Ironman Melbourne

Weiss Powers to 4th Overall with Fastest Bike

Ironman Melbourne Analysis By Garth FoxMSc, Sports Science & Human Performance

Following on from his win at Ironman Cozumel in December, Michael Weiss once again put on a cycling masterclass at Ironman Melbourne on Sunday 23rd March. He not only achieved the fastest bike split of the day in 4:20:50 but also the 3rd fastest marathon time of 2:45:17. His swim time of 52:39 left him trailing the lead group by just over 4 minutes but nevertheless represented a Personal Best in an Ironman swim. Overall he came 4th in a truly world class field in a time of 8:03:46, 2 minutes ahead of the three time world champion, Craig Alexander, and narrowly missing out on a podium place by only 30 seconds. Yet more progress and experience racing in an elite field.

Ride Smart, Run Strong

Michael’s SRM race file shows that he averaged a staggering 315 watts over the entire 180km, which translated into an average speed of 41km/h and energy expenditure of 4920 KJ. Although this average must seem eye-wateringly high to the typical age group athlete who would do well to average 60-70% of that wattage, it still only represented 77% of Weiss’s critical power of 410 watts tested in the month before the race.

Michi’s bike leg was really a tale of two halves as it is clear that the first half was notably more intense as he tried to bridge the time gap to the leading group which contained most of the other serious contenders. The leading group were, however, working well together and even with 12 metres of strictly enforced minimum gaps between cyclists, they managed to maintain the magic 41 km/h (In world class Ironman under ‘normal’ conditions over a relatively flat course, this tends to be the speed averaged by the lead group or the best individual cyclist). Because Weiss was himself riding ‘in the wind’ without the benefit of a group to pace off, he was not able to close the gap in spite of pushing 330 watts and 41km/h for over 2 hours to the halfway point.

From the 90km point Michael was able to save some energy as there was a small but significant increase in wind speed over the second half of the bike leg allowing Michi to drop his power output by almost 10% while maintaining both speed and cadence. It should be pointed out that this sort of ‘on the fly’ adjustment is not usually a conscious decision amongst world class athletes but rather a result of years of training and racing experience.

Click SRM file image to enlarge.

The left to right sloping power profile is often seen in both elite and age group Ironman triathletes irrespective of environmental conditions such as wind or heat, usually, however, for very different reasons. The elites gradually reduce power (probably subconsciously) in readiness for what is often a true run race to the finish line, whereas at the age group level it is usually simply a reflection of lower training volumes and endurance which results in the early onset of fatigue. Although Michael was not wearing a heart rate belt, if he had been, I am sure that the reduction in power output in the second half would have been accompanied by a similar reduction in heart rate. This is usually not the case when an insufficient endurance base has led to the drop off in power.

Metabolic Considerations

Following a 6 day taper period Michi probably had around 2000 kcals of carbohydrates stored as glycogen in his muscles and liver. During the bike leg of Ironman Melbourne he consumed exactly 340g of carbohydrates in the form of energy drinks and gels. This is a rate of about 80g/hr which is already at the upper end of what can be achieved before causing gastrointestinal distress.  This is the equivalent of approximately 1300 kcals. On the run he managed to consume in the region of 1000 kcals which means that over the course of the race he would have had approximately 4300 kcals available as carbohydrate. In terms of energy expenditure we can estimate that he used about 1000 kcals during the 3.8km swim, we know from his SRM powerfile that his mechanical energy expenditure at the crank was very close to 5000 kcals. 

Click SRM file image to enlarge.

During a marathon run it is normal to expend around 3000 kcals. Therefore it is evident that he had an energy deficit over the race of about 4700 kcals. It is highly unlikely that Michi finished the race entirely depleted of his glycogen stores (although I did have to physically hold him upright for several minutes after finishing!) and there may have still been around 500 kcals left in his body. The remaining short fall is necessarily made up from fat metabolism. In Michi’s case we can therefore estimate somewhere in the region of 40% of his energy requirements were derived from fat metabolism. This is a very high proportion considering the power and speeds he was able to sustain but is exactly what we might expect from a world class, highly talented endurance athlete who has built an enormous base of aerobic work over years and years of quality training. You and I will neither be using such a high a proportion of fats or even if we are, we will not be able to go as quickly or produce as much power as Michi, while doing so. That said, it should be the goal of every aspiring Ironman to put in the hours of aerobic training that will at least improve metabolic efficiency. Ironman is not limited by fitness per se, but by fuel metabolism and its efficiency at target race power outputs. Training precision means training with power. Power means SRM.

The sports scientist’s (Garth Fox) view:

1. Age group athletes should endeavour to minimise cadence fluctuations during an Ironman bike leg in order to promote metabolic efficiency.

2. A smart racing strategy in Ironman is to maintain the legal drafting distance because even at 12m from the bike in front, 5-10w can be saved while speed is constant resulting in energy saving.

3. Metabolic efficiency, or the ability to use a large proportion of fat as a fuel source at as high an average power output as possible, is the ‘secret’ to Ironman triathlon performance. Therefore athletes should make great efforts to get the body to use more fat as a fuel source while cycling in order to spare some glycogen for the run when we are all running on fumes. This can done through appropriate diet and training strategies.

Weiss: "Comfort trumps aerodynamics: When doing a bike fit on your Ironman race bike it is important to consider if you are able to hold an aero position for an entire 112mi/180km. A flatter course such as Melbourne gives you less opportunities to loosen up on climbs, by riding with your hands on the base bar or going out of the saddle. A less aggressive cockpit set-up may allow you to push slightly more Watts and nutrition-uptake is much easier. Comfort level is especially noticed in the second half of the bike segment when you see more and more people- even pros- tending to avoid their aero position possibly due to back and/or neck discomfort.

One point of advice for decreasing stress in the neck area, which is a result a constant cervical hyper-extension, is to use one of the new rounder aero helmets such as the Giro Air Attack. By opting for this design you will not suffer aerodynamic disadvantages when looking "down", in other words relaxing the neck. Doing this neck movement with a classic aero helmet, aka one with a "tail", you can cause extra drag while also losing ventilation advantages, another point of comfort."

back to top