Neuromusculoskeletal computer modeling and simulation of upright, straight‐legged, bipedal locomotion of Australopithecus afarensis (A.L. 288‐1)

Abstract

The skeleton of Australopithecus afarensis (A.L. 288-1, better known as "Lucy") is by far the most complete record of locomotor morphology of early hominids currently available. Even though researchers agree that the postcranial skeleton of Lucy shows morphological features indicative of bipedality, only a few studies have investigated Lucy's bipedal locomotion itself. Lucy's energy expenditure during locomotion has been the topic of much speculation, but has not been investigated, except for several estimates derived from experimental data collected on other animals. To gain further insights into how Lucy may have walked, we generated a full three-dimensional (3D) reconstruction and forward-dynamic simulation of upright bipedal locomotion of this ancient human ancestor. Laser-scanned 3D bone geometries were combined with state-of-the-art neuromusculoskeletal modeling and simulation techniques from computational biomechanics. A detailed full 3D neuromusculoskeletal model was developed that encompassed all major bones, joints (10), and muscles (52) of the lower extremity. A model of muscle force and heat production was used to actuate the musculoskeletal system, and to estimate total energy expenditure during locomotion. Neural activation profiles for each of the 52 muscles that produced a single step of locomotion, while at the same time minimizing the energy consumed per meter traveled, were searched through numerical optimization. The numerical optimization resulted in smooth locomotor kinematics, and the predicted energy expenditure was appropriate for upright bipedal walking in an individual of Lucy's body size.

The human gluteus maximus and its role in running

“…Had australopithecines a human-like gluteal configuration, the GM would have had little leverage for extension of the femur, an important function in both human and ape locomotion (Berge, 1994;Berge and Daynes, 2001). In another modeling study (Nagano et al, 2005), it was estimated that if australopithecines had modern human-like gluteal attachments, then the GM would have needed to produce 30% higher forces than those of modern humans during walking. Although Nagano et al primarily modeled the GM as an extensor of the hip (Nagano et al, 2005), they attributed its higher force production to its role as a hip abductor needed to maintain lateral trunk stability on a relatively wide pelvis.…”

A three-dimensional musculoskeletal model of the chimpanzee (Pan troglodytes) pelvis and hind limb

“…In this regard, validation of optimization criteria for predicting movement tasks in humans and chimpanzees is crucial if these same criteria are applied to fossil hominins or other species for performance-based prediction when experimental data are unavailable (e.g. Nagano et al, 2005;Sellers et al, 2005). As such, the model can also operate as a hypothesis generator for direct experimentation, and allow estimation of parameter values that are simply not feasible to measure directly.…”

Evolutionary Robotic Approaches in Primate Gait Analysis

“…Modeling approaches are advantageous in that they allow the complete removal of such constraints and allow the production of models that have no elastic component but are otherwise reasonably lifelike. Bipedal locomotor modeling is a popular activity, with models varying from the highly theoretical (Alexander 1992;McGeer 1992;Minetti and Alexander 1997;Srinivasan and Ruina 2006) to more realistic simulations (Nagano et al 2005;Sellers et al 2003;Yamazaki et al 1996). Modeling approaches have been used both to understand the fundamental mechanics of bipedal gait and also to predict gait parameters: either internal values that are difficult to measure directly or for fossil vertebrates where experimentation is impossible.…”

“…Alternatives mix in degrees of global optimization with a reduced reliance on kinematic constraints. Thus, e.g., models can use global optimization to minimize energy cost within a single step but with the start and end posture defined (Nagano et al 2005), or, alternatively, they can kinematically constrain only part of the motion such as the foot and use global optimisation to control the rest of the body (Nicolas et al 2007). These approaches all have their uses: if kinematics are known then inverse dynamics gives precise values for mechanical work.…”