Sit on bench edge, legs spread.
Hold dumbbell in one hand (e.g., right).
Lean forward slightly, brace back of upper arm against inner thigh.
Let arm hang straight down, palm facing up/forward.
Keeping upper arm stationary, curl dumbbell towards shoulder.
Focus on bicep contraction. Squeeze at top.
Slowly lower dumbbell back to start.
Repeat reps, switch arms.