Tempo running is one of the most important training components. It's essentially a fast run but not flat out. The objective is to improve the fastest pace you can sustain throughout a run. I'll explain what tempos are and why we do them.
When you run fast you produce lactic acid and if this builds up exponentially you will start to feel the burn and have to slow down. However, as I'll explain, later lactic acid is not actually a bad thing,* the main culprit is actually hydrogen ions. It's these ions that if not cleared build up and make your muscles more acidic, which then interferes with the muscles nerve endings and causes the problems you experience including jelly legs at the end of a race!
Just prior to the paces at which lactic acid levels rise exponentially there are a series of paces that you can sustain. Lactic acid levels remain relatively steady at these slower paces but then start to rise when you go faster. It's commonly referred to by coaches as your your lactate threshold point although that's not really a great term as it isn't a single point where this occurs. Instead think of a more gradual curve on a graph indicating rises in lactic acid. The graph would have pace along the horizontal axis and lactic acid levels and heart rates on the vertical axis. You can refer to points on the plotted curve of rising lactic acid as inflection points and it's this series of points that we look at when ascertaining heart rates from the lab testing and not one sudden threshold point. We place my tempo pace between two of these inflection points, so it's a pace range and not an exact single pace.
So why do we want to know all this?
When you run, even at slow paces, you are continually producing and clearing lactic acid but when you exceed a certain pace the rate you produce lactic acid exceeds the rate that you can clear it. This is based on the availability of oxygen. As you run faster you need more oxygen and if your oxygen uptake falls behind the demand then you will enter a state where lactic acid increases and eventually it does so exponentially. We observe this happening in the lab and can produce our graph with the inflection points shown. So were are simply trying to find out when your oxygen demand isn't being met by the amount of oxygen being delivered.
However, if you run fairly fast and very close to this lactic acid turn point you can still deliver enough oxygen and therefore run at a maximal possible pace you can sustain constantly throughout the run. This is what we aim to achieve in a threshold or tempo run. We're simply trying to keep our pace at a point where we can still meet the oxygen demand.s
I prefer to use the term tempo run as opposed to threshold run due to the misconception about it being a single point of going from aerobic to anaerobic.
So during out tempo we’re running at the quickest pace to meet the oxygen demand and if we do this repeatedly over a lengthy period of time we will gradually adapt so that this pace improves and we can therefore sustain a faster race pace!**
How do we determine tempo pace?
In brief, I use a physiological test to ascertain the heart rates when the lactate inflection points occur. As I now know what's going on at a given heart rate I can then run my tempos using a heart rate monitor to control effort.
I must admit that I have not had a test like this since 2011 as I thought I would be retiring! I now simply rely on how I feel and I have found that with experience I am able to run at roughly the desired pace. For me it's slightly quicker than the pace I can sustain for a half marathon. This pace is however variable and can even vary slightly day to day!
A good way to run a tempo without expensive physiological testing is to run fast but with a sensation that you feel you could go just a little quicker. So not all out!
You can also work out a tempo pace and use a gps watch to monitor this pace. A good way of doing this approach is to base the tempo pace on the pace you could sustain for an hour in a race. So which of your personal bests is close to an hour? For some it could be their 10k pace, for others it might be 10 miles and for a world class male it might be their half marathon. My tempo is somewhere between my 10 mile and half marathon pb.
However, it's not this simple as I use more than one tempo pace. I'll run a 20 minute tempo at closer to 10 miles pace and 30 minute tempo at closer to half marathon pace.
Scientists will refer to vOBLA which is the velocity at onset of blood lacate accumulation and this roughly corresponds to the pace that you can sustain for an hour. Scientists also refer to VAT which is is the velocity at anaerobic threshold. However it might be the case that your marathon pace or VM is better for running close to VAT. So this would be a slower tempo.
Intermediate and advanced runners -
For those of you who already understand tempo runs then the following explains my approach a little more.
There are many ways to approach tempo running. There isn't really one specific tempo pace and there are also numerous durations you can use for a tempo run. For me it's the duration which determines which pace or heart rates I will use. Longer tempos are slightly slower than shorter ones.
I will sometimes break my tempo run up. For instance, two times ten minutes. I also use tempos mixed with interval sessions and also tempos within a longer run.
My interval sessions are very varied but here is an example: 5x1000m (5k pace) (2 minutes recovery), (4 minutes rest), 20 minutes at tempo pace, (4 minutes rest), 6x400m (3k pace) (35 seconds recovery). With this type of interval sandwiched tempo I am actually running a slower tempo pace so as to not add to lactate levels but I'm doing this whilst I'm actually clearing lactate that accumulated during the 1000m reps. My coach used to use a hand held lactate monitor and we find that lactate levels actually continue to rise in the minutes after the last rep prior to the tempo. Lactate tolerance is something you will encounter and improve during interval sessions and this tempo allows for an element of lactate clearance whilst still running at a reasonable pace rather than during rest. Lactate clearance mostly occurs during prolonged rest.
My long run is normally not at a slow easy pace. They vary between about 90 minutes and 2 1/2 hours in duration. My runs are varied and can be multi paced, such as 30 minutes steady, 30 minutes tempo, 30 minutes steady. Here I am including my tempo within a longer run. You can see this as killing two birds with one stone but it also means you don't start your tempo totally fresh. This is important as it enables you to more closely mimic the later stages of races (although you might not be exactly at race pace). So for instance, if you ran an hour steady and then increased your pace over the next hour you are able to run in a state closer to the physiological state you might be in during a marathon. It's not precise but it's closer than running from fresh.
Sometimes I will also run a progressive or accumulation run where each 15 to 20 minute segment is slightly quicker than the last, until I'm at tempo pace. This means I'm again running a tempo when already tired. You can also run tempos when glycogen levels are partially depleted.
I also tackle my tempos fresh, especially during the summer track season. My coach uses these different approaches for various reasons and during the year as I progress from winer to summer the emphasis shifts.
Tempo running is one of my favourite sessions. I love zipping along a country lane or good quality trail. When I was younger we weren't set tempo runs, back then I used to just go flat out. I still occasionally do this, almost like a race simulation. I also use time trials in this way. It's sometimes nice to just let rip and find your flow. However, with a tempo you feel nippy but you are slightly holding back. If you don't use a heart rate monitor you can just run quick but not totally flat out. Nowadays I run as many of my tempos without a heart rate monitor as with one as I have found with experience you get to know the pace and how it should feel.
*At a slower pace, when the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when running faster oxygen is more limited, the body will then temporarily convert pyruvate into lactate, which allows glucose breakdown. This process allows energy production to continue. You can sustain this type of anaerobic energy production, at high rates, for about one to three minutes, during which time lactate can accumulate to high levels. During events up to about 10k this will occur.
**You will race faster at distances like 10k, half marathon and beyond. The shorter events like 800m are not so reliant on tempo running although it still has a place.
Contrary to the belief of many coaches and runners, lactate or lactic acid buildup is not responsible for the muscle soreness during the days following intense exercise. The production of lactate and other metabolites during very intense running results in the burn! This is the sensation often felt in active muscles especially in the closing stages of a race. The exact metabolites involved in this burn sensation remains a little uncertain.
The burn, as you have no doubt experienced, is a somewhat uncomfortable sensation but it helps to prevent us from overworking our body. It is like a protective mechanism that stops you from severely damaging muscle tissue. It forces a recovery to allow the body to clear lactate and other metabolites. During intervals we do this during the recovery and rest between reps and sets. However, by running a tempo from an elevated lactate level we then clearing lactate but whilst controlling a fairly fast pace that is sustainable.