Evolutionary Robotic Approaches in Primate Gait Analysis

Abstract

Understanding how primates move is particularly challenging because many of the experimentation techniques that would normally be available are unsuitable for ethical and conservation reasons. We therefore need to develop techniques that can maximize the data available from minimally intrusive experimentation. One approach for achieving this is to use evolutionary robotic techniques to build a musculoskeletal simulation and generate movement patterns that optimize some global parameter such as economy or performance, or to match existing kinematic data. If the simulation has a sufficiently high biofidelity and can match experimentally measured performance criteria then we can use it to predict aspects of locomotor mechanics that would otherwise be impossible to measure. This approach is particularly valuable when studying fossil primates because it can be based entirely on morphology and can generate movements spontaneously. A major question in human evolution is the origin of bipedal running and the role of elastic energy storage. By using an evolutionary robotics model of humanoid running we can show that elastic storage is required for efficient, high-performance running. Elasticity allows both energy recovery to minimize total energy cost and also power amplification to allow high performance. The most important elastic energy store on the human hind limb is the Achilles tendon: a feature that is at best weakly expressed among the African great apes. By running simulations both with and without this structure we can demonstrate its importance, and we suggest that identification of the presence or otherwise of this tendon-perhaps by calcaneal morphology or Sharpey's fibers-is essential for identifying when and where in the fossil record human style running originated.

The Effect of the Achilles Tendon on Trabecular Structure in the Primate Calcaneus

“…Recently, both Sellers et al (2010) and Crompton et al (2010) suggested that evidence for a lengthy Achilles tendon may be found in the trabecular microarchitecture underlying the Achilles insertion. We agreed with these authors that studying the Achilles tendon's effect on trabeculae was an appropriate approach and attempted to test this hypothesis in a small sample of primates; however, our study failed to find any correlation between Achilles tendon morphology and parameters of trabecular microstructure in the region underlying the Achilles tendon.…”

“…The Achilles tendon is comprised of the triceps surae muscle complex merging distally to form a single tendon, which inserts onto the tuber of the calcaneus (O'Brien, 2005;Harris and Peduto, 2006). The Achilles tendon has been found to increase locomotor efficiency by storing energy and returning it in elastic recoil (Alexander and BennetClark, 1977;Alexander, 1984;Ker et al, 1987;Swartz, 1993;Sellers et al, 2010) and is subject to extremely high loads during various activities such as walking, running, and jumping (O'Brien, 2005). Because the Achilles tendon is particularly efficient at storing elastic energy during running, some (e.g., Bramble and Lieberman, 2004) have argued that an elongated tendon was a crucial adaptation that allowed for long distance endurance running in early members of the genus Homo.…”

“…The majority of fossil calcanei discovered have substantial damage to the area where the Achilles tendon inserts, thereby limiting the number of fossils that could potentially shed light on the evolution of this structure. Some researchers have therefore suggested that evidence for an elongated tendon may be found in the internal microstructure of the calcaneus Sellers et al, 2010). Maga et al (2006) examined the trabecular architecture of the calcaneus in several hominoid species and found important, perhaps functionally relevant, differences.…”

Evaluation of the minimum energy hypothesis and other potential optimality criteria for human running

“…), the GRFs were visually and quantitatively less realistic than other simulated variables. Other predictive simulations of human running have had similar issues with short stance times [41,42]. The model is capable of generating more realistic GRF with its existing dynamics, as seen in the data-tracking simulation (figure 3).…”

Arboreality, terrestriality and bipedalism

“…In recent simulation work (Sellers et al 2010), the role of tendon elasticity was quantified by 'virtual ablation'. In this paradigm, simulations are repeated with identical anatomical models except for the structure of interest, which is c h i m p a n z e e g o r i l l a o r a n g u t a n g i b b o n h u m a n r e i n d e e r h a r e g r e y h o u n d Review.…”