Quads are more difficult to work with tubing. I would recommend one legged balances to help your knee stabilization. Stand with your weight in one leg. Other leg can be lifted off the floor a couple of inches. If your balance is weak, try resting the toes very lightly on the floor, still keeping all of the weight in your one leg. Bend the knee slightly without the knee extending past the toes. Flex your torso forward and point your tailbone/butt backwards until you feel your weight distributed into the thigh and hip. There should be NO PRESSURE in the kneecap. If you feel that, you are not sitting your hips back enough and you are probably pushing the knee out over the toes. This is not a very exciting exercise but it is fantastic to help the knees. Hold on each leg for approximately 60 seconds. Alternate back and forth 5 rounds.
As for the butt, I LOVE this exercise and do it all the time for my clients or in cardio classes. Secure the handle of the tubing around your foot. I push it up around the arch of my shoe so that it's pretty snug and isn't going to slide off. Position yourself in a table position, back flat and supported with firm abs. Hold the other end of the tubing with the same side hand--if tubing is secured on right foot, hold in right hand. You want to hold the tubing somewhere in the middle so there is already tension before you start. Kick your leg straight back no higher than hip level. You can also extend the leg, tap the toe to the floor, lift up again to hip level and then bring the knee back beside support knee. Also try little pulses in kicking the leg out--faster tempo but shorter range. This is an excellent butt lifter. Just make sure the tubing has sufficient tension or it will be too easy. Obviously pad your knees well to avoid strain. Tell me what you think and good luck! Cyndie