most lifters have some "sweet spot" below the one-rep max for which mechanical tension on the targeted muscles is at its highest. Adding additional weight won't increase mechanical tension and may actually shift it away from the desired muscles and onto passive structures or other muscles.

In general, performing squats, deadlifts, hip thrusts, bench presses, military presses, chins, and rows will ensure that you’re maximizing mechanical tension across the various muscle groups. However, one exercise alone will not maximize tension on the entire spectrum of fibers within a muscle.

Metabolic stress: Increasing time under tension (TUT) increases metabolic stressand gives you incredible pump, or muscle-cell swelling. This swelling cancause both an increase in muscle-protein synthesis and a decrease in proteinbreakdown, which are essential components of the process by which the bodyrepairs and grows muscle tissue after exercise (4,5,6)

Mechanical tension: This tension is exerted on the muscles from movement andexternal loads to reduce, produce, or control force.

Well, as you descend into the bottom of the squat or lunge (in hip flexion and knee flexion), the rectus femoris is trying to lengthen at the knee but shorten at the hip, and ends up staying roughly the same length. Then as you ascend (performing hip extension and knee extension), the muscle is trying to shorten at the knee but lengthen at the hip, and again ends up staying about the same length. (3)

So, mechanical tension is really the driving force of muscle growth, and muscle damage and metabolic stress are just the physiological results of it