Monday - 4 miles easy
Tuesday - 1-mile warm-up, 5 x 1K @ 5K race pace w/ 400m jog recoveries, 1-mile cool-down
Wednesday - 1-mile warm-up, 10K @ threshold pace, 1-mile cool-down
Thursday - 6 miles easy
Friday - 1 mile warm-up, 12 x 400m @ 3K race pace w/ 400m jog recoveries, 1-mile cool-down
Saturday - 1-mile warm-up, 10K @ threshold pace, 1-mile cool-down
Sunday - 12 miles easy
You probably don't need me to tell you that there is one high-intensity workout too many in this week. Doing four high-intensity workouts per week in a moderate-mileage program for five months straight is just not very smart. I believe that the runners in the study who did so simply weren't able to properly absorb all of that hard work and wound up slightly overtrained.
Consequently, the runners on the "easy" training regimen actually got more out of their three hard workouts per week than the others got out of their four. I would not be at all surprised to learn that the runners on the "easy" schedule, because they were getting adequate recovery between hard workouts, began performing better than members of the "threshold" group in their high-intensity workouts after just a few weeks, such that the results of the second time trial surprised no one.
It's understandable that the researchers who performed this experiment wanted to make the two training regimens sufficiently distinct that they could point to a clear cause for the disparate effects they produced. But if you ask me, the runners in the threshold group were really set up for failure. I would have bet my house on the "easy" regimen producing better results than the "threshold" regimen, because the latter lacked the balance that has proven most effective in the training of runners in the real world for many decades.
Nevertheless, the study provides solid validation for the notion that a modest amount of threshold training goes a long way. The take-home lesson is this: You'll get as much fitness as you can get from threshold training with one hard session per week. Adding a second threshold workout will not give you any extra fitness and may actually inhibit your fitness development by causing you to accumulate fatigue that you carry from one threshold workout to the next, so that you don't perform as well as you should in these workouts and therefore get less benefit from them.
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