I want to chat a little today about some of the factors that come into play to determine how different athletes will perform on different types of race courses.

Hopefully you will be able to use this information to select race courses that give you (and your body type) the greatest chance of success.

I’ve provided data from two (arguably) equally “fit” athletes below:

I want to chat through how some of the differences in these equally fit athletes may come into play to result in one beating the other depending on the course over which they race.

• Height and Weight: Clearly, the biggest difference between these two athletes is in their respective frames. Athlete A is 1.9m (6’3”) tall and weighs 85kg (187lbs). Athlete B is 1.75m (5’9”) tall and weighs 65kg (143lbs). Athlete A has a solid/muscular physique with a BMI of 23.5. Athlete B has a bit more of a ‘runners physique’ with a BMI of 21.2.
• Frontal Area: Because of the differences in height and body dimensions, athlete A presents a greater frontal area of 0.42 meters squared to the wind when riding the bike in the aero position. Being smaller, Athlete B presents only 0.36m. These numbers represent good but comfortable positions for athletes of their respective sizes. In other words, neither of the athletes are set up like Boardman.
• Functional Threshold Power (FTP) and VO2max: Athlete A has a significantly higher absolute functional threshold power than Athlete B — 380 watts versus 300 watts and a significantly higher absolute VO2max — 5.96L/min versus 4.71 L/min. However, let’s see how this difference in “engine size” actually plays out in the real world….

Flat Cycling
When it comes to flat cycling, the greatest retarding force that must be overcome comes from aerodynamic drag that is created by the bike and rider. Unsurprisingly, the rider’s speed on the flat is significantly correlated to the watts that they produce divided by the frontal area of bike and rider. In this example, rider A produces 905 watts for every square meter of frontal area whereas rider B produces only 833. The result is that on a flat course the larger rider will go ~1.4km/h faster on the same relative effort of 80% FTP. In ironman terms, this represents a difference of ~8 minutes over a flat IM bike split (4:11 vs 4:19). However….

Uphill Cycling
When it comes to uphill cycling, the greatest force the cyclist must overcome comes from the combined weight of bike and rider. Therefore, the tables turn. In this case, a much better prediction of speed comes from watts per kilo of bodyweight. In this sense, the rider with a significantly weaker FTP gains the edge at 4.3 versus 4.1 watts per kilo. On a course with a couple of significant climbs, such as 2x16K at 5%, this athlete will make up 3.5 minutes on athlete A despite having an absolute FTP that is 70W lower than athlete A!

Running
Similar to uphill cycling, when it comes to running, energy expenditure is almost linearly related to bodyweight. Therefore, in all running portions of the course, but especially those with uphill gain, the smaller athlete has the edge. In this case, assuming a flat marathon, the difference is 8 minutes, assuming the same relative output (80%) and the same economy of 210 ml/kg/km.

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At least to this point, the winner of the race depends on the race course. On a hilly course with a couple of significant climbs, our smaller athlete will get off the bike with a 4.5 minute deficit but will run the larger athlete down despite having a significantly lower FTP and absolute VO2max.

On a flat course, the bigger athlete will get an 8 minute lead off the bike and will hold the smaller guy off by 2 minutes over a flat run.

Sounds like a pretty familiar scenario, eh? Perhaps with one notable exception — Kona. Despite the absence of significant climbs, the smaller guy usually runs the bigger guy down. There is one more key course element that we need to consider — heat.

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Heat
At 2:50 marathon pace in environmental conditions of 80F with 72% humidity (typical Kona), an 85kg athlete will produce more than 1450W of energy in heat! Unfortunately, the most energy that the athlete will be able to dissipate via radiation, convection and evaporation (even when hydrating at 1.5L/hr!) is 1100W (Dennis and Noakes, 1999). This presents real problems for big athletes at the pointy end of the field in hot races. In the above scenario, while the larger athlete may have the fitness to run a 2:58 off the bike, if he tries to run that fast in 85 degrees he will almost certainly overheat and be forced to slow.

In very hot races, it presents problems for big athletes even in the middle of the pack. At 95 degrees and 60% humidity the 85kg athlete will produce the magic 1100W meltdown point at a pace of ~9:00/mi! Even if the bigger athlete has the fitness to run a 3:00 marathon, they will be thermogenically limited to 3:54 if the day is especially hot.

While it may seem so, the message here is not lose weight and get small at all costs. The greatest proportion of the vast majority of IM races is made up of relatively flat cycling. As previously mentioned, the prime determinant in your performance here is power:frontal area. Your frontal area is relatively fixed by your body frame and dimensions. Therefore, you need the right size engine for your chassis in order to be an effective flat cyclist and ironman. However, if you are an athlete with a larger chassis, choosing flatter, cooler courses may prove beneficial to your relative performance.

Because of the mixture of qualities required to succeed in ironman triathlon, some dependent on pure power, others on power:weight, athletes of all shapes and sizes can do relatively well. However, when “success” comes down to minutes, such as when shooting for a Kona slot, shooting for an AG win or shooting for the finish tape, being aware of your own personal morphologic strengths and weaknesses can make all the difference. When it comes to athletic “talent” a large part of it comes down to “horses for courses.”

Train smart.