Before motion controls entered the mix, video games had a slight problem trying to simulate some action such as swinging a golf ball or serving in a tennis match. These actions could, in theory be simulated by a single button press, but this eliminated the strategy from the aforementioned tasks. The Power Gauge was created to remedy this: a power gauge is basically an action bar that determines how hard the player swings the tennis racket, golf ball, baseball bat, or other object. It is not limited to sports games, however, this is where the power gauge appears most frequently.
By simply pressing a button to start, the meter (or indicator) swings up and down, and pressing a button again stops the meter and determines the power of the shot. In golf games, there is usually another button press used to determine follow through, but this isn't always the case. Even though power gauges have largely been replaced by motion control and newer techniques used to better simulate the action of swinging, the mechanic still appears from time to time.