Figure 2.

Experiment performed with a skeletal muscle myofibril. (a) Resting myofibril set at an average SL of 2.36 μm, when maximum sarcomere dispersion was 30 nm. Upon full activation the average SL was shortened by 51.7 nm and maximum sarcomere dispersion was 54.2 nm. Stretch was performed from 2.33 to 2.67 μm (14.4% L₀), at a nominal velocity of 1 μm s⁻¹ SL⁻¹. Force increased during stretch and it was 1.54 times the isometric force at the end of stretch. (b) Individual sarcomere dynamics during activation and stretch. All sarcomeres shortened during activation by different amounts, which increased the sarcomere non-uniformity to reach 38.3 nm just before stretch. During myofibril stretch all sarcomeres stretched, albeit by different amounts. The dispersion of sarcomeres increased significantly during stretch, to reach a maximum of 326.2 nm at the end of stretch. After stretch, the sarcomere dispersion kept increasing to reach a maximum of 355.5 nm. (c) Dispersion of SLs during experiments with control myofibrils. SLs were non-homogeneous at the rest state, and dispersion increased when myofibrils were activated. Stretch increased SL dispersion. Boxplots represent median and 95% confidence intervals, and circles indicate outliers.