a little bit of background: I started working out more about 6 weeks ago. doing 30 mins of cardio a day and 30 mins strength a day as well. So on my arms day, I will lift weights. Lately i have been feeling like my boobs weigh more and feel fuller than than my usual c-cup, almost like a D- cup. The thing is when i go on a run and use the same Sports bra i used previously for running,my boobs feel painful and heavy. I guess i want to know if this is normal for women when they start lifting and what i can do to make running more comfortable. I am also not pregnant. I am 28, 61 inches, and weigh 130ibs. Please help. Thanks

  • What sorts of exercises are you doing? Which muscles are you targeting? Have you made any dietary changes in terms of what you eat and how much?
    – Sean Duggan
    Jul 11, 2017 at 20:29
  • Hi, I have been doing bench press with 30ibs weights of the straight bar, triceps and bicep curl, the stand up roll with a straight bar, push-ups, some chest exercises on those machines at the gym which i cant figure out what they are called. Thanks
    – Nadege
    Jul 12, 2017 at 13:11
  • @Nadege its lbs instead of ibs
    – Xatenev
    Jul 13, 2017 at 14:07

3 Answers 3


It's not very likely that exercise is increasing your breast size. This study states that estrogen levels typically go down when you are in better shape. More likely, you feel like they are bigger because a combination of other effects.

  1. The muscle underneath could be growing. After only 6 weeks, I imagine this is not a large effect unless you were previously stronger and are getting back to that level.
  2. You are losing fat around the base. Again, this is probably a minor contributor after only 6 weeks, but you are doing 1 hour a day of disciplined exercise, so you could be losing significant weight at the base of your breasts. Imagine a boulder sticking out of the ground, and you dig away some of the dirt surrounding it. If you dig away 1 foot of dirt, the boulder seems 1 foot taller.
  3. You are increasing your testosterone and the fat in your breasts is taking on a more masculine character. Masculine adipose tissue is firmer, but I am not aware of any studies that show hormonal changes will convert existing fat. This is not likely.
  4. You are improving your posture. You should definitely see posture improvements after 6 weeks of the intense exercise you are describing. If your shoulders have gone back and back has straightened, then your ribs will have taken a new position. It is like you have upgraded the pedestal that your breasts are displayed on. This is the most likely explanation for an increase in size. You may have always had D cups, but they have been hiding in the shadow of bad posture.

As for causes of pain while running, it's hard to blame the exercise itself. This article says most people who start exercising experience a reduction of pain.

It would probably be of benefit to know what specific pain you are experiencing. If the pain is close to your ribs, then it may not be related to your breasts at all. It may be the normal pain from working out your pec muscles, aggravated by the bouncing weight on top of them. If so, some stretching or longer recovery time could reduce this. if the pain is inside the breast, it might be because your new posture or fat allocation no longer provides the support it used to. It might be time to try new sports bras.

  • Hi @Zack Bolinger, i always played sports my entire life and worked out consistently but haven't been working out for the last 3 months due to work and vacation which validates your first point. "Upgraded the pedestal", that seems like a very likely explanation because i noticed i sit up more straight now. You definitely make a lot of valid points which i will look into more closely. Thanks
    – Nadege
    Jul 13, 2017 at 14:22

Although I am not a woman I think your problem is quite understandable from a physiological perspective. Let's first relate your problem to a standard situation.

If I start lifting weights and for every volume of fat I lose, I get the same amount of muscles back, I will gain weight. Muscles weigh more than fat and therefore every percentage muscle increase will increase my weight more than an increase in fat. When you are on a weight lifting program, you expect to lose more fat than you gain muscles and therefore you lose weight.

Now back to your breasts. Usually, female breasts mostly consists of fat. There are some milk glands and underneath the fat there is some muscle tissue, the breast muscles. If you are early in your program, you expect to lose fat in the "easy" places, but not in your breasts. Why, I don't know, but it is known that a woman loses fat tissue last on her breasts and belly. By the way, men lose fat last at their belly too.

However, you are gaining muscle tissue and if you do a lot of arm exercises, you will indirectly train your breast muscles. In gaining breast muscles and not losing significant fat tissue in your breasts, they will at first start to become heavier and not smaller. This means, with c-cup fat and extra muscle mass, it might well be that your breasts at first will feel heavier.

Now as a man I do also experience growing breast muscles up to a level where the are pronounced and they aren't that flat on your body. When you run, however, you don't tighten your breast muscles (why should you?) and they will probably freely move along with the rest of your breasts, which are mostly fat. When you're a man and your breasts aren't that pronounced, it is not an issue. If you're a woman and you have exercised your breast to a slender a- or b- cup, it might also be bearable. However, when you just started, your muscle gain and lack of fat loss in your breasts might temporarily be a burden / bother. Once you see your BMI decrease and your fat decreasing, I would assume your breast pains will decrease with your fat.

The issue is that your breasts will be the last to give up the fat, or the second to last and your belly holds on for longer. Either buy a stronger / tighter bra, go biking for now, or run like a kangaroo (with your hands high under your breasts).

  • 1
    Anecdotally, I've heard multiple women complain of seemingly losing breast mass first upon embarking on a weight-loss program. Jul 12, 2017 at 12:48
  • Hi @MacUserT, you are definitely right, I completely forgot the fact that it could be the muscle underneath my breast which actually hurt. I will also consider buying a smaller bra. Thanks, your answer was very helpful.
    – Nadege
    Jul 12, 2017 at 13:14
  • @Nadege: If you believe this to be the correct answer, you can click on the checkmark by the voting buttons to accept it.
    – Sean Duggan
    Jul 12, 2017 at 17:33

Really great answers here! I just wanted to add that my chest muscles -- I'm a guy -- hurt for a few days after I bench press, especially if it has been awhile or I push the weight. So, that might explain some of your pain.

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