Three decades ago, a team of exercise physiologists led by Bertil Sjodin of Sweden's National Defense Research Institute put eight experienced distance and middle-distance runners on treadmills. First, the scientists measured the runners' blood chemistry at various paces, focusing on lactate, a chemical thought to correlate with racing performance. Then they asked the runners to do weekly 20-minute training runs at a pace they called VOBLA--the speed at which there was an "onset of blood lactate accumulation"--what today we would call tempo runs.
The results, published in the June 1982 issue of the European Journal of Applied Physiology and Occupational Physiology, hit the 1980s running community like a bombshell. After 14 weeks of such training, the runners saw their VOBLA paces drop by 4 percent, from 5:43 per mile to 5:29.
Sjodin's was one of several studies to highlight the tempo run as a critical element in training and a linchpin to modern training methods. But it also produced the misconception that there is one perfect pace at which these runs should be done--and that the best way to do them is to find that pace and stick to it for about 3 miles.
That single-minded focus, however, isn't what the latest exercise physiology shows, nor what many top runners are actually doing.
PREDICTING PERFORMANCE POWER
One of the reasons runners have for so long focused specifically on VOBLA is that it appears to be an important predictor of racing performance. "It gives some idea of where someone's 'critical power' is," says John Halliwill, an exercise physiologist at the University of Oregon, who defines "critical power" as "how intensely you can exercise for a sustained time." VOBLA is also one of the easier performance parameters to change--much more responsive to training than VO2 max, for example. In fact, in Sjodin's study, the runners' VO2 max measurements didn't budge.
Jack Daniels, author of Daniels' Running Formula, puts that "critical power" more specifically at about the pace you can hold in a 1-hour race--for most of us somewhere between 10K and 15K. If so, the improvement seen by Sjodin's runners corresponds roughly to a whopping 2-minute improvement in potential 15K times. (Unfortunately, Sjodin's study didn't include before-and-after time trials.)
Other studies have looked directly at the correlation between VOBLA and racing performance. The most recent comes from a group led by Jordan Santos-Concejero when he was a researcher at the University of the Basque Country in northern Spain. In a 2013 examination of 22 nationally and internationally competitive runners (average 10K time 31:35), Santos-Concejero and colleagues found a strong correlation between VOBLA and 10K times. Specifically, their data revealed that each 10 seconds per mile difference in VOBLA correlated to about a 70-second difference in 10K PR.
None of this proves that increasing your VOBLA will make you faster. It might be that high VOBLA is simply a consequence of being fast--a result, rather than a cause. But all of these correlations are why runners and coaches have long been interested in doing workouts at or around VOBLA pace.
That said, there has also been longtime confusion over just what "at or around" means.
CHANGING A REPUTATION
To begin with, only exercise physiologists use the VOBLA term. Coaches and runners prefer to speak in terms of "lactate threshold pace," "threshold pace," or simply "tempo runs." Worse, in research summarized in a chapter of the recent book Physiological Tests for Elite Athletes (Human Kinetics, 2013, 2nd ed.), exercise physiologist Pitre Bourdon, now head of research at Qatar's Aspire Academy for Sports Excellence, found a long list of other similar terms, including "aerobic threshold," "anaerobic threshold," "aerobic-anaerobic threshold," "lactate turnpoint," and others too cumbersome to list. Further ratcheting up the confusion, some coaches have attempted to identify two different thresholds, distinguishing them as lactate threshold and anaerobic threshold--or, in Bourdon's preferred terminology, lactate threshold 1 (LT1) and lactate threshold 2 (LT2).
"I'm a big believer in lactate threshold training," says Paul Greer, coach of the San Diego Track Club, "but it does get confusing."
Breaking through the confusion begins with understanding the role of lactate in muscle metabolism.
Lactate is a chemical with a bad reputation, long associated with running too long at anaerobic paces. Over the years, it has been blamed for everything from post-race sore muscles to the dead-legs feeling you get at the end of fast-paced intervals. But none of this is true. When scientists inject lactate into people, even when they're already working hard on a treadmill, they don't suddenly feel fatigued. "They do just fine," Halliwill says.
