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A History of Legs in 5 Objects

By Stacy Hackner, on 11 April 2017

DSC_0745by Stacy Hackner

My research focuses on the tibia, the largest bone in the lower leg. You probably know it as the shin bone, or the one that makes frequent contact with your coffee table resulting in lots of yelling and hopping around; that’s why footballers often wear shinguards. The intense pain is because the front of the tibia is a sharp crest that sits directly beneath the skin. There are a lot of leg-related objects in UCL Museums, so here’s a whirlwind tour of a few of them!

One of the few places you can see a human tibia is the Petrie’s pot burial. This skeleton from the site of Badari in Egypt has rather long tibiae, indicating that the individual was quite tall. The last estimation of his height was made in 1985, probably using regression equations based on the lengths of the tibia and femur (thigh bone): these indicated that he was almost 2 meters tall. However, the equations used in the 80s were based on a paper from 1958, which used bone lengths from Americans who died in the Korean War. There are two problems that we now know of with this calculation: height is related to genetics and diet, and different populations have differing limb length ratios.

Pot burial from Hemamieh, near the village of Badari UC14856-8

Pot burial from Hemamieh, near the village of Badari UC14856-8

The Americans born in the 1930s-40s had a vastly different diet from predynastic Egyptians, and the formulae were developed for (and thus work best when testing) white Americans. This is where limb length ratios come into play. Some people have short torsos and long legs, while others have long torsos and short legs. East Africans tend to have long legs and short torsos, and an equation developed for the inverse would result in a height much taller than he actually was! Another thing to notice is the cartilage around the knee joint. At this point in time, the Egyptians didn’t practice artificial mummification – but the dry conditions of the desert preserved some soft tissue in a process called natural mummification. Thus you can see the ligaments and muscles connecting the tibia to the patella (knee cap) and femur.

The Petrie also has a collection of ancient shoes and sandals. I think the sandals are fascinating because they show a design that has obviously been perfected: the flip flop. One of my favorites is an Amarna-period child’s woven reed sandal featuring two straps which meet at a toe thong. The flip flop is a utilitarian design, ideal for keeping the foot cool in the heat and protecting the sole of the foot from sharp objects and hot ground surfaces. These are actually some of the earliest attested flip flops in the world, making their appearance in the 18th Dynasty (around 1300 BCE).

An Egyptian flip-flop. UC769.

An Egyptian flip-flop. UC769.

Another shoe, this time from the site of Hawara, is a closed-toe right leather shoe. Dating to the Roman period, this shows that flip flops were not the only kind of shoe worn in Egypt. This shoe has evidence of wear and even has some mud on the sole from the last time it was worn.  This shoe could have been worn with knit wool socks, one of which has been preserved. However, the Petrie Collection’s sock has a separate big toe, potentially indicating that ancient Egyptians did not have a problem wearing socks and sandals together, a trend abhorrent to modern followers of fashion (except to fans of Birkenstocks).

Ancient Egyptian shoe (UC28271) and sock (UC16767.

Ancient Egyptian shoe (UC28271).

sock UC16767

Ancient Egyptian sock (UC16767).

The Grant Museum contains a huge number of legs, but only one set belonging to a human. For instructive purposes, I prefer to show visitors the tibiae of the tiger (Panthera tigris) on display in the southwest corner of the museum. These tibiae show a pronounced muscle attachment on the rear side where the soleus muscle connects to the bone. In bioarchaeology, we score this attachment on a scale of 1-5, where 5 indicates a really robust attachment. The more robust  – attachment, the bigger the muscle; this means that either the individual had more testosterone, which increases muscle size, or they performed a large amount of activity using that muscle. (We wouldn’t score this one because it doesn’t belong to a human.) In humans, this could be walking, running, jumping, or squatting. Practice doing some of these to increase your soleal line attachment site!

The posterior tibia of a tiger.

The posterior tibia of a tiger.

Moving to the Art Museum, we can see legs from an aesthetic rather than practical perspective. A statue featuring an interesting leg posture the legs is “Spinario or Boy With Thorn”, a bronze statue produced by Sabatino de Angelis & Fils of Naples in the 19th century. It is a copy of a famous Greco-Roman bronze, one of very few that has not been lost (bronze was frequently melted down and reused). The position of the boy is rather interesting: he is seated with one foot on the ground and the opposite foot on his knee as he examines his sole to remove a thorn. This is a very human position, and shows the versatility of the joints of the hip, knee, and ankle. The hip is adducted and outwardly rotated, the knee is flexed, and the ankle is everted. It’s rare for the leg to be shown in such a bent position in art, as statues usually depict humans standing or walking.

