Fartlek, which means "speed play" in Swedish, is a form of conditioning which puts stress mainly on the aerobic energy system due to the continuous nature of the exercise. The difference between this type of training and continuous training is that the intensity or speed of the exercise varies, meaning that aerobic and anaerobic systems can be put under stress. Most fartlek sessions last a minimum of 45 minutes and can vary from aerobic walking to anaerobic sprinting. Fartlek training is generally associated with running, but can include almost any kind of exercise One of the main reasons for the success of fartlek training is that it can be adapted to the needs of the individual. Unlike continuous training, fartlek training can benefit participants of field games such as football, field hockey, ultimate frisbee, lacrosse, basketball and rugby, as it develops aerobic and anaerobic capacities which are both used in these sports. To take this a step further, athletes can make the most of the flexibility of fartlek training by mimicking the activities which would take place during their chosen sport or event. It improves aerobic capacity.