Horizontal versus vertical clearance: implications for performance and postural risk in constrained manual...

Objectives. Empirical data on how different workspace clearance dimensions affect manual task outcomes and worker posture remain scarce, despite the acknowledged importance of spatial design in ergonomics. This study investigates the effects of horizontal and vertical clearances on cycle time, error count and postural behaviors. Methods. A within-subject repeated-measures design was employed, where participants (n = 12, mean age 23 ± 3.4 years) performed a simulated assembly task under varying horizontal and vertical clearance conditions. Results. Horizontal clearance has a statistically significant effect on cycle time (F = 36.15, p < 0.001, η² = 0.475), with reduced horizontal clearance leading to longer cycle times. In contrast, vertical clearance did not significantly influence cycle time. Analysis of error counts using a Poisson generalized linear model showed no significant impact of either horizontal or vertical clearance on assembly errors (p = 0.628), suggesting that error rates were not strongly affected by experimental parameters. Postural observations revealed that reduced horizontal clearance resulted in adoption of compensatory postures such as increased shoulder elevation and arm adduction, especially under limited vertical clearance. Conclusion. These findings highlight the importance of optimizing horizontal clearance (minimum of 450 mm) to improve efficiency while managing vertical clearance to reduce ergonomic risk in constrained workspaces.