Monday, February 1, 2016

Horses for Courses - Part III: Race Selection Based on Body Type

by Alan Couzens, MS (Sports Science)

Part I - Horses for Courses
Part II - Are You a Thoroughbred or a Draft Horse?
Part III - Race Selection Based on Body Type

The topic of conversation this month at EC is race selection. Now is the time of year that athletes are filling in their calendars and deciding what races will occupy 2012 (I’ll go into a little more on just how much of the calendar should be “filled” in a future article).

I don’t think it’s unfair to say that deciding which races best suit your strengths is a bit of a mystery for most. In the end, many athletes select races based on a cool location or the history surrounding the race rather than on matching race characteristics to their personal strengths.

The problem is somewhat muddied by the fact that many athletes make inaccurate assumptions about their strengths based on poor context. For one, it is always tough to tease out the fitness variable, especially when ironfolk don’t tend to race that frequently. Put another way, just because your best race to date may have happened on a course with a lot of climbing doesn’t necessarily mean that climbing is your strength. Maybe you were just in the best general shape of your life and would have gone even faster on a flatter course! Additionally, the fact that the vast majority of the field pace so poorly can lead to inaccurate conclusions about relative run strength (or bike weakness).

While there are a number of factors that cooperate to determine which sport is the athlete’s strength, the largest by far is morphology.

I took a look at some of these morphological differences and how they benefit athletes on different hypothetical courses in two previous articles – Horses for Courses Part I and Part II. In this article, I want to use the same speed versus power formulae from Bassett (1999) to apply those athlete types -- the Clydesdale and the Thoroughbred -- to a bunch of different real world courses on the Ironman calendar to better answer the question: which race course will give me the best relative performance for my strengths?

The Horses
I used the same two athletes from the first Horses for Courses article. Both with the same relative fitness (about 70ml/kg/min) but widely different body types: 1.9m/85kg and 1.75m/65kg respectively, the proverbial strong flat cyclist build versus the typical runner build.

In addition, for this article I added an athlete that fits the “medium build” category from Horses for Courses II: 1.82m in height, 75kg with a relative VO2max of 70ml/kg/min.

The Courses
I plugged the three athletes into a sample of different types of courses on the current IM calendar ranging from courses with significant vertical, to courses with high winds, course with extreme heat and humidity to flat, fast courses. These are shown in the table below.

Swim Time
In general, taller, heavier swimmers are benefited in the swim. The pressure drag of the vessel decreases with vessel length. However, this benefit is somewhat negated in wetsuit swims because less of the vessel is under water. Toussaint et al (1989) found a 12-14% reduction in drag when using a wetsuit. When applied to typical elite swim speeds, the relative benefit for wetsuit and non wetsuit swims are shown below.

In general, non-wetsuit swims are 4-5% slower that wetsuit swims (of comparable conditions), slightly more so for shorter athletes due to increased frontal area:vessel length.

Run Time
Usually, smaller athletes will run marginally faster for a given level of fitness due to the negative effect of allometric scaling. The benefit on a flat course, as show in the tables at each respective output is approximately eight minutes for our big versus small athlete over the course of a marathon. I simplified the run data by assuming a flat course (representative of the majority of IM races) so these differences would be amplified on a hilly run course such as St. George.

However, while the cost of carrying extra mass alone is significant, the morphological factor that can have the largest impact on run pace isn’t the negative effect of carrying the extra load but rather the potential for the larger athlete to overheat. While differences in run performance for a big versus small athlete of similar relative fitness may be relatively minor (in the neighborhood of 4%), on a hot course such as Kona this gap widens dramatically.

Under normal conditions (27C, 72% average humidity) the maximum amount of heat that an athlete can dissipate on 1.5L/hr of hydration is in the neighborhood of 1100W (Dennis & Noakes, 1999). While this isn’t an issue for a 65kg athlete who can run 2:45 pace without generating this much heat, an 85kg athlete of average efficiency will hit 1100W of heat at around 3:40/k pace. The heat effect of various hot courses is shown in red below.

A relatively fast larger athlete racing Kona, Texas, Louisville and, to a lesser extent, Wisconsin will often find themselves limited not by fitness but by their ability to dissipate heat on the run.

I deliberately use the word “frequently” here rather than “always,” as relatively small swings in humidity and temperature can have a large impact on larger athletes’ ability to get rid of the heat produced. Wisconsin in particular is subject to a wide variety of conditions. Given the right year, it’s certainly possible for a large athlete to do very well on these courses but on the balance of probability, they fail the criteria to be deemed “big unit friendly.”

Bike Time
Secondary only to heat, the big unit’s other great kryptonite is a road that goes upwards. Again, due to that ugly principle of allometry, smaller athletes will tend to have better power:weight numbers than larger athletes.

While pure power trumps power:weight when it comes to speed on the flat, the reverse is true when going uphill. For this reason, courses with a lot of climbing will offer greater benefit to smaller athletes.
Fortunately, for guys like myself, even the most challenging bike courses offer only a moderate overall grade. We are yet to see an Ironman that incorporates a swim in downtown Denver followed by the Triple-by-Pass ride (12,000ft of elevation) up to Vail followed by a high altitude mountain marathon at 10,000ft. I think we’d see a different type of athlete winning this event. By the standards of possibility, most IM bike legs are relatively tame, with athletes with strong power:weight only narrowing the gap to large athletes on the bike leg.

Additionally, unlike road cycling, where due to the drafting benefit on the flat the climbs become decisive, for Ironman, the climbs offer a much smaller advantage to the smaller athlete. For this reason, we don’t see 120lb athletes excelling in major Ironman events.

Estimated times from Basset’s equations for an 85kg athlete at 300W, a 75kg athlete at 270W and a 65kg athlete at 240W (similar relative fitness level) for each course with typical conditions are shown below.

It should be noted that these estimates do not take into account the relative draft benefit on each of the courses. On some multi-loop courses, particularly courses with wave starts, times will be far quicker than the above for a given power output. Additionally, for windy courses the real draft benefit of sticking with a pack (even when legal) may offer additional advantage to the larger, more powerful athlete.

Putting all of the above together, estimates of total time for each of our three equally fit hypothetical big guy, medium guy and small guy athletes for each course are shown below along with a classification based on the relative performance of each athlete as big guy, medium guy or small guy friendly.

Perhaps most notable is that with only a few exceptions we see that the gap between big, medium and small athletes on any course is quite small. This is the beauty of Ironman racing. We see markedly different athletes, all the way from little guys like Greg Welch or Christian Bustos, all the way up to big guys like Torbjorn or Ain-Alar or Chris McDonald all performing at a world class level on varied courses.

That said, in general, unlike the single sports of swimming (which clearly favors the tall, strong athlete) or running (which clearly favors the small, light framed athlete), Ironman triathlon leans toward the medium sized guy, with 13 of the courses analyzed showing advantage to the medium sized athlete given typical conditions.

The greatest disadvantage to the larger athlete by far comes from hot, humid courses. Unfortunately, the World Championships fits the bill as a hot, humid course in most years and markedly favors the smaller athlete. However, in planning your Kona assault, there are certainly going to be some courses that better suit you as a qualifying event. Hopefully this article will help you identify these and enable you to get the absolute best relative performance out of your fitness in 2012.

Race smart!

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