The Torque-Angle Curve
Muscle force output is fundamentally governed by the sarcomere length-tension relationship and mechanical joint leverage (moment arm). As a joint moves through its arc, both muscle length and moment arm distance change continuously, creating a parabolic or inverted-U shaped Torque-Angle Curve.
Angle of Peak Torque (APT)
The Angle of Peak Torqueis the precise joint angle (in degrees) at which maximum torque is recorded. For example, concentric quadriceps peak torque typically occurs at approximately 60° of knee flexion (0° = full extension). Following hamstring strain injury, the angle of peak torque often shifts toward shorter muscle lengths (e.g. from 30° to 45° of flexion), leaving the muscle vulnerable to strain when stretched during terminal swing phase in sprinting.