The McMillan calculator is always a good place to start:
http://www.mcmillanrunning.com/mcmillanrunningcalculator.htm
Enter a time for a recent race and you'll get a prediction of your marathon pace/time:
Here are some example paces/times based on 10k times:
| 10k time | mara pace | mara time |
|---|---|---|
| 36:00 | 6:27/mile | 2:49 |
| 40:00 | 7:10/mile | 3:08 |
| 44:00 | 7:53/mile | 3:27 |
| 48:00 | 8:36/mile | 3:46 |
| 52:00 | 9:19/mile | 4:04 |
| 56:00 | 10:02/mile | 4:23 |
Of course there is a catch with the above times. The predicted marathon times assume that you have trained adequately for the marathon. This means having done lots of long runs so that your endurance is well trained. For most people, particularly those attempting their first marathon, they won't have done anything like the mileage of long runs to enable them to maintain that pace right to the finish. In practise I'd say it is unrealistic to expect to get within 10-15 minutes of the predicted time for your first marathon. In other words, you'd be wise to add on an extra 30secs/mile. Of course, if you are prepared to do at least 3 20-mile runs, preferably 5, then good luck to you. However, if this is your first marathon, then you might not have the background of mileage to be able to do that amount of training without injury. Life is a compromise - accept your limitations and set yourself a more realistic goal. If you are following a 'get you round' schedule which culminates in just 1 20-mile run 3 weeks before the marathon then you should probably add a minute onto the predicted marathon pace. Pace prediction really is a black art, but don't set unrealistic goals if you are not prepared to put in the mileage.
Many of you will no doubt be following schedules with titles such as 'sub 3:45'. I'm not a fan of this style of schedule as it too can set unrealistic expectations that simply following the schedule will guarantee a target time. Firstly, unless you can run a 48:00 10k, don't expect to be able to run a 3:45 marathon. Secondly, the sort of schedule needed by a middle-aged woman to get 3:45 is very different to that of a young man. 3:45 for a young healthy man is quite a soft target, whereas for an older woman it is much tougher: in fact 3:45 is the London 'Good For Age' qualifying standard. Don't expect to achieve 3:45 following a 3:45 schedule if you're anything other than slim young and male, even if you can run a 48 min 10k. Harsh but fair I think.
Those quoted marathon paces above are still useful though, even if it is unrealistic to be able to run 26.2 miles of that pace. A regular weekly run at that pace will help develop your aerobic capacity. Just be careful you don't become a one-pace runner always running at around that pace. You should do regular sessions of faster running, such as a tempo run or interval session, and the bulk of your running should be much slower, at least 30s preferably 1 minute/mile slower in fact.
I was careful to talk of marathon 'effort' in the previous article, rather than pace, and a great way to measure effort is heart rate. HR pacing for me is by far the best strategy as it takes physiological and ambient conditions into account. It has its detractors though. Some say it is too limiting and they prefer to run on feel. I certainly admire those who can run an entire marathon on feel, but I know several cases of crash and burn where the perception of what pace felt right was somewhat wide of the mark. HR monitoring is an extra piece of information you can use to shape your strategy on the day. It's a very personal thing though and getting your own personal level right is essential. I loath using formulae as everyone is different and the quoted formulae can give errors of +/-10bpm on max HR. MaxHR is a fairly well defined concept, despite inaccuracies in formulae, but then trying to predict marathon pace HR from maxHR on assumptions about someone's lactate threshold is fraught with difficulty. I think I have the answer though.
This is my personal method for determining marathon HR. I've not seen this written anywhere, but it works for me and for the, admittedly limited number of, people whose HR data I've seen. If anyone has further data they can add to support this, then please let me know:
Go out and run a flat fast 10k race. Make sure you're fairly fresh, run it well, even paced, and take your kilometre splits and average HRs. If you've run it well then your HR will not drop towards the end of the race - this just ensures that you have paced it well and given your best. The pace isn't critical and having a pancake flat course isn't that critical either; just avoid big hills as the downhill bits tend to make your HR drop as it's difficult to keep pushing at maximum effort down a big hill. The point here is we are trying to find what your best HR for a 10k is.