Spinario, or Boy With Thorn.

Spinario, or Boy With Thorn.

Bipedalism, or walking on two legs, is one of the traits we associate with being human. It’s rare in the animal world. Hopefully next time you look at a statue, slip on your flip flops, or go for a jog, you’ll think of all the work your tibiae are doing for you – and keep them out of the way of the coffee table.

(OK, I know that was six objects… but imagine the sock inside the shoe!)

Did we evolve to run?

By Stacy Hackner, on 5 January 2015

By Stacy Hackner

A few years ago, spurred by my research on just how deleterious the sedentary lifestyle of a student can be on one’s health, I decided to start running. Slowly at first, then building up longer distances with greater efficiency. A few months ago, I ran a half-marathon. At the end, exhausted and depleted, I wondered: why can we do this? Why do we do this? What makes humans want to run ridiculous distances? A half-marathon isn’t even the start – there are people who do full marathons back-to-back, ultra-marathons of 50 miles or more, and occasionally one amazing individual like Zoe Romano, who surpassed all expectations and ran across the US and then ran the Tour de France.[i] Yes, ran is the correct verb – not cycled.

I’ve met so many people who tell me they can’t run. They’re too ungainly, their bums are wobbly, they’re worried about their knees, they’re too out of shape. Evolution argues otherwise. There are a number of researchers investigating the evolutionary trends for humans to be efficient runners, arguing that we are all biomechanically equipped to run (wobbly bums or not). If you have any question whether you can or can not run, just check out the categories of races in the Paralympic Games. For example, the T-35 athletics classification is for athletes with impairments in ability to control their muscles; in 2012, Iiuri Tsaruk set a world record for the 200m at 25.86s, which is only 6 seconds off Bolt’s world record at 19.19 and 4 seconds off Flo-Jo’s womens record (doping aside). 2012 also saw the world record for an athlete with visual impairment: Assia El Hannouni ran 200m in 24.46.[ii] You try running that fast. Now try running with significant difficulty controlling your limbs or seeing. If you’re impressed, think about these athletes the next time you say you can’t run.

Paralympic_athlete

Paralympian Scott Rearden. Wikimedia Commons.

Let’s think about bipedalism for a bit. Which other animals walk on two legs besides us? Birds, for a start, although flight is usually the primary mode of transport for all except penguins and ostriches. On the ground, birds are more likely to hop quickly than to walk or run. Kangaroos also hop. Apes are able to walk bipedally, but normally use their arms as well. Cockroaches and lizards can get some speed over short distances by running on their back legs. However, humans are different as we always walk on two legs, keep the trunk erect rather than bending forward as apes do, keep the entire body relatively still, and use less energy due to stored kinetic energy in the tendons during the gait.[iii] Apparently we can group our species of strange hairless apes into the category “really weird sorts of locomotion” along with kangaroos and ostriches.

Following this logic, Lieberman et al point out that a human could be bested in a fight with a chimp based on pure strength and agility, can easily be outrun by a horse or a cheetah in a 100m race, and have no claws or sharp teeth: “we are weak, slow, and awkward creatures.”[iv] We do have two strokes in our favor, though – enhanced cognitive capabilities and the ability to run really long distances. Our being awkwardly bipedal naked apes actually helps more than one would think. First, bipedalism decouples breathing from stride. Imagine a quadruped running – as the legs come together in a gallop, the back arches and forces the lungs to exhale like a bellows. Since humans are upright, the motion of our legs doesn’t necessarily affect our breathing pattern. Second, we sweat in order to cool down during physical exertion. (In particular, I sweat loads.) Panting is the most effective way for a hairy animal to cool down, as hair or fur traps sweat and doesn’t allow for effective convection (imagine standing in a cool breeze while covered in sweat – this doesn’t work for a dog.) But it’s impossible to pant while running. So not only are humans able to regulate breathing at speed, but we can cool down without stopping for breath.

