I am concerned at present with my biceps development. Currently my arms measure 15-1/2” and I train my arms using the barbell curl and the seated concentration curl, but results are not coming.
I suggest you do five sets of “Drag Curls” and five sets of “Preacher Curls”. This will give your biceps a workout like never before.
(P.S. Drag Curls are performed by keeping the barbell touching the body as it raises from mid thigh to the chest area. The elbow will fall back rather than come forward as the curl is concluded.)