There is a performance threshold in running, but it’s not the lactate threshold.
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.
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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?