I would like to develop the thighs just above the knees and I have no hack machine.
What type of squat do you recommend?
The following is the exercise substitute you have asked for BARBELL HACK SQUATS.
This exercise is a substitute for the famous Hack Machine, and primarily develops the muscles just above the knee area; providing the heel block is high enough. To check this, heels must be elevated high enough so that, when in the full squat position, the thighs are parallel or horizontal with the floor.
Another point to remember is, the straighter the back, the more resistance is placed on the thighs.
Also, with a straight back, the hips are not working to help the legs, as in the regular deep knee bend.
Stand erect with barbell hanging behind the thighs, heels elevated and spread about 11 or 12 inches.
The knees are spread 16” or 18” apart. Now, as you squat, let the barbell carry forward under the thighs to insure a deeper squat.
As you stand up, remember to keep a straight back, and at completion of squat, do not lock out, never straighten the thighs out completely at the top position (Unlocked squat.)