Is There A Biceps Curl?

by Dr. Mel Siff

The apparently simple biceps curl, although one of the trademarks of bodybuilding, remains poorly understood by gymnasium users and scientists alike. Even EMG (electromyographic) studies have proved notoriously contradictory during attempts to ascertain exactly which
arm muscles are involved at a specific instant during elbow flexion.

Elbow flexion is produced by the cooperative action of the biceps
brachii, brachialis and brachioradialis. Of these, the biceps cross
the shoulder and the elbow joints, whereas the other two flexors act strictly on the elbow. Thus, if strict arm flexion is to take place,
there must be no movement about the shoulder joint. This fact is well known to bodybuilders who execute the curl with elbows dug into the sides of the trunk or with the back leaning firmly against a wall.

Several basic factors profoundly effect which elbow flexors become involved in any type of forearm curl:

- orientation of hand (pronated, supinated or neutral)
- the intensity of resistance to movement
- speed of movement
- degree of shoulder extension/flexion
- degree of shoulder abduction.

A detailed EMG study of elbow flexion performed with variations of
these factors was carried out by Basmajian (Muscles Alive, 1978). His time analysis of activity revealed that there is a completely random sequence of appearance and disappearance of activity in the different elbow flexors of his subjects. In any sample of subjects, there appears to be no predictable pattern among the muscles for activating, sustaining and terminating flexion.

Moreover, muscles which display the greatest activity in individual
subjects only begin the movement first and end it last. He concluded that there is a fine interplay between the biceps, brachialis and brachioradialis throughout elbow flexion, so that it is inappropriate to identify a specific muscle as playing a specific role at any given instant. Most remarkable was the wide variation in the response produced by a given muscle. Although a general trend may be described, the same type or sequence of activity rarely occurs in different subjects.

The long head of the biceps (whose tendon passes through the shoulder joint capsule) shows more activity than the short head in most subjects during slow elbow flexion, during supination of the hand against resistance, and during shoulder flexion. There is little difference in electrical activity between the two heads of the biceps during isometric contraction or during eccentric elbow extension. These observations are directly relevant to the bodybuilder who wishes to exercise a specific head of the biceps more strongly.

Miwa and Matoba (quoted by Basmajian) found that, during slow elbow flexion, biceps brachii is much more active electrically at certain angles of flexion. Unlike the variation of isometric force with angle, the EMG reveals peak activity at 160 degrees, almost nil at 90 degrees (surprisingly, where isometric force is near a maximum), and strong activity at full flexion (where isometric force is relatively low). Clearly, much still has to be learned about the interaction between the nervous and muscular systems.

Biceps brachii is usually active during flexion of the supinated
forearm for all intensities of loading and during flexion of the semi-
prone forearm against resistance (as with 'hammer curls'). However, if the forearm is prone (as with reverse grip curls), the biceps play a minimal role during concentric and eccentric elbow flexion. This finding directly contradicts the traditional belief among
bodybuilders that the biceps continue to play a major role during all forms of elbow flexion. It is brachialis which displays this
prominence, since it is active during fast and slow elbow
flexion with forearm prone, semi-prone or supinated at all
intensities of loading. It appears that brachialis contributes to all
variations of elbow flexion, since its line of pull does not change
with pronation or supination. This fact reveals that the term 'biceps curl' should be eliminated from the exercise manuals and be replaced by the more accurate term 'arm curls' or 'elbow flexions'.

Brachioradialis does not play any significant role during any form of elbow flexion without a weight, although it becomes much more
strongly involved during rapid flexion and extension with the forearm in all three positions of rotation. This muscle, therefore, is seen to act as assistant mover when rapid or strongly resisted flexion occurs.

All three elbow flexors contract strongly when a resistance is
overcome during flexion of the semi-prone forearm. Basmajian
describes the semi-prone orientation of the forearm as the natural
position, the position of rest and the position of greatest
mechanical advantage for most functions of the upper limb. In other words, the hammer curl, with palms facing the sides of the body, rather than the supinated (palms up) curl, should be regarded as the fundamental type of arm curl.

Another interesting finding is that the triceps - traditionally
regarded as only an extensor of the elbow - is strongly active during pulling movements (such as seated rowing) with the elbow flexed. The biceps are powerfully involved while the elbow is close to full extension, but the triceps contribute as the angle of flexion increases, undoubtedly since the shoulder is extended backwards, thereby making use of the long head of the triceps as a shoulder extensor.

The apparently simple act of elbow flexion, often regarded as
synonymous with the so-called biceps curl, displays subtle nuances of functional anatomy which have eluded much of the fitness community for many years. A greater appreciation of the richness of all variations of elbow flexion would contribute significantly to the implementation of more effective normal and rehabilitative training.