Purpose: To investigate the paradoxical increase in metabolic energy cost with a suggested decrease in mechanical load on the lower limbs in Nordic Walking compared to normal walking. We hypothesized that the increase in metabolic energy cost could originate from a difference in walking speed or could be attributed solely to the swinging movement of the arm. Methods: In three different sets of experiments subjects walked on a motorized treadmill while metabolic energy consumption and electro-myographical (EMG) activity of selected arm and leg muscles were measured. The effect of walking speed was assessed systematically for both normal and Nordic Walking. The effect of the swinging motion of the arms was assessed by having subjects walk without poles, with normal poles and with poles that were equipped with wheels at the bottom such that the normal arm motion of Nordic Walking was preserved while push off was prevented. Results: Metabolic load in Nordic Walking was significantly higher (20%) compared to normal walking, which was independent of walking speed. EMG of the arm muscles was significantly higher in Nordic Walking compared to normal walking, while only minor differences in leg muscle EMG were found. Simulating arm motion of Nordic Walking using wheeled poles significantly increased metabolic load compared to normal walking but this did not reach the level of unconstrained Nordic Walking. Similarly arm muscle EMG was increased but remained lower compared to normal Nordic Walking. Conclusion: Increased metabolic load of Nordic Walking cannot be accounted for by walking speed and is only partly explained by the swinging motion of the arms. Significant arm muscles action seems devoted to the push off during Nordic Walking although only moderate relief of leg muscle action is found.