Kamis, 18 November 2010
In the Zone
A lot of people run with a pulse monitor but I'm not sure that everyone is necessarily using it correctly: I certainly wasn't. For me it served as a compensation if a competition or a training session hadn't gone as well as I had planned: at least I had hard evidence that I had tried my best. I'm not sure exactly how I got past this masochistic phase but I think that getting into triathlon has helped. The great thing about triathlon is that every race course is different (sometimes the transition zone alone can add kilometers to the distance) and even the same course from one year to the next can be a very different kettle of fish (current, wind conditions, etc). So, in the same year that I have changed my goals from beating my best time - which no longer makes sense - I have also done just that, and had personal bests in 10k and the half-Marathon... "Go figure" as our American friends would say.
A simplified view is that the human body is powered by 3 main energy systems and, when they run out, it has a 4th "backup" energy system which isn't nearly as effective but is practically unlimited: this is fat oxidation (literally "fat burning") and is what you rely on almost exclusively when you hit the wall (or "bonk" in cycling parlance) and run out of carbohydrate stores in the Marathon. The first system is the catchily-named ATP-PC system or Adenosine Tri >PO3 Creatine Phosphate system if you want to sound impressive. It is able to deliver tremendous power but only for periods of about 10 seconds and is very slow to regenerate. The second system is the Anaerobic system which, as its name suggests, doesn't use oxygen to generate energy; the third system is the Aerobic system which does use oxygen. Both of these systems operate in parallel and use glucose (sugar or carbohydrates) stored as glycogen in the muscles. However, the Anaerobic system generates lactic acid as a by-product and the build up of acidity causes fatigue in the muscles. If you do an activity and increase the intensity with which you do it, there comes a point when you are mainly relying on your Anaerobic system. Everybody has a different tolerance to lactate acid build up but it gets us all in the end. Sports physicians like to measure the point (usually in terms of heart rate) where your body starts to rely primarily on the Anaerobic system (AT or Anaerobic Threshold). There is a lower threshold - the Aerobic threshold (AeT) - below which your body is relying almost entirely on the Aerobic system. Somewhere above this, is a point called the MLSS (Maximal Lactate Steady State) threshold above which lactate acid accumulates in the blood, which is really useful for Marathon runners: it is theoretically the intensity at which you sh/could run a Marathon, supposing that you are efficient enough not to use up all your glycogen before you get to the finish line. The only bugger is that nobody has yet devised a way to measure it that doesn't involve running round a track and pricking your finger to measure the lactate level.
That was the simplified view, haha. To be honest, I have found so many conflicting definitions, especially concerning lactate thresholds and their relationship to the Aerobic and Anaerobic Thresholds, that I just content myself to be know that there are two main thresholds - an upper and a lower, both of which are highly individual and movable with the right training.
If you are still reading, then this is the good bit. Once you have established these thresholds, the theory is that you should do the vast bulk of your training for a long distance event at less than the AeT - which is kind of good news because, in my case, its a pretty easy pace. The idea is that, by consistently training at below the AeT, you are working your Aerobic system and it will adapt more effectively to the demands you put upon it. In particular, it will encourage the body to derive more energy from fat oxidation and help save those precious glycogen stores for later. The bad news is that almost all the rest of the training should be at above the AT, which is damn hard. This training is supposed to increase your AT (what good is that, I hear you ask, it just means I'll have to train even harder!) and increase your lactate tolerance. This is typically the goal of the dreaded "series" where you run very fast for a few minutes say, have a break of 30 seconds or so, and then do it again... and again... The interesting thing is that very little, if any, training is recommended in between the two intensities. Anyway, those are the training sessions I most hate because they are neither light enough to be able to tolerate for a long time, nor are they short enough to be able to put up with easily. However, that is the intensity that you typically run anything from a half-Marathon to a Marathon.
By the way, if you are serious about training, it really is worth getting your thresholds measured properly with a VO2 Max or Lactate Threshold test. There are loads of short cuts around to estimate these thresholds but I think that most of them are quite dubious. The famous formula for your maximum heart rate as a function of age is a good example: it might work on average, but two identically aged people could easily have maximum heart rates differing by 30bpm. Also, the whole point is that training can move the thresholds so you should get them measured regularly.
In trying to keep my heart rate below my AeT I have found it hard to factor in the fact that your heart rate drifts slowly upwards as you run. This is due to the energetic cost of evacuating the heat from your muscles: the drift is very sensitive to the ambient temperature. This means that you should be going ever slower as you run which seems to contradict the perceived wisdom of doing a run where you finish faster than you started. Some people say that you should set the thresholds at a certain pace rather than a particular heart rate; nevertheless, the energetic cost of the heat evacuation is a real cost whether you like it or not. Its taken me a while to accept, but I am really feeling the benefits, in particular I seem to be able to run faster and longer at my AeT. I hope that I notice the difference in the Marathon!