Anthro leg gestures

From my previous post, here are a few ideas on gestures when it comes to the anthro legs. Firstly I look to draw the curves they create. I've posted before about the elastic energy that digitigrade and ungiligate legs reserve whilst walking, this is effectively why they are configured the way that they are. So simplify this to curves as if the legs were bamboo, bending, curving under strain. So long as you remember that with any stance, the ball of the foot/paw/hoof needs to be in contact with the ground under the bodies center of gravity. Keeping that in mind will help you create that curve and make your characters look more grounded.

Anthro-grade stance

Been a few weeks from my last post, had a few things on my mind but it's given me time to sketch out more ideas, particularly on the subject of tails and anthro legs.

To keep the anthro 'stoop' we need to change some of the anatomy. Quadriceps shown in green, gluteals in shades of red, hamstrings in purple and the ilio-tibial tract in cream.

Anthro leg anatomy issues really come down to antho characters standing in a constant 'stoop'. I think that this is some sort of visual misnomer in that it's drawn to emulate the shape of an animals leg but with limited consideration on the extent of its impact to the anatomy. 

Holding a stooped position as a human is hard work, it requires a great deal of force from the quadriceps to keep the knee in partial flexion and the gluteals and hamstrings are under stress to hold the femur at an angle. This is because the weight of the torso is placing the centre of gravity too far behind the feet, the pelvis needs to tilt the torso forward to counterbalance this, bringing the centre of gravity back under the torso. That's why if you try squats in the gym, releasing the stress on your glutes can be done by leaning forward. This stoop is very energy inefficient, and clearly will lead to characters walking not only on bent knees but in a bent forward stance.

There could be a couple of ways to fix this if you wanted to keep the 'dog leg'. Either increase the muscular force the leg can muster (but this still does not change the energy required to hold the leg up, it just means the muscle will be slower to fatigue). Or you shorten the length of the femur. Shortening the distance of the load arm (shown above) makes the stance more energy efficient. This is because the load (the weight of the torso) is now much closer to the pivot (the knee joint), it means that less force is require to lift the load. Much like when using a wheel barrow, this is an example of a second class lever.

Shortening the thigh doesn't solve the problem but it certainly would help.

'A' represents a possible digitigrade stance with a vertical femur. 'B' represents a possible unguligrade stance where the femur is in a stoop. I was not trying to compare digitigrade and unguligrade here, only a vertical femur and one in a stoop.

Taking the stance as a whole it's easier to see that 'B', stood in a stoop with the torso fully upright, would result in the characters centre of gravity being behind it's foot, it's still below the torso but the torso is now more inclined to want to fall backwards because of the stoop, the quadriceps are taking the strain to hold this stance upright.

'A' is digitigrade and the femur is vertical but the knee is still slightly in flexion. If the quadriceps contract too much it will cause the trunk to fall forward. From a balance perspective the centre of gravity is better maintained under the feet of 'A' since the leg is much more vertical but it will of course require a greater level of tone to hold this stance than that of a human plantigrade biped. 

Combining the ideas above:

• shorter thigh
• thigh more vertical than stooped
• larger musculature to lower the fatigue 
• maintains a stance directly under the torso

Is this a more likely anatomically correct look for an antho? One of many configurations for sure!

Standing upright - Part II

It isn’t possible to directly compare a set of quadruped ‘buttocks’ to that of a human because for quadrupeds, like the horse in this example, their behinds are not really gluteals, they are hamstrings. I'll bang on about these muscles groups just once more:

Hamstrings: in quadrupeds serve as powerful hip extensors, driving the animal forwards against the ground reaction and pulling the leg up and backwards to take the next stride, whereas in humans their action is similar but less powerful due to them being almost vertical when stood upright. Importantly, in bipeds they counteract the truck from falling forward.

Gluteals: in a quadruped, are powerful locomotors also extending the hip, in humans these would relate to gluteus minimus and medius and are now adapted to stabilise the hip laterally, most notably when we stand with one leg off the ground, rather than being used for locomotion. In bipeds the gluteus maximus takes more of the role of hip extensor via the ilio-tibial band. Gluteus maximus also counteracts the truck from falling forward.

Take a look at the action of the race horses legs, you can see all that ground force coming from the contraction of the hamstrings at the back and gluteals at the top of the hind limb pulling them backwards and driving the horse forwards. 

The gluteus maximus dominates in humans, its function still makes it a powerful hip extensor but it’s role in stabilising, holding the femur and pelvis in alignment, keeps us stood upright. This makes it a very important muscle for bipeds. (Also worth noting that a large gluteal makes it easier for us to sit down).

Dependent on your furry character’s needs, be them straight legged or bent kneed, their gluteals and hamstrings are going to function slightly differently, be sized accordingly and maybe even positioned differently. All that is going to be aided by the configuration of their pelvis.

Standing upright - Part I

Bipedalism in Humans is by no means a well evolved task. We still have issues of lower back pain, knee joint stresses, ankle injuries and hip fractures. Many of these aliments are conditions of aging but it shows during our life time where we are taking the stresses and risks of standing upright.

