We use the word ‘stress’ constantly—’I’m so stressed,’ ‘work is stressful,’ ‘stress is killing me.’ But what exactly is stress from a physiological standpoint? Understanding what happens in your body during stress is the first step toward managing it effectively.
At Performance Health, we see patients every day whose physical symptoms—headaches, muscle tension, digestive issues, poor sleep—are directly linked to chronic stress. Let’s break down the science behind stress and explore how it affects far more than just your muscles.
The Stress Response: Your Autonomic Nervous System
Stress is fundamentally your body’s response to perceived threats or demands. This response is controlled by your autonomic nervous system, which operates automatically without conscious thought. The autonomic nervous system has two main branches that work in opposition to each other:
The Sympathetic Nervous System: ‘Fight or Flight’
This is your stress response system. When you perceive a threat—whether it’s a physical danger, a work deadline, a difficult conversation, or financial pressure—your sympathetic nervous system activates. This is the ancient ‘fight or flight’ response that helped our ancestors survive genuine physical threats.
When the sympathetic system activates, several immediate changes occur:
• Your heart rate increases to pump more blood to your muscles
• Your breathing quickens to increase oxygen delivery
• Blood is redirected away from non-essential functions like digestion toward your muscles and brain
• Your muscles tense, preparing for action
• Stress hormones like cortisol and adrenaline flood your system
• Your pupils dilate to improve vision
• Digestion slows or stops
• Non-essential functions like tissue repair and immune response are temporarily suppressed
This response is incredibly effective for short-term, acute threats. If you’re being chased by a predator, you don’t need to digest your lunch—you need all available resources directed toward running. The problem is that modern stressors (deadlines, relationship conflicts, financial worries) don’t require physical action, yet they trigger the same response. And these stressors tend to be chronic rather than acute.
The Parasympathetic Nervous System: ‘Rest and Digest’
This is your recovery system. The parasympathetic nervous system promotes relaxation, repair, and restoration. When it’s dominant, your body focuses on essential maintenance functions that were suppressed during the stress response.
The parasympathetic system:
• Slows your heart rate
• Promotes normal, relaxed breathing
• Activates digestion and nutrient absorption
• Reduces muscle tension
• Supports immune function
• Facilitates tissue repair and recovery
• Promotes sleep and restorative processes
Healthy function requires balance between these two systems. The sympathetic system should activate when needed and then the parasympathetic system should take over for recovery. Problems arise when you’re stuck in sympathetic dominance—constantly stressed without adequate recovery periods.
Beyond Muscle Tension: How Chronic Stress Affects Your Whole Body
While we often discuss stress in terms of neck and shoulder tension (which is very real and significant), chronic activation of the stress response affects nearly every system in your body.
Digestive Dysfunction
When your sympathetic nervous system is dominant, blood is redirected away from your digestive organs. This isn’t a problem for brief periods, but chronic stress creates persistent digestive issues. Many patients experience irritable bowel syndrome (IBS), bloating, acid reflux, nausea, or changes in appetite directly linked to stress.
The gut-brain connection is bidirectional—stress affects digestion, and poor gut health can increase anxiety and stress. Chronic stress can alter your gut microbiome, reduce nutrient absorption, and increase intestinal permeability (‘leaky gut’). This explains why people often notice digestive symptoms improving when they successfully manage stress.
Sleep Disruption
Sleep requires parasympathetic dominance—your body needs to shift into rest and recovery mode. Chronic stress keeps your sympathetic system activated, making it difficult to fall asleep and reducing sleep quality. Even if you do fall asleep, elevated cortisol and sympathetic activity can fragment your sleep, causing frequent waking.
Poor sleep then creates a vicious cycle: inadequate sleep reduces your stress tolerance, making you more reactive to stressors the next day, which then further disrupts sleep. Many patients describe lying awake with racing thoughts, an inability to ‘turn off their brain’—this is sympathetic activation preventing the parasympathetic system from taking over.
Immune Suppression
Chronic elevation of cortisol (your primary stress hormone) suppresses immune function. This is why people under significant stress often get sick more frequently. Your body is prioritizing immediate threat response over long-term health maintenance, leaving you vulnerable to infections.
Cardiovascular Strain
Persistent sympathetic activation keeps heart rate and blood pressure elevated. Over time, this increases risk for hypertension, atherosclerosis, and cardiovascular disease. The chronic inflammatory state created by sustained stress also damages blood vessels and contributes to heart disease risk.
Metabolic Dysfunction
Chronic cortisol elevation promotes insulin resistance, increases appetite (particularly for high-calorie foods), and encourages fat storage, especially around the abdomen. This is why sustained stress often leads to weight gain and increases risk for type 2 diabetes.
Cognitive Impact
Chronic stress impairs memory, concentration, and decision-making. Elevated cortisol can actually shrink the hippocampus (the brain region critical for memory formation) and reduce neuroplasticity. Many people under sustained stress describe feeling foggy, forgetful, or unable to focus.
The Problem: Modern Life Creates Chronic Stress
The stress response evolved to handle acute, physical threats followed by recovery periods. Modern life, however, creates a different pattern: chronic, psychological stressors that never fully resolve. You’re not being chased by a predator (acute threat, followed by either escape or death, then recovery). Instead, you have ongoing job pressure, financial concerns, relationship difficulties, information overload, and 24/7 connectivity that prevent your nervous system from shifting into recovery mode.
Many people exist in a state of chronic sympathetic activation—constantly ‘on,’ never fully relaxing. This creates the wide array of symptoms we’ve discussed: persistent muscle tension, headaches, digestive issues, poor sleep, frequent illness, and cognitive impairment.
What This Means for Treatment
Understanding that stress is a physiological state—not just a psychological feeling—changes how we approach treatment. You can’t just ‘think your way out’ of chronic stress. Your nervous system needs actual interventions to shift from sympathetic dominance back to balanced function.
Effective stress management requires addressing both the physical manifestations (muscle tension, postural dysfunction, movement deficits) and implementing strategies that activate your parasympathetic nervous system. This includes chiropractic care to address the musculoskeletal consequences, but also exercise, sleep optimization, breathing techniques, and lifestyle modifications—topics we’ll explore in upcoming articles.
Take Control of Your Stress Response
Stress isn’t just ‘in your head’—it’s a real, measurable physiological state affecting every system in your body. The good news is that understanding the mechanisms gives us clear targets for intervention. Whether you’re experiencing neck pain, headaches, digestive issues, poor sleep, or simply feeling constantly ‘on edge,’ there are evidence-based approaches that can help restore balance to your nervous system.
At Performance Health, we take a comprehensive approach to stress-related symptoms, addressing both the physical dysfunctions and providing guidance on nervous system regulation. If you’re dealing with symptoms of chronic stress, contact us today for an evaluation. Understanding your stress response is the first step—addressing it effectively is what creates lasting change.