Arm Strokes and Posture

1. Principles of Pendulum Oscillation 

  - The time it takes for a pendulum to travel one cycle is only affected by the distance(L_p) between the origin and the pendulum. The weight of the pendulum has no effect.

  - The maximum stroke speed of the pendulum (V_c) is determined by the maximum height of the pendulum motion (h_max).

2. Arm motion

  - The total length of the arm and the angle at which the elbow is bent determine the natural duration of the arm's one-cycle pendulum motion. This can be altered by intentionally applying force to the arm muscles. 

  - The maximum height of the arm as it retracts determines the maximum speed of the arm's stroke.

  - When running, the distance(L_p) between the origin and the pendulum is reduced by bending the elbows a lot to shorten the one-cycle oscillation time.

3. Postural deformity involving the arm strokes

  - Differences in the force applied to the muscles of the two arms, the maximum retraction height (h_max), and the elbow bend angle cause differences in the left and right stroke distance of the arms.

  - Persistent and excessive differences in these forces, heights, and (or) angles are manifested as a tilt of the shoulder line and a difference in left/right arm stroke distances .