Age-related deficits in bilateral motor synergies and force coordination

Background Ageing may cause impairments in executing bilateral movement control. This study investigated age-related changes in interlimb force coordination across multiple trials by quantifying bilateral motor synergies based on the uncontrolled manifold hypothesis. Participants completed the trials with and without visual feedback. Methods Twenty healthy individuals (10 older adults and 10 young adults) performed 12 isometric force control trials for the two vision conditions at 5% of maximal voluntary contraction. All dependent variables were analyzed in two-way mixed model (Group × Vision Condition; 2 × 2) ANOVAs with repeated measures on the last factor. Results The analyses revealed that older adults had greater mean force produced by two hands in both vision conditions (i.e., yes and no visual feedback). Across both vision conditions, the older adult group showed greater asymmetrical force variability (i.e., standard deviation of non-dominant hand > standard deviation of dominant hand) and revealed more positive correlation coefficients between forces produced by two hands as compared with the young adult group. Finally, an index of bilateral motor synergies was significantly greater in young adults than older adults when visual feedback was available. Conclusion The current findings indicate that deficits in interlimb force coordination across multiple trials appeared in older adults.

Multi-Robot Trajectory Planning and Position/Force Coordination Control in Complex Welding Tasks

In this paper, the trajectory planning and position/force coordination control of multi-robot systems during the welding process are discussed. Trajectory planning is the basis of the position/ force cooperative control, an object-oriented hierarchical planning control strategy is adopted firstly, which has the ability to solve the problem of complex coordinate transformation, welding process requirement and constraints, etc. Furthermore, a new symmetrical internal and external adaptive variable impedance control is proposed for position/force tracking of multi-robot cooperative manipulators. Based on this control approach, the multi-robot cooperative manipulator is able to track a dynamic desired force and compensate for the unknown trajectory deviations, which result from external disturbances and calibration errors. In the end, the developed control scheme is experimentally tested on a multi-robot setup which is composed of three ESTUN industrial manipulators by welding a pipe-contact-pipe object. The simulations and experimental results are strongly proved that the proposed approach can finish the welding task smoothly and achieve a good position/force tracking performance.

Interlimb Force Coordination in Bipedal Dance Jumps: Comparison Between Experts and Novices

Bipedal tasks require interlimb coordination that improves with practice and acquisition of skills. The purpose of this study was to compare interlimb force coordination during dance-specific rate-controlled consecutive bipedal jumps (sautés) between expert dancers and nondancers. To analyze coordination of vertical ground reaction forces recorded under each leg, the vector coding approach was used. Although there were no differences in the patterns of interlimb force coordination between groups, the dancers exhibited less variability of interlimb force coordination during the transition phase from weight acceptance to propulsion as well as during the propulsion phase itself. The interlimb force coordination variability was associated with task performance only during the transition phase, which highlights the potential importance of control during this phase. In conclusion, expert dancers were better at reducing interlimb force coordination variability during the task-relevant transition phase, which was related to better performance at maintaining jump rate and jump height consistency.