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Research Article
Muscle force-length dynamics during level versus incline locomotion: a comparison of in vivo performance of two guinea fowl ankle extensors
Monica A. Daley, Andrew A. Biewener
Journal of Experimental Biology 2003 206: 2941-2958; doi: 10.1242/jeb.00503
Monica A. Daley
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Andrew A. Biewener
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Figures

  • Fig. 1.
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    Fig. 1.

    Anatomy of the lateral gastrocnemius (LG) and digital flexor-IV (DF-IV) muscles in the guinea fowl hindlimb, illustrating the sites of transducer implantation. Forces were measured from the common gastrocnemius (G) tendon and the tendon to DF-IV (inset) via tendon buckle force transducers. Note that the guinea fowl does not possess independent free tendons to the lateral and medial heads of the gastrocnemius. Muscle fiber length changes and muscle activity were measured in the LG and DF-IV (inset) of the left hindlimb using sonomicrometry and electromyography, respectively.

  • Table 1.

    Muscle and tendon data

    NMass (g)Lf (mm)Lt (mm)α (degrees)Am (mm2)At (mm2)
    LG67.2±1.117.3±1.298.9±13.620±2888±1157.6±1.9
    DF-IV72.1±0.417.1±5.7184±18.721±9114±441.5±0.2
    • LG, lateral gastrocnemius muscle; DF-IV, digital flexor-IV.

      L, length; A, cross-sectional area; α, fascicle axis.

      Subscripts m, t and f indicate muscle, tendon and fascicle, respectively.

      Values are means ± s.e.m.

  • Fig. 2.
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    Fig. 2.

    Representative recordings of muscle force, length and electromyographic (EMG) activity for lateral gastrocnemius (LG, above) and digital flexor-4 (DF-IV, below) during level running at 1.3 m s-1, from one individual (bird 5). Shaded bars indicate the support phase of the locomotor cycle. Top, silhouettes of the bird show the phases of the stride for one cycle, with the recorded limb in black and the contralateral limb in gray.

  • Table 2.

    Variables measured during level and incline running

    Speed (m s−1)
    0.7 1.3 2.0
    ConditionLevelInclineLevelInclineLevelIncline
    LG
    Peak force (N)20.9±1.929.9±4.226.7±3.935.5±2.933.6±3.4—
    Peak stress (kPa)23±234±631±439±537±4—
    Mean force (N)10.3±1.215.3±2.214.0±2.220.2±1.918.3±1.9—
    Net strain (%)−10.5±2.3−18.0±2.5−12.9±3.3−20.4±2.9−15.2±3.0—
    EMG intensity (%)38±455±957±467±1176±4—
    EMG duration (ms)169±20234±21127±15173±34125±13—
    Tendon energy (J kg−1)1.4±0.33.0±0.92.5±0.64.6±1.83.7±0.8—
    Net work (mJ)32.7±6.379.6±11.856.0±12.292.2±14.484.6±15.7—
    Net work (J kg−1)4.5±0.911.0±1.87.7±1.512.0±1.611.4±2.1—
    Δwork level versus incline (J kg−1)6.54.3—
    DF-IV
    Peak force (N)9.3±1.111.4±1.211.9±1.113.3±1.613.6±1.4—
    Peak stress (kPa)92±17120±24117±18130±34123±22—
    Mean force (N)5.0±0.66.6±0.96.9±0.78.1±1.07.7±0.7—
    Net strain (%)−7.8±5.7−8.6±4.7−1.1±6.0−9.7±3.7−3.3±6.1—
    EMG intensity (%)41±657±655±765±764±6—
    EMG duration (ms)250±9260±19172±20197±7145±9—
    Tendon energy (J kg−1)11.5±4.515.5±4.014.2±2.321.1±8.820.0±6.7—
    Net work (mJ)0.4±3.18.5±5.4−1.9±5.39.8±6.7−1.3±4.9—
    Net work (J kg−1)0.7±1.64.7±3.4−0.8±2.75.3±4.3−0.3±2.7—
    Δwork level versus incline (J kg−1)4.06.1—
    • Values are means + s.e.m.

