“…An optimal state of variability, characterized by a chaotic structure, is required for a healthy and functional movement [93]. The variability in force during motion is associated with non-uniformity in the sarcomere length and depends on the joint angle, type of muscular contraction, muscle orientation related to the joint, and the synchrony and firing rate of motor units [79,92]. The non-linearity of muscle activity was associated with parameters that determine strength, including the speed of contraction, muscle length and composition, cross-sectional area, gender, and age [94,95].…”