I don't know how long your tube things are -- you can run a pole (broom handle, etc.) thru the handles, stand on the tube , put the pole across your shoulders and do "squats" where the you as you stand, the resistance comes from below.
... its a thought.
You can also use the tube thing for rear kick backs w/ resistance. Put one handle around one ankle, the other around the other ankle and lift other leg to side or back for a nice butt burn. Just make sure there is resistance on the kick. Do it slow and hold for good tight form.
Another good resistance thing is to put one handle around something stable (heavy or attached to the ground/wall), put the other handle round your ankle. Stand facing away from where the handle is attached to the wall. Hold on to something in front of you so you don't fall over. Stand far enough away so there is tension in the tubes. Then do knee lifts to the front. The movement is sort of like going from a slight reverse lunge (ankle w/ the handle is the one that goes back, the other leg is the support). Then bring the knee (of the leg w/ the handle) up to your waist. Make sure your back is straight while you are doign this. You should feel the resistance in your buns, hams when you pull your knee up.
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