In exercise theory, the principle of adaptation states that when a body is placed under stress by working out, it reacts with predictable physiological changes (Fahey, 1998). When you engage in a rigorous workout program and clean up your diet, your body responds by getting leaner and stronger.
Unfortunately, the principle of adaptation also means that without regular changes to create increasingly challenging workout routines, the body will plateau and progress slows dramatically. When applied to runners, especially marathon runners who typically engage in long, steady state running, it is essential to include speed workouts in order to keep enough demand on the body to continue to see performance improvements.
It's All About the VO2 max
But how do speed workouts help performance if the goal is not speed?
According to Jennifer Burningham, a Portland-based running coach, "Any type of interval training you do is going to increase the VO2 max." (The VO2 max is a measure of the body's ability to deliver and use oxygen.)
When Burningham does speed work with marathoners, she says her goal is to "fatigue them enough for their bodies to still work efficiently under really tired conditions." As you train, your heart is able to deliver more oxygen to the body, and the muscles, in turn, become more efficient at utilizing that oxygen.
All types of training improve VO2 max, but workouts that include short, explosive bursts of energy, such as interval training, are most efficient. The higher a runner's VO2 max is, the faster and longer they will be able to run (Burfoot, 2001).
How Long, How Far
The type of speed workout, in terms of interval lengths and times, will vary according to the length of race an individual is training for. "The marathoners that I train are doing longer intervals at about twenty seconds faster than their goal pace," said Burningham. "So if their goal marathon pace is an eight-minute mile, then I'm going to have them do their intervals around a 7:40 pace, regardless of the interval."
Burningham favors a "ladder" workout, which involves a series of progressively increasing distances, followed by progressively decreasing distances. For example, a marathon ladder workout may look something like this: 800 meter, 1 mile, 2 miles, 2 miles, 1 mile, 800 meter.
Fast, But Not Too Fast
So how "fast" should intervals be performed for a marathon training program? Burningham explains that, "intervals should be done at no faster than 20 seconds per mile [faster than the goal pace] because there's no reason to go much faster than that – it's not going to give you any benefit."
In fact, it could actually increase the risk of injury. She adds, "if you can run your speed workouts at approximately 20 seconds faster than what your goal race pace is, you're going to be right on the mark to hit your goal race pace."26.2.
Burfoot, A. (2001). Improving your Max VO2. Runner's World .
Fahey, T.D. (1998). Adaptation to exercise: progressive resistance exercise. In: Encyclopedia of Sports
Medicine and Science, T.D.Fahey (Editor). Internet Society for Sport Science: http://sportsci.org.