Quad exercises

The quadriceps straighten the knee, which makes them the main muscle behind the whole squat family. Squats, lunges, split squats and step-ups all run on them. If your knee is bending deeply under load, your quads are working.

Depth is the lever that matters most. A squat to a full comfortable depth trains the quads far harder than a heavier quarter squat does. Single-leg work adds something two-legged squats miss, because the front knee travels forward over the foot in a way it does not during a normal squat.

Heavy squatting is demanding well beyond the thighs. It taxes your breathing and your trunk at the same time, which is useful in conditioning workouts and costly everywhere else. Quality drops quickly once you are tired, so the generator puts heavy squat patterns early in a session on purpose.