In my last article on the benefits of different courses for different size “horses,” I illustrated how different course types may play out for two morphologically very different athletes — a smaller thoroughbred and a large, powerful, draft horse.

However, as my buddy Alex pointed out, I didn’t really give a good indication of how to go about determining which stable you belong in. In other words, are you a thoroughbred or a draft horse?

Now, don’t be too hasty in judging which group you would prefer to belong to. As I suggested in the last article, for a good portion of an ironman race, you’ll be towing a cart (i.e. your bike) around on the flat. Advantage draft horse!

Anyhow, it doesn’t matter too much what you would prefer to be. As Popeye correctly observed, you is what you is. While I am not even close to falling in line with the pessimistic determinists that abound in ex phys — choose your parents wisely, etc., etc. — I must concede that when it comes to your frame (that is, your bone and organ mass) it is a pretty fixed quantity. It is no use aspiring to be Paul Tergat if your bone structure more closely resembles Shaquille O’Neal.

Furthermore, if Shaq had have decided that he wanted to look like Tergat, I would suggest that his mile time would be far worse than what it would be if he were to head out the door right now and run a mile. Fundamentally, you must have sufficient muscle to move your frame. Or, in automotive terms, you must have the right sized engine for your chassis.

The first step in determining what size engine you require is determining the size and weight of your chassis (your bone and visceral mass). The best way to do this is to get a DEXA scan — a three dimensional scan of your body that assesses bone, muscle and fat weight. However, in lieu of this, we can come up with a good estimate of your “frame weight” by getting a broad sense of the length, breadth and girth of your skeleton. By comparing anthropometric (body measurements) and DEXA data I’ve found a good relationship between general skeletal dimension (height x width x breadth) and actual “chassis mass.” This relationship is expressed in the chart to the right.

To find where you fall, plug your own measurements into the following formula:
H x ((BAD+BCD)/2) x ((HB+FB)/2)
Where:

• H = height in cm
• BAD = biacromial diameter: shoulder breadth between the 2 acromion processes (bumpy bit on the back top of your shoulder joint)
• BCD =bicristal diameter: hip width between the 2 iliac crests (the most lateral top aspect of the pelvic bone) For best measurement get someone to place their hand on each crest and hold a tape measure between both hands AWAY from the body (i.e. tape measure doesn’t curve)
• HB = humeral breadth – take a compass and measure the distance between the 2 most lateral bony bits on your elbow – just touch the tip of the compass to each point for best accuracy
• FB = femoral breadth – do the same for the 2 most lateral bony bits of your knee.

Multiply these measurements (in cm) together according to the above formula and see where your frame ranks (along the x-axis) and approximately how heavy your chassis is likely to be (y-axis).

This number can give you valuable information on both course selection (as outlined in my previous article) and also the direction that you may want to take when it comes to working toward your optimal athletic body composition. For instance, if your gross bone dimensions tally to 60,000 cm3, putting you smack bang in the “medium category” but you have obsessively cut weight to less than 65kg, you are likely significantly underpowered when it comes to lugging your bone and organ mass around. Your first priority should be to “upgrade your engine.”

On the flipside, if you are 90kg but your chassis weight is only 45kg and you’re working with a 4.5L engine then you’re not well equipped to towing all of that extra mass. You’re like a Chevy S-10 pulling a fifth wheel. Detach that thing and you’ll fly.

Okay, so I’ve mixed metaphors a bit since starting this piece, but hopefully the importance of identifying and working with your personal body type still got through. Triathlon, more than most sports, affords the opportunity for many body types to be successful. One need only look at the comparative success of Peter Reid and Ain-Alar Juhanson, two athletes of similar height but about 40lbs difference in body mass. With such diverse examples, it can be tough to determine what is optimal for us. Hopefully the above will help to answer that question.

Train smart.