Dynamic Balance Control and Postural Adaptation in Human-Robot Collaborative Manipulation: Within-Subject Experimental Study
Clinical Snapshot
PICO Framework
| P — Population | 14 healthy male participants performing manipulation tasks |
| I — Intervention | Human-robot collaboration with cobots (Robot Free and Robot Plane conditions) |
| C — Comparator | Manual manipulation without robotic assistance (Free condition) |
| O — Outcomes | Postural control parameters (center of pressure trajectories, sway metrics) and nonlinear recurrence quantification analysis indicators |
Bottom Line
This within-subject experimental study demonstrates that human-robot collaboration significantly increases postural sway and reduces stability during manipulation tasks, with 41% increase in postural displacement and 227% increase in sway area compared to manual work. While the structured nature of postural control is maintained (evidenced by nonlinear analysis), the increased physical demand suggests potential ergonomic concerns. The findings indicate that the mere presence of collaborative robots, regardless of their specific function, drives these postural changes. For Australian clinicians, this research highlights the need for comprehensive ergonomic assessment when implementing collaborative robotics in healthcare and industrial settings. The male-only sample and laboratory conditions limit generalisability, but the consistent biomechanical findings across multiple parameters suggest genuine physiological adaptation to human-robot interaction. Further research including diverse populations and real-world environments is needed before definitive clinical recommendations can be made.
Key Findings
P Value: P<0.001 for most primary comparisons
Effect Size: Mean distance increased 41% (1.7 to 2.4cm), confidence ellipse area increased 227% (7.6 to 24.9cm²)
Primary Outcome: Postural sway increased significantly in robot-assisted conditions compared to manual manipulation
Nnt Or Sensitivity: Effect sizes suggest clinically meaningful changes in postural stability parameters
Confidence Interval: Not reported for primary outcomes
Clinical Application
Findings applicable to workplace ergonomic assessments and cobot implementation strategies in Australian manufacturing Relevant to Safe Work Australia guidelines for workplace ergonomics and emerging technologies. May inform TGA considerations for medical/rehabilitation robotics and workplace safety standards Industrial workers engaged in human-robot collaborative tasks, particularly in manufacturing and assembly operations
Abstract
BACKGROUND: The integration of robots into industrial settings has rapidly advanced, aiming to reduce human involvement in demanding tasks while improving overall efficiency. As collaborative robots (cobots) become more prevalent, assessing the physical strain during joint tasks is essential to promote long-term well-being in the workplace. OBJECTIVE: This study aimed to investigate how human-robot collaboration influences workers' postural control and musculoskeletal load during manipulation tasks performed in parallel. METHODS: Fourteen healthy male participants performed manipulation tasks under 3 conditions: without robotic assistance, with a cobot providing load support (Robot Free [RF]) and a cobot constrained to horizontal movement (Robot Plane [RP]). Center of pressure trajectories were computed, and nonlinear recurrence quantification analysis indicators (recurrence rate [REC], determinism [DET], and their ratio) were calculated in the anteroposterior, mediolateral, and anteroposterior-mediolateral planes. RESULTS: Statistical analysis showed greater postural sway in robot-assisted conditions compared to Free. Mean distance increased from 1.7 (SD 0.6) cm in Free to 2.4 (SD 0.6) cm in RF (P<.001) and 2.3 (SD 0.6) cm in RP (P<.001). Mean velocity increased from 2.9 (SD 0.9) cm/s in Free to 4.3 (SD 1.4) cm/s in RF and RP. Confidence ellipse area increased from 7.6 (SD 4.1) cm2 in Free to 24.9 (SD 14.2) cm2 in RF and 23.1 (SD 13.4) cm2 in RP. Sway area increased from 1.5 (SD 0.7) cm2/s in Free to 2.9 (SD 1.2) cm2/s in RF and RP. Nonlinear metrics revealed lower recurrence rates in robot-assisted conditions, decreasing from 0.31 (SD 0.08) in Free to 0.2 (SD 0.08) in RF and 0.2 (SD 0.04) in RP in the anteroposterior-mediolateral plane (P<.001), from 0.33 (SD 0.08) in Free to 0.28 (SD 0.07) in RF (P=.02) and 0.16 (SD 0.03) in RP (P=.007) in the mediolateral direction, and from 0.36 (SD 0.07) in Free to 0.3 (SD 0.06) in RF (P=.009) and 0.26 (SD 0.03) in RP (P<.001) in the anteroposterior direction. Determinism remained stable (values close to 1), leading to higher determinism-to-recurrence ratios for robot-assisted conditions, increasing from 3.41 (SD 0.87) in Free to 5.41 (SD 1.69) in RF and 5.51 (SD 1.11) in RP in the anteroposterior-mediolateral plane (P<.001), from 3.11 (SD 0.63) in Free to 3.64 (SD 0.72) in RF (P=.02) and 3.92 (SD 0.48) in RP (P=.007) in the mediolateral direction, and from 2.82 (SD 0.48) in Free to 3.47 (SD 0.57) in RF (P=.009) and 3.46 (SD 0.45) in RP (P<.001) in the anteroposterior direction. No significant differences were found between the robot-assisted conditions. CONCLUSIONS: Interaction increases postural sway, indicating reduced stability and higher physical demand. This could reflect impaired balance or adaptation. Nonlinear analysis reveals that postural control remains structured. Results also suggest that the mere presence of the cobot is the primary driver of these postural changes.
References
- 1.de Nobile, A., Bibbo, D., Ranaldi, S., Schmid, M., Corvini, G., & Conforto, S. (2026). Dynamic balance control and postural adaptation in human-robot collaborative manipulation: Within-subject experimental study. JMIR Human Factors. https://doi.org/10.2196/79930
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