The movement of the arms acts primarily to balance the legs. For example, as the left leg goes forward and the right leg is back, without counter movement in the upper body, the whole body would tend to rotate to the right. But if one looks further at how the body’s musculature is arranged in spirals up and down the trunk, one can observe a spring like winding and unwinding that occurs in the opposed movement of arms and legs. When the right arm and left leg advance, for example, the arm lengthens the latissimus dorsi and the leg lengthens the gluteus muscles, creating a stretch through the thoracolumbar fascia, and through smaller spinal muscles. These lengthened muscles will then assist in returning the limbs past the line of the trunk to oppose the movement of the opposite limbs. The movement of upper limbs against lower creates a kind of clock spring tension and release between opposing sets of muscles.
What is most important to consider about the arms, I think, is the muscular connection from the fingertips through the arms to the head. The origin of many patterns of misuse is in writing and in the manipulation of implements, the clutching and gripping that is present when learning takes place under stress. There is usually a fair amount of stress that is associated with learning to write – we are trying to write well, we are being tested and compared with our contemporaries. While we are still quite young, we may develop patterns in attempts to control the hands that include excessive gripping, and that later we will repeat because they will generate sensations that we associate with control. If you make a fist and squeeze and allow the contraction to travel up the length of your arm you will notice the increase in sensation, and you may notice, as well, that your shoulder will begin to rise and your neck tighten. You have contracted all of the bones of the arm together, the arm into the shoulder, then the shoulder towards the spine and most particularly, the head. The head will be pulled back and down. This sensation will often come to be associated with control, and we will unconsciously replicate the condition of contraction as we initiate action in the hands. I see very often in the musicians with whom I work….. they have difficulty releasing their necks because their habits for how they use their hands literally cause the head to be pulled back and down. (Though, in fact, once they have established the pattern, it will first appear in the neck!)
In articles on running the one is often advised to make a light fist, or to squeeze the fingers and thumb together. Others write of relaxing the hands. What we need to find is what I would call good tension. Appropriate, unfixed muscle tone that allows the adjustable interaction of all the body’s parts. Dead, floppy hands are associated with fixed shoulders. This is why adding some life to the hands by pressing the fingers against the thumbs may be helpful. But if this becomes a lifeless position, it will lead to the same kind of fixity one is trying to prevent. A posturally neutral condition of the hand will not be one in which the fingers are curled into a fist, not will it be one in which the fingers are over-straightened. If you let your arms hang easily at your sides, without making them limp, you will find that your fingers hang open and gently curved. If you run with your hands like this, frequently bringing your awareness to your fingertips so that your hands don’t become rigid or limp, you will find is easier to avoid lifting the shoulders or becoming fixed in the shoulder joints.
If the angle of inclination of the body increases as speed increases, something interesting happens with arm movement. The increase in the amplitude of the arm swing will not lead to increased arm swing behind the trunk. The reasons for this are simple. When standing vertically, relaxed arms will hang vertically in line with the trunk. Thus, if the arms swing easily, they will travel like a pendulum, to forward and backward points approximately equidistant from the mid-line. In faster running, as the torso becomes increasingly inclined forwards, a relaxed arm will still hang vertically, which will no longer be in line with the trunk. So, at faster speeds, the length of the arc of arm swing will increase, but this will result in the arms swinging further forwards in front of the torso, but not substantially further behind the torso. So the shoulder hop that one sees in sprinters who run with a vertical torso will be avoided. Again, if one looks at how the arms are used in a vertical jump, that is, how the arms can be thrown up along the line of the body to assist in the leap, one can get a feel for that movement in running.