Anthro leg structure 2

I was asked a few weeks ago to help with creating a set of satyr legs. The main point I outlined was:

only look at the biggest forms when filling out the wire frame with muscles. Keep the curves flowing; show the largest sweeps of these shapes to keep them dynamic; have them show the force of the muscles not just their outlines. Don’t get too hung up on individual muscles at the start, that detail is for later when you’re shading, make sure you’re drawing the big forms to start with.

Some ideas to consider on an unguiligrade biped leg.

Gesture: Centre top is an idea of the flowing curves for a digitigrade and unguligrade type. I wanted to get an idea of the fundamental shapes the curves make as if the legs were mechanical; they would be made of curves that would give them spring as they moved.

Form: On the left an idea of where the muscular bulk is as opposed to the bone and tendon areas. All limbs follow the principle that they get thinner the more distal (further from the torso) they become. Take the human arm as example, muscular bulk decreases further down the arm and the limb becomes more sinuous until we get down to just tendons controlling the hand and fingers. This decrease in muscular bulk is worth noting when drawing so as to keep the limb in proportion. On the right is this idea now shown as contours in the forms of the leg.

Function: At the bottom of the image is a movement sequence. Those areas shaded represent the major muscles that are contracting. The quadriceps, (Q) extend the knee just before the 'contact'. On the 'down', the limb is slowed by the hamstrings (H) as the limb takes the torso's full weight. The elastic energy in taking this weight is channelled down into to fetlock or toe joint by long flexor tendons. This energy is released in the 'up' with the gluteals (G) powering the knee to full extension and the hamstrings extending the hip. This drives the torso forwards as I've talked about in previous posts. Note that the 'knee' and the 'toe' joints flex and extend by the greatest degree, the 'ankle' joint is kept relativity stiff. If the ankle was allowed to flex too much the limb would collapse under the weight of the torso.



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!