The scaling of motor output in rapid isometric contractions and dynamic agility sub-movements
Date
2024
Authors
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Publisher
University of Delaware
Abstract
This study investigated the rates of force production and muscle activity in young adults during both isometric and dynamic conditions, aiming to extend the quantification of rate-scaling to whole-body agility-related movements. Twenty healthy participants, free of neurological disorder and musculoskeletal injury, and equally divided by gender were recruited. Participants performed various tasks involving isometric force pulses and dynamic agility sub-movements while muscle activity was recorded via electromyography (EMG) from the lateral gastrocnemius, tibialis anterior, soleus, and peroneus longus. ☐ In the isometric force pulse protocol, the dominant foot of the subjects was secured in a custom force measuring device, and maximal voluntary contractions (MVCs) were recorded for normalization. Participants then performed rapid force pulses at varying percentages of their own MVC, with five sets of twenty pulses each. Dynamic tasks included lateral stepping, forward and backward stops, and a cutting task, all performed at three self-selected intensities. Ground reaction forces and EMG signals were synchronized and collected. ☐ Results showed a significant positive relationship between peak rate of force development (RFD) and peak force across all tasks, with R² values ranging from 0.517 to 0.870. Linear regression models quantified these relationships, and all tasks demonstrated significant rate-scaling (p < 0.001). EMG measures of excitation were significantly associated with peak RFD, indicating modulation of neuromuscular activity. While correlations between task-specific RFD scaling factors and overall agility assessed by the Agility T-Test were not statistically significant, trends suggested moderate associations. ☐ This research provides evidence of rate-scaling from ground reaction forces during simple change-of-direction tasks and highlights the modulation of neuromuscular excitation in response to varying force demands. These findings have implications for sports science, rehabilitation, and training, suggesting potential for dynamic task studies in at-risk populations to evaluate neuromuscular control and intervention efficacy.
Description
Keywords
Agility, Dynamic tasks, Electromyography, Isometric force pulses, Rapid movement, Rate of Force Development