like flexing muscle

The more you use it at a certain task, like weight lifting or climbing, the better it will become. Depending on the activity the muscle will form in a certain and best suitable way, within it's own capabilities & limits. A muscle can be come bulky and powerful for heavy short lifts, or a muscle has the capability to form in a way that it is more lean. Many more form are possible, the potential to form the muscle, lays in the capabilities and limits of the muscle, but more so in the activity given.