Yungoos evolves into Gumshoos at level 20, during the day. Rockruff will always evolve into Lycanroc, but the form depends on the game you're playing. Midday form appears in Sun, and Midnight form appears in Moon. Type: Null evolves into Silvally with high happiness.
Skeletal muscles are the muscles found in your legs and arms and throughout the body. The skeletal system is different from the smooth muscle system in organs like your liver and the cardiac muscle in your heart because the skeletal muscles contract voluntarily.
The reason for this is that, with appropriate training, the heart muscle increases in both size and strength. The stronger heart moves more blood with each beat (this is called stroke volume) and therefore can do the same amount of work with fewer beats. As you get fitter, your resting heart rate should get lower.