Paper recap- "Short Trail Running Race: Beyond the Classic Model for Endurance Running Performance."

Thanks to Kim Nedeau for sharing a spanking new paper with me that I likely wouldn't have seen otherwise.  I thought I'd share it here with a brief summary (though really it should go on my neglected/never started "mountain running science" blog page).  Nothing evolutionary here-- this is pure exercise physiology, and will likely only interest trail runners, but for this demographic it's a great read.

The research: Testing was conducted on 100+ competitive French trail runners before a 27k (16.8 mile) singletrack, technical mountainous trail race with 4,000+ feet of elevation gain.  (Only figure 1 in the paper lets the reader infer that this is an up and down race, not up only...I digress.)  The researchers asked whether the "big 3" factors that predict traditional endurance running performance apply to trail racing, which is quite different.  The 3 factors are:

1) VO2 max: the maximal amount of oxygen an athlete can take in and use to do muscular work.  Essentially, this is a measure of how big the engine is: how well the cardiovascular system can deliver oxygen to the muscles and the capacity of the muscles to use this to power contractions. 

2) Perecent VO2 max at Lactate Theshold: essentially, how much of your oxgyen delivery/usage capacity you're using while running at a pace requiring a slight anerobic energy contribution, which corresponds to about 60 min race effort  You may have a huge VO2 max, but a guy who can race a given distance at a lower relative percentage of VO2 max is more efficient than you and has reserve capacity.  I don't think this is too different than #3:

3) Running economy: the energy required to run a given distance. This is a measure of efficiency. This tends to matter more for longer races where total on-board fuel is an issue (races of 2 hour or more), but a more economical runner can better translate muscular work into forward motion, making her faster over shorter distances too. 

These 3 factors are strongly predictive of running ability in traditional running races-- road races, etc, run on level or mostly level ground, and on pavement/grass/anything homogenous.  That is, an athlete with superior numbers in these 3 tests will probably win (excluding, of course, the impossible-to-quantify factors of toughness and focus.) The researchers suspected that maximal muscular strengh in the legs might be a factor for trail racing, as this has been shown to improve running economy in level and inclined running, and it has predicted race performance in a 26 mile all-uphill mountain race.  (As an aside, that's the main reason I lift: to improve uphill running economy by building a "stiffer spring". Aside aside: this is why flexibility/muscle length in many muscle and tendon groups is inversely related to running economy. The best runners aren't great yogis.) 

The results: The traditional model (the big 3) DID NOT predict race performance in a 16.8 mile mountainous trail race.  Nor did maximal knee extensor strength. The model that best predicted performance was a combination of 3 variables:

1) VO2 max.
2) "Fatigue index". Runners performed 40 maximal reps on a knee extensor machine, which isolates the quadricep muscles.  Fatigue index is a ratio of torque produced during the last 5 reps divided by the first 5 reps. So, fatiguing less in this test means a better fatigue index. 
3) Running economy at a 10% incline.  

This is all very interesting.  Take aways:
--I'm not surprised that VO2-max was predictive of trail racing performance.  It predicts performance in every running discipline.  To race trails and mountains, work on getting a big aerobic engine with short and hard intervals.
--Fatigue index of the quadriceps makes sense too-- extreme uphill/downhill racing is very dependent on these muscles.  For a race with climbs and descents that are moderate in length (but not endless), the quads need to be conditioned for anaerobic energy production, which is what a 40-rep exercise is testing.  And as the authors infer, higher fatigue resistance means that muscle fiber recruitment needn't increase to permit continued force production. Because energy cost of running is dependent entirely upon volume of muscle activated, this is a big deal.  I am surprised, however, that a test isolating the quadriceps was so predictive, as mountain running requires really almost every muscle in the body and especially plantar flexors (calves etc) and hips muscles (all of the glutes, etc). 
--Running economy at 10% incline matters, but running economy on a flat surface was not correlated with trail racing performance. Another study found that flat and uphill running economy are not realted-- again, as I've been saying, don't train for flat running and expect to be good at uphill running, or vice versa. Even in a race that is only (at most) half climbing, running economy while climbing is a highly predictive factor in determining race performance. (Suck on that, downhill specialists!). The authors suggest that the observed fatigue resistance in the runners' quadriceps is resultant from their uphill training and also their cycling (which most performed as cross traning). Therefore they recommend that trail runners should perform uphill training and cycling to improve quadriceps fatigue resistance and therefore trail racing performance. 
--The authors were surprised that maximal force production wasn't a significant factor in race performance. But their test isolated the quadriceps, and as I just mentioned, the quads are only part of what it takes to run fast up and down mountainous terrain for 3 hours.  I don't think they looked at this, but I bet if they compared the running economy measures of their runners to the runners' quadriceps maximal strength tests, there'd be a strong correlation, as has been found in other studies.  So don't take this as evidence that you don't need to do strength training to be a mountain or trail runner, and to their credit, the authors remind us of this. Lift weights and/or do plyometrics to improve your uphill running economy and therefore to kick ass up mountains.

Anyway, this is the first paper I've seen that investigates factors determining trail/mountain running performance vs. level running, and it's nice to see some experimental articulation of how they're different. To wit: "The flatter the running surface (i.e., road) the higher the relevance of laboratory-based phyiological measures of relative VO2 max, %VO2 max and runnig economy".  

Ehrström, S., Tartaruga, M. P., Easthope, C. S., Brisswalter, J., Morin, J. B., & Vercruyssen, F. (2017). Short Trail Running Race: Beyond the Classic Model for Endurance Running Performance. Medicine and science in sports and exercise.

Link to abstract (full text is behind a paywall): https://www.ncbi.nlm.nih.gov/pubmed/29077639
Message me if you'd like the full text.