Solution posted in response to How to Reuse a Worn-out Bike Tube
Cheap exercise equipment
One use for old bicycle inner tubes might be as exercise equipment. You could make a set to do all the body-building work you need at next to no expense. This device can be used in a manner similar to the commercially-available stretchable tubing. To control the tension to your satisfaction, some experimentation will be necessary.
Here's what to do:
1. Cut the old tube crosswise on either side of the valve stem and throw it (the stem!) away. You will be left with a tube 76"-84" long depending on the size of the wheel.
2. Carefully slit the tube lengthwise making a long rubber strip. Stretch this strip to see how much resistance it provides.
3. If it feels pretty good based on how you want to use it, you can rig up handles so that the stretched length gives the right resistance (#5 below). You could even double or triple it if you've eaten your spinach.
4. If you want an easier-to-stretch device, slit the rubber strip lengthwise into two pieces, one 33% of the width of the strip, and the other 67% of the width. See how much resistance these pieces have when you stretch them. Experiment until you are satisfied - used bike tubes are real cheap.
5.Depending on how the devices that you make are to be used, you will have to improvise handles on each end. The simplest would be tying a knot at each end that leaves an opening for your hands or feet. If you want to get fancy, you can use short pieces of old broomstick or a dowel - roll the rubber five or six times around the dowel then secure the free end with several tacks in a row that penetrate all layers.
6. Whatever you do, be sure to check your work before you apply your massive strength.Use at your own risk -- better to be safe than sorry.