Exercise Analysis - Curls

Competitive bodybuilders train like there’s no tomorrow, calculate their diets meticulously and practice posing ‘til they’re blue in the face (literally!). Nevertheless, the most important determinant for on-stage success requires none of these measures. When all is said and done, the critical thing a bodybuilder must do is choose his parents wisely! I learned this lesson early on when my genetically-gifted biceps were the talk of the gym.

When I started lifting weights, my biceps developed fast and were much better than the rest of my physique. In actuality, it had little to do with how I trained them, but this fact was lost on my compatriots, who were constantly asking me for my secret. All I could tell them was to do curls.

I now realize that training the muscles of the front portion of the upper arm is not as simple as my early experiences indicated. First off, the biceps are only one of three muscles situated in this region and aren’t even the prime movers when we flex the arm at the elbow (curl). And while all three muscles are responsible for performing this function, there are a number of ways to do curls, and subtle changes in technique alter which muscle shoulders the brunt of the effort.

The predominant elbow flexor is the brachialis, which originates on the lower portion of the front of the humerus (upper arm bone) and transcends the elbow, attaching to one of the two forearm bones below (the ulna). When it develops sufficient tension to overcome resistance to shortening, contraction of the brachialis causes the elbow to bend. If the upper arm is fixed (as should be the case during any curling exercise where a weight is held in the hand), the forearm will move toward it. If the hand is fixed, the opposite will occur. The latter is an example of a reverse origin/insertion action and is what happens when we perform chin-ups from a bar fixed overhead.

The brachialis is the predominant elbow flexor, but the biceps brachii has more responsibilities because it crosses additional joints. It also possesses two different sections. The long and short heads of the biceps share the same insertion on the radius (the other forearm bone), but have different origins on the scapula. In addition to the elbow, the biceps act at the shoulder.

When the biceps contract and motion at the shoulder is allowed, the arm rises to the front. Stabilizing muscles act isometrically (without changing length) during conventional curls to prevent this unwanted action. But maintaining the arm in a raised position at the shoulder as you train your elbow flexors (supporting it on a structure above your head as you perform curls from a high pulley, for example) is a viable strategy to change elbow-flexor emphasis because it reduces biceps involvement. In this posture, the muscle is shortened and less capable, so the brachialis is featured. It is also common for lifters to alter muscle use by turning their palms up as they curl. This motion is called supination and occurs at the articulation formed between the two bones of the forearm (the radioulnar joint). Supinating increases biceps involvement because the biceps also act at this joint.

The third muscle that contributes to elbow flexion is the brachioradialis, which is quite different than the other two. This muscle is classified as a shunt muscle because the majority of its length lies past the joint where the motion it creates takes place. Owing to this configuration, shunt muscles function more to stabilize joints and are highly disadvantaged when movement is the objective. Nevertheless, brachioradialis involvement on curls can be amplified if its line of pull is favored. The muscle is attached to the radius in line with the thumb, so curls done with the thumb facing up (hammer curls) call it into action. Emphasizing the brachioradialis is important for bodybuilders with an extended space between their biceps peak and elbow because its development fills the gap.

Free weight curls can be done with barbells, dumbbells or a specially constructed bar with bends (E-Z curl bar) that reduce stress on the wrist. Obviously, incorporating supination necessitates the use of dumbbells or some form of loading that allows independent movement for the left and right sides. Curls can also be done on machines or with cables. Variable resistance curl machines have cams that change the moment arm through which the opposing load is applied as movement takes place. This programmed fluctuation is designed to mirror varying muscle capacity at different joint angles. However, it is also important to consider leverage conditions when performing free weight curls. For example, preacher curls (curls with the upper arm braced against a support pad) with the arm positioned at 45 degrees result in minimal resistive torque opposing contraction at full flexion because the weight winds up directly above the elbow. Angling the arm completely downward (using a pad that is vertical), on the other hand, is associated with a considerable load when the rep has been completed, which dramatically decreases the amount of weight that can be used.   

This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.






Go back