Current practices in threshold training are based on well-disproved myths.
Runners have been doing anaerobic threshold runs — also known as lactate threshold runs, just-plain threshold runs and tempo runs — for ages. Within the past several years, however, the primary physiological rationale for these workouts has been obliterated by advances in exercise science. Does this mean you no longer should do threshold runs?
Of course not.
While threshold runs don’t work in the way we once thought they did, they still work. But the new rationale for threshold runs does free us up to approach them in a slightly different way.
In the past, threshold runs were defined as runs performed at lactate threshold speed, or the running speed (on flat terrain) just above which the blood lactate concentration increases rapidly. It was considered very important to run at precisely this speed in such workouts because doing so would stimulate physiological adaptations that increased the lactate threshold far more effectively than running a little slower or faster would do. Therefore, runners took great pains to measure their lactate threshold and lock onto it with the aid of heart rate monitors and split times in workouts.
The problem with this rationale is that the lactate threshold is not a precise phenomenon. Several different protocols are used to measure it, and each produces results that are slightly different from those yielded by the other methods. There is also evidence that the lactate threshold is sensitive to conditions such as fatigue and, therefore, changes a bit from day to day. Consequently, nobody is really able to train consistently at precisely lactate threshold intensity. Thus, the lactate threshold exists only fuzzily in theory and not at all in practice.
What’s more, there is no evidence that the effort to train at precisely lactate threshold intensity stimulates special and unique physiological adaptations that training at slightly higher and lower intensities fails to match. Consider a study by British researchers in which 14 moderately trained runners were separated into two groups that followed slightly different training schedules for four weeks. Members of one group incorporated two conventional threshold workouts — consisting of continuous running at lactate threshold intensity — into their weekly regimen. (Actually, they ran at maximal lactate steady state speed, which is considered synonymous with lactate threshold speed by some scientists and slightly below lactate threshold speed by others, including these researchers.) The second group of runners did a matching amount of variable-intensity workouts in which they alternated between running 0.5 km/hr faster than lactate threshold speed and 0.5 km/hr slower than lactate threshold speed.
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Before and after the four-week training period, all of the runners were tested for their maximum lactate steady state speed and their lactate threshold speed. Those who did traditional threshold runs saw a bigger improvement in their velocity at maximal lactate steady state speed than those who did the variable-intensity workouts, who in turn saw a bigger improvement in their lactate threshold speed, which was fairly close to the speed at which they performed the faster segments of their workouts. What do we learn from these results? Runners seem to improve more at the speed they focus on in workouts, whether that speed is at, above or below the lactate threshold.
This study is just one of many whose results suggest that it is rather pointless to base workout intensities on targeted physiological states or desired physiological adaptations.
Consider another study on exercise at maximal lactate steady state intensity, this one involving cycling. French researchers tested 11 cyclists to determine the power output level that correlated with their maximal lactate steady state on a bicycle ergometer and then asked them to pedal at this power level until they were too tired to sustain it a second longer. The researchers monitored a number of physiological variables throughout the test with a view toward isolating the cause of their fatigue. Interestingly, they found that although heart rate, breathing rate, blood carbon dioxide pressure, blood lactate concentration, and muscle acidity increased significantly, none of these variables reached the level associated with exhaustion during a maximal exercise test. In other words, there was no single cause of fatigue at maximal lactate steady state intensity.