Speed, resistance, and unexpected accelerations modulate feed forward and feedback control during a novel weight bearing task

Abstract

We developed a method to investigate feed-forward and feedback movement control during a weight bearing visuomotor knee tracking task. We hypothesized that a systematic increase in speed and resistance would show a linear decrease in movement accuracy, while unexpected perturbations would induce a velocity-dependent decrease in movement accuracy. We determined the effects of manipulating the speed, resistance, and unexpected events on error during a functional weight bearing task. Our long term objective is to benchmark neuromuscular control performance across various groups based on age, injury, disease, rehabilitation status, and/or training. Twenty-six healthy adults between the ages of 19–45 participated in this study. The study involved a single session using a custom designed apparatus to perform a single limb weight bearing task under nine testing conditions: three movement speeds (0.2, 0.4, and 0.6 Hz) in combination with three levels of brake resistance (5%, 10%, and 15% of individual’s body weight). Individuals were to perform the task according to a target with a fixed trajectory across all speeds, corresponding to a ~ 0 (extension) to 30 degrees (flexion) of knee motion. An increase in error occurred with speed (p<0.0001, effect size (eta2): η2=0.50) and resistance (p<0.0001, η2=0.01). Likewise, during unexpected perturbations, the ratio of perturbed/non-perturbed error increased with each increment in velocity (p<.0014, η2=0.08), and resistance (p<.0001, η2=0.11). The hierarchical framework of these measurements offers a standardized functional weight bearing strategy to assess impaired neuro-muscular control and/or test the efficacy of therapeutic rehabilitation interventions designed to influence neuromuscular control of the knee.

Myotonic dystrophy type 1 alters muscle twitch properties, spinal reflexes, and perturbation‐induced trans‐cortical reflexes

“…Phase III of the experiment (Supporting Information Figure S1C) consisted of movement performance testing designed to examine trans‐cortical sensorimotor reflex pathways (trans‐cortical LLRs). The study used a well‐validated functional weight‐bearing task that elicits LLRs after unexpected perturbations in single limb stance . Subjects stood with the right knee positioned against a padded plate that moved horizontally on a rack and pinion system .…”

“…The study used a well‐validated functional weight‐bearing task that elicits LLRs after unexpected perturbations in single limb stance . Subjects stood with the right knee positioned against a padded plate that moved horizontally on a rack and pinion system . An electromagnetic brake resisted linear displacement of the rack during knee flexion and extension.…”

“…Subjects received two practice trials (five sinusoid cycles each) to learn the position‐matching task. Subjects then performed the position‐matching task across nine conditions that varied the brake resistance (5%, 10%, and 15% of body weight) and sinusoid speed (0.2, 0.4, 0.6 H z ) . Each condition consisted of five sine‐wave cycles.…”

“…In phase 3, overall SLS AE across all nine test conditions was compared between groups by means of one‐way ANOVA. For the analysis of perturbations, previous work indicated that among the nine conditions, the 0.2 H z , 15% body weight resistance condition comprised a moderate‐difficulty task that could be successfully performed even by participants with underlying sensorimotor impairment . All perturbation analyses used data obtained from this test condition.…”

“…Trans‐cortical reflexes occur between the latency of spinally mediated stretch reflexes and volitional activation. Similar to spinal reflexes, they can be elicited by rapid stretch of skeletal muscle, such as during an unexpected weight‐bearing perturbation Altering cortical excitability through transcranial magnetic stimulation yields changes in the magnitude of LLRs, highlighting their potential mutability in response to altered cortical states. Little is understood about the functional correlates of cortical processes in DM1 .…”