why flat feels like uphill
By PaceKit Team · Updated April 2026
One runner's race report captured it perfectly: "My biggest enemy at M2B turned out to be not so much the long downhill itself. Rather, trouble arose when my used-up quads transitioned from 13+ miles of faster downhill to 4+ miles of flat."
This is the defining pacing challenge of Mountains 2 Beach, and it's not something you can fully prepare for by studying the elevation profile. The profile shows a long descent from miles 9 to 19, then a flat section from miles 20 to 26. What the profile doesn't show is how your body recalibrates.
Here's what happens. During the descent, your quads absorb eccentric loading with every step. Eccentric contraction (muscle lengthening under load) is the primary action when running downhill, and it causes more muscle damage per stride than concentric contraction (muscle shortening, as in flat or uphill running). After 10+ miles of this, your quad fibers are damaged at a microscopic level. You don't feel it during the descent because the grade is doing the work for you, and your pace looks great.
Then the road flattens. Now your quads have to generate force concentrically again, pushing you forward instead of absorbing you downward. The damaged fibers can't produce the same force, and the effort required to maintain the pace you were running on the descent suddenly jumps. What felt like 7:30 effort on the downhill now feels like 8:00 effort on the flat. You haven't slowed down because you got tired. You've slowed down because 10 miles of downhill broke your quads.
The solution is not to run the descent slower (though that helps). The solution is to run the descent with good form: short stride, high cadence, slight forward lean, landing with your foot under your center of mass rather than reaching out in front. Every stride where you overstep and brake hard with your quad is a stride that costs you on the flat.
The other solution is mental: know it's coming. Budget for it. If your goal pace is 7:30, plan to run 7:20 to 7:25 on the descent and 7:40 to 7:45 on the flat. That produces an average of roughly 7:30 with a slight positive split that reflects the actual demands of the terrain. Runners who try to run 7:30 on both the descent and the flat will run 7:15 on the descent (too fast, too much quad damage) and 8:00 on the flat (paying for it).