this footage can be tricky.

The answer to the readers question depends a lot on the video footage that is analyzed, but here are a few basics of video analysis and some ideas of how the vertical leap height may be measured from the footage.

1. Camera angle and view needs to be good to make useful measures of heights (see Video Analysis 101 ). Most footage of the slam dunk contests used multiple cameras and they were often zoomed in at just the wrong time, making this difficult.
2. We only need one image of the player at the peak of his jump to measure vertical leap, but we will also require some scaling so that we can convert the pixels in the image into a real measurement of height. To do this we need to have a single image that includes the player, the bottom of the backboard, the rim and the floor directly underneath the backboard. With all these in one frame of the footage we can make a measure.
3. We will also want to know the height of the player so that we can use this height to estimate their vertical leap. We will measure the height of the jump and subtract the players standing height to get a measure of their jump.
4. Even if all the information is available to us to make the measure, it will still be an estimate as the camera angle may be slightly off and this will make our measure less accurate.

Would this method in fact work?  We can try to analyze a slam dunk contest from 2000 and Vince Carter winning with some serious air. Check out the video below:



From this video we can grab a snapshot of the action at 1:44 in the video and do some measures. First we needed to know some standard basketball measures.

1. Width of the backboard is 72 inches
2. Height of the bottom of the backboard is 114 inches above the ground
3. Vince Carter is listed at 6 foot 6 inches or 78 inches
4. Hip height of a standard man is approximately 53% of his total height. Therefore Carter's hip height is about 41.3 inches.

Now we can make some measures of Carters vertical leap height. This footage has a graphic that measures his jump height at 37 inches. We will use this as a measure to see how well we can do at measuring the jump height using our estimates and video analysis. See the image below:

In the image we can see the following measures:

1. We know that the width of the backboard is 72 inches. We have drawn a green line along the bottom margin of the backboard and used this known distance to scale all our other measures.
2. Next we used the blue line to draw a vertical from the bottom of the backboard to the ground. We know this should be 114 inches. Unfortunately as our scale comes from the width of the back board (green line) we couldn't get it to measure exactly 114 inches with our estimates, but we are close at 114.19 inches.
3. Finally we measure Vince Carter's hip height at the top of his jump and with the yellow line. Here we needed the line to go from the floor at the same height as the blue line to Carters hips. We estimate his hip height at 78.9 inches or 6.575 feet which is almost his head height.
4. We can also notice that the camera is not perfectly horizontal with the backboard. We can see that the backboard is not perfectly horizontal accross the screen, although it is close. This angle may reduce the accuracy of our other measures.

Finally we can estimate Carter's maximum vertical leap from this video footage and for this particular dunk. We know his standing hip height is estimated at 41.3 inches and we estimated his hip height at the peak of the jump for the dunk at 78.9 inches. We subtract the standing hip height from the jump height and we get 37.6 inches.

If the measure shown during the broadcast at 37 inches is accurate then our estimate is pretty good and we  can probably try to do the same measures on other broadcast footage of slam dunk contests. All we need is one image with a view of the backboard, the player and the floor below the backboard as well as knowledge of the dimensions of the basketball backboard and height of the player.

We are always interested to hear about your video analysis projects or hear your comments. We are also available to consult to all our readers on their video analysis and biomechanics needs.  

Measuring Your Vertical Leap Using Video Analysis

Before Kobe Bryant or Dwight Howard was considered for a contract in the NBA, they likely had to undergo a series of physical tests and exercises. In fact, most if not all professional and college sports programs require prospective players to complete these "combines", so that they can have a quantifiable way to compare the athletes. Some of the commonly used tests include the 40 yard dash, bench press, and vertical leap. For players in the NBA, the vertical leap test is the most crucial.

The vertical leap test demonstrates how high a player can jump and reach. Ideally, the test shows how high the athlete's center of mass (COM) moves. But since a person's COM is often difficult to determine, the test usually estimates the results by measuring the difference between how high a subject can reach from a standing position, and how high the subject can reach when they jump (either from a stationary or running start). One variation of this test is to simply see how high the athlete can jump and reach. While this latter method measures the maximum height the athlete can touch, it doesn't provide us with how high he/she actually jumped. In simple terms a player with an 9' reach, jumping 1' will reach 10'. A player with a 7' reach, jumping 3' will also reach 10', although it is obvious that the 7' player jumped higher. Simply measuring how high the subject can reach from a standing position before they jump, gives us the additional information needed to calculate how high the athlete jumped.

Professional and college organizations often conduct this test by having the athlete stand next to a tall pole that has little plastic flags extending from it, as shown below. The athlete then jumps and swipes the highest flags he can, and the result is recorded.

If you want to measure your own vertical leap but don't have access to one of these testing devices, you can simply film yourself jumping from a standing position. Besides the basic principles of video analysis (see http://videosportsanalysis.blogspot.com/2009/03/video-analysis-of-sports-101.html), there are two important concepts to keep in mind:

1. In your video clip, you must be able to see an object of known height. This object should also be in the same vertical plane the subject is jumping in. If you're jumping next to a wall, marking a known height on the wall should be good enough. The reason you need to have this information is so the analysis software can scale the distance measurement appropriately (this concept will be shown on the video below).
2. The video analysis software you're using must be able to calculate the distance between two points and be able to use the known height of the object to calibrate the measured distance accordingly; otherwise, the distance between the two points will simply be in units of pixels, which isn't very useful. We need to be able to convert the distance to something like inches or centimeters. If you're interested in finding out more about software packages that offer this type of feature, just let us know and we'll be happy to point you in the right direction.

Below we have a video clip of a subject performing the vertical leap test:



As you can see, we have one point identifying the highest point the subject reached while standing, and one point identifying the highest point the subject reached during the jump. As mentioned in the two concepts above, we have also shown the known height of another object (in this case, the distance from the ground to a point marked on the wall is 37"); and the software automatically uses this information to display the distance between the two points the subject reached in units of inches (23.7").

Compare this subject's results with the likes of NBA superstars Kobe Bryant (38") and Dwight Howard (40"), set to meet in the 2009 NBA Finals. Bryant has been vitually unguardable, draining shots while having defenders' hands in his face, and zipping around opponents with his lightning-quick first step. Howard is a physical force to be reckoned with; players move out of his way when he elevates, to avoid getting "posterized" when he throws down one of his thunderous dunks. It's amazing what these athletes are capable of; and using tests such as the vertical leap allows us to have a more complete understanding of how incredible they really are.