From a purely skeletal perspective, there is more evidence for the evolution of running. Human heads are stabilized via the nuchal ligament in the neck, which is present only in species that run (and some with particularly large heads), and we have a complex vestibular system that becomes immediately activated to ensure stability while running. The insertion on the calcaneus (heel bone) for the Achilles tendon is long in humans, increasing the spring action of the Achilles.[v] Humans have relatively long legs and a huge gluteus maximus muscle (the source of the wobbly bum). All of these changes are seen in Homo erectus, which evolved 1.9 million years ago.[vi]

H. erectus skeleton with adaptations for running (r) and walking (w). From Lieberman 2010.

H. erectus skeleton with adaptations for running (r) and walking (w). From Lieberman 2010.

The evolutionary explanation for this is the concept of endurance or persistence hunting. In a hot climate, ancient Homo could theoretically run an animal to death by inducing hyperthermia. This is also where we come full circle and bring in the cognitive capabilities of group work. A single individual can’t chase an antelope until it expires from heat stroke because it’ll keep going back into the herd and then the herd will scatter. But a team of persistence hunters can. If persistence hunting is how humans (or other Homo species) evolved to be great at long distance running, that’s also the why humans developed larger brains: the calories in meat generated an excess of calories that allowed nourishment of the great energy-suck that is the brain. However, persistence hunting is a skill that mostly went by the wayside as soon as projectile weapons (arrowheads and spears) were invented, possibly around 300,000 years ago. Why? Because humans, due to our large brains, are very inventive, but also very lazy. Any expenditure of energy must be made up for by calories consumed later, at least in a hunting and gathering environment – so less energy output means less energy input; a metabolic balance. Thus we have the reason why humans can run, but also why we don’t really want to. (As an aside, some groups such as the Kalahari Bushmen practiced persistence hunting until recently, although they had projectile weapon technology, probably because of skill traditions and retaining cultural practices. Humans are always confounding like that.)

Which brings up another point: gathering. As I’ve written before, contemporary hunter-gatherers like the Hadza rely much more on gathering than hunting. Additionally, it is possible that the first meat eaten by Homo species was scavenged rather than hunted. There is no such evolutionary argument as endurance gathering. If ancient humans spent much more time gathering, why would we evolve these particular running mechanisms? As with many queries into human evolution, these questions have yet to be answered. Either way, it’s clear that humans have a unique ability. Your wobbly bum is, in fact, the key to your running. Another remaining question is why we still have the desire to continue running these ridiculous distances – a topic for a future post, perhaps.

Sources

[i] http://www.zoegoesrunning.com

[ii] Check out all the records at http://www.paralympic.org/results/historical

[iii] Alexander, RM. Bipedal Animals, and their differences from humans. J Anat, May 2004: 204(5), 321-330.

[iv] Lieberman, DE, Bramble, DM, Raichlen, DA, Shea, JJ. 2009. Brains, Brawn, and the Evolution of Human Endurance Running Capabilities. In The First Humans – Origins and Early Evolution of the Genus Homo (Grine, FE, Fleagle, JG, Leakey, RE, eds.) New York: Springer, pp 77-98.

[v] Raichlen, DA, Armstrong, H, Lieberman, DE. 2011. Calcaneus length determines running economy: implications for endurance running performance in modern humans and Neandertals. J Human Evol 60(3): 299-308.

[vi] Lieberman, DE. 2010. Four Legs Good, Two Legs Fortuitous: Brains, Brawn, and the Evolution of Human Bipedalism. In In the Light of Evolution (Jonathan B Losos, ed.) Greenwood Village, CO: Roberts & Co, pp 55-71.

The Biomechanics of Breasts

By Stacy Hackner, on 24 February 2014

Stacy Hackner_ThumbnailBy Stacy Hackner

Have you ever wondered what biomechanics has ever done for you? Well, if you’re a runner, it can tell you a lot about your gait and efficiency. It tells us why people with long legs are good at running and people with long arms are good at swimming, and the forces they use per stride or stroke. It can teach us proper runner techniques. If you’re a female runner, you may have encountered a problem biomechanical researchers are actively working to solve: bouncing breasts.

I’ve only been a runner since I started my PhD. As you may remember from my last post, I learned from my research that it’s very important for your bone strength to practice weight-bearing activity (sorry, astronauts), which includes running. As professional running goes, for some reason marathon organizers decided to exclude women from participating until the mid 1980s, when just a few women snuck into the Boston and London marathons and achieved quite good times (see Heminsley’s book for an exciting run-down of the sneaking). Since then, women have been participating in most major sports, including (very recently) American football; 36.5% of 2012 London Marathon finishers were female (Brown et al 2013). But sports equipment for women is still catching up, and biomechanics – long applied to gait and stride, torso and head movements – is now being brought in to design a better bra. Most biomechanical studies of breasts involve attaching markers to women on treadmills in clothed and unclothed conditions and filming them with an infrared camera – a slightly awkward study for the volunteers, but it’s worth it for the results.

