Why a long workout doesn’t hurt your immune system — but chronic stress might
Exercise Duration Modulates Cortisol Release and Chronic Cortisol Exposure Jeopardises T Cell Effector Functions
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you exercise hard for 40 minutes, your body releases cortisol — but that’s okay. Your immune cells bounce back. But if cortisol stays high for days (like during chronic stress), it weakens your immune cells and helps some cancers grow.
Surprising Findings
A 5-minute sprint didn’t raise cortisol at all, while a 40-minute workout did.
Everyone assumes high intensity = big cortisol spike. But duration, not intensity, was the key driver—contradicting popular fitness dogma.
Practical Takeaways
If you’re stressed out, prioritize short, intense workouts (like 5-min sprints) over long, grueling sessions—your cortisol levels won’t spike, and you’ll still get benefits.
Not medical advice. For informational purposes only. Always consult a healthcare professional. Terms
When you exercise hard for 40 minutes, your body releases cortisol — but that’s okay. Your immune cells bounce back. But if cortisol stays high for days (like during chronic stress), it weakens your immune cells and helps some cancers grow.
Surprising Findings
A 5-minute sprint didn’t raise cortisol at all, while a 40-minute workout did.
Everyone assumes high intensity = big cortisol spike. But duration, not intensity, was the key driver—contradicting popular fitness dogma.
Practical Takeaways
If you’re stressed out, prioritize short, intense workouts (like 5-min sprints) over long, grueling sessions—your cortisol levels won’t spike, and you’ll still get benefits.
Publication
Journal
Immunology
Year
2025
Authors
T. Luu, Line Fleischer Hach, T. Seremet, K. Leuchte, P. thor Straten, G. Holmen Olofsson
Related Content
Claims (6)
When a person engages in aerobic exercise lasting more than 15 minutes, their body shows an increase in cortisol levels, which is a hormone released in response to physical stress.
In laboratory cell cultures, prolonged exposure to the hormone cortisol increases the growth rate of certain melanoma and breast cancer cells over 72 hours, but does not alter the growth of prostate cancer cells.
Prolonged exposure to normal levels of the stress hormone cortisol over several days reduces the activity and signaling molecule production of a type of immune cell called CD3+ T cells, but a short four-hour exposure does not cause lasting changes.
Prolonged exposure to the stress hormone cortisol is associated with increased levels of PD-1 on activated T cells, a marker linked to reduced T cell function, while short-term exposure does not produce this effect.
A 40-minute high-intensity workout increases cortisol in the blood for over an hour after exercise in healthy adults, but a 5-minute sprint does not, suggesting that how long you exercise matters more than how hard you push for triggering this hormonal response.