Seated dumbbell concentration curls yield 97% biceps activity, in contrast to cable curls or chin-ups. This is why you need to work Isolated Dumbbell Curls or Concentration Curls Into Your Routine
Have a dumbbell in one hand and rest it across the incline bench with a supinated (palms up) grip.
Position your non-lifting hand at the corner or side of the incline bench. The chest should be pressed against the top part of the incline and your feet should be pressed against the floor at a wide stance. This is the starting position.
While holding the upper arm stationary, curl the dumbbell upward while contracting the biceps. Only the forearms should move. Continue the movement until your biceps are fully contracted and the dumbbell is at shoulder level. Hold the contracted position for a second then slowly begin to lower the dumbbells