Human and avian running on uneven ground: a model-based comparison

Abstract

Birds and humans are successful bipedal runners, who have individually evolved bipedalism, but the extent of the similarities and differences of their bipedal locomotion is unknown. In turn, the anatomical differences of their locomotor systems complicate direct comparisons. However, a simplifying mechanical model, such as the conservative spring-mass model, can be used to describe both avian and human running and thus, provides a way to compare the locomotor strategies that birds and humans use when running on level and uneven ground. Although humans run with significantly steeper leg angles at touchdown and stiffer legs when compared with cursorial ground birds, swing-leg adaptations (leg angle and leg length kinematics) used by birds and humans while running appear similar across all types of uneven ground. Nevertheless, owing to morphological restrictions, the crouched avian leg has a greater range of leg angle and leg length adaptations when coping with drops and downward steps than the straight human leg. On the other hand, the straight human leg seems to use leg stiffness adaptation when coping with obstacles and upward steps unlike the crouched avian leg posture.

Stability in skipping gaits

“…Note that our parameter search is broader than the values of k and α so far obtained for bird or human walking, grounded running or running [15,16]. Applying a Newton–Raphson algorithm in this iteration [17], we identified a fixed point when deviations | y i +1  −  y i | were less than 10 −9 .…”

Effects of altered sagittal trunk orientation on kinetic pattern in able-bodied walking on uneven ground

“…When human walkers become aware of changes in the ground level, e.g. a drop, they adjust their locomotor strategies in the step before the perturbation ( Müller and Blickhan, 2010 ; Müller et al, 2012 , 2014 , 2016 ). For the main effect of the step type, our results revealed a significant effect in the pre-perturbation step only in case of the vertical impulse (4% increase relative to level step, Fig.…”

“…For example, when approaching a drop in ground level during walking, an upward rotation of the trunk during the step-down would increase the distance between CoM and foot and thus limit changes in CoM height which in turn would likely lead to reduced changes in kinetic behaviour. Humans might exploit this mechanism that in some way resembles the ability of small birds to adjust their zig-zag-like configured legs when coping with ground level perturbations ( Birn-Jeffery and Daley, 2012 ; Birn-Jeffery et al, 2014 ; Müller et al, 2016 ). In this sense, we expect that the upper body might be transformed into an active component of the human locomotor system in trunk-flexed walking.…”

“…Such asymmetries, found to be necessary for maintaining dynamic balance in pronograde gait ( Andrada, et al, 2014 ), were characterised by a reduction of the effective leg (connecting hip to centre of pressure) length and the GRF in the pre-swing phase as compared to the weight acceptance phase ( Andrada et al, 2014 ; Aminiaghdam et al, 2017 ). Comparing human and avian running on uneven ground, Müller et al (2016) reported that despite striking morphological disparities these species share some common kinematic behaviour (i.e. leg angle and leg length) while negotiating changes in ground level.…”

Reappraising the exteriorization of the mammalian testes through evolutionary physiology

“…It is certainly not a specific matter of the dynamics of flight insofar as birds and bats both fly efficiently and bats have scrotal testicles and birds do not. What is clear, however, is that both birds and mammals evolved during the water-land transition, sharing unique traits of bipedalism and endothermy [21,114]. Bird physiology differs from mammals in three fundamental waystheir lungs are 'stiff', they are constitutively hyperglycemic, and the adrenal chromaffin tissue is dispersed throughout the cortical tissue of the adrenals [61,62,66].…”