Ankle Joint Angle Influences Relative Torque Fluctuation during Isometric Plantar Flexion

Area of Science:

• Biomechanics
• Human Physiology
• Motor Control

Background:

• Muscle length is a critical determinant of muscle force production.
• Understanding how muscle length influences force steadiness is crucial for motor control research.
• Previous studies have primarily focused on force production rather than force fluctuations.

Purpose of the Study:

• To investigate the effect of varying muscle lengths on torque fluctuations.
• To examine the relationship between muscle activity oscillations and torque fluctuations.
• To determine the influence of muscle length-dependent mechanical properties on isometric contraction steadiness.

Main Methods:

• Healthy individuals performed isometric plantar flexor contractions at various intensities (10-70% MVIC).
• Contractions were conducted at three distinct ankle joint angles, representing shorter, neutral, and longer muscle lengths.
• Surface electromyogram (EMG) signals from triceps surae muscles were recorded and processed (rsEMG) to analyze muscle activity oscillations.

Main Results:

• Absolute torque fluctuations increased significantly at longer muscle lengths during moderate-to-high intensity contractions.
• Relative torque fluctuations were higher at shorter muscle lengths.
• Muscle activity oscillations (rsEMG) remained consistent across different ankle joint angles.

Conclusions:

• Torque steadiness during isometric contractions is influenced by both muscle activity and muscle length-dependent mechanical properties.
• Muscle mechanics play a significant role in explaining variations in force output steadiness.
• Future research should incorporate muscle mechanics when analyzing force steadiness.