When a person is climbing they are doing a lot of work in order to lift their body mass against one of the strongest forces in climbing, gravity.  Some of that work becomes what we call Gravitational Potential Energy, which is the energy that is stored due to the pull of gravity and the climbers position above the earth.  If you are lead climbing, that potential energy can quickly change into Kinetic Energy
which is the energy of motion, hence falling.  This is where Newton's Laws of Motion come into play.

                                 Below is an image of where a climbers energies are being distributed throughout a lead climb.

Rock Climbing Anchors: A comprehensive Guide; pg.199

        As you can see from the above image, there is a point when all of the climbers energy is transferred into Kinetic Energy, as a climber, this is a nausiating and scary experience.  Most climbers dont want all of their energy to be transferred into kinetic energy because that means they are moving very quickly.  As a climber you need to devise a way to have a nice balance between safety and efficiency during your climb.  The farther the fall, the faster you go, which increases the risk of hitting something; Then what happens to all your energy? It goes into breaking bones...Not fun at all!   Therefore it is really important to set up protection so that you minimize the chance of injury.  Again, there needs to be a compromise between safety and efficiency.

An important fact that everyone should know is the Law of Conservation of Energy:  Energy can neither be created nor                                                                                                                                                        destroyed, it can only change form.

Therefore the total energy of the climber, their gear, gravitational potential energy, kinetic energy and thermal energy does not change during their descent, it just changes form. 

                                                                                           *NEWTONS LAWS