Why are endurance-trained athletes better at multiple sprints than are speed-trained athletes? There are a couple of reasons. First, endurance-trained athletes are able to consume oxygen at higher rates. Although performance in a single sprint does not require oxygen consumption, the muscles depend more and more on oxygen to release energy as they become fatigued from previous sprints.
The Loughborough researchers found that oxygen consumption increased more in the endurance-trained runners over the course of the workout than it did in the speed-trained athletes and that the more oxygen consumption increased in an individual athlete, the less he slowed down from sprint to sprint.
Endurance training also enhances the capacity to recover from sprinting more than speed training does. A major cause of fatigue in multiple-sprint workouts is muscular acidosis (a drop in muscle pH), which is correlated with rising blood lactate levels. In the Loughborough study, blood lactate levels increased in speed-trained athletes significantly more than they did in endurance-trained runners. And among all of the subjects, the more blood lactate levels increased, the more their sprint performance declined.
It is likely that genes account for a portion of the superior performance of endurance-trained runners in high-intensity interval workouts. People who have good genes for sprinting tend to have poorer genes for aerobic capacity and tend to gravitate toward sports such as soccer and rugby that favor raw speed. Those with favorable genes for aerobic capacity tend to gravitate toward distance running.
But we know that endurance training increases aerobic capacity in everyone, regardless of genetic makeup. Therefore it is safe to assume that differences in training accounted for the lion's share of the performance discrepancy between runners and games players in the Loughborough study.
Traditional endurance training for runners is roughly four parts easy running and one part high-intensity running. Games players do a lot more high-intensity work and a lot less low-intensity training. Counterintuitively, then, it's the large volume of easy training that runners do which makes them better than speed-trained athletes at high-intensity interval workouts. There are many benefits that come from running lots of slow miles, but its ability to enhance performance in interval workouts is almost entirely overlooked.
There are advocates of speed-based training systems for runners (such as CrossFit Endurance) that require runners to do much more high-intensity interval training and much less easy running than traditional endurance training does. These advocates have a strong belief in the value of high-intensity training for distance runners. Ironically, however, what they do not recognize is that runners who do just one speed workout per week and run easy most of the rest of the time will destroy runners who run fast three or more times per week in a single high-intensity interval workout. And whenever a runner is able to perform better in a certain kind of workout, he or she will derive more benefit from it.
Yes, high-intensity training is important for distance runners. But if you want to get the most out of it as a runner, do it sparingly.race.