Upper and lower limb muscle activation is bidirectionally and ipsilaterally coupled.

Area of Science:

• Neuroscience
• Human Physiology
• Exercise Science

Background:

• Neural connections exist between human upper and lower limbs.
• Limb muscle activation can modulate activity in the other limb pair.

Purpose of the Study:

• Extend findings on submaximal exercise to maximal effort.
• Determine ipsilateral or contralateral bias in neural coupling during rhythmic locomotion.

Main Methods:

• Measured muscle activity, joint kinematics, and limb forces in 16 subjects.
• Subjects performed recumbent stepping with varied upper and lower limb efforts.

Main Results:

• Increased muscle activation in passive limbs during active limb effort (bidirectional effect).
• No difference in maximal muscle activation between active/passive limb conditions.
• Neural coupling showed a primary bias from active upper limb to passive ipsilateral lower limb muscles.

Conclusions:

• Interlimb neural coupling impacts muscle recruitment during maximal effort rhythmic exercise.
• Findings provide insight into the neural coupling architecture between limbs.