In This Issue (3.5 min read)

The Cortisol Conversation We Need To Have
The Difference Between Adapting Well vs. Maladapting
Heart Rate Variability: A Useful Yet Underused Training Tool

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The Cortisol Conversation We Need To Have

If you spend any time on social media, you will have likely encountered some version of this warning: that certain types of exercise - strength training, high-intensity interval training, and even long runs - spike your cortisol, throw your hormones into chaos, and should be avoided, particularly by women. The message sounds right with all its medical jargon.

It also happens to be wrong. Let's set the record straight.

The Cortisol Misunderstanding

Cortisol is not the bad guy. It is a hormone released by the adrenal glands in response to physical and psychological demand. During exercise, its release is not a malfunction. It is the point.

When your body is working hard, the brain directs a coordinated hormonal response designed to meet that demand. Cortisol facilitates the release of glucose into the bloodstream, promotes the conversion of amino acids into fuel, and suppresses acute inflammation to protect tissues under stress. This is not damage. This is physiology doing exactly what it evolved to do.

It is worth noting that a significant cortisol spike typically occurs only during high-intensity exercise or prolonged, exhaustive training. A brisk walk does not meaningfully move the needle. At higher intensities, the rise in circulating cortisol is temporary, purposeful, and self-limiting when we are adequately recovering.

The problem is not the spike. The problem is conflating an acute, adaptive response with chronic dysregulation - two entirely different physiological states that require entirely different conversations.

The Difference Between Adapting Well Versus Maladapting

Here is the distinction that social media rarely makes: the cortisol released during a hard workout is what exercise scientists call a hormetic stressor.

Hormesis is the principle that a controlled, time-limited challenge, applied at the right dose, triggers the body to rebuild stronger than before. The temporary discomfort of a heavy lift or a hard interval is the stimulus. Adaptation is the result.

Maladaptation - what was formerly called overtraining syndrome - is a different matter entirely. It occurs when training load consistently exceeds the body's capacity to recover. In this state, cortisol does remain chronically elevated, and the consequences are real: suppressed immune function, disrupted sleep, mood instability, reduced performance, and potential muscle breakdown.

No need to get worked up about cortisol, track this instead.

Heart Rate Variability: A Useful Yet Underused Training Tool

Heart rate variability, or HRV, measures the variation in time between consecutive heartbeats. Unlike heart rate itself, which simply counts beats per minute, HRV reflects the dynamic interplay between the sympathetic (fight-flight) and parasympathetic (rest-digest) branches of the autonomic nervous system.

When your HRV is trending upward or holding steady, training is working. The body is absorbing load, adapting, and building resilience.

When HRV drops and stays down, that is meaningful data - not a reason to panic, but a signal indicating that you may need a recovery day, that sleep has been inadequate, that life stress is compounding training stress, or that volume or intensity needs to be dialed back temporarily.

Most modern wearables like the Apple Watch, WHOOP, Garmin, and Oura Ring track HRV continuously and make it easy to interpret. The goal is not to hit a particular number, since HRV is highly individual. The goal is to understand your own baseline and notice directional trends over time.

Rather than avoiding exercise out of fear of what cortisol might be doing, I encourage you to use HRV as your guide. It gives you real, individualized information about how your body is responding to training - and it puts the decision-making back where it belongs: in your hands, not some TikToker who's got it all wrong.

Warmly,