Agonist-antagonist muscular co-contraction improves rapid corrective responses

Figures

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  Figure 1. Overview of mechanical perturbation trials Different experimental conditions are pictured in different columns including: (left relaxed and co-contracting, middle) (stretched muscle pre-loaded, right) shortened muscle pre-loaded. A description of each component of a trial is described in each row: (top row) participants moved their fingertip to a spatial target when either relaxed (left), co-contracting to generate a level of muscle activity specified with real-time biofeedback (centre-left) or, resisting an applied background load (red arrow) that either extends (centre-right) or flexes (right) the arm. (Second row) A 5 Nm transient load (10 ms ramp, 50 ms duration) was applied to either flex or extend the elbow (yellow arrows). (Third row) participants made a corrective response to return to the target and hold their position as fast as possible. (Final row) the trial was successful if participants reacquired and stayed at the target within 500 ms. Successful trials were noted with a green target color, whereas unsuccessful trials displayed red.

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  Figure 2. Visualization of time-series kinematics and performance metrics for co-contracting conditions, as well as sample participant data across all conditions (A) Time-series elbow displacement post-perturbation for relaxed and co-contracting conditions. Perturbation onset is shown with the vertical gray line, and mean return times are shown for each condition with dashed vertical lines. Solid black horizontal lines visualize the range for successful target recapture across conditions. Discrete comparisons of trial success rate and return times are shown for relaxed vs. co-contracting conditions. (B and C) All data are reported as mean +/− standard error. (D) Sample kinematics following perturbation for an exemplar subject across relaxed, co-contracting, and resisting background (BG) load conditions. Perturbation onset is denoted with the vertical gray line, and the successful target recapture range is visualized with horizontal black lines. Return times are shown with red arrows for each trial. Mean displacement 50 ms post-perturbation (cyan star), maximum displacement (blue square) and maximum overshoot (blue diamond) at their respective times are shown with red symbols. Note: The y…

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  Figure 3. Time-series elbow displacement following perturbation and discrete performance measures when comparing either a total of 5 Nm or 2.5 Nm of muscle activity prior to perturbation conditions Time-series elbow displacement following perturbation when comparing (A) a total of 5 Nm and (D) 2.5 Nm of muscle activity prior to perturbation. Relaxed conditions are included on each plot for reference. Perturbation onset is shown with the vertical gray line, and mean return times are shown for each condition with dashed vertical lines. Solid black horizontal lines visualize the range for successful target recapture across conditions. Discrete comparisons of trial success rate and return times are shown for the total of 5 Nm (B and C), and 2.5 Nm (E and F) of muscle activation conditions. Mean data are shown with solid lines and standard error is shown by the shaded regions and significant post-hoc differences between groups are noted with “∗” for discrete measures. In the discrete data plots, all data are reported as mean +/− standard error.

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  Figure 4. Time-series elbow displacement following perturbation and discrete performance measures when comparing either stretched or shortened muscles were pre-loaded prior to perturbation Time-series elbow displacement following perturbation when comparing across relaxed and (A) when stretched muscles are opposing loads, and (D) when shortened muscles are opposing loads. Perturbation onset is shown with the vertical gray line, and mean return times are shown for each condition with dashed vertical lines. Solid black horizontal lines visualize the range for successful target recapture across conditions. Discrete comparisons of trial success rate and return times are shown for relaxed vs. stretched muscle resisting background loads (B and C) and shortened muscle resisting background loads (E and F) conditions. Mean data are shown with solid lines and standard error is shown by the shaded regions and significant post-hoc differences between groups are noted with “∗” for discrete measures. In the discrete data plots, all data are reported as mean +/− standard error.

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  Figure 5. Time-series EMG of the stretched (solid lines, positive values) and shortened (dashed lines, negative values) muscles following perturbation across relaxed, co-contracting, and single muscle pre-load conditions Time-series EMG of the stretched (solid lines, positive values) and shortened (dashed lines, negative values) muscles following perturbation across relaxed and (A) co-contracting conditions, (B) when stretched muscles are opposing loads, and (C) when shortened muscles are opposing loads. Perturbation onset is shown with the vertical gray lines. Mean data are shown with solid lines and standard error is shown by the shaded regions.

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  Figure 6. Time-series elbow displacement following perturbation and discrete performance measures when comparing either combined muscle activation conditions where either the stretched or shortened muscles were pre-loaded to a higher magnitude prior to perturbation Time-series elbow displacement following perturbation in combination conditions when (A) stretched muscle activity is greater than shortened muscle activity and (B) shortened muscle activity is greater than stretched muscle activity. Relaxed and an exemplar background load condition data are included on each plot for reference. Perturbation onset is shown with the vertical gray line, and mean return times are shown for each condition with dashed vertical lines. Solid black horizontal lines visualize the range for successful target recapture across conditions. Discrete comparisons of trial success rate and return times are shown for the stretched muscle activity is greater than shortened muscle activity (B and C), and shortened muscle activity is greater than stretched muscle activity (E and F) conditions. Mean data are shown with solid lines and standard error is shown by the shaded regions and significant post-hoc differences…

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  Figure 7. Time-series EMG of the stretched (solid lines, positive values) and shortened (dashed lines, negative values) following perturbation when stretched muscle activity is greater than shortened muscle activity and shortened muscle activity is greater than stretched muscle activity Time-series EMG of the stretched (solid lines, positive values) and shortened (dashed lines, negative values) following perturbation when (top) stretched muscle activity is greater than shortened muscle activity and (bottom) shortened muscle activity is greater than stretched muscle activity. Relaxed and an exemplar background load condition are included on each plot for reference. Perturbation onset is shown with the vertical gray lines. Mean data are shown with solid lines and standard error is shown by the shaded regions on time-series plots.