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Kinematics of 90° running turns in wild mice

Rebecca M. Walter

Department of Biology, University of Utah, Salt Lake City, Utah 84112, USA

View larger version (12K): [in a new window]   Fig. 1. A representative turn made by one of the mice. (A–E) Frames 16 ms apart. Feet in contact with the ground are shaded. Phases of the turn are described in the text. Angle in A is the angle by which the rotation of the head and neck precedes that of the body for that frame.

View larger version (18K): [in a new window]   Fig. 5. Percentage of the total 90° of head/neck and postcranial body rotation that occurred during each phase of the stride cycle. Head/neck (open bars) and body (filled bars) rotation were the changes in the angles made by markings 1 and 2 and 2 and 4 with the horizontal, respectively. Flight phase 1 occurred between hindlimb takeoff and forelimb plant and flight phase 2 occurred between forelimb takeoff and hindlimb plant. Most stride cycles contained one of the two flight phases but not both. Values are means ± S.E.M. for the six mice.

View larger version (25K): [in a new window]   Fig. 2. Reduced major axis regression (solid line) of stride frequency and speed for 55 strides from straight runs (open squares). Broken lines show the standard errors for the regression. Superimposed are the averages of the mean stride frequencies for each of the six mice over the strides just prior to (filled circle) and after (filled triangle) the apex of each turn.

View larger version (26K): [in a new window]   Fig. 3. Reduced major axis regression (solid line) of ballistic air time as a percentage of stride time and speed for 55 strides from straight runs (open squares). Broken lines show the standard errors for the regression. Superimposed are the averages of the mean ballistic air times for each of the six mice over the strides just prior to (filled circle) and after (filled triangle) the apex of each turn.

View larger version (25K): [in a new window]   Fig. 4. (A) Sample plot of rotation over time for a turn from one of the mice. Light shading represents forelimb support and dark shading hindlimb support. Thick line, postcranial body; normal line, head/neck angle; dotted line, angle of heading. The area between head and body angle traces (depicted by arrows) is the lead of the head/neck angle over the postcranial body angle. (B) Sample plot of the angular velocity of the postcranial body over time for one of the mice. Shading as in A. (C) Histogram showing the number of degrees rotated per bout for the two greatest bouts of postcranial body rotation during each turn. The angle turned per bout of rotation was determined by integrating between minima on the angular velocity over time curve in B.

View larger version (18K): [in a new window]   Fig. 6. A comparison of the speed–radius relationship seen in five mice with the curve predicted by Greene and McMahon (1979) and human data from Greene (1985). The dimensionless speed (vr) is the speed of the mouse during a turn (v) divided by that mouse's maximum speed on a straight path (vo). The reciprocal Froude number, rg/vo2, is the radius (r) of the mouse's path multiplied by the gravitational constant (g) and divided by the mouse's maximum speed squared.

View larger version (18K): [in a new window]   Fig. 7. Comparison of the effective mechanical advantage for horizontal versus vertical force production in crouched and upright postures. Biewener (1989) defines effective mechanical advantage as the ratio of the muscle moment arm (r) to the moment arm of the ground reaction force (R). For a crouched posture, the horizontal moment arm (Rhor) is smaller relative to the vertical moment arm (Rvert) than for an upright posture. This means that for a crouched posture the effective mechanical advantage for horizontal force production is greater relative to that for vertical force production than for a more upright posture.