Take It Easy: Too Much Exercise Frazzles the Vagus Nerve
Improving physical fitness requires putting stress on your system during vigorous workouts. But the quest for peak performance often backfires—the psychophysiological distress caused by excessive exercise isn’t good for you. Finding a “Goldilocks zone” where your daily workouts put enough stress on your body to improve fitness without overdoing it can be tricky.

Chris Bergland finishing a Triple Ironman in the early 2000s.
Source: Chris Bergland
For example, when I was trying to get in shape for extreme events like the Triple Ironman (7.2-mile swim, 336-mile bike, 78.6-mile run), the risk of injury and burnout was extremely high. Monitoring fluctuations in my heart rate variability (HRV) was a way to make sure I wasn’t overtraining.
The vagus nerve‘s ability to counteract the sympathetic nervous system‘s fight-or-flight stress response is reflected by higher HRV.
In addition to keeping tabs on how my nervous system responded to the previous day’s