Because muscles are connected to the bones by fixed attachments, our limbs can only move by oscillation and not through complete revolution, as the wheels of a steam engine do.
Any movement we execute intentionally is a problem to be resolved: there is a goal to reach, and it must be reached in the simplest way possible.
The principle of least effort…belongs to the instinct rather than to the will. The less we are conscious of it, the more it manifests itself. Mechanical movements will therefore be simpler than the others: any sign of elegance or embellishment is inevitably eliminated. (Compare, for instance, ordinary handwriting to penmanship.)