Ironman triathlon novices: the art of prediction

Comprising a back-to-back 2.4-mile swim, a 112-mile bike ride and a full 26.2-mile run, embarking on an Ironman-length triathlon for the first time involves a journey into the unknown, both physically and mentally. Of course, most triathletes relish this challenge; it’s not just the buzz of overcoming physical adversity that such distances create, it’s also great for putting the trivial hassles of daily life firmly into perspective! However, while all competitive athletes like a challenge, too much uncertainty can be very unsettling, especially for would-be Ironman triathlon novices.

One of the biggest uncertainties of all is knowing exactly what you’re letting yourself in for; you know the (long) distance you have to cover but what you don’t know is how long it’s all going to take you. And that’s important because the duration of your event is going to affect both your pacing and your nutritional requirements, particularly in the later stages of the race.

Unfortunately, predicting your first Ironman time is an extremely imprecise science. You might think that you can just take your steady-state training pace for each discipline and extrapolate out from there. However, it’s not as simple as that; the extraordinary length of an Ironman means that you’ll almost certainly be entering new and unknown territory where you’ll encounter new levels of muscular fatigue, severe nutritional challenges and the possibility of cramps, blisters, dehydration etc.

The art of prediction

Because of its severity, the physiological demands of an Ironman triathlon have always fascinated sports scientists. This explains why there have been a number of studies into what makes a good Ironman triathlete, and what characteristics in a given triathlete help predict a fast Ironman time. For example, one study compared the height, weight, and percent body fat data of accomplished Ironman triathletes with those of elite athletes from the sports of swimming, cycling, and running⁽¹⁾. It indicated that the physiques of these elite triathletes were most likely to be similar to that of elite cyclists.

Other studies have shown that (for short-distance triathletes at least), elite triathletes are likely to be tall, of average to light weight, and with low levels of body fat⁽²⁾. Also, research suggests that body composition – specifically a low level of body fat - is important for an overall fast race time and fast split times in each of the three disciplines⁽³⁾. Meanwhile, a Swiss study on Ironman and ultra-triathletes (up to double-Ironman length) found that faster performance times were predicted by low levels of body fat in both cases⁽⁴⁾. Interestingly, high levels of training volume predicted the best performances in ultra, whereas speed during training predicted the best performing Ironman-length triathletes. In another study published the same year (2015) by the same team of scientists, the most important predictive variables for a fast Ironman race time were an age of 30-35 years, a fast personal best time in Olympic distance triathlon, a fast personal best time in a marathon, high volume and high speed in training (where high volume was more important than high speed) and low body fat⁽⁵⁾.

Unanswered question

Of course, while this is all very interesting, none of the above studies were able to answer the question of how a novice triathlete might be able to better predict his or her race time – only whether their particular physical or training characteristics were likely to endow them with the potential to turn in a good time. However, an early study did take a closer look at this question⁽⁶⁾. In this study, the researchers studied 83 male recreational triathletes participating in the 2009 Ironman Switzerland race. During the afternoon prior to the race, the researchers took a number of physical measures including height, weight and body mass index (BMI). They also took skinfold measurements to determine body fat percentages.

What was different in this study however was that the triathletes had also been keeping comprehensive training diaries, which recorded data for each training session performed in the run up to the event, including the distance, duration, and average speed of training sessions. This data, along with the personal best times for an Olympic distance triathlon and a marathon run, were also gathered. At the end of the race, the times recorded for each triathlete were matched to the data gathered for that triathlete and the results were number crunched to see which (if any) variables predicted race times.

What emerged was that the triathletes’ marathon and Olympic distance triathlon personal best times were strongly related to their Ironman race time (see figures 1 & 2). Also, the average speed when running during training, was related to best times, though less strongly so. In fact statistical analysis indicated that these three variables alone explained 64% of the actual Ironman race time. This somewhat surprised the researchers because they had expected that (in line with previous studies) body fat %, cycling volume, and personal best time in an Olympic distance triathlon would be most related to the Ironman race times.

Figure 1: Marathon performance and Ironman times