The flexor digitorum profundus is one of 3 deep forearm flexors located in the anterior compartment of the human forearm. Like these other forearm muscles, the flexor digitorum profundus performs flexion at the hand and wrist. However, because it inserts into the phalanges, it’s also responsible for finger flexion.
Like many of its surrounding muscles, the flexor digitorum profundus is a fusiform muscle because it’s widest in the middle and then tapers towards the end. In this respect, it’s similar to the whole of the forearm, which is thickest around the middle and slimmer towards the wrist and elbow joints.
Related flexor guides
- Flexor carpi radialis stretch
- Flexor carpi ulnaris exercises
- Flexor digitorum superficialis stretch
- Flexor pollicis longus exercises
Flexor digitorum profundus functions
While technically capable of assisting in wrist flexion, this is not the main function of the flexor digitorum profundus. Its main role is finger flexion, which is extremely important for helping you grip objects in your everyday life. 
It’s amazing how many strength trainees can have muscular arms but a comparatively weak grip. Not only does this show contempt for functional strength, but it also indicates that many people are simply unaware of the many benefits of having a strong grip.
Flexor digitorum profundus exercises
I’m going to show you my favourite flexor digitorum profundus stretch, along with two of the most effective exercises for adding strength to this particular muscle.  The beauty of these exercises is that, although I use dumbbells in the examples, you can also use any weighted object and get virtually the same results.
1. Flexor digitorum profundus stretch
I usually do this flexor digitorum profundus stretch while standing. But if you’re feeling lazy, can’t stand up, or just get a better stretch while sat down, feel free to do this exercise seated.
- Place your arm out in front of you with your elbow fully locked out and palm facing down.
- Extend your palm upwards by bending your wrist so that your palm is now facing forwards (like you’re waving at someone).
- Apply a stretch to your working hand with your free hand by pulling the fingertips of the working hand towards your body.
- Hold the stretch for 10-20 seconds and then repeat with your other arm.
2. Weighted carry
This training drill is most often done with dumbbells or kettlebells since they’re easy to grip and widely available in most fitness facilities. Yet, a pair of loaded shopping bags or weighty household objects will also do the trick quite nicely.
For ease of illustration, I’ll use dumbbells for this tutorial.
- Grab 2 moderately heavy dumbbells and hold them by your sides, hands in a neutral position.
- Ensure that the dumbbells are in the palms of your hands rather than just resting in your fingers (this position may change as you naturally tire during the course of the exercise).
- Squeeze the dumbbells to engage your forearms and maintain this hold for 30 seconds.
- Bump up the duration to 45 seconds and then 1 minute before increasing the weight.
3. Hand grip squeezes
This is one of the best flexor digitorum profundus exercises because it requires just one piece of equipment: a hand gripper.
It’s arguably not quite as functional as the dumbbell hold because you don’t sit down and squeeze grippers in everyday life. No, you carry heavy shopping bags and suitcases.
That said, it’s hard to beat the convenience and simplicity of this exercise. So let’s get into it.
- Hold a handgripper in your hand.
- Squeeze the two sides towards each other by pushing your fingers into one side of the gripper and the palm of your hand into the other.
- Maintain the squeeze until both ends touch.
- Release the contraction under control by allowing your fingers to extend.
- Repeat the motion for 2-3 sets of 10-12 reps.
- Anconeus muscle exercises
- Brachioradialis exercise
- Extensor carpi radialis brevis stretch
- Exercises for the extensor carpi radialis longus
- Extensor carpi ulnaris stretch
- Extensor digitorum stretch
- Extensor pollicis brevis stretches
Pairing the flexor digitorum profundus stretch with one of the two flexor digitorum profundus exercises is a great way to relieve muscular tension while simultaneously building strength.
Oh, and when I say pair, I don’t mean that you need to do a superset. Rather, I’m saying to include both types of exercises (strength and stretch) in your resistance training routine.
Just make sure that you start light on the weight lifting exercises because the flexor digitorum profundus is a very small muscle that doesn’t require all that much resistance to become stronger.
- Vasković, J. (2020, October 29). Flexor digitorum profundus muscle. Kenhub. https://www.kenhub.com/en/library/anatomy/flexor-digitorum-profundus-muscle
- Osanami, Y., Aoki, M., Shirato, R., Saito, Y., Hidaka, E., Miyamoto, H., & Uchiyama, E. (2020). Tensile load on the flexor digitorum profundus tendon during palmar and lateral blocking exercises: Influence on blocking force and distal interphalangeal joint flexion angle. Journal of Hand Therapy. https://doi.org/10.1016/j.jht.2020.07.004