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Author Notes:

Correspondence: lena.ting@bme.gatech.edu; lting@emory.edu

All authors contributed to the design of the experiment.

AS JLM and TB collected the data, while AS and TB processed the data.

AS and LHT analyzed the data and drafted the initial version of the manuscript.

All authors contributed to the revising of the manuscript.

All authors read and approved the final manuscript.

We thank H. Bartlett for assistance with the design of experimental apparatus.

None of the funding bodies had any role in the design of the study, collection, analysis, and interpretation of the data, or the writing of the manuscript.

The authors declare that they have no competing interests.

Written, informed consent was obtained from each subject.

The Institutional Review Board of the Georgia Institute of Technology approved all protocols.


Research Funding:

This work was supported by NSF/EFRI award 1137229, NIH UL1TR000454, NIH KL2TR000455, and the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health under Award Number K12HD073945.


  • Haptics
  • Human-human interaction
  • Human-robot interaction
  • Rehabilitation
  • Rehabilitation robotics

Small forces that differ with prior motor experience can communicate movement goals during human-human physical interaction.


Journal Title:

Journal of NeuroEngineering and Rehabilitation


Volume 14, Number 8


Type of Work:

Article | Final Publisher PDF


BACKGROUND: Physical interactions between two people are ubiquitous in our daily lives, and an integral part of many forms of rehabilitation. However, few studies have investigated forces arising from physical interactions between humans during a cooperative motor task, particularly during overground movements. As such, the direction and magnitude of interaction forces between two human partners, how those forces are used to communicate movement goals, and whether they change with motor experience remains unknown. A better understanding of how cooperative physical interactions are achieved in healthy individuals of different skill levels is a first step toward understanding principles of physical interactions that could be applied to robotic devices for motor assistance and rehabilitation. METHODS: Interaction forces between expert and novice partner dancers were recorded while performing a forward-backward partnered stepping task with assigned "leader" and "follower" roles. Their position was recorded using motion capture. The magnitude and direction of the interaction forces were analyzed and compared across groups (i.e. expert-expert, expert-novice, and novice-novice) and across movement phases (i.e. forward, backward, change of direction). RESULTS: All dyads were able to perform the partnered stepping task with some level of proficiency. Relatively small interaction forces (10-30N) were observed across all dyads, but were significantly larger among expert-expert dyads. Interaction forces were also found to be significantly different across movement phases. However, interaction force magnitude did not change as whole-body synchronization between partners improved across trials. CONCLUSIONS: Relatively small interaction forces may communicate movement goals (i.e. "what to do and when to do it") between human partners during cooperative physical interactions. Moreover, these small interactions forces vary with prior motor experience, and may act primarily as guiding cues that convey information about movement goals rather than providing physical assistance. This suggests that robots may be able to provide meaningful physical interactions for rehabilitation using relatively small force levels.

Copyright information:

© The Author(s). 2017

This is an Open Access work distributed under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/).
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