An intense isometric contraction is terrific for muscle growth for two reasons. First, it quickly recruits the largest motor units because it's a maximum voluntary contraction. Second, isometrics increase the neural drive between the motor cortex in your brain and the trained muscle.
Gymnasts and Big Biceps
Want to know how those rings gymnasts built such incredible biceps? One word: maltese. That isometric movement is, without a doubt, the most effective strength exercise to add biceps mass. But it's also the most dangerous biceps exercise.
Training your way up to a maltese is so risky that I've hesitated for years to even mention the correlation between it and massive biceps. The likelihood of tearing your biceps, jacking up your elbows, or screwing up your shoulders is enormous. You should only embark on that journey with an Olympic-level gymnastics coach.
The Safer Alternative
Alternately, the isometric exercise I recommend for biceps development is the single-arm hang.
- Hang from a pull-up bar with an underhand (palms up) grip with the pinky fingers touching each other.
- Pull yourself up so the elbows are at 90 degrees.
- Next, quickly grab your left wrist with your right hand so the left hand is the only one gripping the bar. Maintain the 90-degree left elbow angle as your forearms, biceps, and upper-back fire to maintain your body position. Try to hold for about 10 seconds.
- Switch sides and repeat with the right hand gripping the bar.