Agonist
Short definition
The prime muscle (or muscle group) directly producing a movement: its contraction generates the main driving torque at the joint.
Full definition
The agonist is the muscle whose contraction is the prime mover of a given motor action: it produces the greatest torque in the direction of the movement and overcomes external resistance (gravity, load). The agonist can change across the range of motion: in the bench press the pectoralis major is the prime mover at the bottom, while the triceps takes over near lockout. In Samson-fit, phase-dependent agonist contributions are defined in the ExerciseMuscleAnatomy table and feed the MIDA engine via muscle_weight and tech_coefficient.
Examples
In the bench press (bottom phase) the agonist is the pectoralis major, contributing 40–55%.