In reality, lactate is simply a byproduct of glucose metabolism. "It's roughly half of a glucose molecule," Halliwill says, "and it still has a lot of energy stored in it that we can use." The association with anaerobic running comes from the fact that no oxygen is needed to break glucose down into lactate, but oxygen is needed to pry additional energy from it. This has led to the misconception that lactate is produced only under anaerobic conditions, when actually it's produced any time you move a muscle--even if only to get off the couch.
At low exercise levels, you use lactate nearly as quickly as it's formed, and the amount that leaks from the muscles into the blood is miniscule. At slightly higher levels--walking, jogging, moderate-paced running--you produce it more quickly but also use it more quickly. More finds its way into the blood, but not much.
Somewhere around marathon pace, things change. By this point, the lactate level in the blood has edged up to about 2 millimoles per liter (2 mmol). That's still fairly low, but if you continue to speed up, it rises more rapidly. By the time you've reached Daniels' 1-hour race pace, it's doubled to 4 mmol, the classic threshold level. Above that, it skyrockets.
Mounting lactate levels sound like a bad thing, but research says they aren't. In a series of papers in the last 15 to 20 years, George Brooks, an exercise physiologist at the University of California, Berkeley, discovered what is now known as the "lactate shuttle."
What he found is that when lactate climbs, the body uses the bloodstream to ship some of it away from the hard-working muscles where it is produced to places where it can be used more effectively. One of these is the heart. Another is the brain. But it also goes to the liver, which can use other energy sources such as fat to turn it back into glucose. Even some lesser-working muscles, such as the arms, appear to pull lactate out of the blood to use as their own fuel, in lieu of glucose.
This shuttling makes it possible for you to run faster, because glucose is the body's high-octane fuel. We can generate energy much more rapidly with glucose than through lactate. So rather than being a sign that our leg muscles are drowning in performance-impeding lactate, the rise of lactate in the bloodstream means the body is shunting it around to places where the power demands are lower, keeping the glucose on hand for the high-demand running muscles. "It helps establish a sort of hierarchy for glucose use," Halliwill says. "The organs that most need it get priority, and others rely on lactate."
That said, rising lactate and increasing fatigue go hand in hand, which means that even if lactate is no longer the evil we once thought it was, finding ways to train the body to use it more effectively--in essence, postponing the point at which blood lactate starts to rise--will also postpone the point of fatigue, with the hope of running farther, faster. This, in fact, is precisely what threshold training, in all of its confusing forms, is designed to do.
PINPOINTING A BLURRY TARGET
Part of the confusion about threshold running is that the term "threshold" implies a magic pace at which lactate levels shoot skyward. But the lactate curve doesn't suddenly kink upward. Instead, it . . . curves. Halliwill compares it to a hockey stick, although he notes, "It's a blurry, rounded-out hockey stick."
In the LT1/LT2 vocabulary, the point where the stick first begins to bend is LT1, and the point of maximum curvature is LT2. But it's not quite that simple, because Bourdon's literature review doesn't find that either of these points is all that precisely defined. Instead, he has identified seven different measures of LT1 and 10 of LT2. Other scientists have identified at least four distinct parts of the bend that can legitimately be labeled as the threshold (see "Multiple Thresholds?" on next page). And if that's not bad enough, none of these are easy to identify without a time-consuming trip to the exercise lab.
Italian coach Renato Canova, who has trained some of the world's top Kenyans and is now the head distance coach for the Chinese Athletics Federation, has been known to draw blood from his runners during training in order to spot improvements in their lactate levels. Alberto Salazar remembers doing enough finger-prick lactate tests during his own workouts that by the end he was running out of unpricked fingers.
Such tests aren't all that expensive (see "Personalized Results" on next page), but most coaches have to use a more pragmatic approach. "Getting into an exercise physiology lab and figuring out the 'sweet spot?'" says Corey Ihmels, who coached Lisa Uhl to fame at Iowa State and is now head coach at Boise State. "That's just not the reality on a college campus." Instead, Ihmels uses workouts that don't require a precise pace identification.
