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 use a lot of isometric contractions when training on the rings. The single-arm hang simulates the effects in a commercial gym-friendly manner.
- Hang from a pull-up bar with an underhand grip with the pinky fingers touching each other.
- Pull yourself up so the elbows are at 90 degrees.
- 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.