Energy determines how long you can run. It is almost the same as fatigue, which is
used in RSC. This is shown in the player option. Click on the little running guy on the
bottom-right center of your screen and it will pop up a chart of the commands you can give
to your character along with the energy percentage. Your energy is also shown as a
percentage. But instead of going from 0% to 100%, like the original RSC, this goes from
100% to 0%, being 100% as having full energy. If you reach 0% when your character is
running, then he/she will walk instead. To regain back your energy, you just have to
simply walk or stand still. Your energy will slowly reach 100%.

Weight

Weight is used in RS2. It determines how fast your energy will consume up. This is
located in the player option. Carrying many loads of heavy items will make your
character's energy wear off much faster.