Descend Every Set.
It's rule #8 in my non-scientific, tongue-in-cheek, list of rules for endurance athletes.
Descending Every Set is super common terminology in the swimming world. Swim coaches often prescribe sets as: "12x200. Descend 1-4, 5-8, 9-12." Descending is referring to getting faster on each repetition. It teaches patience and control, and it trains the ability to push yourself late in a workout or race when you are fatigued. It's a good habit for endurance athletes to have in nearly every race and workout.
Why descending throughout a workout is important
Physiological benefits to descending the workout
There are a few reasons why I think descending throughout a workout or a race is very important. The first is physiological. By starting on the slower end side of things, you make sure that your aerobic system is fully warmed up and operating at high capacity before you get to working really hard. To use lactate numbers, imagine your cycling threshold is 200 watts and 4mmol of lactate. If you have a set of 4x10min and you do your first rep at 215 watts, you've now spiked your lactate up to 5 or 6 mmol, and it will stay close that nearly the entire workout, even with a recovery. You might be so tired from this by the end that your last effort is only 190 watts with still very high lactate numbers.
IF, however, you do your first rep at 190 watts. Your lactate might only be 3 or 3.5 mmol, it falls quickly during the recovery interval and you start back at baseline because it didn't get very high. You continue throughout the workout and maybe even finish the last rep at 215 watts. The lactate reading might only be 4.2 or 4.4 on the last rep, since the aerobic system was operating at full capacity by then.
If you compare the two workouts, they might seem similar. The average power for all the reps was similar. The highest power was 215 watts and the lowest power was 190 watts. But the training effect was vastly different between the two! In example 1, it was primarily an anaerobic workout and didn't really help improve threshold much, since you were well above it the entire time. It will also be more fatiguing, harder psychologically, and require more recovery. In example 2, the athlete stayed below threshold the entire time and it gave them a better training effect, while also giving them the capacity to really push at the end.
The same principle applies in racing.
To be clear, this doesn't mean you should start a marathon at 8:30 pace if your goal is to run 7:30 pace. That's not a practical amount of descending.
Psychological benefits to descending workouts
The second reason I think it's very important is that it teaches patience and confidence. Ultimately, to start at or slightly slower than your goal requires confidence in yourself that you CAN hit the faster power and paces when the race gets tough. Starting too fast is often done out of fear that we can't actually go the pace or power we want to. But you can! Going out with a controlled effort puts you in the driver's seat of your own performance.
Descending Every Set does NOT mean easier
The video above is a good example of Descending Every Set and a good reminder that negative splitting or descending does NOT mean it will be easy. En route to a 12:51 5k (12:54 for Joe Klecker), Woody Kincake and Klecker split 6:30 at the halfway mark. That would have been 13:00 even for 5k, but they closed their 2nd half in 6:21 and 6:24. If you watch Joe Klecker leading up until the very last lap, you can see that negative splitting was no easy feat. He was absolutely on the ropes the last 4 laps of the race and barely made it across the line before collapsing.
Negative splitting put him in control of his race, but he had to be willing to get the most out of himself that day.
Whether it's a workout or a race, be confident in yourself and your fitness. Go out controlled, descend throughout the workout, stay focused, and work hard when it gets tough!