Have you ever wondered why, when you jump from a high place, the impact doesn't cause your legs to crumple up accordion-style, turning you into a hat and feet like in the cartoons?
Probably not, but I've put a lot more thought into this question than you'd expect, so I was delighted to read that Brown University has done a new study showing exactly how legs absorb sudden impacts. As it turns out, your tendons take the hit.
Now researchers at Brown University have documented how muscles and tendons work in concert first to store and then to rid themselves of energy and heat. They found that tendons take on the role of shock absorbers at the time of impact. About a tenth of a second later, the fibrous bundles in skeletally connecting muscles, known as fascicles, absorb the remaining energy. The tendons' role is crucial, the Brown researchers write in the journal Proceedings of the Royal Society B, because they help protect the fascicles against damage from the rapid burst of energy and power generated by the impact.And here's the same thing in lovingly geeky detail:
The researchers focused on two main periods. One, called the force rise, began when the turkey landed. The researchers were surprised to see that muscle fascicle length remained essentially the same. That means, Konow explained, that the jolt of the impact was being absorbed somewhere else: in the tendon. The researchers believe there is a biological reason for this. To protect themselves from the energy generated at the moment of landing, the fascicles leave the impact to the tendons, which stretches like a spring. In fact, electrical pulses recorded in the fascicles indicate the muscle steeled itself against the landing even before the turkey jumped.
Following the jolt of landing comes a period the authors call force decay. During force decay, the tendon recoils to its original length, releasing the energy it had accepted during the landing. "That means the tendon is shunting energy to something that's lengthening," Konow said, "and that's the fascicles. The fascicles are sensing that the force (from impact) is going down and it's safer to lengthen to absorb the energy."Observant Nerd Herders will have noticed the word "turkey" mentioned in the above explanation - and that's what I'm excited about. To test the impact, Brown researchers put sensors in the turkeys' legs then using "a ceiling-mounted pulley and rope system tied to a custom-made webbing harness strapped around the proximal (humeral) wing segment," dropped the birds about 5 feet to see what would happen.
In other words, they bungee jumped turkeys in the name of research.
Yeah, I know, the turkeys probably didn't love it, but it's still rad. This information will have all kinds of benefits in the fields of reconstructive surgery and athletic performance, just to name two. It's not like they tortured the turkeys. They just bounced them for a couple hours. (Admittedly, the turkeys were then knocked out and their tendons were detached and wired to machines. But that's splitting hairs, isn't it? Seriously. Bungee jumping turkeys!)
Also, I saw no indication in the researcher required the birds to pay for the bungee jumps. When I bungeed in New Zealand a while back, it cost me a ton. Furthermore, the surgeon did God-knows-what to my leg tendons in my recent surgery - and I had to pay for that too.
I think these turkeys got a hot deal. This is what I like to call "Win/Win Science."
N. Konow, E. Azizi, T. J. Roberts. Muscle power attenuation by tendon during energy dissipation. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.1435