How come black people seem more muscular than white people

Are you sure this is true?

Can it be said of Afro-Americans living in the US?

Probably in Africa or Australia more important than the amount of light is the different life style, which is more active. The nutrition is different and most likely less rich and not as easily accessible. The inevitable result is less fat and more muscle...

My mistake :-)

Probably, as you said, because the light is absorbed against black skin and so enhances the contours of the body rather than blurs it.

Try using softer lighting when photografing people of lighter skin tone. It could make all the difference. If that doesn't work, you might want to consider highlighting the musclems with body make up.

The darker colors absorb the light, so muscle ridges seem more pronounced. BTW, it is more than likely that photografs you've seen are retouched (but I guess you know that already).

It depands on Body, not on color of skin

well this is related to the human anatomy ....not the light absorbtion or the skin color