Soccer has been classified as an endurance-based or intermittent field sport. The definition of intermittent is "not continuous or coming and going at intervals". Players sprint for short and moderate distances, jog, shuffle, back-pedal, walk, and stand still.
A full speed or maximum effort sprint for 15 to 20 yards should take fewer than 3 seconds. Without going into great detail about human physiology, the body uses two types of energy systems to provide fuel for muscles: aerobic and anaerobic. A maximum effort sprint lasting 3 seconds would be considered anaerobic, using a fuel source called creatine phosphate (PCr). To keep it simple, any max effort run lasting up to 10 seconds would be considered anaerobic, or alactic anaerobic (doesn't produce lactate). The other anaerobic energy system, anaerobic lactic, uses the sugar in muscles and the liver (glycogen) to provide fuel and has a max effort duration of approximately 60 to 90 seconds.
The aerobic energy system uses fatty acids to produce energy for the muscles. Compared to the amount of PCr and glycogen in the human body, the aerobic system is the predominant source of energy for movement. However, that does not mean the best way to condition soccer players is long, slow distance running to build the so-called aerobic base.
Soccer is best described as an Alactic-Aerobic sport. Essentially, athletes must be explosive, covering 5 yards to 20 yards (average duration of a max effort sprint) as quickly as possible; and, they must be able to repeat this type of effort for as long as they are in the game. Therefore, the focus of conditioning should be on developing speed and explosiveness (alactic anaerobic) and the ability to recover quickly for the next explosive movement (aerobic).
The methods to develop this type of conditioning are: Tempo Runs, Repeated Sprint Ability, and High-Intensity Interval Training. A Tempo Run could be a series of 100 yard runs completed in 18 to 22 seconds with a 40 to 60 second recovery. Repeated Sprint Ability could be a series of 30 yard sprints with a 30 yard "Fly-In" and 60 second recovery. High-Intensity Interval Training could be a series of shuttle runs with a work to rest ratio of 1:2. These methods will be discussed in greater detail in our next blog post.