Legs and butt
The most important factor that often determines the success of weight loss or healthy weight gain is caloric intake. When your goal is to lose weight, it is necessary to be in a caloric deficit. You achieve this by taking in less energy from food and drinks than you expend during the day.
If, on the other hand, you want to gain muscle, you should get into a caloric surplus. You would also find out the value for energy intake for healthy weight gain from the calculator, which would recommend that you increase your intake to about 2,750 kcal if you spend 2,500 kcal. So you would be eating an extra 250 calories that your body could use for muscle growth.
Strength training will round out and strengthen your butt and thighs
You don't have to worry. Strength training will not overnight turn you into a professional bodybuilder with biceps bigger than your boyfriend's. On the contrary, it will help shape the figure and get the sexy curves you desire. It should therefore have a place in the training plan of each of you. It not only helps in building the muscles of the butt and legs, but also supports weight loss. Behind the growth of muscles is their ability to adapt to increased load.