For transgender women on long-term hormone therapy, how well their bodies use oxygen during exercise is closely linked to their muscle mass relative to height — but this doesn’t seem to be the case for cisgender men or women.

When you account for muscle mass, trans women, cis women, and cis men have about the same heart and lung fitness level — even if their raw numbers look different.

Trans women who've been on hormone therapy for years can take in more oxygen during intense exercise than cis women, but less than cis men — putting their heart and lung fitness somewhere in the middle.

Trans women on long-term hormone therapy might have similar oxygen levels and fitness as cis women, even after going through male puberty.

Trans women who aren't athletes and take feminizing hormones tend to gain fat and lose muscle in the first year, with muscle continuing to decrease over three years, leading to a more typically feminine body shape.