The principle of specific adaptations to imposed demands dictates that in order for weight training to be beneficial, the workload must constantly progress as the body positively adapts to the previous effort. Simply put, if a lifter can lift 50 pounds 10 times today, then the next time the lifter should attempt 50 pounds 11 or 12 times. Alternatively, progression can take the form of increasing the weight to 60 pounds and then attempting 10 repetitions with the increased weight. Once that is achieved, progression would again continue with more added weight or repetitions. There is no magic number of times a weight should be lifted during a set. The weight should be lifted until the lifter can no longer safely lift the weight with the assistance of a spotter.