Below the Green Line
This is part of a series. I recommend starting with Part 1 about why I negative split. This part will go into how I think and reason about the execution itself on a low level.
While I’ve wondered about negative splits in ultras for over a decade, I didn’t really take it seriously until my buildup to the 2017 Hardrock 100. I had a realization that led to everything else described here:
Even when I had a strong finish, my slowest miles were 60-80% into a race, and often 2-5 minutes a mile slower than earlier in the race.
I hypothesized that if I could run my fastest and strongest miles 80% into the race by absolute pace, almost everything else will take care of itself. The slower first half pace will both be easier to beat, and I’ll have more reserves to do it.
Since then, I have gotten a lot more sophisticated in my planning, but the core concepts are the same. When most runners have a good race, they try to improve by making their fastest miles faster. The critical insight has been to realize that to truly get better, I needed to make my slowest miles faster. This holds true with or without negative splits, as the slowest miles have the biggest room for improvement.
Since most runners already fade the second half, starting faster will accelerate the blowup and make the slowdowns bigger. The only exception is if the runner has gained more additional fitness than the speed-up they are attempting. Even with offsetting fitness, it doesn’t mean it’s a good idea to start faster. Pushing 15-30 seconds a mile faster early in a race is connected with the slowdown later in the race, where most runners lose much more than that through fatigue and longer aid station stops.
Note that for the rest of the discussion, I’ll be assuming difficulty adjusted pace, meaning the idealized pace if conditions were perfect. In practice, the actual pace will need to be adjusted based on ascent/descent, trail difficulty, temperature, weather, night running, and other factors.
The Red Line
Many runners use what I call the red line strategy. The concept of red lining is familiar, but I want to give it a specific definition - the maximum pace at a single point in time that could be maintained for 20% of the race distance. So at mile 40 of a 100, if a runner could maintain a maximum of 9:00 pace for 20 miles, then the red line pace at mile 40 is 9:00. Notice that with this definition, the red lining pace will change throughout the race based on a runner’s condition, but can never go faster than it starts at.
The red line strategy isn’t to run at the red line pace, as that is clearly unsustainable at ultra distances. Instead, the strategy is simply to stay somewhere below the red line, and hang on the second half of the race as best you can.
The dotted red line shows a typical red line race execution, with its corresponding “red line” in bold. At the end of the race, the best case is usually just hanging on. This correlates with a lot of pain and damage.
The Yellow Line
The yellow line strategy is the “traditional” smart ultra pacing strategy. Many ultrarunners recognized for their smart pacing use this strategy. I think of it as the “all day cruising pace”. It’s characterized by starting slower than the lead pack, being patient early on, and consistently passing runners from halfway all the way to the finish.
There isn’t an exact definition of what the line is, but it typically stays flat early in the race, slightly slows by halfway, slows more between 60% and 90% into the race, then has a sizeable kick.
The dotted yellow line shows the yellow line race execution, with it’s red line shown in red and yellow stripes. It allows for some slowdown, but propels the runner up the leaderboard later in the race relative to red line racers. Notice the red line doesn’t dip nearly as quickly this time, and doesn’t crash as hard allowing a bigger and faster kick.
Below the Green Line
One of my biggest breakthroughs came when I defined the green line. The green line is the pace that can be maintained from the current distance in the race to the end of the race if everything goes perfectly. The green line strategy is simple - stay a bit below the green line from start to finish.
The green line is shown in bold. The dotted green line is the green line race execution, and the green and red striped line is the red line for this race. The first consequence of green line racing is quite remarkable. Since the green line can be maintained all the way to the finish, and we’re running slower than that, the average pace we can hold to the finish gets faster and faster as we go! And since the distance to the finish continually gets shorter, the increase in pace accelerates as we “ride the green line” up to a sprint finish. By the time we cross the red line with 20% to go, we’re going faster than any other point in the race, and are free to red line it all the way to the finish. The red line itself barely dips until very late in the race.
Also notice that the green line starts below both the red and yellow line strategies. This should make intuitive sense - the fact that both slow down means they are too fast to maintain that pace for the entire race and therefore must be above the green line.
