Using Power to pace an Ironman

Chris Oubre

I started gathering data with a Stryd for this year's build to Ironman Texas and Ironman Boulder.  I'd like to use that data to help me pace them.  I expect a power based place to help me a lot in Boulder due to the elevation.

Based on a 5k test,  my relevant zones are
Z1 8:49
TRP 8:10
Z2 7:32

From RPE I've found that my TRP is really somewhere around 8:20-30ish.  I live in a pancake flat area and have no hills to train on.  My only extra resistance comes from really windy days. At some point I started using power numbers to pace my workouts.  I've hovered around 275-285 as my targets.  I didn't do an analysis, I just found that to be a comfortable number that gave me the TRP effort.  On my last 18 mile run I averaged 263 for the first 6 miles and 274 for the last 12 miles.


Now it's time to get specific and race plan.  I've gathered average power data and compiled the chart below.  Interestingly it very linear. 

Using the chart below and adding 10s to my 5k based zones (based on my perceived effort) then then the EN specific race guidance for pace athletes translated to power would be
Miles 0-6: Z1 + 30s = 9:29  --> ~250-260
Miles 6-18: z1 = 8:59 --> ~265-270

Thoughts?

Robert Sabo

That sounds reasonable for general guidance if it were flat.  I used power to help pace my  IM marathon at IMLP last year.  While I still had pace goals and checked the heart rate intermittently,  The Watts were for the hills.  During the rollers where I lost some time in previous years I let the wattage drift up 10-20 Watts on the uphills but more importantly I noted the drop in watts as I approached the crest and started pushing a lot earlier then in the past to keep the watts close to range as the hill started to flatten and on the downhill as well.  Of course on the two biggest hills in that race I also had a hard cap closer to 25 W except in the last 5 miles.

Shaughn Simmons

During your race rehearsals how does your run Heart rate compare to second half average bike HR for the first 6 miles of the run off the 5  hour bike effort and at what run pace?

If run HR is equal to or less than bike HR, it should validate your assumptions....

Al Truscott

Chris - While I have been using Stryd now for about 6 months, and have noticed the same linear relation between pace and "watts" as your graph indicates, I am not yet convinced that using the data from the Stryd as the PRIMARY tool for an Ironman is ready for prime time.

Remember first of all that the number we see from Stryd is not watts in the same sense as we get from bike power meters, which are actually measuring force application. Stryd is using data from accelerometers oriented in the three planes of motion, and using their proprietary algorithms to give us a calculated number.

I think Rob and Shaughn are pointing you in the right direction. First of all, if you want to follow a metric for IM run, use HR first and foremost, before pace and power. Second, Stryd #'s may be helpful to rein you in and/or help you pick it up briefly when on a hill. But both Texas and Boulder present unique challenges - heat/humidity and altitude - which you may not be able to replicate well in training. HR will overcome this problem.

Keep in mind that, unless you want to do an actual Ironman 2-3 weeks before your race, you will never be able to duplicate in training what your body will be facing in the last 8-10 miles on race day.

SS is right on when he suggests trying to run the IM marathon at whatever pace results when you keep your HR at the average of the last 90 minutes or so of your (well-paced) bike leg. HR smooths out all the confounding factors such as exhaustion from the first two legs, temperature, humidity, elevation changes, altitude, etc. HR should be understood as giving you a hard ceiling, throttling you back from whatever pace you *think* you should be going, to the *actual* pace - which will undoubtedly be lower then you'd like - your body can handle over 26.2 miles after the bike and swim, given the conditions of the day and the course.

EN athletes have extensive experience with using HR on race day, but we have yet to fully understand how to use "power" in an IM run. If you want to be one of the beta testers, go for it, but understand the risks any guinea pigs have.

Tim Sullivan

@Chris Oubre I would listen to the advice from the super experienced racers above.and run primarily by HR. It will be very hard to keep your HR at the level you want. I have used Stryd during an IM by looking at my watts at a desired HR during the race and have tried to use the watts as a goal for pacing to keep the desired HR 

Chris Oubre

Great advice. On my last RR oddly my watts were more limiting than my HR for the first 2 miles. I wasn’t able to go straight from the bike to the run so my HR had time to drop first. I think I’ll use HR and Power as caps for the day. I’ll use Power on hills to keep my HR steady.