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Fig. 2 | Frontiers in Zoology

Fig. 2

From: Limb phase flexibility in walking: a test case in the squirrel monkey (Saimiri sciureus)

Fig. 2

The limb phase constraint model. The wheel is split into quadrants as described in Fig. 1. Gray arrows represent increases, black arrows directions of constraints and tradeoffs in locomotor mechanics. a) Energetics. Arrow a represents the incentive to move away from the singlefoot gait to avoid limb interference, while point b indicates an approximation of the predicted value of greatest energetic exchange derived from the models and empirical data of Griffin et al. [14], and Usherwood et al. [17], based on pendular and collisional mechanics respectively (see text for details). Point c represents an extrapolation of this into the diagonal sequence, diagonal couplet (DSDC) footfall pattern. b) Roll. Following Cartmill et al. [5], limb phase values can be split into a ‘zone of minimal bipedality’ (where, in walking, tripods and quadrupods predominate, helping to reduce roll), and two zones dominated by unilateral bipods around the pace (0, 100%) and bilateral bipods around the trot (50%). Bilateral bipedality is thought to generate less roll than unilateral bipedality. The gray arrow represents the continuum of maximal to minimal proportions of unilateral bipods, and minimal to maximal proportions of bilateral bipods contained within strides at a given limb phase value. At the edge and outside of the ‘zone of minimal bipedality’ (open circles) a DSDC gait will contain a greater proportion of bilateral bipods (point b) than the equivalent lateral sequence, lateral couplet (LSLC) gait (point a). c) Pitch. Pitching (both fore and aft) moments are minimized in a zone at the simultaneous gaits, increasing as limb phase values approach those of the singlefoot gaits

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