Shifting your weight
Balance is essentially about keeping even distribution of you weight around your center of gravity which must be maintained within the base of the body. This is relatively straight forward while you are standing still but there is an additional level of complexity when you are moving. The key to keeping in balance while moving lies in how you shift your weight to keep your center of gravity within the base of the body.
Before continuing a few concepts need clarifying. Firstly, the center of gravity can be thought of as imaginary vertical pole that dissects the body through the middle point of all the outer limits of the body. This pole changes location depending on the posture of the body. So if you are standing up straight with your arms by your sides the virtual pole goes through the center of your body and hits the ground between your feet. If you raise you right arm the pole shifts to the right to maintain this even distance. Notice that if your try this, when you lift your right arm other parts of your body adjust to re-position yourself (however subtle) such that your weight is also evenly distributed about this pole.
Next is the center of you mass which is the three dimensional center of the mass of your body which is middle point between the lower part of your sternum and back inside your body.
Next concept is the base of the body. You can think of this as a virtual mat that you stand on that changes shape depending on the placement of body parts (normally feet but can be any body part eg standing on your head). This mat can increase in area or decrease, so for example standing with your feet together makes for a smaller mat than when you are standing with your feet wider apart.
The key to balance is keeping your center of mass aligned with the virtual pole that at the same time is hitting the ground within the boundaries of your virtual mat.
Conventional walking means you throw the front leg forward which moves the center of gravity beyond the base mat for the time the foot is in the air. The moment it lands the base mat is enlarged to encompass the new location of the center of gravity hence returning your balance. During this process the center of mass is accelerated forwards and on landing exerts pressure equaling 4 times the mass of the body through the knee of the front leg.
We have a number of issues with this, firstly the whole body is out of balance while the front foot is in the air. Second is the amount of force exerted through the front knee.
What is the alternative. Instead of initiating the step through the front leg, you lift the front leg but drive forward using the rear leg. This keeps the center of gravity within the base of the body and reduces the force exerted through the front knee.
From and energetic point of view, conventional walking casues the energy too travel up as you take the step and then down as the foot lands. When drive from the back leg the energy travels in a straight line in your direction of travel which is far more efficient and causes less wear on the joints.
To stop in conventional walking you need to apply the breaks and push back against the momentum to stop. When driving from the back leg you just stop pushing from the back leg to stop. Less energy and wear on the joints.
A further benefit of driving from the back leg is that you use the full range of muscles, tendons and ligaments of the legs and hips which helps to keep them well conditioned.