      LG, lateral gastrocnemius muscle; DF-IV, digital flexor-IV, EMG, electromyographic activity.

  • Fig. 3.
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    Fig. 3.

    Expanded and averaged recordings of muscle length, force and electromyographic (EMG) activity from the lateral gastrocnemius (LG, above) and digital flexor-4 (DF-IV, below), normalized to a single stride. The support phase of the stride is shaded in gray. Results are shown for bird 4, running at 1.3 m s-1 on the level (left), and at 16° incline (right). The traces of force and length are means ± s.d. obtained from 10 strides, and a single EMG trace is shown for reference. The error bars below the EMG traces indicate the mean ± s.d. for the timing of EMG activity (onset, offset).

  • Fig. 4.
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    Fig. 4.

    Inter-individual (top) and intra-individual (bottom) variation in cumulative energy production by lateral gastrocnemius (LG, left) and digital flexor-4 (DG-IV, right) over the locomotor cycle, shown for level running at 1.3 m s-1. The final value is the net work generated per stride. The traces of average cumulative work output shown across individuals (birds 4, 5 and 6, top) encompass the range of inter-individual variation for both muscles. The mean ± s.d. of energy production over the normalized stride from one individual (bird 4, bottom) illustrates typical levels of stride-to-stride variation for each muscle.

  • Fig. 5.
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    Fig. 5.

    Muscle stress plotted against fascicle strain, forming in vivo mass-specific work loops, shown for three level speeds (0.7, 1.3 and 2.0 m s-1, left to right) and two 16° incline speeds (0.7 and 1.3 m s-1, broken lines) for the lateral gastrocnemius (LG, top) and the digital flexor-4 (DF-IV, bottom) from one individual that was nearest the means for all birds (bird 4). The area enclosed in the loop is the net work performed per unit muscle mass per stride. Arrows indicate the direction of the work loop. Counter-clockwise loops indicate net positive energy, and clockwise loops indicate net energy absorption. Color indicates timing of electromyographic (EMG) activity relative to force and length change.

  • Fig. 6.
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    Fig. 6.

    Summary histograms of peak muscle stress, active fascicle strain, net work per stride and tendon elastic energy recovery per stride (means ± s.e.m.) for the lateral gastrocnemius (LG, left) and digital flexor-4 (DF-IV, right) across speed for level (open bars) and incline (filled bars) locomotion. Shortening muscle strains are negative. See Table 3 for relevant sample sizes.

  • Table 3.

    Effect of incline and speed

    Incline Speed
    Variabled.f.FPd.f.FP
    LG
    Net work1, 536.790.0018*1, 5108.830.0001*
    Mean force1, 517.140.0090*1, 5347.54<0.0001*
    Net strain1, 526.780.0035*1, 553.040.0008*
    Phase1, 510.050.0248†1, 5117.550.0001*
    EMG intensity1, 40.96NS1, 426.310.0068*
    EMG duration1, 45.96NS1, 48.730.0418*
    DF-IV
    Net work1, 57.840.0380†1, 50.59NS
    Mean force1, 513.130.0152†1, 5217.18<0.0001*
    Net strain1, 59.210.0289†1, 51.92NS
    Phase1, 56.03NS1, 543.640.0012*
    EMG intensity1, 42.62NS1, 421.860.0095*
    EMG duration1, 40.17NS1, 4180.850.0002*
    • ANOVA; see Materials and methods for details.

      NS, not significant.

      LG, lateral gastrocnemius muscle; DF-IV, digital flexor-IV, EMG, electromyographic activity.

    • ↵* Significant at the 0.05 level after Bonferroni correction.

    • ↵† P<0.05, but not significant after Bonferroni correction.

  • Table 4.

