The Boston Marathon should be a PR course. After all, the course is significantly downhill—so much so that finish times can’t be considered for world records due to the drop from start to finish. But, late in the race, you often see these uber-fit marathoners struggling to stay on pace; many are even slowed to a walk. What’s going on?

Eccentric Loading

When you run, your body goes through a mindboggling chain of events every time you land, push off and land again. One of the most important is absorbing the impact of landing as you essentially hop from one foot to the next. You’ve probably heard the statistic that you land with 2.5–3 times your body weight with each stride.

During landing, some muscles contract while lengthening (called an eccentric contraction) to slow your drop to the ground before shortening to propel you forward through your stride.

The quadriceps (thighs) are a good example. When you land, the “quads” contract while lengthening, as the knee bends, to keep you from collapsing to the ground. They then quickly reverse direction and shorten, lengthening the leg, to help propel you forward to your next foot plant. And this is done in a split second, thousands and thousands of times across a race (roughly 35,000-45,000 times across a marathon). Is it any wonder why marathoners are sore after that?!

Eccentric contractions (lengthening while contracting) are more stressful to the muscles than concentric contractions (shortening while contracting).  And with a lot of eccentric contractions (like in exhaustive running), the muscle cells can actually begin to tear. These “micro traumas” are very small disruptions in the tissue but accumulate enough of them and your performance during the run can suffer.

runners late in 2016 Boston Marathon
photo: 101 Degrees West

Downhill Damage

Runners, particularly inexperienced ones, are often quite sore after a flat marathon. Tilt the elevation chart like Boston’s course (with the first 16 and last 5 miles of mostly downhill) and the damage is amplified, making even experienced runners look like amateurs by the crest of Heartbreak Hill at mile 21.

Research shows that downhill running results in 54% greater impact forces when landing compared to flat running. And peak braking forces on the legs are increased by a whopping 74% when running downhill.

You’ll hear Boston marathoners say things like, “My legs were trashed.” Or, “My quads felt shredded by mile 20.”  Shredded is right. The muscle cells have literally been torn with lots of microscopic rips in the tissues.

Further, it’s not just the muscle tissues that get affected. Research also suggests that the nervous system (that signals the contract/relax process) doesn’t work as well and there can be significant inflammation from downhill running.  The torn tissues can also leak out the stored glycogen (carbohydrate) that would normally be used for fuel.

The brain gets involved too. The Central Governor Model theorizes that the brain senses this extra damage and sub-consciously (and consciously, as marathoners can attest) creates more fatigue messages so you lose your desire to keep pushing—the old, “Why am I doing this?” line of thinking as you throw in the towel. And, the brain may actually “cut the power” to your muscles to slow your pace to protect the body from more damage. After all, your brain cares less about your personal best and more about survival when it comes right down to it.

The end result is that many Boston Marathon runners “hit the wall,” not because of an energy deficit but because the tissues simply can’t perform anymore, and the brain creates a tidal wave of self-defeating thoughts.

That’s why handling the downhills is one aspect that makes training for and running well in the Boston Marathon so intriguing and a Boston finishers medal such a badge of honor. As 2018 winner Desiree Linden told me, “Boston, unlike other marathons, is a race where you prepare for the course, not just for 26.2 miles.”

It’s not just about being a fast marathoner as you head to the starting line for Boston. It’s about being prepared to handle the downhills. Get it right and you can run fast. Get it wrong and it’s one of the toughest marathons you’ll ever run.

Greg McMillan has been called “one of the best and smartest distance running coaches in America” by Amby Burfoot of Runner’s World. You can try McMillan’s training and coaching for free at www.mcmillanrunning.com.