In bygone days, coaches and sports scientists believed that there was a kind of magic to training at lactate threshold (LT) intensity, or the running pace at which lactate, a product of muscle metabolism, accumulates in the muscles. This belief was based on studies showing that an individual runner’s current LT pace was a strong predictor of race performance at a variety of distances, and that training-induced improvements in LT pace were associated with commensurate improvements in race performance.
Since the time of these discoveries in the 1980s, workouts performed at LT pace, often referred to as tempo runs, have been a staple in the training regimens of most distance runners. The assumption underlying this practice has been that training at LT pace is an especially effective way to increase a runner’s lactate threshold and overall fitness. But when this assumption was actually put to the test, it turned out not to be true.
In a 2008 experiment, researchers at the University of Brighton separated 14 recreational runners into two groups that followed slightly different training programs for four weeks. One group performed traditional tempo runs at “maximal lactate steady state” pace (which is pretty much the same thing as lactate threshold pace) twice per week, while the other group did an equal number of runs in which they oscillated between speeds slightly above and slightly below LT, maintaining each speed for 3 minutes at a time. Fitness measurements were taken before and after the four-week training period.
The results? On average, lactate threshold pace improved slightly more in the group that did traditional tempo runs (9 percent versus 7 percent), while VO2max, a different but equally important measure of fitness, improved more in the over/under group (10 percent versus 6 percent). So it was pretty much a wash.
The practical implication of these findings is that there is nothing special about training at LT pace. Although it is certainly beneficial to do so, running at slightly faster and slightly slower speeds is beneficial in somewhat different ways, so it’s a good idea to include both types of workout in your training.
In addition to being a great complement to traditional tempo runs, over/under intervals, as they are known, work well as a winter treadmill workout because the frequent pace changes alleviate boredom and because the treadmill allows for precise pace settings.
To do over/under intervals properly, you first need to know your current lactate threshold pace. The simplest way to determine it is to determine the fastest pace you could sustain for one hour in a race, a number that falls between 10K and half-marathon pace for a majority of runners. For example, if your most recent 10K time is 52:49 (8:27/mile) and your most recent half-marathon time is 1:58:12 (9:01/mile), your LT pace will be just a little slower than your 10K pace—say, 8:34 per mile.
If you don’t have recent race times, you can estimate your threshold with perceived effort. Run at a pace you feel you could sustain for 60 minutes. Note this pace either by timing a measured segment, looking at the pace on a GPS watch, or checking the speed on a treadmill.
Now you’re ready for your over/under intervals.
Start with 10 to 20 minutes of easy jogging at a pace that’s at least 30 seconds per mile slower than your LT pace.
The main body of the workout consists of 6-minute cycles in which the first 3 minutes are run a little over LT and the next 3 minutes a little under. If you’re running outside, think in terms of pace, aiming to run the odd-numbered segments about 10 seconds per mile below (i.e., faster than) LT pace and the even-numbered segments about 10 seconds above (slower than) LT. So, if your threshold pace is 8:34 per mile, you’ll run the first 3-minute segment at 8:24/mile, the second at 8:44/mile, and so on.
If you’re running on a treadmill, think in terms of speed, first converting your LT pace to speed (that is, from minutes and seconds per mile to miles per hour) and then running the odd-numbered segments 0.2 mph faster than threshold speed and the even-numbered segments 0.2 mph slower than LT. Returning to the previous example, 8:34 per mile converts to 7.0 mph. So, in this case you would run the first segment at 7.2 mph, the second at 6.8 mph, and so on.
Complete a total of 3-6 over/under cycles, depending on your fitness level, and then cool down with another 10-20 minutes of easy jogging. Do the workout every two to three weeks, either adding a cycle each time or running the same number of cycles slightly faster as your LT pace improves.