Triathlon Body Mass and Pacing

Thoughts on Triathlon continued from the last article…

Body Composition: As a cyclist, I know that I perform well when I weigh about 163-165 lbs/74-75kg. I’m 6’2″, and that puts me at about a BMI of about 21. That’s great for cycling, but for triathlon, I’m not sure yet what’s ideal. So the question is: what do I want to weigh? Swimming may benefit from having more power, having thicker arms, and extra body mass won’t really hurt. Cycling generally would also benefit from having extra muscle mass and the power that would come with it. Most events are flat enough that extra watts would yield faster times even if accompanied by extra body mass. But, the big problem is that running is much more efficient at a lower body weight and is also going to reduce the stress on your body in training and racing. As long as you’re healthy, weighing less will usually make you a better, more injury free runner.

So, what’s the sweet-spot that’s going to allow you to swim effectively, bike quickly, and run efficiently? Well, that’s a tough one. I’m tend to think that the optimal triathlete body mass for me will end up being less than it has been for cycling, but I’ll have to feel it out and see how my training and racing goes as I experiment with trying to lose a few pounds. Without going into too much detail right now, I suspect that 155-160 lbs/70-72kg (or a BMI of about 20) will be my personal ideal body mass for triathlon. Hopefully I can preserve most of my cycling power but improve my running speed and reduce my chances of injury enough that it makes the total finish times lower.

Ultimately, any big changes in body composition will be due largely to dietary changes. I think it’s clear from research and personal experience for millions of people that “going on a diet” isn’t a long term or enjoyable strategy to change body mass. Rather, I think it’ll be key to always focus on getting good nutritious food with plenty of plant matter, healthy fats, maybe some meats, and mostly slowly digested/high-nutrient carbohydrate for more intense training, except perhaps for some hard training sessions and for recovery immediately following training sessions. I want to focus on changing eating habits in such a way that I’m still getting plenty of nutrition, but hopefully work with my body to have a less anabolic (muscle building and fat storing) hormonal state, largely through limiting insulin. This would be done primarily through limiting or eliminating sugars and refined carbohydrates in favor of slowly digested carbohydrates a times, like sweet potatoes, legumes, some fruit, maybe oats. And at other times, that will mean increased fat consumption and a reduction in carbohydrate intake generally, which should reduce insulin production and also encourage your body to rely more on fat for fuel because of a lower availability of carbohydrate for exercise. Basically, I’ve come to think that cycling macronutrients in the diet has promise as a training technique to allow for intense workouts with higher carbohydrate intake and increased adaptation to fat burning with a higher fat diet, done in alternating blocks of training.


paces, power, and energy

Calculating energy expenditure swimming is not easily done with any accuracy, so for all intents and purposes I’m going to leave that out of the equation. But, figuring out an optimal pacing strategy for the cycling and running legs of a triathlon is an interesting and potentially very useful academic exercise. In order to finish with the fastest time, you might assume that you want to have even pacing. Or, in other words, you might assume that you should aim for the highest average and most consistent energy expenditure per unit of time throughout the duration of the event. So, that’s going to mean that per hour you’d be burning the same number of calories in the water, on the bike, and on the run. Again, swimming it’s hard to measure energy expenditure, but cycling and running is a little bit more so. If you have a power meter, then you can know exactly what your energy expenditure is and there is zero guesswork about it. For running, you can estimate within a small margin of error what your energy expenditure is at different paces given certain assumptions like body mass. So, then it’s all set, you just figure out what wattage you want to push on the bike and what pace you want to run that’s going to be the highest average you can sustain for those two legs, right? Well, maybe not.

Triathlon isn’t a calorie measuring contest, it’s a race. So, time matters and not power or pacing, per se. So, with this in mind, it’s good to remember that as you increase your speed on the bike (and running, but to a much lesser extent) your power/calorie expenditure goes up exponentially. So, if you want to increase your speed by 10%, then you need to increase your power output by about 20%. Likewise, if you reduce your speed by 10%, then you save about 20% of the energy (per hour) that you’re using to cover that ground. Running, however, is much more linear, and if you increase your speed by 10% then your energy expenditure may go up, say, 11%. So, it seems like saving a little energy on the bike may lose some time but make up for it in saved energy that you can use to run faster. But, the bike leg is the longest, and is generally about 40-45% longer than the run leg. So, what do we end up thinking is the best pacing strategy? Again, I’m sure I will learn more from personal experience what is best for me, but it seems you may want a 95% effort on the bike in order to save just a little extra for the run. That might mean that I sacrifice 2m on the bike in order to try to gain 3-4m on the run. We’ll see how that plays out.

Above is a chart that I made up using a few pace/calorie calculators for running that I found online and some estimates based on personal experience for cycling speed at different powers. We won’t assume all of the numbers are right on, but they’re close enough to be considered very reasonable and more importantly show important trends… Basically, if you want to run faster, then you can have better aerobic fitness or you can weigh less or both. If you want to ride faster bike legs, then 90% of that will be determined wholly by your power output, with minimal impact coming from body mass. The problem is that more power on the bike may be easier with more body mass (and therefore more muscle), but running will be hindered by that extra mass. I think at the end of the day, I’ll be aiming to keep a power level in the low-to-mid 300w range (say 320-350) and a pacing that will put me in the low 1:20s for the run (~4min/km pace). I’m really looking forward to learning how to best approach the body mass and pacing questions. As important as these issues may be, it’s important to always remember that health and fitness comes first. No matter how much you weigh and how well or poorly you pace the event, fitness is key no matter what.