INTRODUCTION:​ The purpose of this study was to investigate the energetic cost, biomechanics, and kinematics of walking unassisted, with three different walkers (four-wheeled, 4W;​ two-wheeled, 2W;​ four-footed, 4F), and two different stride patterns (bipedal, BP;​ step-to, ST). I tested two hypotheses:​ 1) at a fixed speed, walking with a 4F walker, using a ST gait is metabolically more expensive than walking unassisted or with a 2W or 4W walker and 2) the greater cost of using a 4F walker is due to the slower walking speed, cost of lifting the walker, and a disabled inverted-pendulum energy exchange mechanism associated with the step-to gait.

METHODS:​ Ten (5M, 5F) young, healthy, adult subjects volunteered. I trained the subjects to walk with the three walkers and the ST gait. After training, I measured metabolic rate using expired gas analysis, video kinematics, and ground reaction forces while walking over a force sensing treadmill.

RESULTS:​ The net metabolic cost for subjects walking with the 4F walker at 0.30m/s was “only” 84% greater than bipedal (BP) walking at the same speed (p<0.001), much less then 212% reported in the literature. Metabolic cost with the 4W and 2W walkers was just 3% and 10% greater than BP walking at the same speed;​ respectively. Net metabolic power for walking at 0.30 m/s with the 4F walker was not statistically different from the combined metabolic rates for ST walking at 0.30 m/s plus the cost of 4F walker lifting.

DISCUSSION:​ Three principle factors contribute to the greatly elevated metabolic cost of using a 4F walker:​ slow speed, lifting, and the step-to gait. The 4F walker involves a dramatically slower preferred walking speed (4F 0.35m/s vs. BP 1.52m/s). The metabolic cost of bipedal walking at 0.30m/s increased metabolic cost per distance by 73% compared to walking bipedally at 1.25m/s. Lifting the 4F walker comprised 25% of the metabolic rate when using the 4F walker.

Three principle factors contribute to the greatly elevated metabolic cost of using a 4F walker:​ slow speed, lifting the walker, and the step-to gait.