Department for Sport and Health Sciences, Technische Universität München, Munich, Germany.
School of Health Sciences, University of East Anglia, Norwich, UK.
Sci Rep. 2017 Apr 25;7(1):1135. doi: 10.1038/s41598-017-01265-7.
Whether tree canopy habitats played a sustained role in the ecology of ancestral bipedal hominins is unresolved. Some argue that arboreal bipedalism was prohibitively risky for hominins whose increasingly modern anatomy prevented them from gripping branches with their feet. Balancing on two legs is indeed challenging for humans under optimal conditions let alone in forest canopy, which is physically and visually highly dynamic. Here we quantify the impact of forest canopy characteristics on postural stability in humans. Viewing a movie of swaying branches while standing on a branch-like bouncy springboard destabilised the participants as much as wearing a blindfold. However "light touch", a sensorimotor strategy based on light fingertip support, significantly enhanced their balance and lowered their thigh muscle activity by up to 30%. This demonstrates how a light touch strategy could have been central to our ancestor's ability to avoid falls and reduce the mechanical and metabolic cost of arboreal feeding and movement. Our results may also indicate that some adaptations in the hand that facilitated continued access to forest canopy may have complemented, rather than opposed, adaptations that facilitated precise manipulation and tool use.
树冠状栖息地是否在祖先两足类人猿的生态学中发挥了持续作用仍未得到解决。一些人认为，树栖两足动物对解剖结构日益现代化的人类来说风险太大，因为它们的脚无法抓住树枝。在最佳条件下，平衡双腿对人类来说确实具有挑战性，更不用说在树冠中，树冠在物理和视觉上都极具动态性。在这里，我们量化了森林树冠特征对人类姿势稳定性的影响。观看摇摆树枝的电影，同时站在类似树枝的弹弓跳板上，会像戴眼罩一样使参与者失去平衡。然而，“轻触”，一种基于轻触指尖支撑的感觉运动策略，通过将大腿肌肉活动减少高达 30%，显著提高了他们的平衡能力。这表明，轻触策略如何成为我们祖先避免摔倒和减少树栖进食和运动的机械和代谢成本的核心。我们的结果也可能表明，手的某些适应能力使我们能够继续进入树冠，这可能与促进精确操作和工具使用的适应能力相辅相成，而不是相反。
