Lie on side on flat bench, support head.
Hold light dumbbell in top hand.
Bend elbow 90 degrees, upper arm resting against torso.
Start forearm parallel to floor, palm down/neutral.
Exhale, rotate forearm outward (supination) until palm faces ceiling/forearm perpendicular to floor.
Keep elbow fixed.
Hold contraction.
Inhale, slowly return to start.
Repeat reps, switch sides.