Cross-Body Hammer Curl

Move · Resistance Training · Movement, Typed Supps

The brachialis sits underneath the biceps and attaches to the forearm bone that does not rotate, so turning your wrist can neither help it nor hinder it.

Stage by stage

Set-up (Neutral forearm position): A palm-in grip removes the biceps' supination advantage; brachialis is unaffected either way because it inserts on the ulna.
During the set (Brachialis and brachioradialis): Brachioradialis has its best leverage in neutral, and the deeper brachialis carries proportionally more of the flexion moment.
Through the arc (Near peak moment arm): The diagonal path holds the elbow around ninety degrees, where the flexion moment arm is close to its maximum.
Months later (Upper arm thickens): Brachialis growth lifts the biceps sitting above it, which reads as added arm thickness rather than added definition.

Muscles trained

Primary: biceps
Secondary: forearms

Intensity

3.5 METs (Resistance (weight) training, multiple exercises, 8-15 repetitions at varied resistance).

Time to effect

Weeks: Forearm and grip endurance tend to improve quickly, since the diagonal path keeps the neutral grip under tension for a longer arc than a straight-up curl.
Months: Added forearm thickness and a fuller-looking upper arm, driven mostly by brachialis growth, typically becomes noticeable over 2 to 3 months.

Common myth

"Curling across the body is just a hammer curl done sloppily." In reality: The diagonal path is a deliberate change in the resistance angle, not a form breakdown. It changes which portion of the biceps, brachialis, and brachioradialis bear the most load through the range of motion, similar to how changing grip width changes emphasis on a barbell curl.