The classic training scheme involves the development of endurance first and then gradually increasing the speed of an athlete.
At the initial stage of training, it is important to pave the way without striving for a high tempo. Long duration exercise at a low speed, is what is really needed in the beginning. The overall endurance of an athlete develops solely on low speed training sessions when the heart rate is 120-130 beats per minute. “SLOW” means to run 10 km in about 1 hour on easier terrain. It is important for athletes to check their pulse, by using a simple heart rate monitor, or even by putting a hand on the heart or wrist.
The training modes that can be used in the first stage of training preparation are (for four months: May, June, July, August): running at a steady pace, jogging with stepping imitation, and cycling. After having developed a sufficient level of endurance over the summer months, in the fall athletes can proceed to high-speed training workouts.
– by Eugene Goryachev, SkiSport.ru