Dynamic motor practice improves movement accuracy, force control and leads to increased corticospinal excitability compared to isometric motor practice

Abstract

The central nervous system has a remarkable ability to plan motor actions, to predict and monitor the sensory consequences during and following motor actions and integrate these into future actions. Numerous studies investigating human motor learning have employed tasks involving either force control during isometric contractions or position control during dynamic tasks. To our knowledge, it remains to be elucidated how motor practice with an emphasis on position control influences force control and vice versa. Furthermore, it remains unexplored whether these distinct types of motor practice are accompanied by differential effects on corticospinal excitability. In this study, we tested motor accuracy and effects of motor practice in a force or position control task allowing wrist flexions of the non-dominant hand in the absence of online visual feedback. For each trial, motor performance was quantified as errors (pixels) between the displayed target and the movement endpoint. In the main experiment, 46 young adults were randomized into three groups: position control motor practice (PC), force control motor practice (FC), and a resting control group (CON). Following assessment of baseline motor performance in the position and force control tasks, intervention groups performed motor practice with, augmented visual feedback on performance. Motor performance in both tasks was assessed following motor practice. In a supplementary experiment, measures of corticospinal excitability were obtained in twenty additional participants by application of transcranial magnetic stimulation to the primary motor cortex hot spot of the flexor carpi radialis muscle before and following either position or force control motor practice. Following motor practice, accuracy in the position task improved significantly more for PC compared to FC and CON. For the force control task, both the PC and FC group improved more compared to CON. The two types of motor practice thus led to distinct effects including positive between-task transfer accompanying dynamic motor practice The results of the supplementary study demonstrated an increase in corticospinal excitability following dynamic motor practice compared to isometric motor practice. In conclusion, dynamic motor practice improves movement accuracy, and force control and leads to increased corticospinal excitability compared to isometric motor practice.

Keywords: corticospinal excitability; force control; motor learning; position control; visual feedback.

FIGURE 1

Panel (A) depicts the experimental protocol of the main experiments including the two intervention groups: position control practice and force control practice and the control group. In panel (B) the experimental protocol of the supplementary experiments is depicted including the two intervention groups: position control practice and force control practice. The experimental setup is shown in panel (C) while the computerized task is shown in panel (D).

FIGURE 2

Mean errors (pixels) at baseline and post practice conditions from in the position control task in the three groups in the main experiment are depicted in panel (A): the position control practice group (blue), force control practice group (red) and control group (gray). Learning curves from the four blocks of position control practice is shown in panel (A). The delta changes (error) in the position control task are shown in panel (B). Target specific mean errors (pixels) in the position control task at baseline and post practice in the three groups are shown in panel (C). Standard deviations from mean error in the three groups are shown in panel (D) while coefficient of variation in percentage are shown in panel (E). *Denotes a significant difference within group and # denotes significant difference between groups.

FIGURE 3

Mean errors (pixels) at baseline and post practice conditions from force control task in the three groups in the main experiment are depicted in panel (A): the position control practice group (blue), force control practice group (red) and control group (gray). Learning curves from the four blocks of force control practice is shown in panel (A). The delta changes (error) in the force control task are shown in panel (B). Target specific mean errors (pixels) in the force control task at baseline and post practice in the three groups are shown in panel (C). Standard deviations from mean error in the three groups are shown in panel (D) while coefficient of variation in percentage are shown in panel (E). *Denotes a significant difference within group and # denotes significant difference between groups.

FIGURE 4

Transcranial magnetic stimulation (TMS) stimulus-response curves from (A) the position control practice group (blue colors), (C) the force control practice group (red colors) at baseline, post practice and 20 min post practice from the supplementary experiment. Panels (B,D) display summed motor evoked potential amplitudes (MEP) at baseline, post practice and 20 min post practice. *Denotes a significant difference within group and # denotes significant difference between groups.