Walking pattern efficiency during collective load transport

Abstract Background While the locomotor behavior of humans walking alone has been extensively studied, the locomotor behavior of humans transporting a load collectively is very poorly documented in the biomechanics literature. Yet, collective transport could find potential developments in other domains such as rehabilitation and robotics. Research question If collective load transport is made economically one could expect that the center of mass of the ensemble formed by several individuals and the load they carry has the same pendulum-like behavior as a single individual walking alone. The main objective of our study was to assess to what extent this is the case. Methods We recorded the 3D kinematics of movement of the body segments of ten dyads formed by two persons carrying a load together in three successive trials. The individuals carried the load, side by side, along a 13 m straight trajectory. Then, the recovery rate of the center of mass of the ensemble formed by the two individuals and the load they carry (i.e. the rate of transfer between potential and kinetic energy) was computed. Results The values of recovery rate were similar to those found in the literature for individuals walking alone, showing that the external energetic exchanges occurring during collective transport are as efficient as those occurring in single gait. The recovery rate also increased in successive trials, suggesting an improvement of the performance with familiarization. Significance Our results demonstrate the ability of humans to collaborate efficiently for carrying a load. The values of recovery rate we found could be used as a benchmark for the control of collaborative robots.