Training Specificity Part 1: crits and sprint metabolism

The capacity of sprinters?  It takes more than just a killer sprint to win a race (like positioning, but my power meter doesn't record that), we need to consider other factors.  I will do so by considering some interesting power metrics, but they'll tie back into well known exercise physiology, if not by the end of this post then in the next one.  Today we look at neuromuscular power.

As always, charts are from WKO4, build 260.  Unlike usual, I will mostly focus on my own data.  Not for ego, but because I coach no track racers with power data, I end up as the purest sprinter for whom I have data.  That is to say, I'm the only athlete whose WKO4 phenotype didn't change from "sprinter" to "all-rounder" during base training.  To be fair, I'm not even a great sprinter.  This is my power curve from 2015, a year in which I sucked at criteriums.

In crits, repeated accelerations are arguably the most important factor.  This year I started training that ability and it's paying off.  The following is the power readout from two criteriums last sunday (I doubled up).

The course was 0.6 miles with two gentle corners and two right angles.  In each race there was no more than 6 minutes of coasting.  I did over 90 laps of the course this day, and the routine went: turn, accelerate, gain position, repeat.  You can tell that to haul my 163lb bulk back up to speed I had to hit about 600-1000w repeatedly.  The 1200w peak in the first race was an attempt to establish a break, and in the second race it was snagging a prime.

The highest average power for 5 minutes was less than my FTP.  Since FTP can be held for an hour, 5 minutes isn't really a big deal.  I selected a random 20 minutes from the first race and looked at the normalized power: 285w, right near FTP.  Random 20 minute chunk from the second race: 275w NP.  This is where the training specificity principle comes into play.  In order to meet the demands of an event, you have to prepare for them in ways that replicate those demands.  Hence this workout:

Since races are about 45 minutes long at the non-elite level, that workout is 40 minutes of 10 second sprints, one every minute.  Besides matching the neuromuscular demands of a criterium, the normalized power of this workout was 297w, over FTP by a few watts.  Excellent criterium specificity.

I've been learning that one mark of a sprinter or pursuiter (besides the obvious) is the ability to create normalized powers well over their FTP.  If you're well steeped in traditional power analysis, you may be thinking that NP represents the physiological demand if you had been working at a steady state, and you're right.  This doesn't mean that if you can normalize a power that you can recreate it steady state.  Believe me, I've tried.  So let's get into why.

The metric I've been working with is 1 hour NP way over FTP, which really only applies to sprinters and pursuiters, and modestly to all-rounders.  How does this happen?  It comes down to stored energy.  As you can see from the sprints above, I'm pretty good (but not amazing) at recharging PCr stores in my muscles, hitting between 950-1050w consistently.  Were I any better at this I would have normalized a higher power, or perhaps there's an optimal rest-sprint ratio to maximize NP for the workout.  Doing 12 sprints in an hour also normalizes 300w for me while hitting about 1250w each time.

What's this have to do with stored energy?  Phosphocreatine is recharged from two molecules that have higher stored energy, phosphoenolpyruvate and 1,3-bisphosphoglycerate (PEP and 1,3BPG).  PEP is shunted off from the TCA cycle and 1,3BPG is a glycolysis intermediate.  As the reaction ADP+PCr->Cr+ATP proceeds for each sprint, we can safely assume that the PCr levels in a muscle cell are well below normal levels.  This increases the demand for PEP and 1,3BPG and thus the glycolytic and aerobic systems.  See here (page 5) if you're rusty on your standard free energies and why this works.

Glycolysis is probably more taxed in sprinters with good anaerobic power since glycolysis can create energy more rapidly than aerobic metabolism.  Looking at it another way, because the normalized power a sprinter can create is much higher than FTP (here representing the aerobic ability of the athlete), the difference must be made up by stored energy in the form of PCr and glycogen.  This ability to rapidly mobilize non-aerobic energy (during and while recovering from high intensity efforts) is why sprinters and pursuiters can't simply put out their normalized powers at a steady state.  It should be obvious that FTP is also important for criterium racing.  Greater demands on stored energy during the race means there will be nothing left for the final sprint.

Next post will look more closely at the ability of some sprinters and all pursuiters to chew through glycogen at rapid rates.  I'll also look more closely at a couple cases of 1 hour NP > FTP.