Chronic Cardio = Elevated Cortisol

When our body is under stress, cortisol increases the concentration of glucose in our blood so there’s readily available energy for our muscles to use. Cortisol secretion is a natural response to stress, and is a good thing when released infrequently and for short periods. This makes a lot of sense when looking at the lives of our hunter-gatherer ancestors who needed cortisol during times of acute stress. When the caveman (or woman) needed to react quickly to escape a predator, this brief fight-or-flight response and secretion of cortisol was beneficial in helping him or her survive.

Since cortisol is secreted as soon as an activity starts and continues until completion, the duration of exercise is an important consideration.

A study from 1976 in the Journal of Applied Physiology showed no increase in cortisol secretion after 10min (at 75% intensity), yet after 30min it doubled!

Generally speaking, we see an abundant amount of cortisol following long-distance steady-state aerobic exercise.  Mainly because those choosing running, cycling, or swimming are consistently seeking more miles.

A study from 2011 analyzed the cortisol levels in 304 amateur endurance athletes and the average additional secretion above the control was 42%!

cortisol 1

The stress we experience today (40hr+ work week, traffic, etc) is not only very different from our hunter-gatherer ancestors, but many take part in excessive endurance training which only adds more cortisol. This chronic exposure results in an increase in fat storage hormones and decrease in muscle building hormones; and over time promotes more serious long-term consequences like cognitive decline, altered immune function, and damaged reproductive health.

Interestingly, with an activity like walking, cortisol is removed faster than it’s secreted.

Stay Lean!
Coach Mike