You've seen the name in programs. Maybe you've even tried it — elbows tucked, bar lowering toward your upper chest, that weird hybrid feeling between a close-grip bench and a skull crusher. And somewhere in the middle of the set, you wonder: *what part of tricep does JM press work, really?
It's a fair question. Most articles give you the textbook answer — "all three heads" — and move on. But if you've actually done the movement, you know it doesn't hit everything equally. You feel it somewhere specific. Usually right above the elbow, deep in the meat of the arm.
Let's break down what's actually happening Worth keeping that in mind..
What Is the JM Press
Named after JM Blakley — a guy who bench pressed 710 pounds raw at 242 and knew a thing or two about tricep strength — the JM press is a hybrid pressing movement. But think close-grip bench press meets lying tricep extension. But it's not quite either Not complicated — just consistent. Simple as that..
You set up like a close-grip bench. Hands around shoulder width, maybe slightly narrower. Elbows tucked hard to your sides. But instead of pressing straight up, you lower the bar toward your upper chest or lower neck, letting your elbows drift forward slightly. Then you press back up, driving through the triceps Easy to understand, harder to ignore. Surprisingly effective..
The range of motion is shorter than a skull crusher. In practice, the loading is heavier than a typical extension. And the elbow position — that's the key.
Why the Name Matters
Blakley didn't invent the movement to build big arms for the beach. Day to day, he built it to lock out heavier bench presses. The carryover to the top half of the bench is real. That's why powerlifters still program it decades later Worth keeping that in mind. Nothing fancy..
But for hypertrophy? That's where the nuance lives.
Why It Matters — And Why Most People Get It Wrong
Here's the thing: the JM press looks like a tricep exercise. And it is. But it's not a complete tricep exercise. Not the way a well-rounded arm routine needs And it works..
Most lifters treat it as their main tricep movement. Day to day, they load it heavy, grind out sets of 5–8, and wonder why their long head still looks flat. Or why their horseshoe doesn't pop from the side.
The answer is simple: the JM press biases the medial and lateral heads. Practically speaking, hard. The long head? It's involved — but it's not the driver.
If you don't know that going in, you build a program with a hole in it. And holes in tricep training show up fast — especially in poses, sleeves, and lockout strength Not complicated — just consistent. Worth knowing..
How It Works: Anatomy Meets Mechanics
Let's look at the three heads and what the JM press actually does to each Easy to understand, harder to ignore..
The Lateral Head — The Primary Driver
This is the outer head. The one that gives your arm width from the front. The one that pops in a tank top It's one of those things that adds up..
The JM press hammers it That's the part that actually makes a difference..
Why? Consider this: the elbow tucks. Even so, your upper arm stays roughly 45–60 degrees from your torso. Because the lateral head is the strongest elbow extensor when the shoulder is in a neutral or slightly flexed position — exactly where the JM press lives. The torque demand on the lateral head is massive Small thing, real impact..
And because you can load this movement heavier than almost any other tricep isolation, the lateral head gets exposed to high mechanical tension. That's the primary hypertrophy signal That alone is useful..
You'll feel the pump on the outside of your arm, high up near the shoulder insertion. That's the lateral head doing the work That's the part that actually makes a difference. That alone is useful..
The Medial Head — The Hidden Workhorse
Deep under the long and lateral heads sits the medial head. So it's small, stubborn, and often ignored. But it's active in every elbow extension movement — especially at higher forces.
The JM press recruits the medial head heavily because of the load. You're not doing kickbacks with 15-pound dumbbells. You're pressing 185, 225, maybe 315 for reps. The medial head has no choice but to contribute.
Here's the catch: you won't see the medial head. Which means it doesn't create visible shape. But it pushes the other two heads outward. A thick medial head makes the whole arm look denser. The JM press is one of the few movements that loads it meaningfully in a lengthened position That's the part that actually makes a difference. Still holds up..
The Long Head — The Missing Piece
This is where the "all three heads" claim falls apart.
The long head crosses the shoulder joint. Because of that, it originates on the infraglenoid tubercle of the scapula. That means its length changes with shoulder position. To fully stretch and bias the long head, you need shoulder flexion — arms overhead, or at least high in front of you That's the part that actually makes a difference. Took long enough..
The JM press keeps your shoulders in slight flexion — maybe 45–60 degrees. That's not enough to put the long head on meaningful stretch. Still, it's working, sure. But it's working in a shortened-to-mid range. Not the lengthened position that drives the most growth The details matter here..
Compare it to an overhead dumbbell extension, a cable overhead extension, or even a lying extension with the arms drifted back behind the head. Those movements bias the long head. The JM press doesn't.
So if your program is JM press + pushdowns + dips? Worth adding: you're hitting lateral and medial from every angle. But the long head is getting table scraps.
Common Mistakes — What Most People Get Wrong
Mistake 1: Turning It Into a Skull Crusher
The JM press is not a skull crusher. In a skull crusher, the elbows stay fixed and the bar travels in an arc toward the forehead. In a JM press, the elbows move — they drift forward as you lower, then drive back as you press Still holds up..
