What is the one thing most runners have in common? It’s the desire to run faster. Ideally to run faster for longer, actually. No matter the level of runner – whether that’s the “weekend warrior” or the professional athlete – everyone trains with the aim of sustaining a faster pace over a longer time or distance.
Increased speed coupled with enhanced endurance equals better efficiency and in turn is the driving force behind running faster for longer. This is, so to speak, the simple equation of successful training – it’s common sense.
Where opinions divide: how to optimally achieve this ultimate goal of training? The question implies that there is an optimal way of training. That is up for debate. Not debatable is the fact that training, and the outcome of training, is a multi-faceted long-term process. With that in mind there can hardly be that one magic bullet workout: one specific session that will make every runner better, faster and more efficient.
Certainly not when seen in isolation. Successful training is the sum of many different factors: quality workouts on one hand, but other factors like recovery (sleep, nutrition), injury prevention, core strengths, life circumstances or even theoretical understanding of human physiology and how it ties in with training components – all play a role.
And yet there is one specific training stimulus that could be argued for as to be this one “magic bullet”. Remarkably this is something that is fast and fun without the need to push the body to the brink – as VO2 max workouts can do – while it is sustainable providing short-term motivation and long-term gains. Sounds too good to be true?
Muscle Fibres are Key
Let’s take a step back. Before going deeper into this we have to talk about muscle fibres. Because they influence performance in no small way and are absolutely crucial for how fast and long humans (can) run in different circumstances – whether that is an explosive all-out 100 metre sprint or a long day on the trails at slow paces with plenty of elevation.
Hill- and mountain runners fall into the category of long-distance runners – obviously. There are very few moments where we need the speed and explosiveness of a sprinter. Hence we will use primarily the so called slow-twitch muscle fibers (ST, type I).
Slow-twitch fibers use oxygen, therefore they do rely completely on aerobic energy processes and are relatively fatigue resistant, granted given oxygen supply. Compare this to the other fibre type present in the muscle: the fast-twitch fibers (two types of them: IIa and IIx). These are all about explosives and short bursts of speed. They don’t use oxygen to create that energy and as a consequence fatigue really quickly.
A good analogy of this is when we sprint all out: how long can this be sustained? Not very long. This rapid acceleration can be kept up until the fast-twitch fibres are fatigued. They fatigue rapidly and need a long time to restore energy.
Humans are predisposed as to what type of fibres are predominantly present in their muscles. Hence some are “born sprinters” while others more at home over distance events. Ever heard of the kid who finished last in the school sprint but outruns everyone in the 10k?
There is a caveat: fast-twitch IIx fibres are useless beyond explosive movements of short duration. The other type of fast-twitch fibres, the type IIa, can be viewed as a mixture of both type I and type IIx fiber characteristics.
What it means is these fibres are actually adaptable: on one hand type IIa FT muscle fibers can produce higher, more explosive output than slow-twitch fibers, while still having the ability of using oxygen as their primary energy pathway.
This is where it becomes really interesting for runners: it has been proven that these muscle fibers (IIa) can actually be taught how to act with training over time: either like normal fast-twitch fibres, or taking on slow-twitch fibre characteristics.
This is key for us long-distance runners because we rely entirely on slow-twitch fibres. Therefore we have a vested interest in teaching the body to utilize these adaptable Type IIa fibres in a way that they act more in line with slow twitch fibres. With that in mind we want find a way to train Type IIa fibers to do exactly that: act like fatigue resistant ST fibers in order for them to help powering our muscles = run faster for longer.
The Magic Bullet
This is where critical velocity – or short: CV – training comes into play. This is the specific training stimulus I referred to earlier as the “magic bullet”.
In its essence CV training is a form of interval training with a catch: it’s specifically geared toward recruiting the type IIa muscle fibers for distance running purposes.
