They should keep lifting the same weight for the both and after they manage to lift it they should add more weight keeping the weight the same on both of the weights.
Answer:
The correct answer is relative strength. You want to be fair to the other body size, for example, let's say you have a 5-year-old kid and an adult male in his 20s. There obviously is a difference in strength even without testing. Absolute strength would be unfair. It's best to match it up with your relative strength.
