Individuals can cultivate endurance by using a range of methods that yield very specific performance and physiological reactions. When developing a training plan, the individual must decide the kind of endurance that the plan will target, because systems of increasing endurance are enormously different in their application and physiological outcomes.Interval training encompasses the repetitive performance of short to long spells of exercise usually executed at or above the lactate threshold, or at the maximal lactate steady state, combined with stages of low-intensity exercise or complete rest. While interval training was first made popular in the 1950s and is certainly not a new idea, modern sport science literature has encouraged an increased interest in the concept. This literature has exposed many physiological justifications why interval training should be an essential part of the annual training plan for trainees ranging from novices to elite. Fartlek training falls within this category of interval training. ‘Fartlek’ is the Swedish work for ‘speed play’ and is a classic technique for developing endurance. This method of training is a rather unempirical amalgamation of interval and continuous training. For instance, a runner may spread a period of slow running with a period of fast running. This kind of training can be started on flat ground or up and down hills.Fartlek does not either require specific heart rates or workloads. As an alternative, this sort of training depends on the subjective sense of how the exercise session feels. Fartlek training may be most valuable during the general conditioning or preparatory phase of the annual training plan because it tests the physiological systems of the body while jettisoning the dullness and monotony concomitant with daily training. Although Fartlek training is normally associated with running, it can also be used for swimming and cycling. A mockup Fartlek run entails easy running (roughly 70% VO2 max) joined with either short, fast spurts of running or hill work for short phases. Individuals can apply this rudimentary format to swimming and cycling by simply joining interval training, long, slow distance training, and pace/tempo training. A Fartlek training workout tests all structures of the body and is likely to augment VO2 max, increase the lactate threshold, and progress running economy and fuel application. BibliographyBaechle, Thomas R., and Roger W. Earle. NSCA Essentials of Strength Training and Conditioning. 2nd Edition. Champaign, Illinois: Human Kinetics, 2008.Bompa, Tudor O. Periodization: theory and methodology of training. 5th ed. Champaign, IL: Human Kinetics, 2009.Kilgore, Lon, and Michael Hartman. Fit. Iowa Park, Tex.: Killustrated Books, 2011.Reuter, Ben. Developing Endurance. Champaign, IL: Human Kinetics, 2012.