Epaxial muscle function in trotting dogs
Dale A. Ritter1,*,
Peter N. Nassar2,
Mathew Fife3 and
David R. Carrier3
1 Biology Department, Heidelberg College, 310 E. Market Sreet, Tiffin, OH 44883, USA,
2 Department of Geology, Bryn Mawr College, 101 N. Merion Avenue, Bryn Mawr, PA 19010, USA and
3 Department of Biology, 201 South Biology, University of Utah, Salt Lake City, Utah 84112, USA
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Fig. 1. A summary of the methods used to produce EMG activity traces from treadmill data. An accelerometer trace was used to divide each EMG trace into smaller traces that corresponded to a single locomotor cycle. This trace was then rectified, divided into 100 bins of equal duration, and the EMG activity of each bin was calculated by multiplying the number of spikes in each bin by the mean spike amplitude of each bin. EMG activity traces were then averaged on a bin-by-bin basis to produce a mean EMG activity trace for each muscle at each site.
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Fig. 2. Raw EMG data from a dog trotting on the treadmill at 2.5ms-1. All EMG data are from muscles on the animals left side. Footfall diagrams are shown below the EMG traces, with rectangles indicating periods of support by the indicated foot. The cross-hatched rectangles highlight the temporal relationship between muscle activity and ipsilateral rear foot support.
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Fig. 3. Mean EMG activity traces from two trotting dogs, one from the treadmill and one from the trackway. In both cases, mean activity data for a single locomotor cycle are repeated so that the general pattern may be more easily seen. (A) Mean EMG activity traces calculated from 20 consecutive cycles of locomotion from a dog trotting on the treadmill at 2.5ms-1. All EMG data are from muscles on the animal’s left side. Mean footfall diagrams are shown below the EMG energy traces, with rectangles indicating periods of support by the indicated foot. The cross-hatched boxes highlight the temporal relationship between muscle activity and ipsilateral rear foot support. (B) Mean EMG activity traces calculated from 15 locomotor cycles from a dog trotting along a trackway at a speed of 2.0ms-1. All EMG data are from muscles on the animal’s right side. Mean footfall diagrams are shown below the EMG activity traces, with rectangles indicating periods of support by the indicated foot. The cross-hatched boxes highlight the temporal relationship between muscle activity and ipsilateral rear foot support.
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Fig. 4. Mean ground reaction force data for a trotting dog. Data from one step are repeated so that the general pattern may be more easily seen. These data represent the resultant force trace of both limbs, as opposed to single-limb forces, and are averaged from 15 trials of force-plate data. The trace of the large single peak during a step is the vertical (vert.) force. The trace that first drops below and then rises above baseline is the recording of the fore–aft force. The very flat, unlabeled trace is the recording of the lateral force. The average speed of this animal trotting across the force plate was 2.0ms-1.
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Fig. 5. Ground forces relative to epaxial EMG activity, produced by combining the mean force trace with mean EMG activity traces. The primary burst of epaxial muscle activity begins just after peak vertical (vert.) force, activity occurs throughout the acceleration (accel.) phase of fore–aft force production, and activity ceases at approximately the same time that vertical and horizontal forces return to zero. The secondary bursts are shorter in duration, such that they generally correspond to the second half of the acceleration phase of fore–aft force production. decel., deceleration.
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Fig. 6. Ground reaction force vectors calculated from a dog trotting over a force plate at 2.0ms-1. The lengths of the arrows indicate the magnitude of the force vectors. Filled circles indicate the approximate positions of the pectoral girdle and the iliosacral joint. Numbers indicate the percentage of the step cycle (one-half of one locomotor cycle) at which the illustrated force vectors were calculated.
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Fig. 7. The timing of dorso–ventral back kinematics relative to footfalls for three dogs trotting at their self-selected speed. Each trace follows oscillations in an angle with end-points over each girdle, with a point mid-way between the girdles as the vertex. Each trace is an average of five locomotor cycles. The time course of dorso–ventral kinematics is expressed relative to one locomotor cycle. Arrows highlight maximum extension and flexion, and are keyed to the outlines of a trotting dog taken from a video recording.
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Fig. 8. Sample raw EMG traces from a 21.6kg dog trotting at 2.4ms-1 while carrying 3.2kg (15% of body mass) in saddle bags on its back. Both traces are from the same electrode, implanted in the left longissimus dorsi muscle at the lumbar site. The accelerometer recordings are from an accelerometer positioned to record vertical accelerations at mid-trunk. (A) Data from a trial in which half the added mass was carried over the pectoral girdle and the other half was carried over the pelvic girdle. (B) Data from a trial in which all of the added mass was carried mid-trunk.
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Fig. 9. Mean rectified integrated area of the of activity of the longissimus dorsi muscle in the two loaded conditions plotted as a percentage of the mean value in the unloaded condition (= 100% EMG intensity). In three of the dogs the mean EMG activity from the girdles-loaded condition was not significantly different from the unloaded condition. In one of the dogs the mean EMG energy from the girdles-loaded condition was significantly lower than the mean EMG energy from the loaded condition. In all four dogs the mean EMG activity from the mid-trunk loading condition was significantly greater than both the unloaded condition and the girdles-loaded condition.
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© The Company of Biologists Ltd 2001
