What Muscles Do JM Press Work? Complete Anatomy Guide

The JM press is a hybrid movement between a close-grip bench press and a skull crusher—named after legendary powerlifter JM Blakley. This unique exercise builds massive tricep strength that transfers directly to bench press lockout.

Quick Answer

Primary muscles: Triceps (maximum—all three heads), anterior deltoids (high), pectoralis major (moderate-high)

Secondary muscles: Core (moderate), forearms (moderate), upper back (low—stabilization)

The JM press is primarily a tricep exercise disguised as a pressing movement—the angle and path create maximum tricep overload.

What Makes the JM Press Special

Hybrid Movement

It's not quite a bench press (bar path is different) and not quite a skull crusher (you're pressing, not just extending). This hybrid position maximizes tricep loading.

Heavy Loading Possible

Unlike skull crushers which limit weight, the JM press allows much heavier loads because your shoulders assist.

Direct Lockout Transfer

The movement pattern closely mimics the lockout portion of bench press—building strength exactly where many lifters fail.

The JM Press Movement

Setup

| Component | Position | |-----------|----------| | Grip | Close (12-16 inches apart) | | Elbows | Tucked, pointing forward | | Bar path | Toward lower face/chin, then back | | Back | Arch as in normal bench |

The Descent

| Muscle | Action | Activation | |--------|--------|------------| | Triceps | Eccentric control | Very High | | Anterior delts | Controlling descent | High | | Pecs | Minor control | Moderate |

Lower the bar toward your chin/lower face—NOT to your chest like a bench press.

The Press

| Muscle | Action | Activation | |--------|--------|------------| | Triceps | Elbow extension | Maximum | | Anterior delts | Pressing assist | High | | Pecs | Pressing assist | Moderate |

Press the bar back up and slightly toward your feet to lockout—a J-shaped path.

Primary Muscles Worked

Triceps (All Three Heads)

| Head | Emphasis | |------|----------| | Lateral head | Very High | | Medial head | Very High | | Long head | High |

The JM press is primarily a tricep exercise. The close grip, tucked elbows, and bar path create maximum tricep loading. JM Blakley credited this exercise for his massive tricep development.

Anterior Deltoids

Your front delts assist throughout. They're not the primary movers but contribute significantly to the pressing motion.

Pectoralis Major

Your chest helps, especially in the lower portion, but this is NOT a chest exercise. Chest activation is secondary.

JM Press vs Similar Exercises

| Exercise | Primary Target | Weight Potential | Lockout Transfer | |----------|---------------|------------------|------------------| | JM Press | Triceps | High | Maximum | | Skull Crusher | Triceps | Moderate | High | | Close-Grip Bench | Triceps + Chest | High | High | | Board Press | Lockout | Very High | High |

The JM press offers a unique combination of tricep isolation and heavy loading.

Programming JM Press

For Tricep Strength

• 3-5 sets of 5-8 reps
• Moderate to heavy weight
• Focus on tricep engagement
• Full rest between sets

For Bench Press Accessory

• After main bench work
• 3-4 sets of 6-10 reps
• Addresses lockout weakness
• Part of assistance work

For Hypertrophy

• 3-4 sets of 10-12 reps
• Moderate weight
• Focus on tricep contraction
• Controlled tempo

Technique Cues

Grip

1. Narrow—12-16 inches between hands
2. Wrists straight or slightly cocked
3. Firm grip—bar stability matters

Bar Path

1. Lower toward chin/lower face—not chest
2. Elbows tuck and point forward
3. Bar tracks in front of shoulders
4. Press up and slightly back (J-shape)

Elbow Position

1. Elbows tuck toward body
2. Elbows point more forward than out
3. Controlled movement—not flaring

Common Mistakes

| Mistake | Why It's Bad | Fix | |---------|-------------|-----| | Lowering to chest | Becomes close-grip bench | Bar to chin area | | Elbows flaring | Shoulder stress, less triceps | Elbows tucked and forward | | Going too heavy | Form breaks down | Build weight gradually | | Bouncing at bottom | Momentum, joint stress | Control the turnaround | | Bar too far toward face | Dangerous | Aim for chin area | | Grip too wide | Less tricep emphasis | Close grip (12-16") |

The JM Blakley Legacy

JM Blakley was a legendary powerlifter known for massive bench press numbers. He developed this exercise to build the tricep strength needed for heavy lockouts. His credentials:

• 710 lb raw bench press
• Multiple world records
• Known for innovative training methods

When JM Blakley says this builds triceps, it's worth listening.

Finding the Right Bar Position

The JM press takes practice to find the correct groove:

Too Close to Face (Dangerous)

Bar goes toward nose/forehead—this is skull crusher territory and risky.

Too Close to Chest (Wrong Exercise)

Bar goes to chest—this is close-grip bench, not JM press.

Sweet Spot (Correct)

Bar aims for chin/lower face area—the unique position that maximizes tricep loading.

Practice with light weight until you find it.

Weight Expectation

Most lifters can JM press 60-70% of their bench press. Factors:

• Tricep strength relative to overall pressing
• Technical proficiency with the movement
• Individual leverages

This isn't a max weight exercise—it's a tricep builder.

Who Should Do JM Press

Excellent For:

• Powerlifters weak at lockout
• Those wanting bigger triceps
• Bench press specialists
• Anyone plateaued on bench

Build Foundation First:

• Solid close-grip bench technique
• Comfortable with skull crushers
• Understanding of elbow position

Not Ideal For:

• Those with elbow issues (high stress)
• Complete beginners
• Those who can't control the movement

Benefits Beyond Triceps

Lockout Power

Directly transfers to bench press lockout strength.

Pressing Stability

Teaches tight elbow position useful for competition benching.

Variety

Novel stimulus for triceps that have adapted to standard exercises.

Sample Programming

Bench Day Accessory

• Bench Press: Main work
• JM Press: 4x8 @ moderate weight
• Other tricep work as needed

Tricep Focus Block

• Week 1: JM Press 4x8
• Week 2: JM Press 4x6
• Week 3: JM Press 5x5
• Week 4: Deload

Assistance Exercise

• JM Press: 3x10
• Skull Crushers: 3x12
• Pushdowns: 3x15

Key Takeaways

✅ JM press primarily works triceps (all three heads)
✅ Hybrid between close-grip bench and skull crusher
✅ Bar path goes to chin area—not chest, not forehead
✅ Close grip (12-16 inches) with elbows tucked forward
✅ Allows heavier loading than skull crushers
✅ Builds lockout strength for bench press
✅ Named after JM Blakley (710 lb bench)
✅ Practice light until you find the groove

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The JM press looks weird until you try it. Then your triceps will understand. Find the sweet spot, keep those elbows tucked, and build the lockout strength that turns good benchers into great ones.