Inside: Of all the digits on the hand, the thumb is arguably the most important. Learn more about the flexor pollicis longus, the muscle that bends the thumb.

Thumbs help you open doors with doorknobs. They are essential for tying shoelaces, and they help you open boxes of tasty sugary treats.

Our opposable thumbs help elevate us as a species. Although there are several muscles that control your various thumb movements, this post focusses on the muscle that flexes your thumb–the flexor pollicis longus.

Location

The origin of the flexor pollicis longus is in two areas. First, there is a point of origin on the anterior surface of the middle half of the radius. This means when you have your palm facing forward in an anatomical neutral position, you can feel the point of origin when you press about half-way up your radius on your forearm. Remember, the radius will be the lower arm bone that is farther from the midline of your body.

The second point of origin for the flexor pollicis longus is through nearby tissue and bone. To be specific, the Flash Anatomy Muscles Flash Cards say it originates on the “adjacent interosseous membrane and a slip from the coronoid process of the ulna or medial epicondyle of humerus.”

The flexor pollicis longus inserts on the palm side of the top knuckle of your thumb, just above the joint.

Function

Plain and simple, flexor pollicis longus bends the thumb. It bends the top knuckle, the knuckle at the base of the thumb, and even helps move the bone in your hand beneath the thumb.

Common Dysfunction

If it is painful, difficult, or impossible to bend your thumb; you might have a dysfunctional flexor pollicis longus. Since this muscle’s whole function is bending the thumb joints and moving the bone in your hand, if any of those activities are limited or impaired, it’s a safe bet that this muscle isn’t quite working correctly.

Restoring or Maintaining Health

Any time you think that you have injured or torn a muscle, you need to contact your doctor immediately. Your doctor can order all of the appropriate imaging, medicine, and therapy necessary for you to heal as quickly and thoroughly as possible.

However, if you want to keep the flexor pollicis longus healthy, I have some suggestions. For optimal muscle health, you want to both strengthen and stretch this muscle. To strengthen the muscle, practice bending your thumb at the joints and allowing the bone at the base of the thumb to move.

In order to stretch this muscle, practice the opposite actions. This means that you want to extend your thumb (like you’re hitchhiking). You can also gently increase this stretch by using your other hand to encourage your thumb to extend further.

More Information

For those who are interested in technical terminology and all the muscles in the body, I recommend Flash Anatomy Muscles Flash Cards. Any time a client comes to me with pain, I use these flash cards.

Do you have any other suggestions for strengthening or stretching the flexor pollicis longus? Let us know in the comments below.

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