Modelling Cardiac Drift Using GPS Data

Using Linear Regressions to Model Cardiac Drift Using GPS Data

Tracking Heart Rate

Smart watches provide a somple method to track your heart rate throughout your day. Heart rate can provide feedback on sleep quality, training readiness, and overall recovery rates.

Endurance athletes also use heart rate to estimate their max aerobic capacity (VO2max) and training intensity levels. During extended training sessions, there is an upward trend in athletes’ heart rate while working at the same intensities. This phenomenon is called cardiac drift.

Cardiac Drift

The upward trend in an athlete’s heart rate is multifactorial. The primary causes are dehydration and accumulation of metabolites.

Dehydration decreases blood plasma levels which forces the heart to work harder to deliver the necessary blood supply to the working muscles. The decreased blood plasma levels also affects the ability for the blood to accept metabolites that accumulate in working muscles.

To contract, muscles require energy. Endurance athletes predominantly rely on aerobic energy sources like carbohydrates and fat. The breakdown of these energy sources releases by-products that interfere with how efficient the muscle can contract. Therefore, it is important for these by-products to be expelled from the muscle cells. As water levels in the blood diminish, there is less drive for these by-products to exit the cell. Instead, they interfere with the mechanisms in the muscle cell that allow it to contract. This results in less forceful contractions and slower speeds.

When an athlete wants to maintain a given pace, they need to overcome these by-products. To do so, they heart increases its pace to deliver more energy to the muscles and maintain the needed amount of force.

The Linear Model

Below is some code to visualize an athlete’s increase in heart-rate while working at nearly the same rate for 45 minutes.

In the end, we see that the athlete’s heart rate is expected to increase by 16 beats per minute after 45-50 minutes of sustained exercise.

Application

This information can be applied to the critical velocity model. The external expression of an increase in heart rate is the decrease in an athlete’s critical velocity. As such, we should expect to see that the athlete either relies more on anaerobic energy over time to sustain a given pace or that their pace decreases to maximize their use of aerobic energy.