Simply put, progressive overload means that you are consistently lifting or pulling a little more each week (or progressively on a schedule that aligns with your capacity). Lifting weight will break down your muscles. However — and this is where the magic happens — when the muscles grow back, they grow back stronger, but only if you are subjecting them to progressive overload.
The study that kicked off this whole seven-minute workout fad four years ago notes that the secret-sauce is to strategically work different major muscles groups (upper body, lower body, core) each time you do the workout. This allows for one major muscle group to rest while you work the next muscle group, resulting in a super-efficient, super-effective routine.
Recruitment criteria were one or both of sedentariness and dysmetabolism. Thus, we selected subjects who were not physically active or involved in any exercise program; that is, they had a sedentary lifestyle. Moreover, before entering the study, they were carefully screened for metabolic problems which attested a dysmetabolic status, as increased levels of plasma glucose, free fatty acids, triglyceride, and urate in fasting state. Both criteria were verified by means of family doctor databases of subjects.