On my Twitter feed recently, I mentioned my efforts to get down to my training weight & had a question from Mark (@SPARKSIE10).

He asked, “Hey Will, how have you determined your optimum weight? Experience? What’s your target body composition?

I thought this would be a good one to answer as a blog post, because a 140 character tweet will never explain my approach adequately.

Over the years I have used a number of ways to work out what is best for me when I’m racing. And consequently I have also figured what works best when I’m training.

The key ways I’ve used to figure this out are my experience & Stillman height / weight tables.

First of all, my experience…

When I started competing in the early 90’s, I weighed a very meagre 63kg. Yes, I did look almost like a “famine victim”, but I could run 10km in the mid 32-minute range. The problem was that I was a bit poor on the bike if I’m honest – how much power could I realistically expect to produce with so little muscle-mass.

After about a year in the UK in 1996 -with a lot of cycling & weight training – I found that I had gained 8kg, mostly muscle-mass. I was still very lean. And it was at 71kg that among other good races, I did my Ironman PB.

So based on my experience, I reckon that a good race weight for me is around 71kg.

Now the height / weight tables…

A few years ago, looking for some sort of validation of my experience, I came across the very commonly used Stillman tables. These are actually used to calculate a healthy height & weight for the average sedentary person, but with a little manipulation, you can get a good idea of what is reasonable.

The basic calculation for men is an allowance of 110lbs for the first 5ft in height and an additional 5.5lbs per extra inch. Based on this, a healthy weight for an average person of my height is 77.5kg (170.5lbs). But this is for an average sedentary person. Elite marathoners would expect to be 15% lighter (65.8kg), but at this weight, I’d expect to be way down on cycling power. I felt that perhaps halfway would be a reasonable figure, giving a race weight of 71.6kg. This should allow me to run a good Ironman marathon without sacrificing my bike split.

[The basic calculation for women allows 100lbs for the first 5ft and 5lbs per extra inch.]

One more calculation I could consider here is my BMI. A BMI below 22 seems to be generally accepted as a good mark for an endurance athlete. This would require a maximum race weight of 71.3kg.

Clearly a race weight is something I wouldn’t want to hold for too long. Among other things, I look extremely thin, too thin if you were to ask my wife! From experience, I aim to train at 2.5kg more. This lets me hold a little more body fat during my training.

But weight in & of itself is not the whole story. One also has to factor in body composition. Based on figures for elite marathoners, cyclists etc, it’s not unreasonable to race at between 5 & 10 % body fat, but much below 10% is likely to be risky for an endurance athlete to maintain for too long a period. Certainly I find that at those sorts of numbers for prolonged periods, I’m both very hungry all the time & susceptible to upper respiratory infection. There are also potential hormonal issues involved at very low body fat levels. And I feel cold really easily. After all, I do live in England!

Once you achieve your desired body fat levels, you have to ask yourself seriously whether it’s worth shifting muscle mass in order to make your target race weight.

As you’ll see from all of the above, there’s a high degree of “feel” in this approach. Each person will differ slightly, if not a fair bit from these numbers. The main thing to keep in mind is that simply being lighter may not actually be the best way to go faster.