For more than a decade, HIIT, or high-intensity interval training, has been touted as a miracle workout for its efficiency. We’ve been told that HIIT produces the most positive training effects in the least amount of time: , . But new research suggests that most endurance athletes鈥攅ven weekend warriors鈥攎ust slow down to get fast.
That shouldn鈥檛 come as a surprise. High-performance athletes have long realized the benefits of training slow, says Matt Fitzgerald, author of a new book on the subject called 鈥80/20 referring to the ratio of slow to high-intensity training. Research is starting to show that even for amateur athletes who train much less than elites, 80/20 training will better improve race performances than HIIT alone. How slow? staying below your aerobic threshold, or where you can no longer talk comfortably while exercising.
Exactly how many hours a week one must exercise to benefit from the 80/20 rule is still under investigation, though Fitzgerald says it鈥檚 been proven effective for runners covering as little as 35 miles a week. 鈥淪tudies are finding that even at the recreationally competitive level鈥攆or the weekend warrior who鈥檚 only working four to five hours a week鈥攑eople improve more when they take a mostly slow approach to training,鈥 Fitzgerald says.
Why 80/20 training improves performance ultimately has to do with recovery. Leading researcher on the subject and the man who coined 鈥渢he 80/20 rule,鈥 at Norway鈥檚 University of Agder, believes too much training at a mid-range intensity flattens the training response, 鈥渨ith the classic sign being elevated resting heart rate and blood lactate response, but depressed maximal heart rate response during high intensity work,鈥 he wrote in an e-mail. 鈥淭he athlete’s physiological transmission gets stuck in the middle gears.鈥
In other words, if you’re constantly working out at a moderate intensity, you’ll be too fatigued to give your best effort in hard, speed-building workouts. The result: suboptimal race times. 鈥淚t鈥檚 like being chronically mildly sleep deprived,鈥 Fitzgerald says. 鈥淵ou don鈥檛 know what another hour of sleep will do for you until you get it.鈥 Athletes don鈥檛 know how fast they can go, he argues, until they train slow.