But why run below the green line instead of on it? Wouldn’t we be faster running that pace exactly? This is often the intent of yellow line racing, and also its downfall. The green line is an idealized pace when nothing goes wrong, and something always goes wrong in an ultra.
The picture above oversimplifies the green line. In practice, it is not so smooth. A bad stomach, muscle cramp, afternoon heat, or other factors will temporarily dip the line, as the line itself can be bottlenecked by the most limiting factor at any moment:
The reason we stay sufficiently below the green line is to give a buffer for all of these problems, which are hard to predict individually. If the green line dips below the dotted line, we’re now running faster than we can sustain by definition, and the green line will now continuously fall unless we slow our pace or can quickly resolve the issue to raise the green line.
All of this together paints the picture I laid out in my original post. Running under the green line keeps a runner nearly fresh for the first half of the race, and even in the second half there is plenty left in the tank. If we’re wrong about where the green line is, we still have options. If we’re too aggressive in our estimate, we end up with a yellow line race which is not too bad. If we’re not aggressive enough, the green line keeps pushing up faster and we can ride it to an extremely fast finish.
Here’s a standalone picture of a green line race. The green line gets faster and faster, and the red line doesn’t dip much.
Now the yellow line race. We start above a sustainable pace, but not by much. The green line for the race slowly drops until our race pace dips below that in the second half of the race. Now that the slower pace is sustainable, we can ride the green line up late in the race to the finish. The red line drops a bit the first half, but drops more the second half.
And the red line race, where the initial pace is the farthest above the green line, and the sustainable pace declines throughout the race. The red line drops the most out of any of the races, and ends quite low as we blow up holding on for the end.
Pushing the Green Line Up
The green line strategy may produce slower races at first. This could be because we’re not conserving enough early on, or it can be because we’re not pushing hard enough later on. Let’s talk about both.
We want to start by identifying and eliminating the weak links keeping the green line down, then increase our overall pace as we resolve these limiting factors. This should be done carefully - get cocky and you’ll revert back to yellow line racing. But there are a lot of ways to improve here.
Much of pushing the green line pace is traditional race strategy. Heat management is an easy place to start, along with nutrition, hydration, and electrolytes. And starting out slower means it’s easier to manage these.
The other aspect that’s new and unique to negative split racing is managing the slow pace both physically and mentally. Physically this includes doing training at the planned race pace on similar terrain to build biomechanical efficiency at that pace.
On the mental side, I’m a fan of Dr. Jim Loehr’s concept of the energy quadrants applied to sports that have active periods and rest periods. In short, he describes staying in a “high positive” state of calm and confident engagement during active competition, but dropping to a “low positive” state of peaceful relaxation in between rounds. Ultras don’t work this way because of their length. I’ve found focusing on combining the two and slowly dialing from low positive to high positive over the course of the race is the right approach. It keeps cortisol and the endocrine system as dialed back as possible for most of the race, but in the second half I slowly move to a higher energy state as I push more and more to the finish.
But what if you can’t turn it up late in a race mentally, even when you’ve conserved appropriately?
A lot of my own improvements came from visualization exercises. I would constantly imagine the second half of my races, gradually picking it up, passing more and more runners, and unleashing a huge kick at the end. The exercises helped me prepare, but it still took lots of practice executing in races to find the right lines. Sometimes I would push too early or too hard and blow up. Other times I would leave performance on the table. One mental trick I would frequently use is to not increase the pace at all until I thought I could sustain the kick until the end, then flip a switch and really just hammer to the finish (which was a lot of fun!) But over time I learned this was not an optimized strategy. If I misestimated the distance the crashes were harder than a gradual dial-up. But I’d encourage playing with multiple strategies and see what works for you.
A final word about fully leveraging green line racing involves aid stations. Because I feel so good the whole race and have far fewer things go wrong, I can dial in my stops much further. I prepack everything I need into packs, and never really need to stop at aid stations to troubleshoot anymore. I generally only get water from aid stations now, and can often skip stations completely. Using this I can average <5 minutes total at 100 mile aid stations while the others around me are likely spending 30-60 minutes. That’s all time back at the finish!
Estimating the Green Line
How do I estimate the finish time and pacing strategy, especially when the race isn’t flat and controlled? Stay tuned for part 3 where I’ll detail my process.