It's not all about slow running

I got a pleasant surprise at Lordshill. Finding that the policewoman conducting me across the road shouting "Go Susie" was actually my training buddy, was pleasant enough, but that wasn't it. Finding I had a sprint finish in me after 10 hard hilly miles, run at an alarmingly high heart rate, was the surprise, and quite significant in what it implies.

I had a surprise in the Cardiff Marathon along the same lines. My pace held up for the whole race. After 26 miles I felt fresh, and was able to sprint round the Millennium Stadium like a mad thing.

These 2 events could be dismissed as 'superior endurance brought on by high mileage training', but there is far more to it than that. I think for the first time since starting my methodical base training, I am seeing evidence that my Lactate Threshold is going up.

OK, here comes the science: Lactate Threshold (LT) is a point on the lactate vs heart rate curve, defined by a specific level of blood lactate (4 mmol/litre I believe). This is of course largely meaningless to the majority of us who don't have access to a laboratory. What it means in reality is it's the point above which you will start accumulating lactate rapidly, get 'the burn', and start to run out of steam quickly. In terms of measuring it, it's generally taken to be the maximum average heart rate you can sustain for an hour of racing. (We'll come back to this point later)

LT is an important notion when it comes to training. For me, it's easier to measure than maximum heart rate - just go out and race. I think it is more relevant to one's training than maximum heart rate. Quoting training paces as %s of maximum heart rate is as much a generalisation as the formulae used to estimate maximum heart rate. It's all very well saying that marathon pace heart rate is 80% of max, and training to that, but in the case of a well trained athlete, marathon pace could be much higher (I believe as high as 90%). The difference is the higher LT of the well trained runner. Training at a level relative to your LT gives a pace far more relevant to the individual and their current state of fitness.

This is all very well but what does the LT mean and why is it so important?

At this stage, I'll issue the usual caveats of me not being a sports scientist, and not being a qualified coach. I'm an enthusiastic amateur. Got that? Good!

Us base trainers bang out loads of slow miles. It gets results! We see our pace improving month by month. We run slowly. We run aerobically. We are developing aerobic capacity. Right?

Well no. Not as I see it.

You'll often hear me say "It's not all about slow running". Slow running certainly has an effect. With plenty of slow running, pace at a given heart rate will improve, but for me this is all about running economy, not about aerobic capacity (although we may be talking semantics here!). For a given heart rate, ignoring possible improvements in the stroke volume of the heart, you are using the same amount of oxygen and hence burning the same amount of fuel as the slightly less fitter you of a few months back. If you are now able to run faster, then it is simply that running at a given speed isn't using so much power as it used to: your running economy is improving. To me, aerobic capacity is something more than this: it is all about the ability of the slow-twitch muscle fibres to burn lactate, and consume oxygen. I'll explain.

We all know that we have fast-twitch and slow-twitch fibres; well you probably do if you’ve found your way to this article. We may all know that fast-twitch fibres produce lactate as a by product of their function. What we might not know is that slow-twitch fibres can use lactate as a fuel, burning it aerobically to power us along. As we run, there is a balance between fast- and slow-twitch, with the slow-twitch gobbling up all the lactate produced by the fast-twitch fibres. As we increase our speed though, the balance starts to shift in favour of the fast-twitch fibres (our anaerobic system), with the slow-twitch fibres (our aerobic system) overwhelmed and unable to mop up all the lactate. Lactate levels rise, and rise ever more sharply as speed increases.

I see aerobic capacity as the ability to mop up lactate. The higher your aerobic capacity, the higher the heart rate you are able to run at without accumulating lactate. In other words the higher your lactate threshold.

So now we see another way to improve our performance. If you can train in a way to raise your LT, then you will be able to race at higher heart rates. We have a double whammy speed improvement: not only is all the aerobic running making us faster for a given heart rate, we can then sustain a higher heart rate and hence go faster still.

You’ll certainly get an improvement in running economy from slow running. It is just possible you may see an improvement in LT from slow running, but far less likely. To see improvements in LT you need to train nearer to your LT, ie faster. You need to run at paces where you are creating lactate, and forcing the aerobic system to work to burn off the lactate. With just slow running there’s not sufficient lactate to provide this type of training stimulus, hence: “It’s not all about slow running”.