When we discovered the skeletal remains of Australopithecus afarensis commonly known as ‘Lucy’, we had proof that bipedal hominids were around 3.5million years ago. When we look at her pelvis we can see more in common with our species than that of our distant relations like chimpanzees who are better adapted to climbing and quadruped walking. Lucy’s anatomy showed us that moving from quadruped to biped relied on a reconfiguration of the bony plains of the pelvis and the function of some locomotor muscles to provide lateral support while walking.

The ilia of most quadrupeds are thin and flat to the back of the torso, a gradual bending of these has formed the bony rounded ridge of the iliac crests, giving an anchor point for muscles bearing lateral support, very important for stabilising the hip of a biped.

This video is taken from the BBC’s ‘Prehistoric Autopsy’ Series. You can clearly see how similar Lucy walks compared to modern humans. In contrast the Chimpanzee on the right does not have the required skeletal and muscular configuration of its hip to allow it to walk effectively on two legs.

Pelvic configuration in humans has slowly adapted to provide quite a host of requirements: the most advantageous configuration of musculature for locomotion, transfer of weight during locomotion and to hold the torso upright during locomotion, along with providing the space to adequately hold the internal viscera, and importantly, the birthing passage for offspring. Because of the above, I feel that the pelvis is one of those areas that is quite pivotal in considering an anthro characters design. Without having to delve too deep into bio-mechanics  it’s good to take a look at some of the requirements needed to make a pelvis fit our characters given needs to see what ‘rules’ we may need to follow when making them more anthropomorphic. 

Walking on 2 legs not 4 - Stride and energy

So what would make X-Men's Beast run faster than a human? Well there are a couple simple things that we can observe from those animals that can easily outrun us. Firstly, as a biped plantigrade our maximum stride length is really rather short, a longer stride covers more ground and generally makes a faster runner. (What could break that rule would be an elephant, a plantigrade, that moves it's legs very fast when it charges). 

Digitigrades like a cheetah and unguligrades such as horses have a stride advantage by having longer limbs distal from what would be the knee joint. Simply a lengthening of the metatarsals.

The length of the femurs represented above are equal in length across the different classes for comparison.

That's an advantageous change in bone configuration but driving the power is a muscular change. Secondly, animals like horses have short fibred muscles on their lower limbs that attach to long tendons for elastic energy storage. This increased spring creates a mechanical advantage in the limb, meaning the muscles become more economical as they do not need to generate as much force per stride.

Check out just how thin the lower leg is on a horse, those long tendons and the canon bone are really the only thing they've got; there's no muscle. Find more plates like this Here.

This video is taken from "Inside Nature's Giants - The Race Horse" - (Channel 4). It's a dramatic example of just how much force is stored in the tendons once they are under stress. Energy that would otherwise be lost is recovered via this elastic strain energy. This would make Beast's flat hand very energy inefficient whilst running, and even the bony arch of the human foot is rather inflexible and still a long way from holding the capacity of elastic strain of even a digitigrade.

So if you were designing a character that's a serious fast runner - biological or mech, you might want to give them a shorter thigh in relation to the lower leg to extend that stride and go easy on the musculature of the lower leg, giant muscles don't always create giant forces, that depends on their position on the limb in terms of leverage! Of course, these are not the only things to consider for a set of biped digitigrade legs...

Some ideas on larger herbivore types. That cervical curve is really going to dip if we make a character with those distinctive rounded shoulders with a neck in a 'stoop'. The nuchal ligaments are going to have to act like a crane arm to help stop that neck collapsing - it's rather unstable. So I've also highlighted some context as to large stabilising muscle shapes of the neck. I think this would really limit head rotation. Also the cervical vertebra in this configuration would have to be bulkier to take the stress of the lateral rotation.

Great video on cervical spine rotation.

S-spine, C-spine

Comparison of axial skeletons of a human and canine, arrows note the number and directions of each spinal curve. (Not to scale).

We encounter an extreme number of issues when converting quadruped anatomy to that of a biped. Essentially it boils down to the evolution of each systems handling of its centre of mass. Human bipeds balance their weight over 2 legs, with the centre of mass moving between each stance leg, however a quadruped dog shifts its weight between fore and hind limbs during movement.

The spines of each system are therefore adapted to cope with each of these extremes. The S-shape spine of a biped has 4 notable curves, creating it's distinctive S shape. This maintains the centre of gravity when standing from the top of the spine down through the feet. These curves also facilitate weight transference with minimal effort. 

The C-shape spine of quadrupeds have only 3 notable curves that are near opposite to biped curves. The C-shape comes from the thoracic and lumbar regions curving upwards. I've drawn the canine above stood upright, this would bring it's centre of gravity in front of its feet, causing it to be unbalanced and fall forward. The curvature of its spine, particularly at the lumbar region would not support the weight of an upright torso, the curve is in the wrong direction.

This shows that we simply can't start our anthropomorphic characters by just standing a quadruped up on 2 feet. This and other anatomical issues make this a poor starting point, however, should we wish to maintain a degree of our chosen animals features in our anthropomorphic bipeds we can start adapting this anatomy into likely possibles. Lets explore these possibilities...