rule"). In one description of the workout, beginning pace during the effort portions is intended to fall about at the runners "5K pace", with subsequent shorter intervals being taken at faster pace as the runner is able, and with recoveries varying from walking and easy jogging for newer and other runners needing "more recovery between hard efforts", to half-marathon/marathon "race pace recovery" or 5K/10K race pace "moderate recovery" for more experienced runners. In more sophisticated presentations, the workout is adapted to particular periods of a runner's "training year":[F]or example... in a base building period... the efforts remain completely aerobic, but very near the top of the anaerobic threshold. The recoveries are floats, rather than easy jogging. During this [period], the run more resembles a tempo run with a higher level of intensity than what a tempo effort in one [continuous] strong effort can typically offer. During the quality [periods] of training, the recoveries can be a jog, while the efforts delve into the anaerobic realm. The efforts should be done by feel and can range in... pace from 1500m... to 10k race pace, again depending on the time of year. Other forms Three speeds version In order to add more variety and complexity, runners can add another speed into the run. Within any run, “there is no reason why three different paces should not be included." This would change a normal fartlek by doing a jog, run, and a full out sprint. Mailbox version Runners hypothetically “run hard for two mailboxes, recover for three, run hard for three, recover for two." When executing this type, the runner continues like this for the allotted time or distance determined. Dog park version Runners speed up when they get close to a dog in order to pass them; after passing the dog, they would then slow down for the recovery period. Music version Many runners use music while they run. Runners can use their music as a template for their fartlek run by changing their speed according to different parts of a song. For example, they can speed up during the chorus and slow down for the rest of the song. Popular beginner's description Fartlek can simply include periods of jogging combined with short periods sprinting, or, for beginners, walking combined with jogging; e.g., a person may be asked to “sprint all out from one light pole to the next, jog to the