About a week ago for my biomechanics class we took a trip to the lab and got to partake in some motion analysis work. It was simply walking back and forth across the room while being surrounded by 6 high speed light sensitive cameras while having those reflective balls taped onto all my major joints on my body. The computer in turn spit out a computerized version of my walking gait along with more data on angles, velocities, and accelerations of the various limbs then anyone would know what to do with. My one thought while doing this little class experiment: how cool would it be to use this with myself or in coaching.
Not having a couple hundred grand lying around as a poor grad student/runner, my dreams were dashed. That is until a few days later when I came across a video on Jay Johnson’s site of him filming using a cheap high speed camera. Of course, I had to get one too and that led me to my poor man’s version of motion analysis.
First, I’ll go over the simple steps of creating this poor man’s motion analysis and then we’ll go over some of the practical uses.
First step is get a camera that allows for High Speed. This is your only expense. Normally even the cheap high speed cameras cost over a grand, but Casio recently came out with a set of cheaper high speed capable cameras. I opted for the cheapest, the Exilim FS-10. It only cost me $135 and can shoot at 210, 420, and 1000 Frames per second (FPS).
Just as a quick refresher, regular video’s shoot at 30 FPS. In the video below, I’ll show examples of shots taken at each FPS. The 210 FPS looks great. The 420 FPS looks okay, the quality suffers for the increased frame rate, but it is definitely usable. The 1000 FPS is very blurry and requires a lot of light in order for it to be usable. The 210 FPS works great for track/running as it allows for a good quality video at a high enough frame rate so that you can see every part of the stride clearly.
Below is some quick video I shot today with the Camera. It’s off my teammate running at 210 FPS, and then some videos of me jumping at the different frame rates. It was a rainy overcast day so the lighting wasn’t great, so take that into account.
All this technology junk is great, but what can does this high speed actually allow us to do? Basically, shooting in high speed allows us to see everything much better. At 210 FPS, you can see every part of the stride exactly. Especially if you combine this with a program that allows you to advance one frame at a time (almost every video watching program on the computer lets you do this. For example, Windows Media Player allows this). In a regular video, if you advance frame by frame you miss portions of the stride and/or you get blurred images. It’s impossible to see exactly what’s going on. For example, you couldn’t see exactly where the foot is striking the ground. At 210+ FPS, you can.
But, it’s more than that. If we combine this with motion analysis software you get all sorts of great data. But wait, motion analysis software costs hundreds if not thousands of dollars right? Wrong! Go get Tracker video analysis software for free at the link below.
While tracker is a simple program, it does almost everything that you need. It’s a little harder to figure out at first, but once you do, you realize the potential. It was made to aid in physics problems (i.e. for HS or intro college Physics courses), but it works well for biomechanical analysis.
The unique thing about tracker is that it allows for you to set the frame rate that the video was shot at. This is VERY important, because then it allows for calculations of elapsed time which is very useful in analysis. Most other free programs don’t have this option.
What can we actually do with this software combined with the camera:
1. Measure Time intervals- Ground Contact Time
This is really neat and useful. We can look at things that we normally couldn’t measure and put a number on it like all those research studies we’ve read do. For instance, want to know what ground contact time is, you can measure it! This could be useful for comparing left foot and right foot ground contact, or to look at fatigue from one interval to another or one lap to another in a race. See an increase in GC time, fatigue is setting in. This has big implications during sprint training or for sprinters. If the goal is to work on pure speed and you see ground contact time increasing, then they’re not recovering enough and you’re implanting slower motor patterns.
Besides that we can use it to measure swing time on each leg. Which when compared from leg to leg could give us an idea on asymmetries.
2. Measure reactivity/strength endurance
This ties in with ground contact time, but by figuring out ground contact we can test for reactivity and strength endurance. Use a simple reactive hoping test and measure the ground contact and you get a value for their reactivity. Do a repeated reactive hopping test for 1-3min or so and measure the initial ground contact time, and then the ground contact after 1min, 2min, etc. and compare the values and you get an idea of strength endurance.
3. Measure distance and velocity.
If you stick a meter stick in the picture and use that to calibrate distance, we can now use the motion analysis software to measure distances and velocities. Now we can compare stride lengths at various paces or stride length of the left and right side. Taking this a step further, you can even measure changes in hip height or knee height during the stride.
Since we know distances and time, the software can calculate velocity. This is a little more tedious, but it can be well worth it. The software allows you to plot points on the video. You can click where the knee is to mark it, then mark it for each frame throughout the stride and all of the sudden you have the velocity of the knee throughout the stride and the change in position of the knee throughout each stride. Do this with any body part and you get a ton of data. Use it any way you want. An example might be seeing the velocity at the right ankle as it moves through the swing phase. Maybe one foot moves through faster than the other.
4. Measure angles
We can now look at the angles of the various body segments and how they change throughout the stride.
5. A ton of other things I haven’t looked into yet, including:
-Changes in velocity in horizontal or vertical component
-accelerations in any direction
-A bunch of statistics.
The bottom line is that with this camera, combined with some free software, you can have all sorts of data at your finger tips. The data is only good if the coach can translate it into something that can be practically used. The possibilities are endless.
I can’t wait until I get to film some of my High School guys. You can hide flaws at 30 FPS, but they become crystal clear at 210+FPS.
To end, a summary of things I intend to use this camera/software combo on with coaching:
-Analyze running form easily
– Look at asymmetries in their running stride
-Measure strength endurance
-Look at Ground Contact times at various speeds and under fatigue and to what degree it changes.
-Look at stride lengths as biomechanics change.
-Look at foot contact position in a lot of runners
-Compare angles of the shin at ground contact
-Look at the degree of hip extension among runners at various speeds.
There you go, for $135 you have the cheapest quality motion analysis that you can get. Hopefully I’ll get some good footage and data up on the blog in the future that we can all look at.