Train fast, get slower

The correct training pace has been a bit of a crusade for me lately. On the one hand I've been trying to get people to speed up their running, introducing the idea of a tempo run into the Tuesday night runs, but on the other hand I've been trying to persuade folks to slow down their intervals on a Thursday night.

"Slow down? Are you serious?"

Yes!

Most of us in the typical running club are aiming at running distances of 5 miles or more, competing as we do in Cross-Country and road races. The shortest race most of us ever do is a 5k or the wonderful Victory AC 3.65 mile short handicap race. This being the case, there is generally no need to train faster than your 5k race pace. Think about this next time you are blasting round the first of your 400m intervals - do you reckon you could keep going for a few more repetitions without a recovery?

Probably not.

In fact for most of your training year, you'd be better running your intervals at 10k pace and doing a few more of them than perhaps you are accustomed. So do you reckon you could keep going for another 24 of your 400m reps?

I thought not.

Now before I continue let's get one thing straight for those of you who answered yes to those questions, thinking "24 laps chatting away to Jocasta and Henry - no problem". I'm not saying the slower the better. I'm talking about training at the appropriate pace for your aspirations. There may well be some of you who have aspirations of outdipping Christine Ohuruogu to take 400m gold. For you, a 400m rep that leaves you on the verge of depositing the remains of your bacon, lettuce and tomato on the steps of the pavilion, followed by a 20 minute comatose recovery may well be the way forward. For the rest of you it's time to rein in those competitive instincts and look at the bigger, and longer, picture.

But surely, the faster I do my speedwork, the faster I'll be able to run a 10k?

No!

As bizarre as it sounds, doing fast anaerobic speedwork (your 1-mile pace and faster) will make you a slower distance runner.

The message is that you can't be a master of all distances. If you are training at the sort of paces that a middle distance runner runs then you'll become a better middle distance runner, but unless you are very careful you'll become a worse 10k runner.

To understand why this might happen it helps to understand a little about energy systems:

There are 3 main energy systems: Creatine Phosphate (CP), Anaerobic and Aerobic.
The CP system provides fast energy for just short bursts of activity of just a few seconds. This is 100m sprint territory and as distance runners we can pretty much ignore it, so I will!

The anaerobic system is another high activity, high demand system which can provide energy for efforts of up to a couple of minutes. We're still in sprint territory here but longer distances up to 400m, although it is still important at longer distances (but read on...!).

The aerobic system is the major system for distance runners for anything from 800m upwards. It specialises in efficient supply of energy for long periods of time.

Those are the main energy systems. Let's look at the last 2 in more detail, starting with the Anaerobic System.

The Anaerobic System uses a method known as anaerobic glycolysis to supply energy. Molecules of glycogen are broken down, without the need for oxygen - hence 'anaerobic', to produce a molecule called ATP which fuels the muscle contractions. It is a fast energy source, suited to fast speeds, but is inefficient: for every molecule of ATP produced, a molecule of pyruvate is produced. This by-product has to be dealt with, and this is where the Aerobic System comes in.

The Aerobic System takes fuel and efficiently combines it with oxygen to produce more molecules of ATP for fuelling the muscle contractions. This fuel can be in the form of fat (most of us have heard the term fat-burning) or pyruvate. We can therefore see how the anaerobic and aerobic systems work in harmony: the anaerobic system taking glycogen and quickly but inefficiently fuels the muscles, while the aerobic system mops up the pyruvate produced to provide a slower but more efficient energy system. Along side this is the fat burning system, the 'other half' of the aerobic system. While there are limited supplies of glycogen, as marathon runners will attest, the fat burning system can go on and on. Fancy an ultra anyone?

If we consider the aerobic system as actually 2 systems, then with the anaerobic system we can see how the 3 systems work in harmony. At slow speeds we have the fat burning system providing most of the energy, with the aerobic and anaerobic providing only a little. At higher speeds the other half of the aerobic system is more heavily used, and at high speeds it's mostly about the anaerobic system. Personal trainers have made us aware of a 'fat-burning zone' implying that at low speeds you are just burning fat, but the truth is that all 3 mechanisms are in use all of the time but the relative weight of them changes with the speed being run. Even at rest, the anaerobic system is being used to some extent but as the speed increases the balance starts to shift in favour of it. We tend to think of the anaerobic system as being the prime source for sprinters, but this plays down the importance of the aerobic system. In the 400m, only half the energy comes from the anaerobic system, the rest being aerobic. In the 1500m, only 20% of the energy comes from the anaerobic system. By the time we get to 10km less than 5% of the energy is from the anaerobic system.

