Monday, February 1, 2016

Power-Based Race Simulations

by Gordo Byrn

I thought that I’d share how I build a power-based race simulation rides for ironman. It’s not particularly complex (at least to me). The “art” comes from interpreting the fatigue that the athlete will carry into the marathon and not screwing up the run with an inappropriate bike-power strategy.

I’m going to use real data from a buddy in his 50s who is slightly slower than what it takes to qualify for Kona.

Review the past:

  • Look at last IM - 3131kj, NP 165w, AP 150w, 5:50
  • Estimate FTP by reviewing season bests - 200w

Ask the athlete what he or she thinks - “I’d like to hold 160-170w for five hours.”

Consider how the athlete has run in the past - Very well relative to training as well as age-group peers.

Consider the requirements of the course - Last IM was CDA, upcoming IM is AZ. So a different output profile is required, and optimal. Given the previous race, combinations of 170w (AP - uphill grade) and 140w (AP - downhill grade) would likely prove useful.

170w is 85% of FTP and that is taxing for the average athlete. However, older and smaller athletes can hold a much higher percentage of FTP than Big Units. So, I think a key aspect of preparation is flushing out if there’s going to be a metabolic limiter to the race strategy. If the right uphill number is less than 170w then I want the athlete to find out well before race day.

Bringing it together, and applying the lessons from my Core Block concept, the Big Day will progress to:

PC 400s swim to start and transition (not more than 20 minutes) to a 3,500 kilojoule ride (longer than race day to increase metabolic load compared to race day) that is structured as:

  • 60 minutes at 150w AP (540 kj)
  • 60 minutes of 10 minutes 170w / 5 minutes 140w (540 kj)
  • 15 minutes Easy (115 kj)
  • 90 minutes of 20 minutes 170w / 10 minutes 140w (810 kj)
  • 15 minutes Easy (115 kj)
  • 120 minutes of 40 minutes 170w / 20 minutes 140w (1,080 kj)
  • Hold 150w AP until you hit kilojoule target (about 33 minutes)

Transition to a 10k run as a reality check on bike depletion. Run 2k relaxed then 8k (5 miles) at the bottom of your steady HR zone and check pace. If you’re more than 40s per mile adrift from normal paces (late in a long run) then the bike strategy needs to adjust.

In this athlete’s case, 150w AP was “proven” by his marathon in CDA, so the key variable to adjust is power on the uphill grades. In most other cases, the key variable is average power across the ride and ensuring zero power spikes over FTP.

Another key variable to assess is average kilojoules per hour output versus average carbohydrate intake per hour. There’s no magic ratio, but only exceptionally efficient athletes can get by with less than 50% replacement rate (270 kcal of carbohydrate per hour for our case study). In my own racing, I was slightly over 60% replacement rate (cycling) when I ran my best.

This is more than an 8-hour training day so you want to use it very sparingly and plan appropriate recovery. The workout above is the end point for where you’d want to point your Big Day Training.

At the end of your Big Day, relax, take a deep breath and know that you have at least two more hours to go on game day!

Be humble and remember that our best training performances set a ceiling under which we operate during our races.


Gordo is the founder of Endurance Corner. You can find his personal blog here.

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