Others say the key is simply to run at what feels like the right effort level. As Liana Bernard, a former 10K All-American turned competitive road racer, puts it, it's about "running hard, but not to the breaking point."
(See "Finding Your Threshold" on next page for a more detailed description of the perceived effort.) "I've seen it with GPS watches and watches that monitor heart rate," says Layne Anderson, head track and cross country coach at the University of Iowa. "Kids become too analytical and start to overthink things. I like to keep it simple. You don't want it so fast it becomes a time trial, nor so slow it's no more than a glorified recovery run."
Ihmels agrees. "I annoy a lot of 18-year-old perfectionists," he says, "but that's the reality. They have to figure it out for themselves."
Given the reality of a threshold curve, much of the confusion may be innate to the threshold-training process, and the runner would do well not to lose sleep over it. In fact, experiencing stress over a specific threshold can affect how we train.
TRAINING ON THE CURVE
The simple fact is that nobody knows why running at or near lactate turnpoint--wherever that exactly lies--might make the body's lactate processes more efficient. But experience shows that training at this level can shift the entire lactate-increase curve to higher speeds.
"A lot is based on coaches' experiences and anecdote," says Halliwill. "It would be hard to find definitive studies that said this is the one true way. What we can say is that when people train through a variety of approaches, whether it is lactate threshold specifically, or interval training at higher intensity, we see that critical pace--that threshold--shift out to higher intensities of exercise."
Some coaches, however, aren't even sure training precisely at threshold is worth aiming for. In his new book, Running Science, Owen Anderson notes that lactate levels can vary with everything from how much sleep you had last night to what you had for lunch. British coach Peter Thompson, now residing in Eugene, Ore., takes it a step further. "Threshold varies daily," he says. "It's almost an obfuscation. Some coaches pick out threshold as a crucial thing, but it's a consequence of a program where others factors are [also] taken care of."
Even if you do think running at or near threshold is relevant (and many coaches do), the name of the game today isn't dialing in too precisely on a specific pace. Instead, today's coaches seem to talk more about progression and effort.
Ihmels, for example, often works via progression runs and 2-mile cut-downs. "We start at a conversational pace, then build," he says. "At some point the kids will hit threshold."
Scott Simmons, coach of the American Distance Project in Colorado Springs, Colo., adds that traditional threshold runs don't actually mimic racing anyway, because in racing you're rarely running precisely at threshold. "Whether it's the mile or the half marathon, you're actually pushing through that threshold," he says, "because that's what the competition demands: to push through and run as fast as you can on the other side."
Traditional, steady-paced tempo running, he adds, isn't as effective at achieving this goal. "It's better than not doing anything, but it's not the best." Like Ihmels, Simmons is a fan of progression runs. Such runs, he says, might start out a minute a mile slower than current 10K race pace, then increase mile by mile until the final mile is at goal pace, or even faster. "We call them predator runs," he says: "[It's] how a predator will increase tempo to catch prey, especially as they get close."
Simmons cautions that such runs shouldn't be extraordinarily intense. "It's not that extreme a workout," he says. "We want to incorporate the specific demand of the race, but we don't want the training to be a race."
Other coaches are also playing with multiple levels of thresholds.
Thompson's approach, which he calls "new interval training," is based on using perceived effort to yo-yo blood lactate levels up and down, somewhere in the vicinity of the traditional threshold pace, in essence training the body to deal with, then quickly recover from, the conditions that produce elevated lactate.
Elite coach Brad Hudson takes a different approach, but also believes in variety. "There's a lot of different tempo runs you can do," he says. "I think there's a misconception that all tempo runs are done at a 4 mmol lactate level."
A similar idea can be found in the latest edition of Daniels' Running Formula, in which Daniels, a longtime advocate of the 20-minute tempo run, now includes a mix of shorter, faster tempo runs and longer ones (as slow as marathon pace) extending an hour or more.
But ultimately, it may be that Simmons is right, and it's all about turning yourself into the predator. "I really believe in threshold running," says Bob Williams, former Pac-10 steeplechase champion and distance coach at Concordia University in Portland, Ore., "because it helps the athlete feel that sense of toughness they experience when they compete. I think it's a process of adaptation, psychological as well as physiological."
