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First published online March 27, 2009
Journal of Experimental Biology 212, 1163-1169 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027938
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Mechanics of generating friction during locomotion on rough and smooth arboreal trackways

Andrew R. Lammers

Department of Health Sciences, Cleveland State University, 2121 Euclid Ave, Cleveland, OH 44115, USA


Figure 1
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  		Fig. 1. Cross section of a cylindrical branch trackway with vertical force (FV; shown in blue) and mediolateral force (FML; shown in green) represented by solid arrows. Normal components (FV,normal and FML,normal) are represented by arrows with dotted lines, and shear components (FV,shear and FML,shear) by arrows with dashed lines. Torque around the long axis of the branch trackway, generated by muscular exertion and not as a result of substrate reaction forces applied tangentially to the branch, is represented by the yellow dotted arrow ({tau}CC,musc) [see Lammers and Gauntner (Lammers and Gauntner, 2008Go) and the Materials and methods section for further explanation]. {theta} represents the angle formed by the normal force vector and a horizontal line passing through the long central axis of the branch trackway. Note that the arrows represent applied force, which is equal and opposite in direction from the substrate reaction force.

 

Figure 2
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  		Fig. 2. Limb phase versus duty factor. Note that the axes are reversed, as per the convention of Hildebrand (Hildebrand, 1976Go). Only hindlimb trials are shown; the number of trials is somewhat greater than the sample sizes indicated in Tables 2 and 4 because trials with no force trace could be incorporated. Rough trackway is indicated by black stars; smooth trackway by filled gray circles.

 

Figure 3
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  		Fig. 3. Sample plots showing substrate reaction forces versus time (A,B), µreq versus time (C,D) and Fshear and Fnormal versus time (E,F). Within each trial, forelimb force traces were recorded first, followed by the ipsilateral hindlimb traces. These traces are shown on the left and right of each plot, respectively. A, C and E show traces from the rough trackway, and B, D and F illustrate results from the smooth trackway.

 

Figure 4
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  		Fig. 4. Box and whisker plots indicating peak (A) Fshear, (B) peak Fnormal and (C) peak µreq between substrate textures (rough=60 grit, smooth=painted paper) and between limbs (forelimb, hindlimb). Each box represents 50% of the data, each whisker corresponds to 25% of the data, the asterisks indicate outliers, and circles designate extreme outliers.

 

Figure 5
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  		Fig. 5. Plots of (A) peak normal and (B) peak shear forces versus {theta} (contact position of the manus or pes around the pole). (C) Peak µreq versus {theta}. To emphasize the overall direction of the relationships, 68% confidence ellipses were drawn for each group (black=forelimbs, gray=hindlimbs; dashed lines and stars=rough trackway, solid lines and circles=smooth trackway).

 

Figure 6
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  		Fig. 6. Schematic of contributions to shear force (except for craniocaudal force) in forelimbs and hindlimbs. (A,B) Vertical force (FV) and the shear component of vertical force (FV,shear) for the forelimbs and hindlimbs, respectively. (C,D) Mediolateral force (FML), the shear component of mediolateral force (FML,shear), and the torque generated by rotational forces around the long axis of the branch trackway ({tau}CC,musc) for forelimbs and hindlimbs, respectively. Symbols and colors are as shown in Fig. 1.

 

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© The Company of Biologists Ltd 2009