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. 2022 Jun 7;11:e72871. doi: 10.7554/eLife.72871

Figure 6. Three-stage approach to hit TIII.

(A) Force due to ankle dorsiflexion (green) and the discharge behaviour of the selected motor unit (MU) pair during a successful attempt of hitting TIII (yellow) for a representative subject. The subject used a three-stage approach to achieve the target task: stage 1: increasing the force to orderly recruit both MUs; stage 2: reducing the force until MU1 stops firing while the cursor is placed along the vertical axis; stage 3: slightly increasing the force again to manoeuvre the cursor inside TIII. Grey circles mark the characteristic force values of each stage. Stage 1: maximum force while both MUs are active; stage 2: minimum force after MU1 stopped firing; stage 3: force during hit of TIII. The corresponding cursor movement for each stage is shown on the top. Grey intensity increases with stages. (B) Characteristic forces (due to ankle dorsiflexion) are shown with their median and quartiles at each stage of control for all subjects across all conditions during all TIII hits in the last 5 days of training. Each dot represents a subject, and corresponding values are connected via the lines. Black bars indicate a significant difference with p<0.05.

Figure 6.

Figure 6—figure supplement 1. Various successful trials of hitting TIII for different subjects, conditions, and training days.

Figure 6—figure supplement 1.

The top figure in each segment shows the discharge activity of motor unit (MU)1 and MU2 (selected MU pair) and force due to dorsiflexion (green) during the initial force task. The bottom-left figure shows the discharge activity of MU1 and MU2 and the force (green) during a single successful TIII instructed trial, while the bottom-right figure shows the corresponding cursor movement towards TIII (yellow). The grey intensity of the cursor trajectories increases over time within the trial. (A) Direct movement towards TIII besides the initial difference in recruitment threshold. (B) Indirect movement towards TIII. (C, D) Indirect movement towards TIII for an MU pair in which the higher threshold MU (MU2) was initially recruited after and de-recruited before the lower threshold one (MU1). DR: discharge rate.