One of the primary principles of coaching is that there are no magic-bullet workouts, whether for threshold runs or anything else. Another is that if you do the same workout, over and over and over, you may become very good at it, but your overall progress is likely to stagnate. In other words, the blurry hockey-stick shape of the lactate curve and equally blurry definition of "threshold run" can be worked to your advantage. Rather than running the classic 20-minute tempo run every week, try being a predator. Or do 2-mile cut-downs. The nice thing about the confusion over threshold is that it offers a nearly endless variety of workouts, some of which should be effective for anyone.
NUMBERS GEEKS BEWARE.
There is no single, well-defined lactate threshold. Over the years, at least four definitions have emerged.
This is the level at which blood lactate hits 4.0 mmol per liter, which was the definition of VOBLA used in Sjodin's landmark study. For most runners, it occurs in about the middle of the lactate curve's upward bend and is probably the pace most coaches have in mind for 20-minute tempo runs. Some call it the anaerobic threshold, but that doesn't mean your body has suddenly gone anaerobic. Its primary shortcoming--a big one--is that it ignores the fact that individual lactate curves vary, meaning that LT4.0 doesn't represent the same level of effort for everyone.
This definition uses geometry to attempt to find the point of maximum curvature in the lactate curve's "hockey stick" bend. The idea is to compare the curve to a straight line drawn between the beginning and end of the bend (i.e., across the entire threshold range), seeking the point at which the actual lactate level is farthest from the straight line--one way of defining the midpoint of the bend. In work with Australian rowers, Pitre Bourdon, now head of research at Qatar's Aspire Academy for Sports Excellence, found that this came in at slightly lower workloads (the rowing equivalent of pace) than LT40.
This is the point where the lactate curve first appears to start bending upward. Many coaches associate it with blood-lactate levels of 2.0–2.5 mmol, but Bourdon put it slightly below 2.0. Coaches who use the term "anaerobic threshold" for LT4.0 generally refer to this point simply as the lactate threshold, but the terminology is extremely inconsistent. LTVISUAL has the advantage of remaining unaffected by whether an individual's lactate levels run consistently high or low, but it tends to come at a fairly slow pace.
In addition to varying with speed, blood lactate changes with run duration. At moderate speeds, such as LTVISUAL, it spikes as you're warming up, then declines. At higher paces, such as LT4.0, it continues to rise as the tempo run progresses. Not surprisingly, there's an intermediate level at which it stays constant for 20 or 30 minutes. In a 1993 paper in the Journal of Sports Sciences, a team led by Sissel Tomten of the Norwegian University of Sport and Physical Education, Oslo, found that this occurred at a blood-lactate level of about 3.0. South African exercise physiologist Tim Noakes, author of Lore of Running, therefore suggests that LT3.0 might be a better measure of threshold pace than either LT4.0 or LTVISUAL. (Bourdon's work with LTDMAX placed that measure also at about LT3.0.)
FINDING YOUR THRESHOLD
You don't have to draw blood to find your threshold pace.
There are at least six other methods to get you into the right pace range.
01) EXPERIENCE AND FEEL
Alberto Salazar once described the classic 20-minute pace as "fun fast." Layne Anderson, at the University of Iowa, says it "feels like a 75 percent effort . . . comfortably hard." You can also find this pace with the help of an experienced coach. "Know your athletes and communicate with them," says Andrew Begley, who in addition to coaching his wife, Olympian Amy Begley, also works with high school and college kids. "If they are able to hit a pace consistently through a tempo and tell you it was a hard effort, they are likely running at threshold pace. If they fall off the pace, or have too much left in the tank at the end, they were likely running too fast or too slow. We prefer to use this method for our athletes because it keeps the dialogue open."
02) EXTRAPOLATION FROM RACE PACE
Under race conditions, most runners can run about 50–60 minutes at lactate threshold, says Jack Daniels, author of Daniels' Running Formula. For elite males, that's roughly half marathon pace. For age-group competitors, it might be 10-mile or 15K pace. For others, it might be 12K or 10K pace.
