Lee

News flash: Not all rebounders are created equal. OK, you probably already know that. Anyone who has bounced on a high-quality rebounder and a cheap rebounder knows that the cheap rebounder feels more like bouncing on a cement block, and the high-quality rebounder feels much “softer” and more “gentle on the body”.

But what about the difference between different brands of high-quality rebounders? For instance, you might see some people on the web raving about the Cellerciser and some raving about the Needak. How do you choose? I wondered the same thing, and since I and one of my friends had both decided to purchase rebounders, my friend bought one kind and I bought another. I’m not going to tell you yet you bought which.

We put them next to each other, and took turns bouncing on each. We both agreed there was a difference. We both agreed which one we like better. And I, being a scientist, engineer, and Inventor couldn’t resist finding out exactly what the difference was between the two. So, I set out to do a more scientific comparison than just experiencing the feel of the two.

In many ways, the Needak and the Cellerciser appear to be of very similar construction. The taper on the springs is a little different, but when measuring the amount of vertical mat deflection with a 180-pound person standing on each, the total deflection was almost identical. Clearly this was going to require more sophisticated measurements, so I went down into my basement and unpacked some accelerometer instrumentation I used years ago in designing solar racing cars at MIT. Next, I designed a circuit to Interface the accelerometer to a data acquisition system…

With the data acquisition system hooked to a laptop computer and the accelerometer attached to my belt. I bounced some on each rebounder, adjusting my rate of bouncing and height of bouncing to be identical on each. Here are the acceleration waveforms:

Notice that for both the Needak, and Cellerciser rebounders, the peak g force is above 5gs. That means that briefly during each of these bounces, the force on my ankles, legs, back, etc. was five times the force from my normal weight. Of course, if you don’t bounce as vigorously as I was bouncing the force will be less. In any case, one quality measure of a rebounder is that it doesn’t keep your body at peak force stress for very long.

Let’s look at the acceleration profiles side-by-side.

Notice that while my body experienced a peak force of about 6gs on both the Needak and Cellerciser, the Needak had my body above 5gs for about twice as long as the Cellerciser. In this measure, the Cellerciser is significantly better.

Next let’s notice the rate at which the force on the body is ramped up on each bounce on the two rebounders:

Note that the time that it takes for your body to go from 1g to 5gs of is about twice as fast on the Needak as it is on the Cellerciser. Our bodies do not like stresses to change rapidly. Slower change is better. So, we see that in this aspect also, the Cellerciser is better for you.

Overall, the slower a rebounder can come to producing a sinusoidal acceleration waveform as you bounce, the less shock there is to your system. The Cellerciser comes significantly closer to producing a sinusoidal acceleration waveform when you bounce energetically. The less energetically you bounce, the less difference there is between the Needak and the Cellerciser, but even at a moderate-energy bounce, the difference is quite noticeable, and (as you see above) quite measurable.

So now I can tell you what I didn’t tell you to begin with. The Cellerciser feels better to bounce on. And now we can all see why! What I still haven’t told you is that when my friend and I flipped a coin to see who would buy what type of rebounder to begin with, my friend wound up buying the Cellerciser. Now I have done all this great work, and I need to get rid of my Needak and buy a Cellerciser. Anybody want a used Needak?