Triathletes know that over-biking can lead to poor performance on the run. This over-biking has typically been defined as ‘pushing too many watts.’ Pacing plans built around FTP and TSS have reduced the over-biking problem in a lot of instances – but not all. At every half and full iron-distance race there are triathletes walking the run course – many of whom followed their pacing plan perfectly.
Sometimes improper fuelling or hydration may be to blame. But observations suggest there may another culprit – a core temperature that’s too high at the end of the bike. Most triathletes find that their core temp rises when they transition to the run. If they ended the bike with too high of a core temp, it’s easy to picture how their core temp on the run could quickly climb to an unsustainable level.
One strategy to avoid problems is to maintain core temp on the bike at a level that anticipates the challenges of the run. In other words, your threshold core temp during a triathlon bike leg may need to be lower than if you were not running after riding.
Determining threshold temps
Once you’ve been training with CORE for some time, you’ll likely have a good idea of how high your core temp can rise before you start to have performance declines. A heat ramp test is the first tool to estimate this threshold temp. After that, longer endurance-paced and tempo-paced efforts can give you a more precise threshold temp. Pay attention to your perceived effort during the workout, and then analyse results afterward in training software. You’re looking for the core temp where either heart rate increases as power/pace stays the same, or where heart rate stays constant while power/pace drops.
Note that this threshold core temp may differ between cycling and running.
Determine core temp rise
Next, you’ll want to test if your core temp rises off the bike when at race pace. The following bike/run workout is one way of doing that. The durations are suitable prep for a half iron-distance race but can be adjusted for shorter or longer races. Ideally, weather conditions will be similar to what you expect on race day.
- After a warmup, ride for 75 minutes at planned race pace (this can be an interval session if desired). Keep your core temp at (or just below) the threshold you’ve identified for the bike. Stay hydrated, and it’s fine to take additional cooling measures.
- Immediately transition to a 40–50 minute run at planned race pace (this also can be an interval session). Monitor your core temp, heart rate and pace. Use whatever cooling measures will be available on the course.
Afterwards, ask yourself these questions:
- Did core temp rise on the run?
- If so, did it rise past the threshold where you get performance decline?
- Did the performance decline (decoupling of pace and heart rate) occur at the core temp you expected?
If your core temp did rise on the run to unacceptable levels, repeat the workout after a few days of recovery. This time, during the ride keep your core temperature lower. One suggestion is to reduce your bike threshold temp by the amount that your temp rose during the run.
On race day you may find that you need to lower your power output on the bike to keep your core temp low enough to run well afterward. If so, you’ll be faced with a strategic decision: do you sacrifice time on the bike to run to your full potential? But before you make such a decision, be sure that you’ve optimised all of your cooling strategies on both the bike and the run.