Researchers study how eccentric muscle contractions trigger lasting fatigue.
This was a cruel, cruel study. Researchers in France asked 23 volunteers to complete a 6K downhill trail run, dropping more than 1264 metres in elevation, as quickly as possible. They averaged about 35 minutes – but the after-effects lasted for days.
It has long been known that downhill running is particularly hard on the legs, since it requires strong eccentric muscle contractions as you brake on your way down, which cause microscopic damage to muscle fibres. Downhill runs are often used as a reliable way to induce delayed-onset muscle soreness in lab studies, but they can also deaden your legs during the race itself (as many Boston marathoners will attest).
The new study was published in the Scandinavian Journal of Medicine & Science in Sports and led by researchers at the University Savoie Mont-Blanc and the outdoor gear company Salomon (including many of the same researchers who published a review on the physiology of uphill and downhill running that I wrote about recently). It aimed to explore the relative contributions of peripheral (in the muscles) and central (in the brain and central nervous system) fatigue after downhill running.
The short answer is that a run like this produces plenty of central and peripheral fatigue. Maximum voluntary force from the quads dropped by 19 per cent immediately after the run, and by 25 per cent for the calves. Much of the decline was because the muscles themselves weren’t working as well, but “voluntary activation” – a measure of how big the signal from the brain to the muscles is – also declined by seven to eight per cent.
One interesting thing to note is that this level of fatigue is pretty similar to what’s seen after far longer trail races like the 160K Ultra-Trail du Mont-Blanc or the 320K Tor des Géants. That suggests that the downhill sections of hilly races are the dominant cause of muscle damage/fatigue, and how fast you go down the hills makes a big difference too.
Two days later, the muscles themselves were mostly back to normal, but voluntary activation remained suppressed and pain remained elevated. That may be because the lingering inflammatory markers associated with eccentric muscle damage are still sending signals back to the brain to avoid using full force.
Part of the reason this study jumped out at me is that I once did a very short mountain race in Australia’s Blue Mountains that basically involved running a kilometre or so on flat ground followed by a kilometre or so up a very steep mountain, then turning around and running back to the start. It can’t have been more than a few minutes of downhill running, but it was very fast, and I have truly never been so sore in my life as I was after that race. I could barely walk for a few days, and couldn’t run for a week.
In theory, I’d like to say that knowing about the relative roles of central and peripheral fatigue in downhill running will allow me to better prepare for my next downhill race, perhaps by doing more downhill training to prepare my muscles for those eccentric contractions. In practice, after my experience in the Blue Mountains, my firm policy is that I only race uphill or flat.