Can I change my muscle size and shape?

I actually find this to be an interesting question.  The easy answer is, yes, you can change your muscle size and shape.  By using the proper variables you can gain muscle mass, lose muscle mass and as you get leaner the fat off the top of your muscles will naturally cause those muscles to be more defined.  Now having said that, I also want it to be clear that while muscle size and shape can be changed, you don't exactly get to pick to have your legs look just like so-and-so's or the abs of your favorite movie star or a famous booty.  You will still be you.  You will be the best you can be and others will notice.  Be proud of your hard work, even if you don't get to pick and choose.
David Buer
Our muscle shape is genetically predetermined. The number of muscles in your body and their number of muscle fibers can’t be changed. But you can increase the size of your muscle fibers, which changes your body’s shape and size overall.
An exercise routine that includes resistance training will stress and break down muscle tissue, allowing it to rebuild stronger and bigger. To build muscle you will also need to take in enough calories and nutrients, especially carbs and protein. The Academy of Nutrition and Dietetics says adults who are strength training need at least half their calories each day from carbs. And when it comes to protein, the recommended daily allowance for the average adult is about 0.4 grams per pound, per day. Finally, be sure to stay hydrated.
The muscular system is made up of approximately 600 individual muscles that overlap each other in an intricate system. Each muscle is created with a set number of muscle fibers (genetically chosen). You cannot increase or decrease the number of muscle fibers in a muscle. Your muscle shapes are genetically chosen as well. Some people have long muscles with short tendons (the fascia that attaches muscle to bone), while others have short muscles with long tendons.

Unfortunately, unless you decide to have surgery, you cannot change the shape of the muscles you were born with (i.e., increase a "peak" in a muscle or make a short muscle long). You can, however, change the size of muscle fibers and thus change the shape of the muscle overall (i.e., make a muscle bigger or fuller). Muscles can hypertrophy (get larger overall) or atrophy (get smaller overall). When you live a sedentary life, muscles can atrophy because they are not being challenged. However, when you begin to participate in resistance training or challenging physical activity, muscles will hypertrophy.

Muscle shapes are determined by your genetics. Train to get the most out of your heredity.

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