Most of us have heard of glycogen and are aware of the importance of carbo-loading to ensure the muscles and liver are well stocked with it, and are aware of the importance of it for endurance running and marathons. Many of us might be surprised to find then that it's the anaerobic system and not aerobic system that uses the glycogen. The anaerobic system breaks down the glycogen and produces pyruvate as a by-product which the aerobic system then combines with oxygen. Any pyruvate that doesn't get used in this way breaks down into lactate and hydrogen ions. The lactate has to be disposed of by being shuttled away by the blood. We will often refer to lactate build up causing 'the burn' during sprints, but in fact it's the hydrogen ions which actually cause the burn, producing an acidic environment which is toxic to the muscles, reducing their efficiency. High levels of lactate, and hence hydrogen ions cannot be tolerated for very long.

At rest there is a small amount of lactate in the blood (around 1mmol/l) as the anaerobic system is always there ticking away in the background. We then start a low level of exercise and lactate levels actually drop as the pyruvate is gobbled up by the aerobic system. The pace increases and the anaerobic system is called on a bit more, producing more pyruvate, but the aerobic system uses it all and lactate levels remain under control. At marathon pace, things are still under control although lactate levels have now risen to maybe 2mmol/l as the balance starts to shift. As we get past half marathon pace towards 10k pace the anaerobic system is now being called on more heavily but the aerobic system can still cope - lactate levels are up around 4mmol/l but are not increasing by much and we can sustain this pace for as much as an hour (a pace known as the Lactate Threshold). As the pace increases, the aerobic system is increasingly unable to cope with the amounts of pyruvate output by the anaerobic system and lactate levels rocket. We are now at paces which can only be sustained for a few minutes before we have to stop - we are passing into true anaerobic territory.

A key indicator of distance running capability is the lactate threshold (LT). By training the aerobic system to utilise pyruvate we can run at higher and higher heart rates, at faster speeds, for longer and longer without lactate levels rising. To train the LT you typically run at speeds around the LT - simple!

So what's wrong with sprint training?

Nothing, if you want to be a sprinter.

There's a certain intuitive logic that says that if you want to race at a particular speed then you should train at that speed. Train at sprint speeds to be a sprinter. By training at fast speeds, eg mile pace and upwards, you are training your anaerobic system. You are making your body able to produce more and more anaerobic power, which in turn produces greater quantities of pyruvate. This unfortunately has the effect of swamping your muscles in lactate, as the aerobic system is unable to cope. The result is your lactate threshold actually drops. For every bit of anaerobic training you do, you have to do far far more aerobic training to compensate. When it comes to the likes of Haile Gebrselassie, where he's developed his aerobic system to the best it's humanly possible then the differentiator for him is his ability to open up a killer sprint in the final 100m of a 10000m and pip Paul Tergat to Olympic gold. For the rest of us mortals, why concentrate on the last 1% of a race when we can make the most improvements by concentrating on the other 99%? For 10k training the aerobic system is king.

By doing too much anaerobic style training you are tipping the balance of your energy systems in favour of your anaerobic system and leaving your aerobic system struggling to control the levels of lactate produced. It may sound odd, but for distance running of 10km and upwards, having a weak anaerobic system is actually a virtue. Without the large amounts of lactate, we can run at a high heart rate and high pace for long periods of time without lactate build up. By working on pushing up your Lactate Threshold by regular doses of training around the LT, and by avoiding going into our anaerobic zone, we become better distance runners.

So next time you feel like blasting those 400m reps to leave you a quivering wreck after the first few, think again. Throttle back, keep it at 10k pace, take some fairly short jog recoveries and do a few more repeats than you otherwise would have been able to - you're aerobic system will love you for it.



Refs: Energy system contribution during 400m to 1,500m running, by Matt R. Spencer, Paul B. Gastin and Warren R. Payne. New studies in Athletics, no. 4/1996.