The breast in three dimensions. Zhou et al 2012.

The breast in three dimensions. Zhou et al 2012.

First, let’s look at a breast from an anatomical perspective. Breasts are composed of milk glands and ducts, fat, connective tissue, and Cooper’s ligaments. The latter are fibers that attach the breast to the underlying fascia and pectoral muscles; throughout life, and in vigorous exercise, they can stretch or break and cause sagging and breast pain. Imagine a laundry line with wet clothes hanging on it – now shake it: that’s what happens during intense exercise. Of course, these forces have been measured, which can be difficult as unlike bones and muscles, they squish and deform, and each of the above types of tissue reacts to running forces differently. During the beginning of a running stride, the breasts are found to accelerate at up to 3 G (where G is the force of gravity – at that point in time, it’s like the breast weighs 3 times as much). This is considerably more than the rest of the trunk, and puts strain on Cooper’s ligaments. You can then imagine that each breast goes through a cycle of acceleration, stasis, and deceleration for each stride, like your head when stopping and starting in a car. For each stride, the breasts move forward into the air and backward into the ribcage, in what is called anterior displacement.

The figure-8 movement of breasts in a digital reconstruction. Image via ShockAbsorber website.

The figure-8 movement of breasts
in a digital reconstruction.
Image via ShockAbsorber website.

Now it gets more serious. In addition to being displaced anteriorly, breasts move in three dimensions. When running, the goal is generally to move forward. In order to do this, you need to move up as well. And with each step, you also sway side to side. Breasts respond to this combination of forces by actually moving in a figure-8, experiencing additional vertical and horizontal displacement. Studies show that it’s these three directions of displacement rather than acceleration that cause breast discomfort and pain; the worst seems to be vertical displacement, which peaks at mid-flight. At this point, the Cooper’s ligaments are basically floating upwards and then being tugged back down during deceleration (not to mention the fat and glands moving about internally). This is important to know for bra design, as many sports bras take the approach of “flattening everything is best” – however, as we’ve now learned, flattening will only reduce anterior displacement! Flattening bras can also cause breast pain, so it’s lose-lose situation.

Now let’s discuss what a bra actually does. The everyday padded bra is an attempt to compromise comfort, sexuality, and stabilization, often emphasizing one to the detriment of the other two. The goal is to hold the breasts in an uplifted position so they appear firm and don’t jiggle around too much while walking or climbing stairs. Sports bras, on the other hand, prioritize stabilization, as they’re to be worn in high-impact activities. Many sports bras take the approach that flatter is better, which as I’ve shown is not quite the case, but they do prevent one kind of displacement. Regular, everyday support bras lift the breasts up, reducing strain on the Cooper’s ligaments, but in tests of treadmill running do little to prevent any kind of displacement. Running bare-chested causes the most displacement, and – in the case of marathons – can lead to a breast injury experienced by men as well, where the nipples chafe against the fabric of the shirt. (This is actually very common, and there are marathoner web forums devoted to sharing prevention tips.) A newer kind of sports bra attempts to encapsulate rather than flatten, and researchers from biomechanics and textile manufacturing have been collaborating on new design. This bra holds each breast separately and matches the figure-8 to the overall movement of the torso, reducing displacement in all three directions.

As more women get into sports (which is particularly important for the prevention of osteoporosis), making us comfortable and keeping us engaged should be a high priority for sports equipment manufacturers. Most runners can find shoes that fit, as shoes have been tested and re-designed for the last thirty years, and have a high profile in the press. Despite the increase in women running, 75% of female London marathoners still reported a problem with their sports bra, with the prevalence higher among larger-breasted women. However, proper fitting technical sports bras receive significantly lower press coverage than proper running shoes. Clearly, there is more work to be done!

 

Sources

Brown, N., J. White, A. Brasher, and J. Scurr. 2013. An investigation into breast support and sports bra use in female runners of the 2012 London Marathon. Journal of Sports Sciences 2013:1-9.

Heminsley, A. 2013. Running Like a Girl. London: Huntchinson.

Scurr, J., J. White, and W. Hedger. 2010. The effect of breast support on the kinematics of the breast during the running gait cycle.  Journal of Sports Sciences 28(10): 1103-1109.

Zhou, J., W. Yu, and S.P. Ng. 2012. Studies of three-dimensional trajectories of breast movement for better bra design. Textile Research Journal 82(3): 242-254.

Update: The post originally stated that Cooper’s ligaments connect breast glands to the clavicle; this was incorrect.