A biomechanical study of load carriage by two paired subjects in response to increased load mass

Abstract

The biomechanics of load carriage has been studied extensively with regards to single individuals, yet not so much with regards to collective transport. We investigated the biomechanics of walking in 10 paired individuals carrying a load that represented 20%, 30%, or 40% of the aggregated body-masses. We computed the energy recovery rate at the center of mass of the system consisting of the two individuals plus the carried load in order to test to what extent the pendulum-like behavior and the economy of the gait were affected. Joint torque was also computed to investigate the intra- and inter-subject strategies occurring in response to this. The ability of the subjects to move the whole system like a pendulum appeared rendered obvious through shortened step length and lowered vertical displacements at the center of mass of the system, while energy recovery rate and total mechanical energy remained constant. In parallel, an asymmetry of joint moment vertical amplitude and coupling among individuals in all pairs suggested the emergence of a leader/follower schema. Beyond the 30% threshold of increased load mass, the constraints at the joint level were balanced among individuals leading to a degraded pendulum-like behavior.

Biomechanical effects of the addition of a precision constraint on a collective load carriage task

“…[14]. Then based on the external work, the percentage of energy recovered of the CoM PACS in the sagittal plane was computed (called recovery rate RR in [16,27]). This parameter assesses the amount of energy transferred between the potential and the kinetic energy (equation (2.2)),RR=100true0Wkf+Wv−WextWkf+Wv.The closer the value of RR to 100%, the more consistent the locomotor pattern is with the inverted pendulum system (IPS) model of locomotion [14,28–30].…”

“…The forward kinetic (Wkf ), as well as the vertical (Wv) and external work (Wext) of the CoM PACS were computed according to the method of Bastien et al [14]. Then based on the external work, the percentage of energy recovered of the CoM PACS in the sagittal plane was computed (called recovery rate RR in [16,27]). This parameter assesses the amount of energy transferred between the potential and the kinetic energy (equation (2.2)),…”

Interacting humans use forces in specific frequencies to exchange information by touch

“…One possible candidate may be the physiological delays involved (35). Within the [2.15-7] Hz band we observed that the influence in the [2][3][4] Hz frequency sub-band correlated better with the task performance (Supplementary Fig. 2).…”

“…A subsequent study showed that one participant specialized in producing tangential forces while their partner was involved more in producing radial forces, related to finer positioning 37 . A differentiation of roles was also found in a study where two participants had to carry a load together 3 , with one participant applying consistently more force than the other, leading the researchers to suggest that the participant applying more force was the leader. On the basis of the present results, it can be argued that even if the Target Participants were the ones producing more force, it was the Synch Participants’ that influenced more the other.…”

“…Physical interactions help us learn skills, like learning to walk from our parents 1 , 2 . It helps us coordinate and work together in daily life, like lifting a table together 3 or dancing with a partner 4 . It lets us welcome and comfort others, and we use physical interactions to assist others, like helping an elderly person to stand up, or helping a rehabilitation patient to move.…”