Adaptations for economical bipedal running: the effect of limb structure on three-dimensional joint mechanics

Abstract

The purpose of this study was to examine the mechanical adaptations linked to economical locomotion in cursorial bipeds. We addressed this question by comparing mass-matched humans and avian bipeds (ostriches), which exhibit marked differences in limb structure and running economy. We hypothesized that the nearly 50 per cent lower energy cost of running in ostriches is a result of: (i) lower limb-swing mechanical power, (ii) greater stance-phase storage and release of elastic energy, and (iii) lower total muscle power output. To test these hypotheses, we used three-dimensional joint mechanical measurements and a simple model to estimate the elastic and muscle contributions to joint work and power. Contradictory to our first hypothesis, we found that ostriches and humans generate the same amounts of mechanical power to swing the limbs at a similar self-selected running speed, indicating that limb swing probably does not contribute to the difference in energy cost of running between these species. In contrast, we estimated that ostriches generate 120 per cent more stance-phase mechanical joint power via release of elastic energy compared with humans. This elastic mechanical power occurs nearly exclusively at the tarsometatarso-phalangeal joint, demonstrating a shift of mechanical power generation to distal joints compared with humans. We also estimated that positive muscle fibre power is 35 per cent lower in ostriches compared with humans, and is accounted for primarily by higher capacity for storage and release of elastic energy. Furthermore, our analysis revealed much larger frontal and internal/external rotation joint loads during ostrich running than in humans. Together, these findings support the hypothesis that a primary limb structure specialization linked to economical running in cursorial species is an elevated storage and release of elastic energy in tendon. In the ostrich, energy-saving specializations may also include passive frontal and internal/external rotation load-bearing mechanisms.

Musculoskeletal modeling of an ostrich (Struthio camelus) pelvic limb: Influence of limb orientation on muscular capacity during locomotion

“…This step allowed the TCS to be removed from the bone and 227 reattached in a different area to facilitate the dissection process while still preserving the 228 overall relationship of digitized points on a given bone between sessions. 229 Building a musculoskeletal model required points to be expressed in the segment 230 ACSs (Figure 2 and Rubenson et al, 2007Rubenson et al, ,2011. The pelvis reference frame was defined as 231 follows: the origin at the midline of the pelvis halfway between the left and right side hip 232 joint centres; the unit vector IL SUL (x-axis; positive being anterior); the cross-product of the 233…”

“…Prior to walking and running trials, static calibration trials were 188 performed in order to identify several key anatomical landmarks necessary to construct 189 segment Anatomical Coordinate Systems (ACS; see Rubenson et al (2007Rubenson et al ( ,2011) for 190 details).Anatomical landmarks were identified using a 6-marker pointer device and expressed 191 in the segment TCSs. The static calibration trials thus allowed for the reconstruction of each 192 segment ACS across walking/running strides using the motion data of the segment marker 193 clusters alone.…”

Three-dimensional anatomy of the knee joint of ostriches (Struthio camelus)

“…These descriptions can be used to further study the biomechanical Ostriches (Struthio camelus) are well known for their exceptional bipedal running 10 abilities (e.g., Alexander et al 1979). Their muscular, three-dimensionally mobile legs 11 (Rubenson et al, 2007) are attractive subjects for studies of mechanical forces in the knee 12 because they are able to accommodate large dynamic loads (Rubenson et al, 2010;such as undergoing genetic assimilation (Sarin et al, 1999), or indicating key changes in 63 locomotor function that correspond to altered loads on sesamoids (Hutchinson, 2002)? 64…”

Macroscopic and microscopic study of integuments on ostrich (Struthio camelus) foot

“…These nearly 150 kg birds can run steadily for 30 min at a speed of over 60 km/h, with each step longer than 5 m (1,12). In recent years, some researchers have focused on the muscles of the pelvic limb (18), meat (4), long bones (3), supra-jointed toe posture (7), articular cartilage (20), serum glycosaminoglycan and proteoglycan (11), economical bipedal running (16), and toepad from the anatomical perspective (8).…”