As a former gymnast and swimmer, my body has always been rather muscular. At this point in my life, I do not want to be "bulky". I workout almost every day and just ran my first half-marathon. I figured that my legs would slim down with all of the long-distance running I did, but I didn't lose an ounce. I feel like no matter what I do, I cannot lose weight - specifically muscle mass. Has anyone experienced success in losing muscle mass...and if so, what did you do?!?!?!
Sister, I am with you. I have experienced the same thing with successfully completing Half Ironman. I have had LOTS of advice (opinions, crazy theories) from people, so I am not going to give you advice. What I will tell you is, muscle mass is an awesome thing especially as the aging process kicks in (every day)! Sometimes we confuse the increased inches with added fat and water that surrounds the muscle mass. Something that has works for me in reducing these inches is sticking to ONLY whole grains(no processed flours or breads), vegatables, some fruits and lean meats. However I do believe that everyone's body has different chemistry. Good Luck and muscle mass is not a bad thing!
The first reply was right on for the healthy aging. You really don't want to lose muscle mass because the action of the muscles on the bones is what keeps the bone density as high as it can be.
That being said, your problem is actually the type of muscle you have. There are two types, slow twitch and fast twitch. Slow twitch are the "endurance" muscles that are active all the time - they also call them postural muscles - allow you to do all the activities of daily living. The fast twitch come in two types, the "true" are the smallest percent of all your muscles. They are the ones that are used for very high intensity things - lifting a heavy weight, jumping, sprinting as fast as you can, gymnastic moves. The second type are the intermediate muscles that can help either of the other two do what they do best. They can be aerobic (allow you to be a good runner, swimmer, cyclist by responding at higher intensities that the slow twitch can), or they can be anaerobic (help with really high intensity things that have to be sustained for longer than 30 seconds - running a 400 m, doing a 3 minute floor exercise).
The slow twitch are the ones that stay relatively small. The people you see who don't have bulky muscles (I am guessing what you would like to be) have a higher than normal percent of slow twitch fibers (greater than 60% - some are up in the 80% range). Those muscles and at that percent make them really good at long distances, but they have no kick. The fact that you were a gymnast tells me you probably have the more normal percent of fast-twitch fibers (about 40%). They are a larger fiber to begin with and hypertrophy more when they are "trained". That is because the ratio of nerves to muscles is lower than in slow twitch. So even though you are training them to be aerobic now, they are still a larger muscle and respond by increasing their aerobic capacity - storing glycogen is probably the main reason they stay large.
Glycogen is their preferred fuel, and the amount stored in the muscles can double. It is stored with water so that keeps the size. That is also what makes the muscles efficient, but if you want to reduce the size of the muscle for a short time, eat a high protein diet, low carbohydrate, for about 3-4 days and the glycogen stores in the muscle will be reduced and the water will be gone too, and the muscle size will get smaller. But remember, that is not a permanent change unless you stop training and don't need to glycogen anymore.
So, be happy that you have good muscles for bone health, and keep active, and get mad at your parents about your muscle genetics that are keeping you from being as "small" as you think you want to be!
I dont think it is healthy or wise to lose muscle mass you should get your body fat tested. Depending on your body type you will not be able to lose muscle mass. When you train for marathons it will make you lose a lot of body fat. I have a bulkier lower body but marathon training has made my legs a lot thinner also lifting weights has helped. but cutting my body fat through my eating habits have helped the most. I try and eat very clean I am a vegan raw foodist.