I don’t belong to the clenched-fist or air-clutching school of studied stylists…the mirror of perfect running action, fully-relaxed even under extreme pressure, arms driving straight through and carried easily at a natural height. The minute you clench that fist you tense the arm muscles and the shoulder muscles and encourage swaying and loss of balance. That is wasteful. All your energy should be directed in moving forward over the ground.
— Arthur Lydiard, 1926
There is not much more that I believe needs to be added from this chapter than the opening paragraph which is listed above. Run fully-relaxed, moving forward. No wasted motion. No wasted energy.
But remember, as Lydiard said to finish this chapter…
To perform at his best an athlete must be racing fit, and the better his condition before he starts racing, the more racing he can stand and keep improving. If he is not well-conditioned first, his performances will level off after a race or two and even fall away.
Phillips Running 