Temperature Impact on IM Bike Times
Temperature Impact on IM Bike Times
On my race rehearsal yesterday, the temperatures rose from 80 to 106 heat index during the ride. Once the heat got above ~90 the perceived exertion level started to increase significantly. As the temps continued to rise the power levels could not be maintained. Hr was only at 130 but the brain would not allow the legs to fire at a greater rate and generate more heat that could not be removed from the body. How to deal with pacing in the conditions???
I think we all will agree that heat impacts run pacing. I have not seen any major discussion on impact of temp on the bike. For a first pass I took the bike data from IM LOU 2009 and 2010 for comparison. We have bike times on the same course with significantly different temperatures. So changes in ride time can be contributed mainly to the impact of temp. We will ignore the impact of wind. Winds were in 2009 avg 9mph NNW, 2010 avg 6 mph SE. So it looks like at first pass the cooler year had more wind.
Assuming a 6 hr bike time, the LOU 2009 average temp (Heat Index) on the bike was 67 and for 2010 it was 89, a good size difference. By noon the Heat Index was 93 and it rose to 97 by 4:00. Those out longer on the bike course rode in higher heat.
Ok so if we normalize the bike times against the course record, we can capture the relative bike time as compared to an anchor point by bike finishing placement. Now we plot the normalized times for the two years and we get the following chart.
Once we got past the 2 best bike splits for each year, we see that bike times slow a noticeable amount. The longer you were on the course; you experienced increasing temperatures for a longer duration. This shows up in the 2010 bike times getting consistently slower than 2009 as you move deeper into the bike field.
If you calculate the delta between the two curves and then plot it against the times for the 2009 bike split, you get a chart that shows the pace impact for a 2009 finishing time with 2010 temperatures. So from below we see that if you had a 6 hr bike split in 2009, your 2010 split is likely to be 9 % slower or a 6:32 split.
What this does is confirms in my head that temperatures need to come into play when establishing you bike pace strategy for a race. I don’t yet the answers yet as to a quantifiable way to factor temperature into our bike pacing strategy but I will work on it. Any suggestions are welcome.
Matt
0
Comments
Patrick, below are my bike numbers for 2009 and 2010. I rode 2% lower IF in the heat and could still run after. I think the trick is finding the balance of heat generated by your effort, the level of sweet produced to cool the body and staying hydrated.
I've done several very hot races: IM CDA 2003 and 06, IM MOO 2005, and Kona 09. My impression is the same as Matt's - in order to survive on the run, one mustn't try to keep the IF as high as the plan, but to follow RPE and hydration needs downward. Also, it pays to remember that the temp is not constant, but rising throughout the day, so this is a progressive phenomenom, meaning 0.72 @ 9 AM but wither to 0.65 by 2 PM (or 1 for Coach P). That combination of rising temp and progressive tiredness will be harder to model for the bike than the run, I suspect. There is no model for the 112 mile stand alone time trial in heat as there is for the open marathon.
Matt I have nothing smart to add but I would like to THANK you again for your work on this. I love the way math, science, and physiology come together in this sport. Much appreciated!