Let’s consider the jump, the ultimate expression of verticality, and model for locomotion.
Place your feet about hip width apart, knees and feet pointed forward. It may help to use a mirror to ascertain that you begin with a fairly vertically oriented spine. See that your upper back is not behind your lower back, and that your pelvis is not pushed forwards or arched. If you notice that you are leaning backwards or hunching forwards or tipping your pelvis forward or backward, attempt to correct the condition without adding effort. Think of allowing length and decompressing to undo retractile forces. Center your weight slightly in front of the balls of your feet to stimulate your extensor reflexes (more on that later).
To jump and land in the same place, you will hinge at the hips, knees and ankles. Make sure that you incline your trunk forward when you hinge your hips. No ballet jumps, with the torso vertical. Your back should remain long and should not arch or round if you allow your hip joints to release. Your head should not be pulled back and your neck should remain long and in line with your spine. When ready, hinge and jump vertically. Try a couple of small jumps first. Notice that a small jump will not require that your legs straighten completely. Notice that the joints of your legs work equally and simultaneously, both in flexion and in extension – in other words, you do not extend the ankles as an afterthought. Try to sense that the whole body extends to jump. You are not just jumping with your legs, but you are letting the legs follow the extension of the trunk. Do not bypass the vertical and arch your back – this will not help you to go up, and will actually expend energy in going back that could be used to go further up.
If we look at the action of the major two-joint muscles involved in this action, we will see something interesting: the overall length of hamstrings, quadriceps and gastrocnemius muscles remains unchanged through the work phases of extension. [See Effects of the lower leg biarticular muscles in jumping] For example, while jumping, the hamstrings are lengthened at the knee, while they are shortened where they cross the hip joints. The quadriceps are shortened at the knee, and lengthened where they cross the hip joints. This means that if you are running with the natural principle of extension that I am putting forward, you will not get tight muscles. If, however, you are planting your foot in front of you and dragging yourself along the ground, you will experience tight hamstrings (as many runners do), because you will be unnecessarily shortening them. Personally, I have been able to run these last 20 years or so without stretching, including 100, 200, and 400 yard sprints on the track and scores of distance races, and I have experienced no reduction in my range of movement. I have no trouble touching my toes, and, with a little encouragement, can still place the palms of my hands on the floor while standing with straight knees (this is a lousy thing to do to your back – don’t do it!).
Note what your feet do as you jump and as you land. Notice how the legs extend to get the feet to the ground as quickly as possible. The same is true in a horizontal jump. If you leap over a puddle, notice how your foot reaches forward to find the ground before you fall upon it.
Nearly everything that you need to run is contained in the movement of a jump. While jumping, consider landing on your heels. I say consider it, because you will probably not be able to do it. Nor should you. It would be a good way to hurt yourself. In landing on your heels, you would defeat many of the shock absorbing mechanisms that have evolved in man. If you land on the ball of your foot, you use the whole system of springy muscles that propelled you upwards to absorb your weight as you descend, perfectly preparing you to launch yourself upwards again.
Now try this. Prepare to jump again, hinging at hips, knees and ankles. Instead of launching yourself vertically, extend yourself along the line that your trunk is in when you incline it forwards. Instead of jumping with two feet, try using one foot to launch yourself alone the line of your inclined spine. Your other foot will come under you as you move forwards in space. This is running. A full body extension inclined in space, the degree of inclination depending on the extent of the extension – how far you intend to leap. A long leap will be faster, and will more fully extend all of the involved joints. Fast running will result in a body that is fully extended from the head to the toes. The forward lean of the body allows the pelvis to incline to the extent required to straighten the leg without distortion (extra effort) of the trunk. Your legs work only as well as the torso which moves them, and a distorted torso (arched back, collapsed chest) will always lead to imbalance in leg action.
Notice how your foot lands if you jump forwards in this manner. Do you land on your heel? Probably not. If you want to absorb shock well, you will never do so by landing on your heel. Also, if your trunk is inclined and your leg extends well along the line determined by the trunk, then it will be more difficult to run into the legs, landing on the heels as the legs recover. A well extended leg recovers itself. After extending, the hip, knee and ankle will flex to recover the leg. But, as the leg completes the recovery cycle and heads for the ground, the joints are again beginning to extend. Only an ankle that is rigidly held will remain flexed, leading to excessive heel-strike. The foot should be reaching for the ground, to get the weight of the leg gently on the ground before it takes the moving body’s weight.
Consider landing on the heel. If you are running on uneven ground, this is a very dangerous thing to do. If you land on the heel, you will not have the adaptable musculature of the foot working to prevent your foot from rolling to the side. If, on the other hand, your leg reaches the ground ahead of your weight, with your toes or the ball of your foot landing first, you will adjust to the uneven surface before your full weight is on your leg. Thus, the feet are very important as sensory organs. As stated above, in both walking and running, your foot reaches the ground before your full body weight is upon it, giving a brief moment for messages from the feet to integrate with sensory input from the eyes, and mechanisms in the vestibular system (ear canals and otoliths), and for subsequent adjustments in muscle tone that will create appropriate changes to deal with surface changes, as well as with your changes in intention (acceleration, deceleration, changes in direction, etc.).
See: The biarticular muscles