Uploaded March 2026 | Updated September 2026, 2 weeks ago
In a biceps curl, the mechanical challenge isn't constant. It changes drastically based on the position of your arm relative to gravity.
To understand why, let's look at this simple mechanical principle:
Torque = Force × External Moment Arm
Since the gravitational force (the dumbbell weight) stays the same, the torque (load on the muscle) depends entirely on the external moment arm, which is the horizontal distance from your elbow to the weight.
Here is how the resistance profile changes:
🔥 Forearm parallel to floor (90°): Maximum moment arm = Maximum torque. Since the distance is the longest here, the external load on the muscle is at its peak.
❄️ Weight stacked over elbow: Zero moment arm = Zero torque. When the weight aligns directly over the elbow joint, the moment arm is effectively zero. The weight is "resting" on the joint rather than loading the muscle.
💡 Want to dive deeper into muscle anatomy and movement?
Check out the Muscle & Motion Strength Training app - link in bio!
In a biceps curl, the mechanical challenge isn't constant. It changes drastically based on the position of your arm relative to gravity.
To understand why, let's look at this simple mechanical principle:
Torque = Force × External Moment Arm
Since the gravitational force (the dumbbell weight) stays the same, the torque (load on the muscle) depends entirely on the external moment arm, which is the horizontal distance from your elbow to the weight.
Here is how the resistance profile changes:
🔥 Forearm parallel to floor (90°): Maximum moment arm = Maximum torque. Since the distance is the longest here, the external load on the muscle is at its peak.
❄️ Weight stacked over elbow: Zero moment arm = Zero torque. When the weight aligns directly over the elbow joint, the moment arm is effectively zero. The weight is "resting" on the joint rather than loading the muscle.
💡 Want to dive deeper into muscle anatomy and movement?
Check out the Muscle & Motion Strength Training app - link in bio!