    Effect of relative EMG intensity on net work per stride and mean force

    EMG intensity
    Level Incline
    d.f.FPd.f.FP
    LG
    Net work1,13790.07<0.00011,87165.91<0.0001
    Peak force1,137160.41<0.00011,8780.76<0.0001
    DF-IV
    Net work1,1471.09NS1,1014.450.0373
    Peak force1,1478.520.00411,1010.24NS
    • ANOVA; see Materials and methods for details.

      NS, not significant.

      LG, lateral gastrocnemius muscle; DF-IV, digital flexor-IV, EMG, electromyographic activity.

  • Fig. 7.
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    Fig. 7.

    Mean muscle force and net work per stride against relative electromyographic (EMG) intensity for lateral gastrocnemius (LG, left) and digital flexor-4 (DF-IV, right), during locomotion on the level (open circles) and incline (filled squares). For clarity, results are shown for one representative individual (bird 3); however, the pattern of change from level to incline was similar across individuals, as indicated by the mean slopes and r2 values given in the text.

  • Table 5.

    Effect of net strain, mean force, phase and Δvelocity on work

    LG DF-IV
    Factord.f.FPd.f.FP
    Phase (A)1,26816.70.00011,2689.40.0024
    Mean force (B)1,26868.7<0.00011,2687.90.0052
    Net strain (C)1,2689.20.00261,2681.3NS
    Δvelocity (D)1,26818.1<0.00011,2680.6NS
    A×B1,2680.6NS1,2689.60.0022
    A×C1,2681.6NS1,2680.1NS
    A×D1,26860.01501,26831.7<0.0001
    B×C1,2684.30.04001,2680.1NS
    B×D1,2680.9NS1,2689.40.0024
    C×D1,2680.2NS1,2680.4NS
    • General linear model ANOVA; see Materials and methods for details.

      × denotes interaction.

      NS, not significant.

      LG, lateral gastrocnemius muscle; DF-IV, digital flexor-IV.

  • Fig. 8.
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    Fig. 8.

    Net mass-specific muscle work against (A) net strain, (B) mean force, and (C) phase relationship between force and strain for lateral gastrocnemius (LG, i) and digital flexor-4 (DF-IV, ii). Symbols indicate different individuals. Statistical results for the effect of each variable on work from a general linear model are shown in Table 5.

  • Fig. 9.
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    Fig. 9.

    Contribution of gastrocnemius (black portion) and digital flexors (white portion) to total center of mass (COM) work during incline running at 0.7 (middle) and 1.3 m s-1 (right), compared to the contribution to be expected if all muscles in the limb contributed equally to mass-specific work for incline running (H; left).

  • Fig. 10.
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    Fig. 10.

    Schematic illustration of the effect of phase (between length and force) and strain pattern on digital flexor-4 (DF-IV) muscle work. The center panel shows the relationship between phase and work for the DF-IV (Fig. 8Cii). If the muscle undergoes a stretch-shorten cycle (large Δvelocity) and muscle force and length are symmetrical, no net work results (A). However, if peak force precedes peak length, the muscle absorbs energy (B), and if peak force lags behind peak length, it produces energy (C). However, if the muscle contracts with constant velocity, whether positive, negative or isometric (as shown in D), phase has no impact on work. This explains why the interaction term, phase×Δ velocity, is a larger factor underlying DF-IV work than phase alone (Table 5); a change in velocity during force production (Δvelocity) is required for phase to be an important factor in work. Vertical lines in A-D indicate peak force.

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Research Article
Muscle force-length dynamics during level versus incline locomotion: a comparison of in vivo performance of two guinea fowl ankle extensors
Monica A. Daley, Andrew A. Biewener
Journal of Experimental Biology 2003 206: 2941-2958; doi: 10.1242/jeb.00503
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Research Article
Muscle force-length dynamics during level versus incline locomotion: a comparison of in vivo performance of two guinea fowl ankle extensors
Monica A. Daley, Andrew A. Biewener
Journal of Experimental Biology 2003 206: 2941-2958; doi: 10.1242/jeb.00503

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