Answer: Yes, it is usually optimal to train a muscle through its functional ROM. But your trainer is right to have you start your curls with a slight bend in the elbows because that will maintain tension on the biceps brachii muscles. Here's why.
Three's Company
Three major muscle groups are involved in the biceps curl: the brachioradialis, the brachialis and the biceps brachii. While each has independent attachments and functions, they collectively work toward a common task - to flex (bend) the elbow.
Brachioradialis - Although mainly considered a forearm muscle, the brachioradialis actually initiates the biceps curl. This muscle attaches to the radius (forearm bone) near the wrist at its lower end and attaches near the elbow on the humerus (arm bone) at its upper end. The mechanics of the brachioradialis, which are dependent upon these attachment sites, make it strongest for about the first 30 degrees of the biceps curl. Once elbow flexion is initiated, the brachioradialis gives way to the brachialis and biceps brachii.
Brachialis - The brachialis muscle lies under the biceps brachii. Its lower end attaches to the ulna (the other forearm bone) and its upper end attaches to the lower end of the humerus. It is this attachment arrangement that dictates the strength of this muscle through the middle ROM of the biceps curl. From about 30 degrees to 100 degrees, the curl is dominated by the brachialis.
Biceps Brachii - The biceps brachii is the largest and most visible of the biceps muscles. It consists of two heads, a long and short, both of which attach near the elbow on the radius bone of the forearm. On the upper end, each head attaches separately on the scapula (shoulder blade).
Because of its attachments (so close to the elbow and so high on the shoulder), the biceps brachii is not a significant contributor to elbow flexion during the first half of the biceps curl. It's not until the elbow has passed 90 degrees of flexion that the biceps brachii assumes the majority of the workload.
The forces exerted upon the biceps brachii decline slightly as you pass beyond 135 degrees; still, it's important to continue the move until the arm is fully flexed.
Tips & Tricks
Starting the biceps curl with a slight bend in your elbows (as your trainer suggests) creates continuous tension in the biceps brachii. Although doing so decreases ROM somewhat, it actually helps minimize the brachioradialis contribution and focuses the force onto the biceps.
One method that helps segregate the three muscle groups is called '21s.' First, you do seven reps from the bottom position (zero degrees) to the mid position (90 degrees) of the curl to concentrate on the brachioradialis and brachialis muscles. Then you do seven reps from the midpoint (90 degrees) to the top position (beyond 135 degrees) to concentrate on the biceps brachii. Finally, you finish with seven full reps to finish off all three muscles. M&F
Tim Fritz, CSCS, is a freelance health and fitness writer in southeastern Florida. He has a bachelor's degree in nutrition science. Contact him at tcfritz@hotmail.com.
