Aidan Charles: Heat Adjusted Power Targeting & Race Pacing

Forward - Heat pacing or heat adjusted power is a known, but under-utilised strategy in sports today. Hotter marathons are statistically slower than cooler marathons and this is primarily because of the body's need to divert resources from power generation to cooling.

Aidan Charles and Vivien Rindisbacher  have been acquiring data and working on a mathematical approaches to define heat pacing. We are supporting their research as they refine their models and the team are also welcoming athletics who are able to contribute their training and racing data. 


Aidan Charles is the Head Coach of Charles Coaching & Nutrition Services. The team of coaches support endurance athletes of all levels, from young athletes and development teams to elite athletes. With vast academic and practical knowledge, founded on his coaching experience and professional racing experience with the Nerac Cycling Team, Charles has an open approach to sharing performance insights. 


Aidan Charles - Heat Adjusted Power Targeting & Race Pacing  

As temperatures rise, athletic performance degrades due to a loss in aerobic efficiency. Using power, ambient temperature and now core body temperature data, athletes and coaches can use tools like our Heat Adjusted Power Model to adjust pacing targets to ensure that they choose optimal pacing for races and stress the intended physiological systems during training.

All competitive cyclists feel the effects of a hot summer day – especially early in the first warmer days of the spring and summer. This is for a good reason, because the loss of aerobic efficiency due to heat has a bigger performance impact than almost any other variable that an athlete may face regularly, and the effect varies from athlete to athlete. Failure to acknowledge the adjustments needed due to increased ambient and core body temperature can lead to over-pacing, over-training, and significant setbacks to an athlete’s race day performances.

We set out to create an individualized and ongoing gauge of power loss due to temperature to help athletes understand how to adjust their training and ensure they target accurate pacing during races. As a result, we used a combination of real-world data and lab-test data to create a Heat Adjusted Power Model for use by athletes and coaches. 


Collecting and Modeling Real-World Data

First, we analyzed over 150 athletes and two years of data.  After gathering peak performance data at different temperatures, we built a factor model (i.e., our Heat Adjusted Power Model) to represent everyone’s power output degradation at higher temperatures. While the decrease in output varies depending on various environmental and individual variables, we observed an overall average power output loss of 0.7% to 1.1% for every 5-degree increase in temperature starting from 50°F. 


Individualized Heat Adjusted Model Data vs. Lab-Based Case Study

The next step in quantifying the effects of heat was to personalize this model. Using an athlete’s power files, core body temperature and our Heat Adjusted Power Model, we can give athletes heat-adjusted peak power outputs in specific temperatures, ranging from 50-100 °F. In a case study to validate our individualized Heat Adjusted Power model, we conducted two lab-based aerobic assessments at 63°F and 82°F. 

Using our model and the test subject’s power data, we determined a modeled Functional Threshold Power of 364w at 63°F and 326w at 82°F - a 2.9% decrease for every 5-degree increase in temperature. Between the two lab tests, we observed the rider’s power at a RER 1.0 (a widely accepted lab-based value for a rider’s Functional Threshold Power) decrease from 373w at 63°F to 342w at 82°F - a 9% difference and a 2.3% change for every 5-degree increase in temperature.

heat adjusted power


Comparison of the Heat Adjusted Power Model & Lab Data


FTP at 63°F

FTP at 82°F

FTP % Loss

Lab Aerobic Assessment Data

373 w

342 w

9.1 %

Athlete’s Individual Heat Adjusted Power Model Projection

364 w

326 w

11.6 %


The Next Steps

All athletes and coaches feel the subjective implications of training and racing in the heat, but it has been hard to quantify the impact on an individual’s performance outside of lab-based studies. As passionate coaches, we are excited to have a refined model that helps us understand, measure, and mitigate the effect of heat on an individual athlete’s core body temperature in training and racing performance.

As we continue to collect more athlete data and account for variables such as humidity, wind conditions, and athlete’s varying fitness levels over time, we are excited about the potential heavy implications for the changes in the approach to training in the next few years. 

You are able to support our research and also measure your own progress by signing up at