Muscle Minute TUESDAY - Meet the Extensor Carpi Radialis Brevis

That is a long name for a small muscle, but don’t let the size of the ECRB fool you. This muscle has been the main source of elbow pain in 1-3% of the US population, with incidence upwards of 10% in people who work with repetitive upper extremity movements. It is one of three muscles that attach to the lateral epicondyle via the common extensor tendon (CET), but it is unique in its function and position. Let’s take a deeper dive.

Origin	lateral epicondyle of humerus (via CET)
Insertion	base of the 3rd metacarpal
Action	wrist extension and radial deviation
Innervation	deep branch of radial n. (C5, C6)
Antagonists	flexor carpi ulnaris

The Real World Extensor Carpi Radialis Brevis (ECRB)

The common extensor tendon (CET) is the shared attachment of four muscles: extensor carpi radialis brevis (ECRB), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU) and extensor digitorum (ED). Of these four muscles, the ECRB is the deepest. It is also known as one of the prime movers of wrist extension, along with extensor carpi radialis longus (ECRL), with the latter originating a little more proximal on the lateral supracondylar ridge of the humerus.

Remember, muscles that lie closest to the joints act as stabilizers more than prime movers, and that is what makes the ECRB prone to injury. EMG studies have shown that it acts as a stabilizer to the forearm flexors for gripping as well as a prime mover for wrist extension during supination (a requirement for the tennis backhand among other things). That is a lot of work.

Get a grip. Make a tight fist. Notice how your wrist extends in order for you to do this. Now try to make a tight fist and keep your wrist in neutral. Does your grip feel weaker? A strong grip requires wrist extension (ECRB) in order for the finger flexors to maintain optimal length tension.

That’s a lot of work for a small muscle, which means by design, it isn’t meant to work alone. The tennis backhand is a complex series of movements with lots of players. Protection of the ECRB is dependent on coordinated activity of the opposite subtalar joint (ankle), hip and thoracic spine. It is also dependent on its antagonists, the finger flexors, maintaining normal length.

Here’s a short list of why this matters:

Trigger points in the wrist and finger flexors may neurologically weaken the ECRB
The ECRB acts as a stabilizer AND a prime mover
It is synergistic with the opposite side butt (gluteus maximus)

Conventional thinking says: The ECRB is often injured because it is weak. Strengthen it.

Real World Thinking says: The ECRB is often placed in a position of injury because it is overworked, acting as a stabilizer for gripping and a prime mover for wrist extension. it is a small muscle that is not designed to work alone, and its optimal function may be altered by trigger points in its antagonists and/or lack of movement in joints of the opposite lower extremity.

Make sure you aren’t blaming the wrong thing when it comes to tennis elbow.

Because nobody has time to be in pain.

Until next time…