Monday, September 1, 2014

Know your Enemy – Part III: Optimal Pacing for Different Courses

by Alan Couzens, MS (Sports Science)

In previous articles on "getting to know your enemy" I looked at minimal power/gear requirements to get around different courses in good shape. In this final article in the series, I want to investigate the question of: "what if you have some extra energy/power to play with? What is the best place to use this extra mojo on different types of courses?"

Bike versus Run Pacing
Let’s start by looking at how much energy you want to devote to the bike versus the run on different courses.

In a previous post on energy pacing your ironman, I looked at the most generally optimal way to distribute your energy across the ironman bike and run to yield the best total time. This theoretical combo will change a little with hillier courses as outlined below (click the picture to blow it up).

To some extent, the hillier the course and the slower the bike speeds, the more energy the athlete should devote to the bike portion of the course (and the more the course favors an athlete who is stronger on the bike). This relationship is outlined above for five different pacing strategies all equaling 200W for an 80kg athlete, from a bike heavy 240/160 (bike/run) to a run heavy 160/240 (see my Energy Pacing I article for translation of run "power" outputs into marathon times).

When planning your pacing strategy for your race sims and your race, use the above as a starting point for different combos to experiment with in accordance with the elevation gain of your race course. Note that, even for a hillier course, a negative split, that is, devoting more energy to the run versus bike, is still optimal. It is just the margin of this negative split that changes.

Within Bike Pacing (Floors and Ceilings)
Finally, once you have a good idea of the optimal overall way to pace your bike and run, some thought needs to be given to how much range you’ll allow yourself within the bike portion. When is it worth it to put out a little more energy at slow parts of the course, and how much is "a little more"? To answer this, I modeled a few different climbing strategies for an 80kg rider (FA=0.4m^2) with an FTP of 320W on some simple hypothetical courses…

For each course (where practical), I looked at the following pacing strategies:

  • Hammer the climb at just below threshold (300W) and coast the descent
  • Ride the climb at a moderately hard intensity (260-275W) and pedal easy on the descent (130-200W)
  • Ride a completely even power split on the climb and descent

Our first course is a dead flat 112 mile ironman course on a calm day -- perfect course, perfect conditions.

Our second course is a steady grade of 2% up for the first 56 miles followed by 2% down for the next 56.

Our third course is a solid climb of 5% for the first 56 miles followed by a 5% descent for 56 miles.

And the final course would be a doozie… a climb of 10% for 56 miles followed by a 10% descent for 56 miles yielding bike splits in the 9+ hour range!

The results of each strategy with same energy (TSS) output for each course are shown below, with the optimal strategy for each highlighted in yellow:

On flat courses an even power split within the bike will yield the fastest time for a given energy output: 4.3% faster than the variable mod-hard/easy approach outlined above. However, when the road starts to go up, as Robbie Ventura is fond of saying, it makes sense to go (somewhat) fast when the course is slow. In the case of a 2% grade, a strategy of climbing "one gear up," in this case at a moderately hard intensity and descending easy is preferable to both a "hammering and coasting" approach (5%) and a constant power output approach (7.5%).

When the road really starts to go up (at grades of about 5% or greater), the optimal strategy becomes climb solid (close to but not over) threshold and recover by coasting on the descent. In this case, this strategy yields a 6% faster time for the same energy output when compared to a mod-hard/easy approach and a 12% faster time than a constant power strategy. Pretty significant.

Finally, when the road "goes ballistic" at 10% or more, climbing at threshold is both advantageous and bordering on necessary for a bigger athlete. In this case, the model indicates 7.3mph at 300W for an 80kg athlete! Just as interesting, by coasting on a 10% grade the athlete reaches a velocity of 58.8mph. By putting on the 80/11 and spinning at 100rpm at close to threshold at 271W, he only goes 3.4mph quicker!! Puts the energy cost of pedaling on descents into perspective!

Clearly, when it comes to race day pacing, it does make a difference how you distribute your energy over the bike course, with a tactical approach yielding time/energy differences of 5-7.5%, or 15-30 minutes on typical ironman courses. It makes sense to alter your power output based on speed fluctuations throughout the day, or as RV says, go fast when the race is slow. In the case of the above athlete, a strategy such as the 10/20/30/40/50 rule would be a good one:

  • Coast at >50km/h
  • Pedal Easy at >40km/h
  • Pedal Steady at >30km/h
  • Pedal Mod-Hard at >20km/h
  • Pedal Hard at >10km/h

For the less retentive, the two key points -- the ceiling and the floor -- being coast at >50km/h and go a gear up at <30km/h. Go Easy-Steady in the middle of that.

Obviously, your choice "rule of thumb" will depend on the athlete’s zones and how hard they’re going to race the event. In the case above, this would be for an athlete of ~4w/kg FTP shooting for a "steady" average power. For an athlete with a lower FTP or an athlete racing a gear down, they may move everything down one, e.g. coast at 40km/h etc. but point being, for a hilly course, having your own tactical plan of where you will go "hard" and where you will "back off" is critical to getting the fastest bike split from a given energy output.

The first step in that is to get to know your enemy (intimately).

Train smart.


Part I - Virtual Recon of Your Race Course
Part II - Course and Gear Selection
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