A Dura-ball is a big ball designed for the weight room. The advantage of a Dura-ball is that it allows you to start the crunch in a hyperextended position, which puts a stretch on the abs and allows you to strengthen them through a complete range of motion. The Dura-balls are also beneficial because they are an unstable base of support. Training on them gives you greater stability when you're competing, as well as in everyday life. The best way to lose weight is aerobic exercise and dieting.
Most strength training consists of anaerobic exercise.
The anaerobic lactic acid energy system inside the muscle cells is where the muscle gets the energy to lift weights. The anaerobic energy system is far less efficient than the aerobic system, so that much more fuel is burned by anaerobic activity than is burned by doing the same amount of work aerobically. Metabolic rates can stay elevated hours after an anaerobic workout, while the metabolic rate drops along with the heart rate after an aerobic workout. More fat is burned for a longer period of time by working out anaerobically. Dieting does not work well because when you restrict the amount of calories consumed per day, your body reacts by lowering your metabolic rate so that less calories are needed, instead of burning more fat to make up for the lost calories.