The commonly used workout strategy that involves variations in workout intensity is called interval training. This approach combines periods of high-intensity exercise with periods of lower intensity or rest, enhancing cardiovascular fitness and metabolic efficiency. Interval training can be applied to various forms of exercise, including running, cycling, and strength training. This strategy not only helps improve overall performance but also makes workouts more engaging and time-efficient, which is especially beneficial for those with limited time to devote to fitness.