Does arm swing provide mechanical and metabolic benefits during human running?

Abstract

Previous research has shown that the primary function of arm swing in running is to counteract the angular momentum (about the vertical axis) generated by the swinging legs, but with no apparent benefit in reducing the demand for metabolic power. We investigated the mechanical and metabolic consequences of restricting arm swing. We hypothesized that restricting arm swing would increase torso rotation (a compensatory strategy to counteract the angular momentum generated by the swinging legs) and thus increase metabolic power demand. Thirteen subjects ran at 3 m/s for randomized conditions of normal arm swing, arms held behind the back (Back), arms held across the chest (Chest), and arms clasped on top of the head (Head) while we measured the 3‐D motions of the body and net metabolic power (W/kg). Compared to running with normal arm swing (32±2 deg, mean ± sem), subjects modified upper body motion by significantly increasing torso rotation by 12.9% (Back; p < 0.05) and 43.2% (Chest; p < 0.05). However, torso rotation was not significantly greater for the Head condition (7.2%; p = 0.33). Compared to running with normal arm swing (9.84±0.17 W/kg), restricting arm swing increased the net metabolic power demand by 2.9% (Back), 8.8% (Chest), and 13.3% (Head; all p's < 0.05). We conclude that normal arm swing provides both mechanical and metabolic benefits by minimizing the amount of torso rotation needed to counteract the angular momentum of the swinging legs.