Certified Personal Trainer (NSCA) Practice Exam

The biceps brachii produces the greatest torque during the upward movement phase of a standing barbell curl when the elbow is at 90 degrees of flexion. At this position, the muscle's moment arm—the perpendicular distance from the line of action of the force to the axis of rotation (the elbow joint)—is at its longest. Torque is defined as the product of the force applied and the distance from the pivot point (moment arm). Thus, when the moment arm is longest, it maximizes the torque the biceps can generate, allowing for the most effective lifting force during the curl. In contrast, at both the beginning and end of the movement, when the muscle is either fully extended or fully contracted, the length-tension relationship is not optimal for generating maximal force. Specifically, at full extension, the muscle is at its longest, reducing the potential for generating effective torque. Similarly, when the biceps is fully contracted at the end of the curl, the moment arm decreases as the elbow approaches full flexion, leading to decreased torque production. The 45-degree angle also does not maximize the moment arm for torque, making 90 degrees the optimal position for torque generation in the standing barbell curl.