menopause and muscle mass

I am 49 and just entering menopause and have noticed that my muscle mass is depleting( and unfortunately slowly being replace by fat cells). I swim about 15000 ( 3000 5 days per week) meters a week and lift weights 2-3 days per week. My last meet was horrible and wonder if my poor performance is linked to this loss of muscle. I am not taking hormone replacement therapy because I don't have the other nasty symptoms of night sweats and hot flashes. My only other complaint is not sleeping well. (awake at 2 a.m. and have trouble returning to sleep). My question to you women who have already come out the other side is really this- menopause is here to stay, no way around that. But does that mean I have to swim so poorly?? Obviously there are still 45-55 year old women who are still quite fast. Would horomone replacement therapy help me there? When lifting weights, should I do more weight and less repetition? Should I cut my yardage some so that I have more rest? I know there was an article on this in Swim magazine, but it didn't address these specific questions. Thanks for any input.