All W2 earnings (regular wage and salary employment) have Social Security deducted. If you are an independent contractor and get 1099 earnings, it is a little more complicated, but if you file your taxes properly, you will also have Social Security deducted and it will build up (social media income probably falls in this category). Bodybuilder drug sales or much of posing income, and even personal training, would not qualify unless the income is reported or a 1099 is submitted by the self employed individual or the person paying the bodybuilder, etc. (unlikely in most or many cases). Some employer earnings do not qualify for Social Security. For example, many school teacher pension plans and some government employees do not deduct Social Security for their employees, but these employees have big traditional pensions instead. But they would still have Social Security deductions on weekend or side jobs.
The Social Security formula mainly gives you a “proportionate” monthly check to what you paid in, however favoring the little guy over the big guy from a proportionate standpoint.