Gym lore has it that preacher curls isolate the lower biceps and that you can change the shape of yours by doing heavy preachers. That’s wrong on both counts.
The ability to isolate one part of a long muscle like the biceps while the other part remains less active exists only in the imagination. There’s no proof such a phenomenon is possible. Of course, lack of proof never stopped a gym myth. That particular one is perpetuated by the fact that the lower portion of the biceps appears to be more prominent, which is misleading. The majority of the growth actually takes place in the brachialis. The biceps brachii originates on the scapula, or shoulder blade, and it attaches to the radius, one of the forearm bones, at the elbow. Because it crosses two joints, the biceps has a variety of functions. It can supinate your forearm (turn the palm up). It also flexes, or bends, the elbow and affects the shoulder in several ways.
The brachialis lies underneath the biceps, where it inserts at the elbow. It originates on the midshaft of the humerus (upper-arm bone) and inserts into the other forearm bone, the ulna. The ulna does not have the radius’ unique ability to rotate. The brachialis can flex only the elbow, and, as it doesn’t cross the scapula, it doesn’t affect shoulder movement.
When a muscle crosses over two joints, as the biceps brachii does, it must be stretched at both joints in order to be maximally recruited. (There are other variables, but they don’t relate to this discussion.) If the two-joint muscle isn’t stretched at both joints, as is often the case in isolation exercises, it’s recruited less. Less is the key word here. It’s not that you can’t work the muscle, but the muscle’s ability to work is reduced, which reduces your potential for development. Isolation is also a very misleading word in training. True isolation rarely occurs. If the two-jointed muscle is recruited less, then an increased share of the workload shifts to the one-joint muscle. That applies to the preacher curl as follows:
The biceps brachii is the two-jointed muscle. As preacher curls place the elbows up on the bench, the shoulder is in a position of passive flexion, which recruits the biceps less, and the one-joint muscle, the brachialis in this movement, is recruited more. The increased recruitment of the brachialis makes it grow, and that pushes up the ‘lower’ biceps, which perpetuates the gym myth that you can isolate your lower biceps with preacher curls. The myth appears to be true, but the explanation is wrong.
Bodybuilders who are trying to change the shape of their biceps often overdo both poundage and volume’a foolish mission. You can’t change the genetically determined shape of your biceps no matter how many preacher curls you do. Though they train alike, the world’s best professional bodybuilders all have differently shaped biceps.
Overtraining on preacher curls can strain the brachialis, which causes pain around the elbow; you don’t usually feel pain on top of the biceps. Another way to strain that muscle is through heavy lat training.
The preacher curl is a safe movement if you use common sense and don’t bounce the weight at the bottom or overdo the sets, reps or poundage. If you experience ongoing aches and pains when you attempt preacher curls, you may simply be overstressing the brachialis. To remedy that, eliminate preacher curls and lat training to give your brachialis muscles a rest. Then put either preacher curls or lat training back into your routine, but not both right away. Build the sets and poundage back up slowly.
Editor’s note: Visit www.softtissuecenter.com for reprints of Horrigan’s past Sportsmedicine columns that have appeared in IRON MAN. You can order the book, Strength, Conditioning and Injury Prevention for Hockey by Joseph Horrigan, D.C., and E.J. ‘Doc’ Kreis, D.A., from Home Gym Warehouse, (800) 447-0008 or at www.home-gym.com.