Have you ever wondered why it is that our four-legged friends are so much faster than us? Everything from a rabbit to an elephant can outrun us. It is not a size issue and it is not just because they have more legs. In fact, the fore-legs of most quadrupeds are actually anatomically similar to our arms. Ostriches are about the same size as us and have two legs yet they can leave Usain Bolt in the dust. The animal kingdom is full of biomechanical wonders that mother nature has provided through adaptation. We humans are far inferior physically because we are exponentially superior mentally. We can think ourselves out of danger, therefore there is no need for us to be super-hero fast.
The secret to animal speed has to do with the conservation of energy. Running with four limbs on the ground forces the animal to be flexed at the hip. This bent-forward position is especially efficient when it comes to generating backward force for propulsion. When the hind leg is tucked in close to the body it is in its greatest state of potential energy. This means that the muscles used for forward locomotion (glutes and quads) are stretched to the max and ready to contract through their complete range of motion. The second advantage this forward bend has is that when a hind leg pushes against the ground, the energy goes straight in to the hips which are perfectly aligned with the long axis of the spinal column. Just like a person pushing a door shut with a cane, the position most capable of transfering all energy is with a rigid force perpendicular to the movable object. This body position allows all the energy to go straight through the body and out through the front “legs”. This is called a structural advantage because the bony parts of the body are aligning so as to rely less on stabalizing muscles and more on the rigidity of the skeleton to transfer energy. The same structural advantage is used when a construction worker carries a 90lb bag of concrete mix on his shoulder rather than in his arms.
If a “four-legged” animal suddenly stood upright and ran on two legs, the structural advantage would go away. In this position, any energy that the now shortened prime-mover muscles produce will be transfered in to a spine that is pointing towards the sky. In order for the muscle exertion to result in an overall forward displacement of the animal, the energy must be harnesed and sent back down the spine and in to the ground through the driving leg. This is where rhythm and timing become more important. The way this is done in animals such as the ostrich is the use of a counter-balance at the top of the body. This is the reason for their long necks. We obviously have to achieve this energy transfer by other means. For us, it’s our arm swing that allows us to absorb and re-direct ascending energy during locomotion. In order for our spine to most effectively transfer energy it must maintain its natural “S” shape. Great muscular stability is necessary for this to happen. If our spine straightens and bends with each stride all our generated energy will go towards that internal motion. This is why our core muscles (erector spinae, multifidus, abdominals, etc) are essential to proper and efficient locomotion. Our upright posture requires muscular rigidity known as functional integrity. (I don’t call it functional advantage because it clearly is not advantageous)
Due to the hours spent sitting in cars, chairs and couches, our core stability is lacking. Usually when you hear the word “core” you think of crunches and abs. The core of you body has a more important role that making you look good on the beach. The main function of the afrementioned core muscles is to stabalize the spine so that work done at either end of the body does not go to waste. When people have weak cores they will adapt a forward lean position when they run or walk. Take a look around. You will be surprized by the number of people hunched over at the hips. Now walk by a mirror and be amazed. You do it too! Our bodies will always cheat and take the path of least resistance. The forward lean is a compensation that attempts to regain our primal structural advantage. We have learned this method for years , however with a conscious effort to maintain an upright posture and a proper exercise routine, you will one day be moving straight all the time.