Whether arm swing is a passive, natural motion caused by the rotation of torso or is an active motion that requires active muscle work has been a critical discussion on arm swing that could illuminate its benefit and function. A recent study concentrated on the energy consumption during walking showed that at low speeds arm swing is a passive motion dictated by the kinematics of torso, no different from a pair of pendula hung from the shoulders. Active upper extremity muscle work, controlled by the brain, only takes part when there is a perturbation and restores that natural motion. However, at higher speeds, the passive motion is insufficient to explain the amplitude of the swing observed in the experiments. The contribution of active muscle work increases with the walking speed. Despite the fact that a certain amount of energy is consumed for the arm movements, the total energy consumption drops meaning that arm swing still reduces the cost of walking. That reduction in the energy is up to 12 percent at certain walking speeds, a significant saving.

The inter-limb coordination in human locomotion, questioning whether the human gait is based on quadruped locomotion, is another major topic of interest. Some research indicates that inter-limb coordination during human locomotion is organized in a similar way to that in the cat, promoting the view that the arm swing may be a residual function from quadruped gait.