Peak pressure experienced by the human hand during suspension and vertical climbing

Reconstructions of potential arboreal capabilities in extinct human ancestors (hominins) are typically inferred from upper limb morphology. Arboreal environments are complex with multiple support sizes and orientations. However, data are limited on how arboreal support variables may affect hand loading during arboreal activities. Using a custom-built climbing frame with interchangeable support diameters (45 mm, 80 mm, 105 mm), we investigated the effects of support diameter and horizontal/vertical orientation on the pressure experienced by the human hand during postural and locomotor suspension and vertical climbing (n=14 participants each). Support diameter had a consistent effect on suspension and vertical climbing normalized peak pressure values, but thumb positioning or postural versus locomotor activities had no significant relationship. The 45 mm diameter had significantly greater normalized peak pressure values compared to the 80 mm and 105 mm diameters. Postural and locomotor activity differences were only observed during vertical climbing but varied with support diameter size. Suspension and vertical climbing frequently load the third ray but distal-proximal peak pressure location patterns differ with support orientation. Support diameter and, less so, orientation influence the magnitude of loading in the human hand during the investigated arboreal behaviors. Peak pressure location patterns can distinguish suspension and vertical climbing locomotor categories within our experimental setting.