Fartlek training method is used for developing endurance.The word 
'fartlek'is a swedish word means 'speed play'.this training method lays emphasis on both the aerobic and anaerobic systems.In this method ,speed is not preplanned so it is left upto the individual.Self discipline plays a vital role in fartlek training method.The rate of heart beat ranges between 140 to 180 per minutes.Such examples are-warmup, jogging or slow running.
Advantages
1.It keep the heart rate up allowing an athelet to get good cardiovascular endurance.
2.It is good for aerobic and anaerobic fitness.
3.It is not rigid but flexible in nature.
4.In this training method no equipment is required.
Disadvantages
1.It is difficult to see how hard the trainee is making efforts.
2.Sometimes the athelete is likely to drop efforts.
3.It may cause accidents because it is not pre planned.

Endurance can be defined as the ability to withstand stress over prolonged periods of time. An endurance sport is therefore any sport in which there is a prolonged physical stress.

Types of endurance:
According to the nature of activity, the endurance is classified into following types:

1. Basic Endurance- Also known as aerobic endurance,because basic endurance depends mainly on aerobic endurance.In fact, basic endurance is the ability to perform movements in which large number of body muscles are involved and the activity is performed at slow speed or pace for a long duration.
2. General Endurance- General endurance means doing sports activity in  the condition of fatigue.General endurance is not specific to any sports.It is developed through general exercises. The better the general endurance , better the performance in sports.
3. Specific Endurance- Specific endurance is the ability to resist the fatigue caused by a particular sports activity.As the nature of fatigue is different from sports to sports, the specific endurance is different from sports to sports.For example, the specific endurance for a wrestler is to combat effectively in three rounds or six minutes, whereas it is 4 rounds for a boxer.

1. Speed Endurance- Ability to resist fatigue in activities that last up to 45 seconds.For example.400m sprint.
2. .Short-term endurance- Ability to resist fatigue in activities that start from 45 seconds and last up to 2minutes.For example.800m race.
3. Medium-term endurance- Ability to resist fatigue in activities that range from 2minutes to 11minutes.For example. 1500 m race.
4. Long-term endurance-  Ability to resist fatigue in activities that last more than 11 minutes.for example. 5000m cross country, 10,000m race, and marathon requires such type of endurance.

Adventure sports are usually outdoor sports which involves intense and sometimes life threatening actions,which create an adventurous atmosphere.

Endurance may  refer to an ability to keep going through a tough situation involving hardship, stress, etc 
Fartlek running involves varying your pace throughout your run, alternating between fast segments and slow jogs. Unlike traditional interval training that involves specific timed or measured segments, fartleks are more unstructured. Work-rest intervals can be based on how the body feels. With fartlek training, you can experiment with pace and endurance