Which muscle is primarily affected by the L4 nerve root?

The muscle most significantly affected by the L4 nerve root is the anterior tibialis. This muscle is primarily responsible for dorsiflexion of the foot, which is a critical movement for walking and maintaining balance. The anterior tibialis is innervated by the deep peroneal nerve, which receives its nerve fibers from the L4 root among others.

When assessing any neurological concerns or potential nerve root injuries, it's important to understand that the L4 nerve root plays a key role in the function of the anterior tibialis. Dysfunction or impairment of this nerve root can lead to weakness in dorsiflexion, commonly evaluated in clinical settings by testing the ability of the patient to lift their toes off the ground.

Other muscles listed have different primary functions or are innervated by different nerve roots. The extensor hallucis longus also plays a role in foot dorsiflexion but is primarily innervated by L5, rather than L4. The gastrocnemius, responsible for plantarflexion, mainly corresponds with the S1-S2 nerve roots. The biceps’ function and innervation are related to the brachial plexus and primarily involve the C5-C6 nerve roots, which are unrelated to the lumbar spine.