But after yet another disappointing marathon finish, he decided to take Fitzgerald’s advice to slow down. The result: He felt fresher all week, and when it was time for sprints, he nailed his target times. Five months later, at the age of 47, Rzepiejewski ran a 2:59 marathon.
Slowing down to speed up seems counterintuitive, especially at a time when high-intensity workouts like CrossFit and Tabata are all the rage and gymgoers have been conditioned to believe that gains come only through grueling work. But many coaches argue that the high-intensity trend has gone too far. “The majority of recreational athletes are doing way too much high-intensity exercise,” says Iñigo San Milán, director of the Human Performance Laboratory at the University of Colorado. “They end up with injuries. And they are not getting faster.”
Instead, a growing body of research suggests that 80 percent of your workouts should be done at a slow speed, with just 20 percent at medium to fast. At this ratio, you’re able to get all the performance-enhancing benefits of high-intensity work while avoiding the injury risk and burnout that often come along with it.
The 80/20 approach was discovered by exercise physiologist Stephen Seiler, a sports scientist with Norway’s University of Agder, who has spent the past decade analyzing the way elite athletes structure their training. “We started to see a pattern from different sports all converging on about the same distribution,” says Seiler. Whether they were marathoners, sprinters, rowers, or speedskaters, the majority of athletes spent their workouts well below race pace, and about a fifth of the time at higher intensities. “When elites emphasize lower intensity, they are less likely to get sick and have hunger swings, and they tend to be less tired and in a better mood,” says Boulder-based coach Mat Steinmetz, whose clients have included three-time Ironman world champion Craig Alexander.
That’s true for the rest of us, too. In a 2013 study, the University of Stirling in Scotland had male recreational cyclists follow the 80/20 approach and then switch to 57 percent of their time at low intensity and 43 percent at middle intensity. The gains in power and speed after 80/20 training were more than twice as high. Another study, published in March in the Journal of Sports Physiology and Performance, compared runners logging 30 to 43 miles per week. Half followed 80/20 and the others spent most of their time at middle-to-high intensity. The 80/20 group improved their 10K times by an average of 41 seconds — a huge gain for a six-mile race.
But dialing back is a lot harder than it sounds, mostly because people are terrible at judging the actual intensity of their workouts. In fact, we spend most of our time — 45 to 75 percent, according to studies — in a middle-intensity no-man’s land. “Moderate intensity isn’t intrinsically bad; it’s just not as productive. You’re not getting the body-adapting benefits of high intensity or the gentler muscle-conditioning benefits of low intensity. You’re creating fatigue,” says Fitzgerald. “To get your fastest and fittest, your workouts need clear delineation.”
Here’s why: High-intensity workouts recruit fast-twitch muscle fibers that provide extra power late into a race or game. They also boost blood vessel elasticity, build a stronger heart, and up pain tolerance. All that time in the slow zone, meanwhile, primes your muscles to be able to crush the high-intensity sessions. During tough bouts, your fast-twitch muscles rapidly burn through glucose for fuel, which creates metabolic by-products like lactate and hydrogen ions that — if not cleared from the muscles — inhibit muscle contraction and the breakdown of food for fuel. The result? You slow down. The slow-twitch muscles are responsible for recycling that otherwise toxic lactate back into energy, enabling you to stay on pace. Low-intensity training also revs the growth of mitochondria, which helps the body burn fat efficiently and fends off soreness and fatigue.
Still, trading fast for slow is a tough sell. “We often joke about it,” says triathlete Tim O’Donnell, the top American at the 2013 Ironman World Championships in Kona. “When I ride with friends who are not professional athletes, they ride a lot harder than I do.” O’Donnell, as it happens, is a newcomer to taking it slow. Burned out after eight years of training hard, he cut the number of high-intensity sessions from six to three a week and moved the bulk of his effort to a “controlled and comfortable” pace (of course, that still translates to a 6:45 mile). The new approach paid off this past spring, when O’Donnell took first at the St. Croix half Ironman. “I’m training with less intensity and racing at a higher level,” he says, “because I’m not drained from overkill.”
Limit moderate-to-high sessions to one or two days a week, and never make them back-to-back.
Minimize the Middle
Some moderate-intensity training, or tempo running, is necessary to prep for a race. Just make it part of your 20 percent. To ensure you stay out of the middle-intensity zone, ask yourself, “Could I imagine holding this pace forever?” If the answer isn’t a strong yes, dial back speed.