Transition from shod to barefoot alters dynamic stability during running

Introduction: Barefoot running recently received increased attention, with controversial results regarding its effects on injury risk and performance. Numerous studies examined the kinetic and kinematic changes between the shod and the barefoot condition. Intrinsic parameters such as the local dynamic stability could provide new insight regarding neuromuscular control when immediately transitioning from one running condition to the other. We investigated the local dynamic stability during the change from shod to barefoot running. We further measured biomechanical parameters to examine the mechanisms governing this transition. Methods: Twenty habitually shod, young and healthy participants ran on a pressure plate-equipped treadmill and alternated between shod and barefoot running. We calculated the largest Lyapunov exponents as a measure of errors in the control of the movement. Biomechanical parameters were also collected. Results: Local dynamic stability decreased significantly (d = 0.41; 2.1%) during barefoot running indicating worse control over the movement. We measured higher cadence (d = 0.35; 2.2%) and total flight time (d = 0.58; 19%), lower total contact time (d = 0.58; -5%), total vertical displacement (d = 0.39; -4%), and vertical impulse (d = 1.32; 11%) over the two minutes when running barefoot. The strike index changed significantly (d = 1.29; 237%) towards the front of the foot. Conclusions: Immediate transition from shod to the barefoot condition resulted in an increased instability and indicates a worst control over the movement. The increased instability was associated with biomechanical changes (i.e. foot strike patterns) of the participants in the barefoot condition. Possible reasons why this instability arises, might be traced in the stance phase and particularly in the push-off. The decreased stability might affect injury risk and performance.