Most people think the biceps is just an elbow flexor—the muscle that curls your arm. But supination (rotating your forearm so your palm faces up) is actually a primary bicep function that's often overlooked in training.
What Is Supination?
Supination is the rotation of your forearm that turns your palm from facing down to facing up. Think of holding a bowl of soup—you supinate to keep the soup from spilling.
The opposite movement—turning your palm down—is called pronation.
The Biceps as a Supinator
Here's what many people don't realize: the biceps is actually the strongest supinator of the forearm. While it's famous for elbow flexion, it's mechanically very efficient at supination.
This is why:
• Curling with a supinated (palms-up) grip maximizes bicep activation
• Rotating from neutral to supinated during a curl adds extra bicep work
• Neutral grip (hammer curls) reduces bicep involvement
Training Implications
Supinated grip curls:
• Maximum bicep activation
• Biceps works for both flexion AND supination
• Standard barbell and dumbbell curls
Neutral grip curls (hammer curls):
• Reduced bicep activation
• Increased brachialis and brachioradialis work
• Biceps still flexes elbow but doesn't supinate
Rotating dumbbell curls:
• Start with neutral grip at bottom
• Rotate to supinated at top
• Adds supination work throughout the rep
• Maximizes bicep function
Why This Matters
For muscle activation: If you want maximum bicep work, supinated grip is superior. The biceps is working harder when performing both of its functions.
For balanced development: Including neutral grip work (hammer curls) shifts load to the brachialis. A complete arm program includes both.
For function: Real-world activities require supination strength—turning doorknobs, using tools, carrying objects. Training supination builds functional strength.
Simple Test
Try this to feel the bicep's supination function:
1. Hold your arm at your side, elbow bent 90 degrees
2. Start with palm facing down (pronated)
3. Rotate your palm up against resistance (someone pushing down, or holding a weight)
4. Feel your bicep contract powerfully
You're not flexing your elbow—you're supinating. And your bicep is doing the work.
The Bottom Line
The biceps is both an elbow flexor AND a forearm supinator. For maximum bicep activation, use supinated (palms-up) grip. For balanced arm development, include neutral grip work too. Understanding this dual function helps you train more effectively.