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First published online December 2, 2005
Journal of Experimental Biology 208, 4599-4611 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01940

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Patterns of strain and activation in the thigh muscles of goats across gaits during level locomotion

Gary B. Gillis^1,*, John P. Flynn², Polly McGuigan² and Andrew A. Biewener²

¹ Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
² Concord Field Station, Harvard University, Old Causeway Road, Bedford, MA 01730, USA

View larger version (29K): [in a new window]   Fig. 1. Schematic illustration showing crystal implantation scheme for the vastus lateralis and biceps femoris. Note the unipennate fiber architecture of the vastus as well as the locations of the three pairs of crystals: proximal, middle and distal. The anterior portion of the biceps, which has parallel fibers, was implanted with a single pair of sonomicrometry crystals.

View larger version (12K): [in a new window]   Fig. 2. Plots showing stance duration (A) and swing duration (B) as a function of speed in goats during treadmill locomotion. Note the substantial decrease in stance phase duration with increasing speed in comparison to the relatively constant swing phase duration over the same speed range. Different symbols represent different individuals (N=7).

View larger version (48K): [in a new window]   Fig. 3. Patterns of hip (A,C,E) and knee (B,D,F) joint angle excursions from one individual at all gaits, in red, superimposed onto fascicle strain patterns of the biceps and vastus, respectively, in black. The right-hand y-axis corresponds to the joint angles, the left-hand y-axis to the strain. Stance and swing phases are shaded dark and light gray, respectively. Note how biceps fascicles generally shorten during hip extension and lengthen during hip flexion. Vastus fasicles are generally stretched during knee flexion and shorten during knee extension.

View larger version (46K): [in a new window]   Fig. 4. Patterns of activation and strain in the biceps femoris (A) and vastus lateralis (B) during three strides of slow trotting. Data are from the same individual trotting at 2.0 m s–1. Dark gray shading represents the stance phase; light gray shading represents the swing phase. The biceps remains fairly isometric during the interval in which electromyographic activity is present in late swing and early stance and then shortens rapidly and substantially later in stance. The vastus is generally stretched during much of its activation period early in stance before shortening late in stance.

View larger version (27K): [in a new window]   Fig. 5. Schematic diagram showing the relative timing of electromyographic activity in the biceps femoris (BF) and vastus lateralis (VL) during walking, trotting and galloping. Stance and swing phases are shaded dark and light gray, respectively. Note how the stance phase takes up a relatively small fraction of the stride during galloping. Both muscles are consistently activated prior to foot-down at the start of stance, and both become inactive during stance. The biceps is consistently activated and deactivated earlier than the vastus.

View larger version (16K): [in a new window]   Fig. 6. Plots of relative EMG intensity in the biceps (A) and vastus (B) over a range of speeds. Intensity increases with speed in both muscles and is highest during galloping and lowest during walking. Different symbols represent different individuals (N=3 for biceps, N=5 for vastus).

View larger version (52K): [in a new window]   Fig. 7. Patterns of strain in the biceps (A) and vastus (C) during walking, trotting and galloping from three strides to show characteristic length-change trajectories during different gaits. Idealized strain trajectories are shown for the biceps (B) and vastus (D). In the biceps, strain trajectories can be divided into three discrete phases; in the vastus, four discrete phases are defined (described in more detail in the text). Dark gray shading represents the stance phase; light gray shading represents the swing phase.

View larger version (23K): [in a new window]   Fig. 8. Plots of fascicle strain (A–C) and strain rate (D–F) in the biceps and vastus as a function of speed. For the biceps (A,D), N=5 for all speeds except 4.0 m s–1 where N=4. All animals exhibited walking at 1.1 and 1.5 m s–1, trotting at 2.0, 2.5 and 3.0 m s–1 and galloping at 4.0 m s–1; at 3.5 m s–1, two animals used trotting, one galloping, and two both trotting and galloping. For the vastus (B,C,E,F), N=7 for all speeds except 4.0, where N=6. All animals exhibited walking at 1.1 and 1.5 m s–1, trotting at 2.0, 2.5 and 3.0 m s–1 and galloping at 4.0 m s–1; at 3.5 m s–1, four animals used trotting, two galloping, and two both trotting and galloping. All vastus data are from middle implantation locations.

View larger version (47K): [in a new window]   Fig. 9. Patterns of vastus strain in proximal (blue), middle (red) and distal (green) sites from two individuals showing subtle (A) and more substantive (B) variation. Note the overall similarity in strain trajectory in timing, even in B, where strain magnitude was much greater in the proximal location.

View larger version (21K): [in a new window]   Fig. 10. Stretching (positive) and shortening (negative) strains in the vastus during stance from proximal, middle and distal fascicles during walking (W; black), trotting (T; gray) and galloping (G; white). Although strains tend to be highest in the middle region, this pattern was not present in all individuals, and differences between sites were not significant. Data shown are means from four individuals. Error bars represent standard errors.

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