03) CONCONI TEST
Based on a 1982 paper in the Journal of Applied Physiology by a team led by Italian biomedical researcher Francesco Conconi, this test is conducted with a heart rate monitor. The idea is simple. At slow-to-moderate paces, heart rate increases linearly with pace. But there comes a point where that no longer holds, and your heart rate starts to level off, no matter how fast you run. The point where this occurs, Conconi suggested, is the lactate threshold.
04) VDOT TABLES
Daniels and his one-time associate, Jimmy Gilbert, created this measure of what Daniels now calls "your current running ability" at least as far back as 1979. Using tables in Daniels' book, you can convert your current race pace for any standard distance into a VDOT metric that allows you to determine your training paces, including your threshold pace.
05) 3200m TIME TRIAL
In a 1987 study in the International Journal of Sports Medicine, a team spearheaded by University of Virginia researcher Arthur Weltman attempted to correlate 3200m time-trial paces with laboratory-measured lactate-turnover paces. Their result gives paces substantially faster than Daniels' VDOT tables, with an 11:56 time trial (equivalent to 12:00 for 2 miles) giving you a 6:10 threshold pace. Daniels' VDOT tables, by comparison, would put the pace at 6:32. The precise formula is threshold pace (in meters per minute) equals 509.5 minus 20.82 × 3200m time in minutes.
06) 30-MINUTE TIME TRIAL
Like the Conconi test, this one is also heart rate based. In a 2000 article in Inside Triathlon, cycling and triathlon coach Joe Friel argued that all it takes to find your lactate threshold effort level is to monitor your heart rate during a 30-minute, solo time trial. "It must be solo," he added recently on his blog. "Doing this as part of a race or with training partners will change the outcome." During the first 10 minutes, your heart rate will speed toward the lactate threshold plateau. It's the average heart rate during the final 20 minutes that matters. Friel adds that if you do the test in a race setting or with pacers, it needs to extend to 60 minutes--exactly paralleling Daniels' advice.
But which of these is best? In a 2005 study in the Journal of Strength and Conditioning Research, a team led by Joseph Houmard, an exercise physiologist at East Carolina University in Greenville, N.C., had 27 distance runners and triathletes do the last four of these tests, then compared the results to lactate blood work determined on a treadmill. Their conclusion: Forget the 3200m time trial and the Conconi test. Both gave paces at least 10 percent too fast. The best was the 30-minute solo time trial, with the VDOT tables not far behind.
To find your precise threshold, nothing beats a lab test. And thanks to the advent of reliable hand-held lactate monitors that can measure your lactate level in under a minute from a single drop of blood, such tests are now easy to do.
The process takes about an hour, counting warm-up and cool-down, says Sean Coster, a Portland, Ore., exercise physiologist who routinely does such tests through Portland's P.A.C.E. Therapeutic Associates. "All we have to do is create a set of progressively faster runs."
Tests can be conducted on a treadmill or, for a more realistic measure, on a track--although the latter requires good pace control. A heart rate monitor is also useful.
After warm-up, the test typically involves four to seven 3-minute repetitions, starting at what Coster calls moderate effort and progressing to 10K pace or faster. An all-out effort is never needed. "Between each one, we can have 1 minute of rest," Coster adds. Basically, it's an easy interval session.
In the last 10 seconds of each interval, Coster has the runner check the heart rate monitor. Then, as soon as the interval is over, he pricks a finger to draw a small amount of blood. Other testers, particularly in Europe, draw blood less painfully from the earlobe, but sweat can interfere with the test, Coster says, making the finger preferable.
What emerges is your own personal lactate curve, from which you can determine, both as a function of pace and heart rate, your own LTVISUAL and higher points on the hockey-stick bend, such as LT4.0, LT3.0, or LTDMAX "The retail price is about $125 to $150," Coster adds.
Elite coach Brad Hudson recommends repeating such tests periodically. "Twice a year, if you can," he says, noting that testing is available at many research hospitals and universities. It's also possible to combine the results with a VO2 max test.
If budget is a factor, Hudson suggests trying to join a research study. "I just had three athletes do it back East," he says. "They volunteered at a university."