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I recently came across the strange factoid that all animals that can jump do so to roughly the same height (within an order of magnitude). The argument was that the work done by muscles in a single contraction is proportional to their mass, and the amount of energy required to jump is also proportional to their mass. The secondary issue of power could be solved by an approach like the click-beetle uses, where they store the energy in their shell slowly, then release it quickly.

I'm an engineer, so my first thought is that a ratchet could be used to circumvent this sort of limit. If I could cycle a muscle 2-3 times and use a ratchet to store that energy, I could release 3x more energy and jump higher. As an engineer, it seems like a no-brainer.

But I can't seem to find any biological example of such a ratchet. The closest I could find was the muscle proteins that cause contraction in the first place. But that didn't fit the image of the structure I cared about because it was literally millions of these ratchets and the result felt "too smooth" for the concept I was searching for.

So my question is whether biology has a structure that operates like:

  • Powered by a muscle that gets to contract multiple times (or another chemical process which cycles a small number of times. 2-10 is fine, 10 million is not)
  • Stores the energy of each contraction
  • Releases that energy in one burst.

Mentally I'm thinking of a ratchet that I could crank down with 3-4 pulls of a lever, and then release all that energy at once, but I'm open to other biological structures which meet the above requirements.

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  • $\begingroup$ It's a very interesting concept, the only thing I can think of that's at all similar is neurons, which slowly gain charge, then release it when they transmit the signal. $\endgroup$ – Astrolamb Mar 14 '18 at 23:24
  • $\begingroup$ Do contractions for giving birth count? :) $\endgroup$ – Armatus Nov 6 '18 at 18:54
  • $\begingroup$ @Armatus It's not quite what I had in mind, but it sure is darn hard to argue that it doesn't count =D As I commented on your answer, I was looking at jumping heights and the rapid explosion of energy needed to jump higher, but contractions certainly are using a ratcheting like motion... just to gain mechanical advantage rather than storing power! $\endgroup$ – Cort Ammon Nov 6 '18 at 19:05
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First I would in return ask why the actin-myosin coupling should not qualify - the many repetitions of this contractile unit never contract at exactly the same time, and their combined contractile force certainly accumulates in a ratchet-like fashion across the microsecond time scale (with other units contracting before previous units have relaxed). Just because it's a lot of them doesn't make it less ratchet-like :)

With this restriction though, and looking for a "macro-scale" example, I am not aware of anything fitting your description. If I think about it as follows, it also seems intuitive that this wouldn't evolve.

A ratchet as you describe, let's say able to store up x contractions of a muscle for instantaneous release, can also be thought of as a series of x muscle contractions coupled in series across time. It would be equivalent in output to coupling x muscle contractions across space and executing all of them simultaneously. In other words, growing x times the muscles achieves the same benefit.

When it comes to the probability of evolving, what's more likely: an entirely new mechanism to store mechanical energy across time and allow building up, or a simple duplication of the same tissue? The currently existing muscles answer this question: duplication. This can be seen in the different structures that muscles have across living species (muscles in animals, similar contractile mechanisms elsewhere).

The smallest contractile unit in muscles are myosin heads coupled to actin filaments. Duplicate this unit (repeatedly) in two dimensions of space to obtain a myofibril. Multiply the myofibril many times and you reach a single muscle fibre. In fruit fly larvae, this is where it stops - each muscle consists of a single fibre. By the time you're at the adult fly though, the muscles that power the wings consist of a handful of packed parallel fibres. As you go down other routes along the evolutionary tree towards the mammals, you end up at muscles that consist of masses of fibres packed into fascicles, of which many are packed into an individiual muscle. As described above, at each level you have a "many-ratchet", because fibres and fascicles don't contract at exactly the same time everywhere.

So yes, you could evolve a ratchet. Or you could just evolve a bigger muscle. If many animals happen to stop evolving more muscle at around the same absolute potential jump height, that to me suggests that this is a universally beneficial jump height to evolve for terrestrial animals regardless of body size.

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  • $\begingroup$ Even the fastest striking animals we know of (mantis shrimps) don't use a ratchet mechanism. They do have to 'lock' their muscles though (with some sort of spring mechanism) in oder to release all the energy build up by muscles in a minimised time window. nature.com/articles/428819a $\endgroup$ – Nicolai Nov 6 '18 at 12:27
  • $\begingroup$ The reason I don't count actin-myosin is because my particular interest is in jump heights. The maximum jump height for an animal turns out to be constant, whether you are a mouse or a cheetah. It's limited by how much energy a muscle contraction can bring to bear divided by the mass of the muscle. I'm looking at how to store mechanical energy in other forms that could escape this limit. $\endgroup$ – Cort Ammon Nov 6 '18 at 18:59
  • $\begingroup$ Even with a constant maximum power output per gram of muscle (which is basically the limit imposed by the nature of actin and myosin as a contratile mechanism), there should still be the ratio of jumping muscle to remaining body mass as a limiting factor that could be tweaked to evolve higher jumps. $\endgroup$ – Armatus Nov 6 '18 at 19:15

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