Fartlek is Swedish for speed play and that somewhat accurately describes what fartlek training is all about. A fartlek workout consists of periods of faster running separted by periods of slower running. These periods are usually measured in terms of time, as opposed to distance, and, therefore, can provide a great way to get a workout in without having to worry about hitting a specific time. This is, of course, as opposed to interval training which is similar but measures fast periods in terms of distance.