If you want bigger arms, you can't ignore the brachialis. This often-overlooked muscle sits underneath your biceps and, when developed, literally pushes your biceps up and out—making your arms look significantly larger.
Brachialis vs. Biceps: What's the Difference?
Biceps brachii:
• Two heads (long and short)
• Crosses the shoulder joint
• Functions: elbow flexion AND forearm supination
• Most active with supinated (palms-up) grip
• The "show muscle" on the front of your arm
• Single muscle, no heads
• Only crosses the elbow joint
• Function: elbow flexion ONLY (no supination)
• Most active with neutral or pronated grip
• Hidden under the biceps, visible on the outer arm
Why the Brachialis Matters for Arm Size
The "push-up" effect: The brachialis sits directly underneath the biceps. When it grows, it pushes the biceps up and outward, making your arms appear larger even if your biceps haven't grown.
Arm width: The brachialis is visible between the biceps and triceps on the outer part of your arm. Developing it adds width and thickness to your arm profile.
Overall arm mass: Many lifters focus only on biceps and miss significant arm growth potential. The brachialis is substantial muscle mass you're leaving undeveloped.
How to Target the Brachialis
The brachialis is most active when your forearm is in a neutral or pronated position (because the biceps is mechanically disadvantaged in these positions):
Best brachialis exercises:
1. Hammer curls
• Neutral grip (palms facing each other)
• The go-to brachialis exercise
• 3-4 sets x 10-15 reps
2. Reverse curls
• Pronated grip (palms facing down)
• Also hits forearm extensors
• Use lighter weight than regular curls
• 3 sets x 12-15 reps
3. Cross-body hammer curls
• Curl across your body toward opposite shoulder
• Different angle of brachialis activation
• 3 sets x 10-12 each arm
4. Rope hammer curls (cable)
• Cable provides constant tension
• Maintain neutral grip throughout
• 3 sets x 12-15 reps
Programming for Brachialis Development
Include at least one brachialis-focused exercise in each arm workout:
Sample approach:
• Bicep exercise 1: Barbell curl (supinated)
• Bicep exercise 2: Incline curl (supinated, long head)
• Brachialis exercise: Hammer curl (neutral)
• Optional: Reverse curl (pronated)
This ensures you're hitting both biceps heads AND the brachialis.
Common Mistakes
Ignoring neutral grip work: If all your curls are palms-up, you're under-developing the brachialis.
Going too heavy on hammer curls: Ego lifting leads to swinging. Control the weight through full range of motion.
Neglecting reverse curls: They feel awkward because you're weaker in this position, but they're effective for brachialis and forearm development.
How to Know If Your Brachialis Is Underdeveloped
Visual check: Look at your arm from the side. If there's not much visible muscle between your biceps and triceps on the outer arm, your brachialis likely needs work.
Training history: If you've never done hammer curls or reverse curls regularly, your brachialis is probably lagging.
Proportions: If your arms look good from the front but thin from the side, brachialis development can help.
The Bottom Line
The brachialis is the hidden key to bigger arms. It sits under your biceps, and when developed, it pushes your biceps up and adds width to your arm. Target it with hammer curls and reverse curls—exercises that minimize bicep involvement and maximize brachialis work.
Don't skip neutral grip work. Your arms will thank you.