The official docs gloss over this. That's a mistake.
If your elbows don't move, you're doing a close-grip bench with a weird bar path. That shifts load to the anterior delt and pec. The tricep stimulus drops.
Mistake 2: Going Too Heavy, Too Fast
Blakley pressed 700+ pounds. You're not Blakley. Practically speaking, the JM press rewards control. Think about it: the eccentric — especially the transition from lowering to pressing — is where the magic lives. Rush it, and you lose the stretch-mediated hypertrophy on the lateral head Less friction, more output..
Three-second negatives. Explode up. Pause at the bottom. That's the rhythm.
Mistake 3: Flaring the Elbows
Elbows tucked. Always. Think about it: the moment they flare, the lateral head loses apply and the anterior delt takes over. You might move more weight. Your triceps get less Worth keeping that in mind..
Mistake 4: Using It As Your Only Heavy Tricep Movement
This is the big one. On the flip side, the JM press is a fantastic supplementary heavy movement. But it shouldn't be your only compound tricep lift. Still, close-grip bench, weighted dips, board presses — these all have different force curves and shoulder positions. That's why rotate them. Don't marry one.
This is the bit that actually matters in practice.
Practical Tips — What Actually Works
1. Program It Second, Not First
Start your tricep session with a long-head-biased movement. Overhead cable extension. Dumbbell overhead extension. Something with the arms high. Get the long head fresh, stretched, and pumped It's one of those things that adds up. Less friction, more output..
Then hit the JM press for 3–4 sets of 6–10 reps. The lateral and medial heads are fresh enough to handle heavy load. The long head is
…fresh enough to handle heavy load. The long head is already primed from the earlier stretch work, so you can really drive the lateral and medial fibers with maximal poundages. Aim for 3–5 sets of 4–8 reps, using a weight that lets you maintain strict form on every rep And that's really what it comes down to..
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2. Pair It With a Stretch‑Focused Finisher
After the heavy JM work, switch to a movement that maximizes time‑under‑tension in the stretched position. A single‑arm overhead triceps extension with a moderate‑to‑heavy dumbbell, performed for 3 × 12–15 reps, does the trick. Hold the bottom position for a full two seconds, then control the ascent. This not only pumps blood into the long head but also reinforces the lengthened‑position hypertrophy that the JM press alone can’t provide Most people skip this — try not to..
3. Use a Controlled Eccentric
The eccentric is where the stretch‑mediated signaling for growth is strongest. Consider this: take 3–4 seconds to lower the bar from full lockout to the chest‑level pause. In real terms, if you’re using a barbell, let the weight settle on your sternum before pressing up. If you’re on a cambered bar or using a specialty implement, keep the same tempo—speed kills the stretch stimulus and shifts the load toward the anterior deltoid.
4. Rotate the Grip
A narrow, shoulder‑width grip emphasizes the lateral head, while a slightly wider grip (hands just outside the plates) shifts some tension toward the medial head. Worth adding: alternate every 2–3 weeks to keep the fibers from adapting to a single stimulus. You can also experiment with a neutral grip (palms facing each other) on a cambered bar or a Swiss bar; the change in forearm rotation subtly alters the angle of pull on each triceps head.
5. Mind the Elbow Path
Think of the elbows as “track” that guides the bar. On top of that, as you descend, let them travel forward just enough to keep the bar close to the body, then pull them back as you press. This “J‑shaped” path ensures the lateral head stays engaged throughout the entire range. If you feel the elbows drifting outward, stop the set—your form is compromising the target muscle.
6. Incorporate Accommodating Resistance
Because the JM press has a relatively short range of motion, adding bands or chains can increase tension at the top of the movement, where the triceps are strongest. On the flip side, loop a light band around the bar and anchor it to a sturdy rack; as you press, the band tension will increase, forcing the triceps to fire harder at lockout. This method also teaches you to finish the rep with a true extension, eliminating half‑reps And that's really what it comes down to. Took long enough..
This is where a lot of people lose the thread The details matter here..
7. Recovery and Frequency
Given the high neural demand of the heavy JM press, limit it to once every 5–7 days. Pair it with a lighter, stretch‑focused triceps accessory on a separate day to keep the muscle under frequent tension without overtaxing the central nervous system. If you’re a seasoned lifter who can handle higher volume, a two‑day split—heavy JM press on day 1, high‑rep overhead extension on day 4—can produce excellent hypertrophic results.
Conclusion
The JM press is a powerful tool for building the lateral and medial heads of the triceps, but it’s not a magic bullet. Treat the JM press as the heavy‑lifting anchor of your triceps routine, but never as the sole driver—rotate in complementary exercises, control the tempo, and give your nervous system the recovery it needs. Its true value lies in how you integrate it into a broader, stretch‑centric triceps strategy. By positioning the shoulders in slight flexion, emphasizing a full eccentric, respecting elbow mechanics, and pairing the lift with movements that bias the long head, you create a synergistic environment where each triceps head can grow to its fullest potential. When executed with these principles in mind, the JM press transforms from a niche specialty lift into a cornerstone of any serious arm‑development program.
