Biomechanics Evolution

Achilles Tendon: The Missing Link? (repost 2007)

Getting Your Avatar Moving Better Than a Monkey

Dr. Bill Sellers of the University of Manchester has just announced that he has made a computer model that demonstrates that tendons are an important structure to store and return energy. Well, this may be big news for my 70 Priest in World of Warcraft, who soon may be modeled to have a bit more spring in his step. Already, my undead priest is able to walk and dance better than the gnomes can, but he is hardly able to run. Now, what does the announcement mean to the rest of us and what did Dr. Bill say about his computer modeling?

“What we’ve found is that muscles are attached to bones by tendons at the end and these tendons are big springs that store energy. If we make a model without tendons, it turns out that it’s rubbish.” Unfortunately a view of the model indicates that it seems to resemble what I imagine his recent model of 5 dinosaurs moving would look like. Dr. Bill did make the news earlier this summer with his announcement that his computer model of T. Rex showed T. Rex was fast as well as fearsome.

Well, a model in which the knee hardly bends while running, no quadriceps is visible, and the longitudinal arch of the foot (and plantar fascia) is not playing a role in gait is also rubbish. Without a computer model, one can see what happens to the gait in which one has a rupture of the Achilles tendon. There is no active propulsive phase. Erdemir et. al. with Neil Sharkey wrote in JBJS in 2004 about how the plantar fascia may transmit the energy stored in the Achilles tendon to the forefoot. The statement about storage of energy in the tendons was most recently made fairly close to the University of Manchester, in the British Journal Nature by Bramble and Lieberman in 2004. “Collagen-rich tendons and ligaments in the leg store elsastic strain energy during the initial, braking part of the support phase, and then release the energy through recoil during the subsequent propulsive phase. To use these springs effectively the legs flex more in running than in walking…” Further back Cagagna, Thys and Zamboni made similar hypotheses in 1976 and Ker in 1987 wrote an article titled “The spring in the arch of the human foot” which included the foot within the gait model as a place of energy storage. Certainly the running shoe market will soon include energy return systems which mimic the storage system of the plantar fascia via storage within bending plates of metal or plastic rather than “springs”. Computer models must be made to mimic the system they purportedly model and therefore we need tendons present in the model. In other literature they are often modeled and pictured as being the equivalent of a “spring”.

Please note, there is a statement in much of the lay press indicating that gorillas do not have an Achilles tendon. They do, it is, however, much smaller and shorter than that found in humans.

A debate over who was best able to run fast and at what stage of our evolution could we do this is of interest, but another interesting question is when did we figure out that we could set traps for our prey and not run or make weapons, be it a stick, a spear, or a bow and arrow, that would keep us from having to run quite as fast as our prey. Since our sprinting speed can only be sustained for around 15 seconds, at some point our ancestors found that it is not the sprint that helps us, but our intermediate distance running or our endurance running that will allows us catch up and serve up our prey. And better yet, our brain, which will let us run smart, and perhaps, not have to run much at all. Then all our running can eventually evolve to running for pleasure and less to finding food. Hence the evolution of food down to a power bar or a squeezable container of gel.

It is important also to note that much goes into having an upright bipedal gait and at least as much into having a running gait. While many animals are considered to have adapted to more forms of gait than humans, I’d view it as more than just two forms of gait. Just watch a steeple chaser to see more than 2 in just a few seconds. Well, I wasn’t entirely serious about the steeple chaser. I view our different speeds and distances that we cover as contributing to different gait types. These gaits involve different energy systems to power them. A sprint of 100 meters, a sprint of 800 meters, a mile race, and a marathon employ different aspects of our energy systems to accomplish them. While our speed will not overcome most of our competitors, our sagely wisdom, ability to plan and yes, even our intermediate and distance running will have a tremendous impact.

I also like both computers and computer models. I look forward to seeing a quadriceps, gluteal muscles, posterior tibialis muscles and many other factors added into the computer based simulation. Just a few years ago at the Iowa College of Podiatric Medicine I viewed a work in progress: a simulation of gait using a cadaver limb with the lower limb muscles loaded and pre-programmed to tense at the time in which a normal gait would have them do so. This “action” model nicknamed “Dead Man Walking” was set up so that one could alter the use of the lower limb muscles in a stride. Hopefully more will come of both kinds of studies and those writing about it will describe accurately the work and the words of the author. I plan to seek out more of Dr. Seller’s own words, which are thought provoking, and a bit less of the third party interpretation.


Bramble DM and Lieberman DE (2004) Endurance running and the Evolution of Homo. Nature, 432: 345-352.

Erdemir,A Hamel,AJ, Fauth, AR, Piazza,SJ Sharkey,N
The Journal of Bone and Joint Surgery (American) 86:546-552 (2004)
Dynamic Loading of the Plantar Aponeurosis in Walking
Ker, RF et. al. The spring in the arch of the human foot. Nature 325: 147-149 (1987)

Cavagna GA et. al. The sources of external work in level walking and running. J. Physiol. Lond 262: 639-657.

Hicks JH: The foot as support. Acta Anat (Basel) 25: 34, 1955.

Lapidus PW: Misconceptions about the springiness of the longitudinal arch of the foot. Arch Surg 46:410, 1943.

Ward, E et. al. 2003. In Vivo Forces in the Plantar Fascia During the Stance Phase of Gait. Journal of the American Podiatric Medical Association Volume 93 Number 6 429-442 2003