One of the most widely believed myths in endurance sports is the notion that fatigue occurs much faster at exercise intensities slightly above the lactate threshold than it does at exercise intensities just below the lactate threshold. Not true. At any given submaximal running speed up to a near sprint, a slight increase in speed only slightly reduces the duration that speed can be sustained. The speed associated with the lactate threshold is no exception to this pattern.
To make the point more concretely, the duration you can sustain your lactate threshold speed plus, say, 0.25 mph will be only slightly less than the duration you can sustain your lactate threshold speed. You won’t suddenly fall off a cliff, as even many running coaches believe. The reduction in time to exhaustion associated with accelerating from lactate threshold speed to lactate threshold speed plus 0.25 mph is equivalent to the reduction in time to exhaustion associated with accelerating from any slower speed by an equal amount. There is simply no performance threshold at the lactate threshold.
Of course, lactate threshold intensity in running is defined as the running speed at which lactate begins to accumulate rapidly in the working muscles and blood. But if this is the case, then why doesn’t fatigue occur much faster at exercise intensities slightly above the lactate threshold than it does at exercise intensities just below the lactate threshold? Because lactate does not cause muscle fatigue. That’s another myth.
An interesting proof that there is no performance threshold that correlates with the lactate threshold is to be found in a comparison of world record paces (or speeds) across the full range of standard running race distances. Compare the current men’s world records in the half-marathon and the marathon. Zersenay Tadese’s half-marathon world record of 58:23 converts to a pace of 4:27 per mile. Patrick Makau’s marathon world record of 2:03:38 converts to a pace of 4:43 per mile. The latter pace is roughly 6 percent slower.
In trained runners, the lactate threshold typically equates to roughly a 60-minute maximum pace, so it is safe to assume that Tadese was working just a smidgeon above lactate threshold intensity in his world-record effort. Nobody can sustain LT pace for a full marathon. Thus, world-record pace for the half-marathon is slightly below LT and world-record pace for the marathon is slightly above it. The marathon distance is, of course, double that of the half-marathon, and yet, again, world-record pace for the former is only 6 percent slower than that for the latter. That’s hardly a performance threshold.
Let’s now see how much the world’s best runners slow down when the race distance is doubled in shorter events that are both run well above lactate threshold intensity. Kenenisa Bekele’s 5,000m world record of 12:37 converts to a pace of 4:03.6 per mile. The same runner’s 10,000m world record of 26:17 converts to a pace of 4:13.8 per mile, which is 4 percent slower. This is less than 6 percent, but when you consider the fact that doubling the half-marathon adds 13.1 miles of running whereas doubling the 5K adds only 3.1 miles of running, you must conclude that the relative slowdown is proportional.
This pattern continues at even shorter distances. World-record pace at 3,000m is 6.7 percent slower than world-record pace at half the distance, or 1,500 meters. But look what happens when you move from the distance that is considered the longest sprint, 400 meters, to the distance that is considered the shortest “distance event,” 800 meters. The difference between world-record pace for 400m and world-record pace for 800m is a whopping 17 percent.
Now that’s a performance threshold, and it stands out not only from longer efforts but from shorter ones as well. World-record pace at 400 meters is 11 percent slower than world-record pace at 200 meters, which is virtually identical to world record pace at 100 meters (although comparisons between performance at 100 and 200 meters are skewed by the tremendous influence of the start in these events).
So there is a very real performance threshold in running — a relative speed that, when increased slightly, results in a huge drop in time to exhaustion. But that performance threshold occurs nowhere near lactate threshold speed. Instead it falls somewhere between the maximum speed that is sustainable for 45 seconds and the maximum speed that is sustainable for 100 seconds.
What causes this performance threshold? Why can’t trained runners run nearly as fast for 800 meters as they can for 400 meters when they can run almost as fast for 400 meters as they can for 200 meters and almost as fast for a marathon as they can for a half marathon?
It is tempting to point to physiological fatigue mechanisms such as muscle cell depolarization that are in play in maximal efforts of 45 to 150 seconds. Muscles function somewhat like electric batteries, which require a strong difference in polarity to work at full power. During very high-intensity exercise, the muscles lose much of their polarity, just like a battery that’s running our of “juice,” and this causes a loss of muscle contractility and performance. However, research suggests that muscle cell depolarization cannot alone account for the loss or performance that occurs in sustained high-intensity efforts.
So what else is going on? Samuele Marcora believes that fatigue occurring in all maximal efforts lasting longer than half a minute or so is voluntary. The discomfort associated with the effort of sustaining a very high intensity of muscle work output becomes so great that the athlete essentially gives up. If this idea is new to you, you’re almost certain to receive it skeptically. Since I don’t want to get bogged down in defending it here, I will address your skepticism by referring you to my interview with Marcora.
What I would like to suggest here is that the performance threshold that runners encounter between maximal efforts of 45 and 150 seconds is associated with the activation of perceived effort as a cause of fatigue. In a 200-meter sprint, runners reach their maximal velocity at around 60 meters and start to slow down at around 150 meters. Thus, fatigue does manifest even in 20-second maximal efforts. But Marcora believes that fatigue in such short efforts is in fact caused by physiological factors, as everyone else believes. While there is obviously a very high perception of effort in a 200-meter sprint, this suffering does not trigger a conscious decision to slow down because the athlete knows it’s going to be over with soon enough.
When the races get longer, however, the psychological challenge exceeds the physiological challenge. And at some point, perception of effort, or psychological suffering, causes the runner to voluntarily restrain himself before there is actually any physiological necessity to slow down. That is the cause of the performance threshold that falls between 400 and 800 meters.
Do I have proof that this is so? Not direct proof. But an interesting 2009 study by researchers at the University of Essex in the United Kingdom provides oblique support for my conjecture. Nine subjects were asked to pedal absolutely as hard as they could on stationary bikes for 5 seconds, 15 seconds, 30 seconds, and 45 seconds. They were instructed not to worry about being unable to sustain maximum power in the longer efforts. The idea was to start each effort at absolute maximum intensity and then hang on as best they could.
That’s not what happened, though. Power data revealed that the subjects started the 45-second maximal effort at a slightly lower intensity than they started the shorter sprints. They couldn’t help themselves. Perceived effort data revealed that the subjects were not suffering as much 15 seconds into the 45-second effort as they were 15 seconds into the 30-second effort and at the end of the 15-second effort. This is what you would expect given that the subjects disobeyed instructions and restrained themselves slightly at the beginning of the 45-second effort, but it’s most certainly not what would have happened if the subjects had obeyed instructions. In that case they would have been suffering just as much at the 15-second mark of the 45-second sprint as they were at the 15-second mark of the 30- and 15-second sprints, with the consequence that they would have been suffering a lot more at the end of the 45-second sprint.
I believe that, probably based on past exercise experience, the subjects anticipated that they would reach an intolerable level of suffering if they truly went all-out for 45 seconds, so they paced themselves to avoid intolerable suffering and thus self-limited their performance.
They chickened out, as Marcora believes we all do in races longer than 400 meters.
About The Author: Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.