TLDR: 2 manufacturers claim springs are better for anyone worried about their (old) joints, while AI search and everyone else thinks bungee cords are better (lower impact). How does the claimed science (linked) stand up?
I have used rebounders (mini trampolines) for fitness before and want to again. however, I’m now older and have more joint issues/arthritis and the last thing I want to do is spend a bunch of money just to hurt myself. (sadly, I did that taking a yoga class FFS)
The last time I bought one, only springs were available, now it’s almost all bungee cords. Two manufactures (Needak linked above, and also Cellerciser) claim springs are superior.
I googled the heck out of this and have come to you. When I read about the G forces (see link) I just don’t know if I should believe it or not.
I see a lot of affirmative claims and zero studies or other evidence. I think if you have arthritis or problems with joints you should look for exercise methods that help strengthen and protect them rather than use a “mini-trampoline” to reduce impact.
yes, that is also happening. but for cardio, this is what I want to do. I’ve done it before and it’s FUN - of all things - and every other cardio option I’ve considered is not as good.
I remember the first time I got a rebounder I enjoyed it so much the first time I was on it, I didn’t think it was really working me until I was sore the next day. Really, sore, in fact.
I appreciate you responding, but what I wonder is if anyone is going to go to the link and read it? maybe I’ll copy/paste.
from the link (an example of something I don’t know how to analyze)
we spend a significantly longer amount of time decelerating on a bungee rebounder, and therefore, are placing extended stress upwards of 4 times our body weight on every organ and joint. This can be irreversibly destructive over the long term. High-quality springs, in contrast, explode on every bounce, capturing all of those g-forces, providing just the right amount of feedback and resistance to ensure joints are protected on landing, but the body is not unnecessarily exposed even a millisecond longer. Milliseconds matter when it comes to 4 times your bodyweight, as when you bounce on a bungee rebounder for even 5 minutes, you’ve exposed every system in your body to 300-500 more fractions of seconds of unnecessary stress than a high-quality spring rebounder.
Just from a purely scientific level, the page you linked to is basically nonsense. For example:
In general, rebounders apply between 2-4 g-forces on the human body during bouncing – this means anywhere from double to quadruple your weight is forced onto your body. That is a lot of g-forces! By their very nature, bungee cords do not store a huge amount of potential resistance, and likewise, as they are used, one can actually feel them heat up as they stretch and contract. This results in a bounce that is elongated – ie, the curve of resistance as you land is quite long. This increases the amount of time you are exposed to these strong g-forces – this includes all of your joints and muscles.
There’s a direct relationship between time exposed to g-force (acceleration) and the level of acceleration given a certain starting velocity. If the bungee takes longer to decelerate you, it means it applied a lower acceleration.
Whether that’s better or worse for you is a different question. And there’s some complication with peak vs. average acceleration, which the link didn’t go into, though my intuition is that it’s not very significant.
I doubt any of this really matters much in practice except at the extremes. You could have extremely stiff bungees or a trampoline that might cause injury, but assuming you get a model appropriate for your joint health, there really isn’t going to be a practical difference. I’d be far more worried about injuring myself by falling off somehow.
You can imagine a very weak bungee that just barely carries your weight–it’ll take forever to cancel out your motion, but at the same time you’ll never feel much more than 1 g, which is to say that it basically just feels like standing there. Which pretty much anyone can handle indefinitely.
There is something of an interesting question, which is how joint damage increases with acceleration. 3 gees will decelerate you twice as fast as 2 g, since you have to subtract the 1 g from ordinary gravity. Is that a good tradeoff? Hard to say! The damage from the extra forces might not increase linearly; 3 gees could be 5 times as bad as 2 gees for some length of time.
But regardless, for a given amount of bounce there’s no real difference between the bungee and the springs. If one of them displaces for longer, it’s because it’s softer and is applying less force.
I suspect it’s true that springs store more energy for a given volume, which means they can be stiffer, and you can therefore bounce higher. Maybe good, maybe bad. But the tradeoff is the same, and it’ll be applying higher forces to achieve that height.
I bought a mini trampoline (w/springs) a decade ago and used it religiously. I used wrist weights as well and got a decent workout. Ultimately I got bored of bouncing around in front of the TV while watching high-energy music videos (but that’s just me). The rebounders in your link are a LOT more expensive than the one I used…are they really that much better?
In terms of physics there is zero difference between springs & bungee cords. They both obey the laws of elastic stretch & rebound.
What might matter is how stiffly or gently any given trampoline rebounds. Either of which could be achieved by a spring or a bungee of suitable parameters.
Bottom line: this is manufactured bunk to sell one or the other category of similarly elastic whatchamacallit.
ETA: And ref @Stranger_On_A_Train just below, whether your use of your rebounder is so vigorous that you hit the device’s elastic limits. But springs & bungees both have a fixed limit beyond which things get bad. So don’t do that.
There can physically be a large difference between peak (instantaneous) acceleration versus the averaged acceleration depending on how linear the springs are. If the springs/bungies get to the limit of their linear(-ish) expansion and suddenly become more rigid, the jerk increases sharply and the instantaneous acceleration can be magnified, and it is the resulting sharp change in velocity that does damage. Whether this would make any difference on a mini-trampoline in terms of injury…probably not, but that kind of assessment really falls into the ‘noise, vibration, & harshness’ (NVH) category of somewhat subjective experience.
Right; it’s certainly possible for there to be some difference here (and springs can be designed to exploit this with non-linear winding and such), but in practice, for something as simple as a trampoline, it’s unlikely to be very significant. The springs and bungees will be used well within their linear range. The trampoline would bottom out before you got to that point, which is a far stronger non-linear effect.
Well, not necessarily. In simple theories of springs (e.g. Hooke’s law) they are treated as being linear energy storage devices, and that’s approximately correct for steel coil springs (less so for rubber bungees but still okay as a first approximation within a specified range), but some materials have large hysteresis and internal damping while others have high restitution qualities. Again, the difference probably isn’t very significant for a mini-trampoline with an average weight person bouncing on it, but when you need to get just-so dynamics from a satellite instrument deployment mechanism or a car door that closes with just the right level of smoothly confident ‘chunk’ those mechanical property differences matter.
I wish I knew! I think it might have been the 1980s when I got my first one (last century, anyway) and the last one I bought was …maybe 2019? I went to the local Big 5 and got one for $35. They all had springs then. Now those around or under $100 all have bungees.
I think this is what the link is claiming.
well, the thing is, I want a good cardio workout so I would work up to doing a significant amount on it. Not sure how much, but not just 10 minutes a couple times a week. More like, 30 minutes 5 times a week. OK, not sure but you get the idea. For YEARS, ideally.
So long term (such as I’ve got!) it might matter.
So if the bungees do cause even a tiny amount more impact on my joints, I don’t want them.
I’m aware there are other issues (springs breaking, etc) but springs vs bungees was the main one I was stuck on trying to figure it out.