If you have run a good 10k race, take the average HR for the race, subtract 10bpm and that is your marathon HR.
The above naturally factors in a number of variables. If your lactate threshold (LT) isn't particularly well developed then your marathon HR will be correspondingly lower. Some elites can run marathons at a ridiculously high percentage of maxHR, but of course their 10k pace is even higher: well above threshold. Slower runners are unable to push hard for the duration of a 10k, running at a much lower level compared to LT, so their marathon pace is proportionally lower.
For most people, 10bpm corresponds to about a 40s/mile drop in pace, which is in line with the slowing down formula used in the McMillan pace tables, and often quoted as 'Horwill's Law' after coach Frank Horwill who uses the rule that pace drops by 4s per 400m lap every time the distance doubles - a drop of 16s/mile for every doubling. (See this month's Running Fitness magazine). I personally think it's nearer 5s per 400m lap for slower runners and nearer 3s per lap for elites - you can never entirely generalise these things across elites, club runners and beginners.
You have to know how to use your marathon HR, as your HR will not be constant for the full marathon distance. You need to start the marathon nice and relaxed and let your HR gradually rise over the first 2 miles to eventually hit your marathon HR. If you find you've hit your HR after the first few hundred metres then you've gone off too quickly - slow down! You should then be able to maintain this level until after half way, maybe up to 16 miles. At this point your aim should be to maintain your pace as your HR naturally starts to rise. By now you may find yourself slowing, which is almost inevitable in a marathon, but try to at least maintain your HR if not your pace. If you've paced correctly you should be able to let your HR rise by maybe 1bpm every mile until by the end of the marathon it is at the sort of levels you see in a 10k. If you can do this then you've paced well.
People assume that as you hit the wall your HR rockets, but in fact the opposite is true. Your HR is simply a reflection of your bodies demand for oxygen. If you slow down then regardless of how hard you think you are pushing then your HR falls. Other factors such as heat and dehydration can affect your HR of course, but if you run out of fuel to burn, your heart doesn't need to pump oxygen to your muscles.
Of course, going into a marathon armed only with a HR level and the assurance that Susie says this is the HR you need to run at, wouldn't fill me with a huge amount of confidence. There is a test we can do to verify this HR though. In a marathon we are effectively running at a steady state where lactate levels are static. Any increase in lactate means we will be unable to sustain the pace. Increasing lactate will mean an increase in HR - see my article on cardiac drift. We can use cardiac drift, or rather its absence, to verify that we have the right marathon HR:
Go to a track, or find yourself a nice flat sheltered street loop. I have one near home that is exactly 1.5 miles, although knowing the distance isn't absolutely critical unless you also want to verify your marathon pace. A track is ideal but we don't all have a track local to us. Choose a nice cool windless evening or at least try to ensure you're not going to be getting significantly hotter as you run, which will push up your HR. Winter evenings training for London are perfect. Set off as if you are starting your marathon and aim to hit your marathon HR after a good warm up of 2 miles. Now maintain your pace, noting your lap times, and trying to keep your laps very even. If you can keep going for 8 miles, maybe 10, without any increase in your HR, then you are running at or below your marathon HR.
I've blogged some of these tests in the past: 1, 2, 3. I shall be trying one in the next few weeks. They are actually very good training runs. 8 or 10 miles of marathon pace is quite a tough workout, and excellent marathon preparation. Your lap times also give you a very good fitness indicator and a good prediction of marathon time. As your training progresses you should hopefully see your pace improve. I like these tests - you are verifying your fitness and pace, and yet you are not compromising your training - you'll actually improve as a result of doing the test.
I'll report back on one of these pace tests next week as I'm planning on doing a 10 mile marathon pace run midweek before the national XC champs, in place of the Tuesday and Thursday speedwork. I'll aim for 7:15/mile and hope that my heart rate sits at 145bpm or less for much of the run. If I can manage that then I'll be happy that I'm on target for my 3:15 London Marathon. I'll try not to panic if I don't quite make it, as there are 8 weeks left, but I was running at 7:00/mile last night at my threshold of 150bpm, so it's looking promising.
Have fun training!
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