Human-Human Interaction Forces and Interlimb Coordination During Side-by-Side Walking With Hand Contact.

Francesca Sylos-Labini,Francesco Lacquaniti,Andrea D'Avella,Yury Ivanenko

doi:10.3389/fphys.2018.00179

Francesca Sylos-Labini, Francesco Lacquaniti + Show 2 more

Open Access

https://doi.org/10.3389/fphys.2018.00179

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Abstract

Handholding can naturally occur between two walkers. When people walk side-by-side, either with or without hand contact, they often synchronize their steps. However, despite the importance of haptic interaction in general and the natural use of hand contact between humans during walking, few studies have investigated forces arising from physical interactions. Eight pairs of adult subjects participated in this study. They walked on side-by-side treadmills at 4 km/h independently and with hand contact. Only hand contact-related sensory information was available for unintentional synchronization, while visual and auditory communication was obstructed. Subjects walked at their natural cadences or following a metronome. Limb kinematics, hand contact 3D interaction forces and EMG activity of 12 upper limb muscles were recorded. Overall, unintentional step frequency locking was observed during about 40% of time in 88% of pairs walking with hand contact. On average, the amplitude of contact arm oscillations decreased while the contralateral (free) arm oscillated in the same way as during normal walking. Interestingly, EMG activity of the shoulder muscles of the contact arm did not decrease, and their synergistic pattern remained similar. The amplitude of interaction forces and of trunk oscillations was similar for synchronized and non-synchronized steps, though the synchronized steps were characterized by significantly more regular orientations of interaction forces. Our results further support the notion that gait synchronization during natural walking is common, and that it may occur through interaction forces. Conservation of the proximal muscle activity of the contact (not oscillating) arm is consistent with neural coupling between cervical and lumbosacral pattern generation circuitries (“quadrupedal” arm-leg coordination) during human gait. Overall, the findings suggest that individuals might integrate force interaction cues to communicate and coordinate steps during walking.

Highlights

When humans walk side by side they can hold each other hands and cues from interaction force may be advantageous for postural stability, sport training or physical rehabilitation
We described a novel approach to evaluate human-human interaction forces during side-by-side walking with hand contact
Even though the participants reduced oscillations of the contact arm, the rhythmic patterns of EMG activity of the proximal upper limb muscles were similar to those of normal walking when both upper limbs were oscillating (Figure 3)

Summary

Introduction

When humans walk side by side they can hold each other hands and cues from interaction force may be advantageous for postural stability (as, for example, in infants and elders or during unstable walking conditions), sport training or physical rehabilitation. Despite the importance of haptic interaction in general and the natural use of hand contact between humans during walking, to our knowledge there are no studies that examined and interpreted the interaction forces during side-by-side walking with hand contact to understand the neuro-mechanical processes underlying human-human physical interactions. Such studies may provide insights into the role of interaction forces in the dyad’s ability to communicate and interpret intended motion during locomotion

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