Figure 5.

Normalized muscle velocities vs. time for a randomly selected free throw attempt both in its entirety (left) and bounded by ±5 muscle lengths per second (l̂₀/s) (right) to highlight the upstroke phase. Muscles that only cross the shoulder are shown in orange, while the biceps and triceps muscles are shown in maroon. The remaining muscles that cross the elbow and/or wrist are shown in blue. Note that there exist two major zeros crossings during which many of the muscles change the direction of their contractions. The first instance occurs during the upstroke where the wrist extends as elbow flexes with similar but opposite angular velocities–while the shoulder continues to rotate upwards causing the net excursion time derivative for the bi-articulating muscles of the elbow and wrist to offset each other. The second instance defines the start of the power stroke phase where either the angular velocities of the elbow and/or wrist create a net zero tendon excursion time derivative or the muscles of the shoulder change the direction of their contractions (if they do at all). The muscles that only cross the shoulder do not exhibit this first zero crossing as they typically experience contraction throughout the entire upstroke without a change in direction (i.e. constant upward rotation about the shoulder joint), but will often exhibit the second zero crossing as a result of the cubic spline algorithm and the local extrema generated in the shoulder angle trajectory. As the biceps and triceps muscles cross over both the shoulder and elbow joints, they do not experience a zero crossing during the upstroke phase (i.e. the direction of both rotations are consistent and nonzero during this phase), but they do, however, exhibit typical zero crossings at the start of power stroke phase brought on by a major change in the direction of elbow rotation.