Muscle Group of the Week: Posterior Forearm Compartment
The superficial muscles of the posterior forearm include six to seven different muscles.
Wait, six to seven? How can there be an uncertain number of muscles in this area? Do some people possess one extra muscle that others don’t?
No, that’s not it. In addition to the six irrefutable posterior forearm muscles known as the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi, you have one other muscle that’s up for debate: the anconeus. We’ll elaborate on why the anconeus may or may not be part of this muscle group when we move onto the next section.
So onto that section! What does the posterior forearm compartment (plus that one odd-guy-out muscle Mr. Anconeus) do?
What Does it Do?
Any movement involving outstretched fingers or a perpendicular hand-wrist angle activates the posterior forearm muscles. When a server at a restaurant balances a tray on a flat hand, the posterior forearm compartment is in action – the semi-pronated flexed elbow is also putting one of these muscles to work.
Repetitive hand/finger/wrist actions that quickly rotate between flexion, extension, and side-to-side movements also put wear on the muscle group. A sign language interpreter, constantly stretching and contracting the area in short bursts, is another example of a profession involving prolonged periods of posterior forearm activation. Band conductors and basketball players execute similar repetitive motions when performing as well. Really, most types of musicians and athletes wear out the wrists/fingers/forearms on a regular basis.
More specifically, what does each individual muscle do?
Brachioradialis
- At elbow Joint
- Forearm flexion when semi-pronated
- Forearm stability during flexion, pronation, and supination
Extensor carpi radialis longus
- At wrist joints:
- Hand extension
- Hand abduction
Extensor carpi radialis brevis
- At wrist joints:
- Hand extension
- Hand abduction
Extensor digitorum
- At metacarpophalangeal (connects palm to fingers) and interphalangeal (between fingers) joints 2-5:
- Finger extension
Extensor carpi ulnaris
- At wrist joints:
- Hand extension
- Hand abduction
Extensor digiti minimi
- At metacarpophalangeal joint 5:
- Finger extension
*Anconeus
- At elbow joint:
- Forearm extension assistance
- Elbow stabilization
*Functionally, the anconeus muscle is more closely related to the triceps brachii than it is to the forearm extensors. It’s actually a continuation of the triceps muscle and performs the same actions at the elbow joint. For this reason, the anconeus is often grouped with the upper arm muscles instead of the forearm.
Making it Strong
The complex movements of the upper limbs are best performed with strong forearm muscles! We addressed how to strengthen the anterior forearm compartment in a previous article, so what can we do to beef up the posterior forearm compartment?
Dumbbell Wrist Extension
Elastic Band Finger Extension
Resistance Band Wrist Extension
Close Grip Pull Ups
Close Grip Pull Downs
The Best Stretches
Now that your upper limbs are recovering from a good set of pull downs, what’s the next step to keep them flexible? Those fine motor skills don’t just depend on strong forearms – they need flexible joints too!
Clasped Finger Extension
Tilt Forward Wrist Stretch
Cat’s Cradle String Trick
Arms Back Brachioradialis Stretch
Keeping it Happy
If you read the section of the previous article about treating the anterior forearm, you’ll find that the posterior forearm treatment is its exact opposite. The same methods – pin-and-stretch technique, deep tissue massage, heat therapy, stem machine, ultrasound, etc. – are all effective, but will be applied to the posterior forearm instead. After removing adhesions from the posterior forearm, the weakened anterior forearm compartment will benefit from the strengthening modalities such as PNF stretching.
Now You Know!
Brachioradialis and the extensors have some very important work to do. Keep the elbow joint strong so you can draw that glass of water towards your face with ease! Mobilize those wrists and fingers to be sure you can give the best high-fives!
Katrina Jenkins
Author, Licensed Massage Therapist
Katrina Jenkins graduated from Towson University in 2013 with a Bachelor’s Degree in Health Science and worked as a nurse’s aide briefly before pursuing her true passion. She graduated from the Massage Therapy Institute of Colorado in April 2016 with honors and completed the Touch of Healers Scholarship Program the following summer. She has been a part of the Moyer Total Wellness Team since the summer of 2017.
Resources
Barnes, D. (2022). Brachioradialis: Action, Origin, Insertion, & Innervation. [online] The Muscular System. Available at: https://themuscularsystem.com/upper-limb/forearm/brachioradialis.html#google_vignette [Accessed 22 Apr. 2025].
Chaudhry, M., Aminullah, H., Sinkler, M.A. and Arain, A. (2021). Anatomy, Shoulder and Upper Limb, Forearm Compartments. [online] PubMed. Available at: https://www.ncbi.nlm.nih.gov/books/NBK539784/.
Grujičić, MD, R. (2023). Superficial posterior forearm muscles. [online] Kenhub. Available at: https://www.kenhub.com/en/library/anatomy/the-superficial-extensors-of-the-forearm.
Grujicic, R. (2021). Metacarpophalangeal (MCP) joints. [online] Kenhub. Available at: https://www.kenhub.com/en/library/anatomy/metacarpophalangeal-mcp-joints.
Jackson, J. (2022). Brachioradialis exercises and workout routines with dumbbells, without weights, and for rehab. [online] Critical Body. Available at: https://criticalbody.com/brachioradialis-exercises/.
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