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June 2001

Non-Coach's Column - (from Paul Briscoe)

A Closer Look At Some "Rules Of Thumb"!

As a biologist, I realised from a very early stage that most biological processes and phenomena cannot be accurately predicted by simple mathematical formulae or models. There are two reasons for this: firstly, most plants and animals display considerable variability, even within a single species - this is especially true of humans; secondly, most biological processes and traits are influenced by many different interrelated factors which cannot easily be separated out and considered in isolation. A very simple example of this from running is the relationship between height and ideal running weight in male athletes. Looking at the average for the population as a whole, ideal weight in pounds is about twice the height in inches - i.e. around 140lbs for a runner of 70’’. The problem is that weight is also influenced by other factors such as build, bone density/thickness and leg length etc. etc.. Therefore, using the simple formula of multiplying height by 2 is not reliable when applied to an individual unless that individual is close to the average for all of the factors which affect the height/weight relationship.

So what point am I trying to make? Well, articles in the athletics press often quote what I shall call "rules of thumb", apparently based on science, to be applied when planning training, diet etc.. All too frequently, these are misguided because they either cannot be reliably applied to all individuals (e.g. the height/weight ratio above) or are incorrect because they fail to take account of all the variables. I now intend to take a more detailed look at some instances where I believe authors have extrapolated a little too far in the name of science!

One commonly stated piece of advice in running magazines is that you should run slowly to burn off fat. If you’ve read my previous ramblings you will know that recent research has shown this to be nonsense - whilst you do burn more fat per mile during a slow run, you actually burn off more fat overall by running faster because of the enormous effect of vigorous exercise on the body’s metabolism. I now want to look at this from a different angle. In fact, fat and carbohydrate metabolism are closely related and any excess food you eat over and above what you need, whether it be carbohydrate, fat or protein, is ultimately converted to fat. Conversely, if your energy requirements exceed what you eat, there will be a net loss of fat. Therefore, the total energy balance may be far more important than the proportion of fat burned during exercise in determining weight loss - regardless of what speed you run, you will only lose weight if your total energy expenditure is greater than your intake in food. So it is the training regime which burns up the most energy overall which will give you the best chance of losing weight - i.e. running faster and more often, primarily because of the extra "kick" given to the metabolism. So just how much energy can the metabolism account for? An "average" sedentary person burns up around 1400kcals/day to maintain their metabolism and say 600kcals/day on walking/working etc. - a total energy requirement of at most 2000kcals/day. In the mid 1990’s when training for the 3 Peaks, I regularly consumed 5,000kcals/day (my Hot X Bun Diet - as featured on BBC Radio 2) and still lost weight! As only around 1200kcals of this was used in running 12 miles/day - this means that my metabolism may have accounted for up to 3200kcals/day - i.e. an extra 1800kcals!! This simple balance, whilst not precise, certainly suggests that the boost to the metabolism can easily account for as much energy as the running itself. You are most likely to lose weight during periods of increased training (and hence increased energy expenditure) and your weight will stabilise once your appetite grows to compensate. Another point worth noting is that as you get older, your metabolism slows down. This is possibly why Max had to cut out a meal in order to lose weight, whilst younger runners eat more as they increase their training and still lose weight. I have already found that I don’t need to eat quite as much as I did 5 years ago - damn!!!

Heart Rate Monitors (HRM’s) feature regularly in the athletics press these days. Most articles instruct you to determine your maximum heart rate and then train at between 70 and 85% of this figure - your "aerobic range". Whilst this is fine for those simply trying to keep fit, I have always had my doubts about it for serious runners because it sounds too prescriptive. I therefore spoke to Sarah Rowell, who is a recognised authority on the subject; Sarah only confirmed my worst fears! The 85% figure is supposed to signify the aerobic (lactate) threshold, above which you go into oxygen debt, but whilst 85% might be the average figure for the population as a whole, the true threshold may vary from one individual to another. Regular vigorous exercise increases the aerobic threshold and the true threshold for endurance athletes commonly reaches 90% or more of maximum heart rate - when she’s fit, Sarah’s own threshold is nearer 95%!! Therefore, if you use an HRM as suggested by most articles I have seen, you are unlikely to be training as hard as you should! I have always preferred the old-fashioned method of using the way I "feel" to determine what effort to put in and I only use my HRM as a reference tool. It is certainly possible to use an HRM successfully, but you clearly shouldn’t rely on percentages when calculating your aerobic range.

A more contentious issue is that of age-graded tables for racing. There is no doubt that we all slow down as we get older. It is therefore perfectly sensible to have different age categories/prizes in races and age-graded records to give older runners an added incentive. My reservations relate to the use of age-graded tables to compare race performances across different age groups - e.g. comparing a 2½ hour marathon by a 30 year old with a 3 ½ hour marathon by a 60 year old. My instincts tell me that such a comparison is unlikely to be reliable due to all of the variables involved and the assumptions made in putting together the tables. Firstly, age does not affect us all in the same way - due to differences in physiology, physique or even environmental factors, each individual will reach their peak at a particular event at a different age and will then exhibit a different rate of deterioration over the years. This means that using the tables to compare performances of an individual across the years is not very reliable. The second problem with age-graded tables is that the "sample size" is far greater for younger ages - for 20-40 year olds there are plenty of world-class athletes coming fairly close to world record times (say within 5%), indicating that these records really do come close to the limit of human endeavour. However, at 50 years plus, there are far fewer runners competing seriously and there are rarely more than a handful of runners coming close to the records. Statistically, off such a small sample size, this means there is a high probability that world records for older age-groups are not truly representative of what can be achieved! I strongly suspect that, over the years, world record times for older age-groups will continue to fall relative to those for younger runners.

It has long been believed that athletic performance deteriorates with age at the rate of about 1% per year. However, sports scientists are now apparently starting to rethink - some of this 1% may actually be due to "lifestyle" changes as we get older and it appears that athletes who are able to keep training intensively exhibit a more gradual fall-off in performance. Traditionally, most of the top runners from previous generations gave up serious training as they got older and became involved in coaching or administration. Even nowadays, our priorities do change as we get older and most of the veteran runners I know don’t train anything like as hard as they used to. In some cases this may be partly due to injury problems, but much of it is because there is less incentive to train hard - your times are slower, the rewards fewer and it is also more difficult to keep your weight down! Most younger elite athletes are sponsored and prize money can be significant. This is not the case for older runners, so you certainly need to be very determined to train right up to your limit - all the more difficult bearing in mind the lifestyle changes. One final related point is that most of the runners setting age-graded world records in the older categories have only entered the sport since the early 1980’s and have therefore not been running all their lives. It may well be that when some of the current crop of younger elite athletes get older, having highly conditioned bodies all of their adult lives will allow them to take huge chunks off age-graded records - although, of course, they could be completely crippled!!

If you’ve found all this heavy going, I’m sorry, but there is certainly plenty of food for thought and I hope I’ve done enough to convince you that you shouldn’t always take everything which claims to be backed up by science as gospel!