What are “normal movements” in atypical populations?

Abstract

Redundancy of the motor control system is an important feature that gives the central control structures options for solving everyday motor problems. The choice of particular control patterns is based on priorities (coordinative rules) that are presently unknown. Motor patterns observed in unimpaired young adults reflect these priorities. We hypothesize that under certain atypical conditions, which may include disorders in perception of the environment and in decision making, structural or biochemical changes within the central nervous system (CNS), and/or structural changes of the effectors, the central nervous system may reconsider its priorities. A new set of priorities will reflect the current state of the system and may lead to different patterns of voluntary movement. Under such conditions, changed motor patterns should be considered not pathological but rather adaptive to a primary disorder and may even be viewed as optimal for a given state of the system of movement production. Therapeutic approaches should not be directed toward restoring the motor patterns to as close to “normal” as possible but rather toward resolving the original underlying problem. We illustrate this approach using, as examples, movements in amputees, in patients with Parkinson's disease, in patients with dystonia, and in persons with Down syndrome.

Normal aging reduces motor synergies in manual pointing

“…Taken together, the previous studies as well as the present study provide converging evidence that normal aging affects the organization of variability in multidegree of freedom movements, with older adults making less flexible use of motor abundance. Note that the overall postural variability was lower in older relative to younger adults in the present study, indicating that the relationship between neuromuscular noise and the amount and structure of movement variability is not straightforward, but is likely be mediated by adaptation processes (Latash and Anson, 1996). We propose that in the present study, older adults may have achieved similar levels of end point accuracy by using lower amounts of motor abundance.…”

Amount and structure of force variability during short, ramp and sustained contractions in males and females

“…3b), the two-way ANOVA showed gender differences, 3 males had larger contribution from tangential forces to Fx than females (F = 5.2, p = .02), 4 respectively 30.1 ± 35.1 % vs. 10.2 ± 7.6 %. For the endurance contraction (Fig.…”

“…4 Further, the amount of variability increased with contraction level while the structure of 5 variability changed according to an inverted U-shape function in the task-related force and 6 tangential force Fy during discrete contractions. Finally, the amount of variability also 7 increased with contraction time in the task-related force and tangential force Fy.…”

“…2 The contributions of tangential forces (Fy and Fz) to the task-related force (Fx) were 3 calculated as the percentage contribution of each tangential force compared to Fx. 4 The error of performance was calculated as the difference between the exerted force signal Linear analysis of the force signals was performed to quantify the amount of variability.…”

Spastic movement disorder

“…Therefore, the changed regulation of spastic gait should be considered as optimal for the given state of the motor system (cf. 39 ).…”