When stressful thoughts consume your day, it can feel as though stress is strictly a mental problem. The reality is that stress materializes as both emotional and physiological symptoms—your brain and body are inseparable.

Whether you are running from a lion or preparing for a presentation at work, your brain and body share a single response system for all stressors—the autonomic nervous system (ANS).

Knowing how your body uses the ANS to react to different situations can help you build awareness and identify practices that transform your stress reaction into a reasoned response.

Stress vs. Rest

The ANS functions like a tug-of-war game between two subsystems: your activation (sympathetic nervous) system and your rest (parasympathetic nervous) system. Both regulate essential body functions like heart rate, respiratory rate, and digestion.

Your sympathetic nervous system is well known as the driver of your activating, fight-or-flight response, while the parasympathetic nervous system kicks in during calmer moments as your rest-and-digest network.

Both systems dial their activity up or down based on messages from your brain and spinal cord. These systems can be active at the same time, or one can take over and dominate the other.

When activated, they trigger a cascade of changes in your body:

If your fight-or-flight system starts to dominate, there are some rest-and-digest functions that stop altogether, while others simply scale back.

Your rest-and-digest system has multiple players (e.g., your heart, lungs, liver). If your fight-or-flight system dominates, some parasympathetic players quit (e.g., digestion pauses while you’re running). Others may use a different tactic; for example, as you warm up for a jog, your body will shift its temperature-regulating strategy and reroute blood from your internal organs to your skin in an effort to shed heat.

Finding Balance

Life’s stress levels naturally fluctuate. When your body remains in a stressed-out, fight-or-flight mode, it can take a serious toll on your health by slowing your recovery time, weakening your immune system, and impacting your mental state.

Our ANS was designed to help us deal with brief episodes of high-intensity stress (e.g., running from a predator), but our modern lifestyle contains multiple chronic stressors that rarely shut off (e.g., job pressure, balancing childcare and work, sleep deprivation, and constant device stimulation).

It’s all about balance. You don’t want your fight-or-flight system to be in a constant state of activation, but you also don’t want it to remain inactive—it is essential for your survival ability to respond to stress as well as maintain your body’s equilibrium.

Managing Your Stress

We are often unaware of the tug-of-war inside our ANS because it functions involuntarily and reflexively. Becoming more in tune with the physiological effects of stress can help you regulate your response or deploy strategies to bring you back into balance.

Check out these tips to identify and reverse imbalances sooner:

  • Become more self-aware: Techniques like meditation can help you become more in touch with how activated or relaxed your body is. Taking a moment during the day also offers an opportunity to reset imbalances when you sense them and may even improve your sleep.
  • Sense imbalances sooner: Consider how wearables, like Oura, can give you the opportunity to follow patterns of stress within your body and measure their impact more objectively. You can even see your body’s ANS balance and reduce stress by monitoring your heart rate variability.
  • Improve your resilience: Increasing your fitness level and improving your sleep both boost your body’s ability to bounce back from stressful periods. If you’re looking for ways to rest and restore, consider these ideas.


  •  Stults-Kolehmainen, Matthew A., and John B. Bartholomew. “Psychological stress impairs short-term muscular recovery from resistance exercise.” Medicine and science in sports and exercise 44, no. 11 (2012): 2220-2227. (link)
  • Morey, Jennifer N., Ian A. Boggero, April B. Scott, and Suzanne C. Segerstrom. “Current directions in stress and human immune function.” Current opinion in psychology 5 (2015): 13-17. (link)
  • Slavich, George M. “Life stress and health: A review of conceptual issues and recent findings.” Teaching of Psychology 43, no. 4 (2016): 346-355. (link)