Female gains in body fat starting around puberty can result in a cycle of diminished physical fitness.

true or false

This is very likely False, but also might be true in some cases. However, as a rule of thumb in general it shouldn't be true. There is no evolutionary reason why physically women would become weaker during puberty as a result of increases of body fat (which shouldn't be at all noticeable given a normal childhood). There are also a lot of female teenagers competing in sports during puberty which goes against this.