How temperature tunes muscle mechanics during eccentric contractions

Figures

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  Figure 1. Eccentric contraction of the mouse extensor digitorum longus. Example force profile (A) of the extensor digitorum longus muscle when stretched (B) during a tetanic contraction. Magnified force trace from (A) with annotated dynamic components contained within the eccentric response (C). Phase-1 slope corresponds to the rapid rise in force development seen immediately after the initiation of stretch. After which the muscle transitions into a shallower, phase-2 response. However, at high enough velocity (and lower temperatures) muscles may present with an initial decrease in force response, prior to the steady-state phase-2 response, typically referred to as muscles ‘give’.

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  Figure 2. Sensitivity of the eccentric Phase-1 and Phase-2 response to temperature. The relationship between lengthening velocity and the rate of force development for Phase-1 (A, C) and Phase-2 (B, D). The relationship between absolute lengthening velocity (A-B) and velocity normalised to temperature specific Vmax (C-D). Repeated measures correlations for 17°C (n=6), 27°C (n=5) and 37°C (n=6).

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  Figure 3. Sensitivity of the force-velocity relationship to temperature. The force-velocity relationship at 17, 27 and 37 degrees Celsius for the extensor digitorum longus muscle when measured as the muscle lengthens across L0 (A, C) and at the transition point between Phase-1 and Phase-2 (B, D). Given reduction seen in concentric maximum shortening velocity (Vmax) (A-B), the eccentric lengthening velocities were normalised to temperature specific Vmax (C-D). The concentric force-velocity relationship was determined by fitting a hyperbolic-linear function (11, 22) to the data, while the eccentric force-velocity relationship was fit with a hyperbolic function (12, 22) to the 17°C (n=6), 27°C (n=5) and 37°C (n=6).

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  Figure 4. The presence of ‘give’ during eccentric ramps of the extensor digitorum longus. Scatter plot presents the V/Vmax ramp applied to each muscle (rows of data) (A). Colour filled circle indicates the presence of muscle ‘give’, grey circles indicate no muscle ‘give’. The fastest stretched muscles (lengthened between -0.45 to -0.58 V/Vmax) were pooled to allow for quantitative comparisons of muscle ‘give’ (B). The transition point between phase-1 and phase-2 (C) and the amount of muscle ‘give’ (D) show significant temperature dependence. One-way ANOVAs were used to assess statistical significance, where significant main effects were detected, post hoc comparisons were conducted using the Bonferroni correction and the threshold for statistical significance set to P<0.05. * P<0.05, **P<0.01. 17°C (n=6), 27°C (n=5) and 37°C (n=6).

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  Figure 5. The force-length-velocity surface plot at varying temperatures on the extensor digitorum longus. The relationship between muscle lengthening velocity, and force production and length at 17°C (A), 27°C (B) and 37°C (C). Heatmap is the rate of force development.

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