The classic way to improve LT is to do Tempo Runs. These are runs where you run the middle few miles at a pace near to your LT. There is a difference in opinion though as to what the best pace is. I’ve been following the Hadd method, where you always run below your LT, keeping it strictly aerobic. Within the framework of the Hadd principles of daily running, the idea of pushing up the LT from below makes sense: the softly softly approach. Other methods have you running much faster, pulling up the LT from above. This may be more ‘optimal’, but you need to ensure this is compatible with the rest of your regime: these runs can be quite tough!

An indicator Hadd uses of improvements in LT, is the ability to sustain a pace and heart rate for an hour. Once you can do your steady runs at a solid pace without any cardiac drift, then it’s time to move your training HRs up a notch: an indication that your LT has risen. Trouble is, during the summer, with the heat, and my love of off-road running, I haven’t had a chance to verify my lack of cardiac drift (although my pace at my steady HR has noticeably improved). Hadd also uses his ‘Hadd test’ to estimate LT. Unfortunately, I’ve not been doing too many of these either, largely for the same reasons. As I race fairly regularly though, I have been trying to get in indication of LT from my races.

I've tended to race according to heart rate. This is not a bad way of doing it if you know what heart rates you need to run at. My marathon HR tends to average out at 145bpm over the whole race. 142bpm seems a sensible level to start out at: my 'marathon pace'. At London earlier in the year, I went off at nearer 145bpm and paid for it at the end - I faded markedly. At Cardiff I made sure I stuck to 142bpm - I breezed in.

I have been using heart rate to train by, according to the Hadd principles. I do regular steady runs, marathon pace, around 140bpm+. As my training has progressed, my pace at this heart rate has got faster and faster, from 8:50 18 months ago, to 8:20 6 months ago, and now around 8:00. The training has been going well and these improvements are great. I also do tempo runs and long intervals at 145bpm+. Finally I think I am seeing, from racing, that my LT is improving and I should be racing and training at higher HRs.

My LT at the start of the year was no higher than 154bpm. This was what I averaged for the well paced all-out Stubbington 10k. My ability to carry a pace for an hour would mean my LT is a beat or 2 below 154bpm. Here’s a way of estimating it: the Runner's World race pace calculator has me running 12.16km in 1 hour dead, based on my Stubbington time. 12.16km/h is 7:56/mile. My 10k pace was 7:46. My current pace vs HR relationship is 40secs/mile for every 10bpm increase, so a 10 second drop in pace is just over 2bpm. Hence My LT was probably 152bpm. OK?

Racing faster than this always seems a bit scary, so I was quite alarmed at Lordshill to find my heart rate up at these levels. How could I sustain that for 10 miles? I have to confess I held back a little! Even so, my average heart rate for the race was 154bpm. I was running for well over an hour though (1:19:55), so let’s try to predict my LT pace again. The Runner’s World calculator predicts I would run 12.28km in 1 hour dead given that 10 mile result – faster than Stubbington, despite the hilly course – a clear improvement over the course of the year. My 10-mile pace is 8:00/mile and my ‘LT pace’ is 7:52. A pace improvement of 8 seconds is a rise in HR of 2bpm. My LT estimate is thus 156bpm, a 4bpm rise over the course of the year.

Thing is, these estimates/predictions are a bit self-fulfilling. Knowing what I believe my LT to be, or indeed my marathon HR at some 10bpm lower, I tend to race at those HRs. The result is I felt I could have gone faster at Cardiff. I held back at the start to try to keep my HR down to 142bm (152-10). Likewise at Lordshill, when I saw my HR shoot past 154bpm, I held back, fearing I would blow up in the hilly final stages.

So the plan for tomorrow’s flat and fast Hayling 10, is to go out at a speed closer to what I used to consider my 10k pace and try to hold it together for the full 10 miles. If I’m right that my LT is now higher, and in fact higher than even the 156bpm predicted from my Lordshill result, then I should be able to do this. It will feel very fast, but I’m going to try to sustain a pace of 7:30/mile, to bring me in nearly 5 minutes faster than Lordshill. Do or die!

I’ll let you know how I get on. It’s going to be a cold one!