In the last post I talked briefly about going anaerobic. The word anaerobic means to be without air and, at its simplest, it’s when the body cannot get enough oxygen for the work being done. More accurately, anaerobic metabolism occurs independently of oxygen – the distinction being there can be oxygen present but for whatever reason it’s not being used. I’ve experienced this on occasions when my heart-rate has been lower than 130 bpm but I can feel the signs of working anaerobically. If I were training by my heart-rate monitor I’d shoot on past this and for many years I never realised it was holding back my running.
Going anaerobic is quite normal. As I said in the last post we do it the moment we begin an exercise as simple as getting up off the sofa. The problem with going anaerobic is that we can only handle a limited amount of it. While that’s not an issue for daily tasks like going upstairs, it quite often turns out to be the limiter for runners exerting themselves for significant periods of time.
Going anaerobic produces all sorts of by-products that feel uncomfortable, as well as using up fuel stores much quicker than aerobic metabolism. While fuel isn’t an issue in shorter races, some of the by-products are. For example, carbon-dioxide is a by-product which results in you breathing heavier. The faster you run, the quicker by-products build up which is why you get out of breath very quickly when you sprint.
Not all by-products are bad. One which you may have heard of is lactate, also incorrectly referred to as “lactic acid”. Historically because it’s easy to measure it was originally thought to be the root of all the problems and most people still associate it with bad things e.g. runners saying “my legs were full of lactic acid”. So while it’s technically wrong to say it causes bad things, the real world uses it in this sense because it’s become the norm and coaches use it because it correlates to the waste products which are bad. I’m not going to buck the trend!
Three ways your body handles going anaerobic
Lactate Clearance – any time lactate is being produced, the body shuttles it out of the muscles to other areas of the body where it can be broken down or used as fuel. This is done by monocarboxylate transporters (MCTs). While you don’t need to remember the name of these, it is worth understanding the body can only build a finite number of them. This means only a certain amount of lactate can be cleared. Typically this is an hour’s worth while running at Threshold. In fact it’s the other way around in reality, your Threshold is defined by the MCTs. When you’re doing a run of less than an hour, you can run proportionately faster than your Threshold.
When the level of lactate production is equal to the level of lactate clearance, the body is referred to as being in a Steady State. The lactate neither increases nor decreases. Most people train here because the steady state doesn’t feel bad. It’s a combination of aerobic and anaerobic energy.
Lactate Tolerance – if the rate of lactate production exceeds the rate at which it can be cleared out then all the body can do is tolerate it by buffering the acids. Just as there is a limit to how many MCTs can be built, there is a limit to how much lactate tolerance can be built through training.
Slowing down – the third way the body responds to a build-up of lactate is the one most of us have experienced – it slows us down.
If we go out very fast, we use up lactate tolerance quickly and can then only run in a steady state at best. When the anaerobic energy production or MCTs run out, all we have left is aerobic energy to fuel us and drop down to the aerobic level. This is something most have experienced in half and full marathons.
The slow down can be voluntarily reset at any time by dropping back to aerobic mechanism. After a period of this, the lactate has cleared out and we’re able to pick up the speed again. Most runners unconsciously know this as they push themselves to the point of getting out of breath, slow down and then later find the energy to give it another effort.
Implications for training
Anaerobic training, such as speedwork and intervals, has its benefits but they are limited, less than 10% of your parkrun is anaerobic ! There is only so much clearance and tolerance that can be built by the body. Spending your time training anaerobically only provides so much benefit. All those rest periods keep resetting the anaerobic systems.
These limitations don’t change for the best runners, they are just as limited in the anaerobic department as the rest of us. The difference is they have better aerobic systems. Quite often they have a naturally large aerobic system but they’ve also improved it through training and that’s where all of us should be spending the majority of our training time.
This is best encapsulated in a picture from Keith Livingstone’s Healthy Intelligent Training book. The Anaerobic contribution is the same in both but, the bigger the aerobic contribution, the more that can be achieved i.e. running faster.