A biceps curl is one of the most common movements used to build size and strength in the upper arm. The Spider Curl is a popular variation performed lying face-down on an incline bench. This position isolates the biceps by preventing momentum and minimizing assistance from other muscle groups. Lifters often question the specific impact of this exercise on the two heads of the biceps muscle, particularly whether it effectively targets the long head for balanced arm development.
Anatomy of the Biceps Brachii
The biceps brachii is a two-headed muscle running along the front of the upper arm; both heads originate at the scapula. The short head begins at the coracoid process, a bony projection on the front of the scapula. Since it crosses only one joint before attaching to the forearm, its function is primarily focused on elbow flexion.
The long head originates from the supraglenoid tubercle, a small bump on the scapula above the shoulder joint socket. Because the long head crosses both the shoulder and the elbow joints, it is known as a bi-articular muscle. This means its effectiveness in flexing the elbow is highly dependent on the position of the shoulder joint.
The Unique Mechanics of the Spider Curl
The Spider Curl is performed by resting the chest against an inclined bench, typically set at a 45 to 60-degree angle. From this position, the arms hang straight down, suspending the weight. This setup forces the biceps to be the sole muscle group responsible for lifting the weight, preventing the use of momentum or body swing.
The position of the upper arm relative to the torso determines the movement’s mechanics. Lying face-down naturally places the elbows slightly forward, in front of the body. This forward placement involves a degree of shoulder flexion, meaning the arm is slightly raised. This specific joint angle significantly affects which of the two biceps heads is primarily engaged.
Why Spider Curls Emphasize the Short Head
The long head of the biceps assists with shoulder flexion, in addition to flexing the elbow. When the arm is already in a position of shoulder flexion, the long head is placed in a pre-shortened state. This mechanical disadvantage, known as active insufficiency, significantly reduces the long head’s ability to generate maximal force during elbow flexion.
Since the long head is slackened at the shoulder, its contribution to the curl is minimized. The short head, whose origin is unaffected by the shoulder’s forward position, must take on the majority of the mechanical tension. Therefore, the Spider Curl is highly effective for isolating and emphasizing the short head of the biceps. This focus is beneficial for developing the “peak” or height of the muscle belly.
Exercise Variations for Long Head Development
If the goal is to specifically target the long head of the biceps, a different shoulder angle is needed. To maximize the long head’s activation, the muscle must be placed under a greater stretch at the start of the movement. This is achieved by extending the shoulder, which means positioning the upper arm behind the torso.
Incline Dumbbell Curl
The Incline Dumbbell Curl is the most common exercise to achieve this stretch. It is performed by sitting on an incline bench set back at a lower angle, typically 30 to 45 degrees. This position forces the arms to hang behind the body, creating maximum tension on the long head at the beginning of the curl.
Drag Curl
Another effective variation is the Drag Curl, where the elbows are consciously pulled backward and kept behind the torso as the weight is curled close to the body. Both the Incline Dumbbell Curl and the Drag Curl utilize shoulder extension to place the long head in a mechanically advantageous, lengthened state, allowing it to contribute maximally to elbow flexion.