Simple lower extremity two-joint synergy

Area of Science:

• Biomechanics
• Motor Control
• Neuroscience

Background:

• The central nervous system (CNS) employs synergies to simplify the control of multi-joint movements.
• Previous research established two-joint simple synergies in upper extremities, but their existence in lower extremities was less clear.

Purpose of the Study:

• To investigate and describe the presence of a simple synergy in lower extremity movements.
• To determine if established upper extremity synergies are applicable to lower limb motor control.

Main Methods:

• Subjects performed isolated knee or ankle movements in the sagittal plane at maximal speed.
• Recorded joint kinematics and electromyographic (EMG) signals from key lower limb muscles (biceps femoris, rectus femoris, soleus, tibialis anterior).

Main Results:

• EMG patterns typically exhibited a triphasic pattern during discrete movements.
• Observed simultaneous activation bursts between knee flexors (biceps femoris) and ankle plantar flexors (soleus).
• Demonstrated similar activation patterns between knee extensors (rectus femoris) and ankle dorsiflexors (tibialis anterior).

Conclusions:

• A two-joint simple synergy appears to exist in the lower extremities, mirroring findings in the upper extremities.
• This synergy likely aids the CNS in simplifying the postural control aspects of motor tasks.
• The findings suggest a generalized motor control strategy across different limb segments.