that's a tough one
You would have to look at the person's overall work capacity, which is usually only measurable by some type of full body benchmark workout. The challenge is, there are few assessments that truly measure strength, endurance, stamina, flexibility and overall work capacity in one.
If you had to look at one non performance based metric, I would look at their overall body composition (body fat %). This is usually a good teller of their overall health and will give you a starting point on whether to design a program geared toward weight loss, hypertrophy, performance enhancement, etc.
