yes but it also gets stronger.
Muscles are heavier and more dense
The only way to get muscles bigger is to lift heavier weights
Most of the muscles of the body are exercised when running. Of course the foot and leg muscles are needed the most but the muscles of the torso and upper body are used as well.
Running and walking does use the same muscles in the body. Three of the main muscles used in the legs are hamstrings, quadriceps and gluteal muscles.
Mostly your Quad muscles
by running
because you use alot of muscles when running
The lower the weights, the stronger and leaner your muscles will become with more repetitions. If you want bigger muscles, you should try heavier weights.
quads calfs
yes it will
By running
Running long distance will require more energy. For this number of mitochondria will increase in the muscles.