Underrated & Underworked Muscle #3:Flexor Digitorum Profundus!

In this Fitness-Tip Friday series I’m emphasizing a set of muscles that are significantly underrated as far as their overall importance – and therefore underworked by the vast majority of people! First we discussed the tibialis anterior, then last week the serratus anterior, and this week’s underrated & underworked muscle is the flexor digitorum profundus (aka FDP)!!

There are a whopping 19 muscles in each forearm… but the single LARGEST, STRONGEST, and arguably MOST IMPORTANT of these is the FDP! It makes up the bulk of the forearm mass that sits on the medial underside of the forearm (circled in image above). Yet the vast majority of people don’t use the ONE technique that works it more than anything else!

But first, why is it so important to train…?

Well, here are just a few of the many reasons:

1. The FDP is the primary determinant of your grip strength, which is essential in order to effectively train a large portion of your body (esp. back muscles)
2. Because it determines grip strength, the FDP therefore largely determines how firm your handshake is (which has been proven to subconsciously convey strength, confidence, and reliability)
3. It is the ONLY muscle in the body that flexes the ends of your fingers (distal phalanges)!
4. Functionally the forearm flexors are the single most used skeletal muscle group in modern society
5. Due to a principle called muscular irradiation, the stronger your FDP is the more effectively you’ll be able to work not only the other forearm muscles but also your upper arm muscles, including the biceps, triceps, and deltoids
6. As mentioned above, the FDP is the largest of all forearm muscles… so focusing on it will give you the biggest bang for your buck with forearm training, and built forearms simply look awesome!! (After all, they’re usually the only muscles anyone can clearly see when your shirt is on… which for most people is 99% of the time they’re out and about)

So what’s the secret to working and developing the FDP?? It lies in #3 in the list above. It is the only muscle that flexes the ends of the fingers… so you need to place resistance direction against flexion of the last digit of the fingers! (See image #1 below). All other wrist and finger movements engage a whole host of other forearm muscles, taking load off the FDP.

But wait… there’s more. In order to maximize FDP engagement, you need to work it close to its point of maximum extension (i.e. longer muscle fiber lengths), which can only be done if the wrist is hyperextended (bent backwards – see GIFs below). So to put those two together, you need to place resistance directly against flexion of the fingertips while the wrist is hyperextended!

GIFs 1 and 2 below show precisely how that can be done with either a cable machine or dumbbell and a bench! The GIFs could only be long enough to show the eccentric (aka negative) phase… but the concentric phase is just to perform the exact same motion in reverse by flexing the fingers and then flexing the wrist back to neutral (after ensuring that you dropped the weight as far down to the ends of your fingertips as you can)!

APPLICATION: Stop ignoring the flexor digitorum profundus and start reaping the incredible benefits of training it directly!!!

Relevant Research Article(s):
      1) Anatomy, Shoulder and Upper Limb, Hand Flexor Digitorum Profundus Muscle

Related Dr. Gains YouTube Video(s):         
      1) How to Build ALL 8 Forearm Flexors (4 Finger Flexors + 4 Wrist Flexors = Big & Ripped Forearms!) 💪

      2) BEFORE YOU BENCH PRESS, Understand the Anatomy Behind it! (Incline, Decline, Close Grip, Wide, Form)

GIF #1 – FDP Isolation Using Cables

Image #1 – Close-up of resistance on fingertips

GIF #2 – FDP Isolation Using a Dumbbell