Analysis of Rubenson et al. (2011; Fig. 7) indicates that hip adduction, not abduction, should be resisted in the course of stance phase in locomoting ostriches, and as a result abductor muscle activity is predicted, a moment that many hip extensors generate anyway. Nevertheless, hip adduction capacity is much more limited–only the IC, AMB1, two and IFI muscle tissues have clear actions in hip adduction. (Smith et al. (2006): Table 2) assigned adductor actions to other muscles such as the flexor cruris (FC) heads, PIFML and OM whereas we findHutchinson et al. (2015), PeerJ, DOI 10.7717/peerj.38/these to become abductors. Certainly, the actions on the two heads of AMB may oppose each other (Table 4), so it would be fascinating to understand how they may be coordinated. The ITC muscle’s parts have clear roles in medial rotation, but their actions in flexion/extension differ with limb posture (see also Gatesy, 1994), rendering it significantly less clear irrespective of whether (or when) they play a predominant hip extensor (e.g., Rubenson et al., 2006) or hip flexor (e.g., Smith et al., 2006; Smith et al., 2007) role in ostriches or other birds. How any birds balance this complex interaction of long-axis and ab/adductor moments at the hip or other joints remains nearly unexplored (but see Gatesy, 1994), but modelling (and simulation) approaches which include ours present a single method to tease apart the complexity. Bates Schachner (2012) found that Alligator and Struthio had equivalent hip extensor moment arms but there were big abduction and modest adduction moment arms in their ostrich, in addition to large long-axis rotation moment arms. The functional and evolutionary implications of these variations stay unclear, and dependent on understanding force balance concerning the hip joint in extant archosaurs for example Struthio. Complicated function isn’t restricted to proximal muscle tissues, nevertheless. Complicated anatomy of distal limb muscles can be a pernicious problem in avian locomotor biomechanics, and hard to render realistically in biomechanical models like ours. Because the Text S1 describes, we could not model all origins (or subdivided tendons; e.g., digital flexors) of all muscle components. Indeed, in some circumstances the origins are diffuse–e.g., M. C 87 site gastrocnemius medialis originates mostly in the medial side of your proximal tibiotarsus, but the surrounding fascia it PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19996384 is attached to continue proximally past the knee joint, through the proximal patella along with other structures. It can be not clear if some of these distal muscles exert significant moments in regards to the knee joint (some forces could be going straight to their distal origins in the tibiotarsus), and the dynamics of your patella (not represented in our model except as a static wrapping surface) further complicates matters. Therefore, it really is unclear how forces are balanced across ostrich (or other avian) knees, complicating comparisons with other species (e.g., Higham, Biewener Wakeling, 2008; Andrada et al., 2013). Young, Scott Loeb (1993) and Johnson et al. (2008) noted that some muscles in cat and rat hindlimbs seemed to have intrinsically stabilizing properties, shifting from flexor to extensor moment arms in a linear fashion with growing joint flexion. Eight modelled ostrich limb muscle tissues also show this pattern: the AMB1, AMB2, IC, ITCa, ITCp, ITM, ITCR and ISF exhibit stabilization function in flexion-extension (Figs. 9 and 10). Weaker evidence for self-stabilization is present for the OM muscle in hip ab/adduction (Fig. 14) as well as the four ankle flexors in flexion/extension (TCf, TCt, EDL, and FL; Fig. 18),.