Made famous as a term by professional running coach Tom “Tinman” Schwarz (hence the also widely used term “Tinman Pace”), the key concept behind CV is the need for greater speed endurance and running economy, which requires that those adaptable fast twitch fibers become efficient consumers of oxygen (i.e. act like slow-twitch fibres instead of blasting energy in one short spurt), which in turn will increase the all so important “cruising speed” a runner can sustain (= lower fuel consumption, or lower heart rate at faster speeds = run faster for longer).
This concept isn’t totally new, it isn’t rocket science and has been around in one form or another, under different names, in the past. Personally, though, I quite prefer the way Schwarz explains, conceptualises and makes the use of CV in training highly practicable.
Critical velocity is a “comfortably hard” pace runners can sustain for about half an hour. The fundamental idea being: run faster for longer.
In practice this means running intervals (time, distance, rest and repetitions are completely flexible depending on the specific runner) at a pace that Schwarz describes as “somewhat hard” or that one can hold for about half an hour.
This rather lose description lends itself to run these intervals on perceived effort, rather than the need for hitting a specific pace (given human performance can differ week to week, day to day – what feels ‘comfortably hard’ today may feel really tough another week due to life circumstances….) and therefore offers unique flexibility to all levels of runners, plus lends itself to be used on hilly terrain or trails as well.
Nonetheless, the training paces calculator Schwarz provides on his website is highly useful, at the very least as a guide, or on a more measured flat course can provide clarity around pace ranges to target. As an example for a 20min 5k runner, the calculator will provide guidance around all paces (from my experience it’s highly accurate), but most importantly around critical velocity pace:
Regardless of whether one goes by perceived effort or specific pace, the importance is not to run too fast. This is tricky because as runners we often feel we need to train as hard as possible in order to stimulate improvement. A wrong and dangerous assumption.
Make no mistake: CV pace isn’t easy. This not a moderate Z3 effort. This pace is challenging while at the same time allowing for an effort that leaves the runner with a positive experience of being able to complete a strong workout with the tangible feeling of having the ability to do “one more”, if required. It stretches the runner but doesn’t break the runner.
Ignoring this key concept would defy the logic of the workout. CV training shouldn’t leave you dead and buried at the end of training. Yes, it’s fast and challenging but the sort of “enjoyable fast effort”. If you can’t sustain the pace of the “on” interval for the entire workout then you’re running too fast.
Again: this is not all-out stuff. This is controlled, fast, sustainable, fun. Not something you dread of doing the next day. Rather something that can be used consistently, every week, in different forms. Something that offers motivation through progression. Totally flexible, providing an ever new, exciting and varied training stimulus.
In a nutshell: critical velocity training is the idea of engaging all musculature- and motor units for optimal improvement of speed endurance without accumulating too much fatigue and the subsequent need of sacrificing mileage.
Example workouts
As mentioned before, CV training is versatile, completely adaptable to the individual runner and the way one feels on the day or even the terrain encountered – as for us who run hills, training by perceived effort is a much better gauge than attempting to hit a specific pace.
Some of the workouts that I tend to do (I’m far from a professional runner):
- 5x 5min @ CV pace / 2min jog recovery
- 8x 3min @ CV pace / 1.5min jog recovery
- 3x 10min @ CV pace / 2.5min jog recovery
There are plenty of other variations, of course. Also: Tom Schwarz likes to add some faster work after completion of the CV workout. Like a few 200m reps @ mile pace, or short 30sec bursts, for example.
Putting it into practice
How runners can find their CV pace is simple: go by perceived effort. It should be hard, but manageable. Something that can be sustained for about half an hour if on a continues run (alternatively take current 5k pace +5sec to 10sec on top as a rule of thumb ). If one struggles badly to finish the second rep, it’s way too fast. It should feel like a workout, of course, but it should not feel like a “going to war” workout.
Another way is to use the pace calculator on Tom Schwarz’s side, adding the most recent 5k or 10k race/TT time. With a variety of different training paces, the output will provide the prescribed CV pace.
As I’ve mentioned him a few times by now, it’s only fair to let Schwarz explain the concept of critical velocity in his own words and I recommend spending the eight minutes watching this:
Uphill Runner 
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