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First published online March 31, 2007
Journal of Experimental Biology 210, 1378-1390 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.001545
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Mechanics of cutting maneuvers by ostriches (Struthio camelus)

Devin L. Jindrich1,*, Nicola C. Smith2, Karin Jespers2 and Alan M. Wilson2,3

1 Department of Kinesiology, Physical Education Building East 107B, Arizona State University, Tempe AZ, 85287-0404, USA
2 Structure and Motion Laboratory, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire, AL9 7TA, UK
3 Structure and Motion Laboratory, Institute of Orthopaedics and Musculoskeletal Sciences, University College London, Royal National Orthopedic Hospital, Brockley Hill, Stanmore, Middlesex, HA7 4LP, UK


Figure 1
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  		Fig. 1. Experimental setup. (A) Plan view schematic of experimental arena. Ostriches ran along a narrow trackway until encountering a barrier placed directly beyond a force platform. Turns where ostriches stepped on the force platform were recorded and analyzed. Three-dimensional positions of 13 points on the body and legs were measured with a camera-based motion analysis system. (B) Points placed on the left side of an ostrich (with the exception of Spine, equivalent points were placed on the right side). Points were placed near joint centers for the hip, knee, ankle and MTP. (C) Angle convention used to analyze kinematic data. The X-axis was aligned axially along the fore–aft axis of the body and along leg segments. The Y-axis was approximately normal to the plane of motion of the joint. The Z-axis was normal to the X and Y axes. The two ground points identified the force platform in the tracking system but were not used for analysis.

 

Figure 2
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  		Fig. 2. Body rotation and deflection of the COM during the stance period of four conditions, straight running steps with the right (SR; magenta line) and left (SL; black line) legs, sidesteps with the right leg (TR; blue line) and crossovers with the left leg (TL; green line). Both angles are expressed in initial movement direction reference frame. Angles were scaled to percentage of the stance period, and averaged. Vertical whiskers denote s.e.m. at each phase of stance.

 

Figure 3
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  		Fig. 3. Relationships between turn magnitude (deflection; {theta}d) kinematic and force parameters important for turning. All four conditions are shown: straight running steps with the right (magenta triangles) and left (black circles) legs, sidesteps with the right leg (blue plus signs) and crossovers with the left leg (green crosses). Linear relationships from least-squares fits are indicated by black lines, and r2 values indicated for each relationship.

 

Figure 4
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  		Fig. 4. Stick figure representation of representative (i.e. trials with deflections closest to mean deflection for each turn type) trials for three types of running turns. Magenta line denotes force vector (of arbitrary scale for visualization). In Top View representation, only COM (black circle) and foot (green point) are shown, and magenta line denotes average forces for all trials in the indicated turn condition.

 

Figure 5
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  		Fig. 5. Forces and free moments for four different conditions. Colors, labels and error bars as described in Fig. 2.

 

Figure 6
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  		Fig. 6. Comparison of fore–aft forces generated during turning to forces predicted by simple turning model. Sidesteps are plotted as blue plus signs (+), crossovers as green crosses (x).

 

Figure 7
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  		Fig. 7. Body and joint angles during the stance period for four conditions studied. Colors, labels and error bars as described in Fig. 2. Asterisks denote significant differences between kinematics observed during turning and corresponding straight runs with the same legs. MTP, metatarsal–phalangeal.

 

Figure 8
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  		Fig. 8. Net torques about joint axes during the stance period four turning conditions. Colors, labels and error bars as described in Fig. 2. Descriptors in parentheses denote direction of positive angle changes. MTP, metatarsal–phalangeal.

 




© The Company of Biologists Ltd 2007