These bands are great additional tools for home gyms or even commercial gyms. I loop them over the pull up bar to use them as cable machine type of workout. But it doesn't have the constant resistance like the dumbbells or weights have. Use biceps curl as an example, when you pick up a 40lbs dumbbell from the rack. It gives you that 40 lbs resistance at the moment it lift off the rack, and continues to do so in any position of the exercise. VS these resistance bands have virtually no resistance at the starting position of biceps curl exercise. Its resistance increases as you raise the forearm and decreases as you lower the forearm back to the starting position. You don't get the constant resistance as the weights give you. So if you're serious about body building, then weights/dumbbells are a must and probably are more effective than these bands.