Understanding Delayed-Onset Exercise-Induced Pain in Individuals with Chronic Pain Syndromes

Introduction

Two patients with chronic musculoskeletal pain and Ehlers-Danlos Syndrome (EDS) recently demonstrated similar but unexpected responses to routine exercise interventions. Their experiences prompted me to reexamine my understanding of exercise-induced pain in individuals with chronic musculoskeletal conditions.

Patient Case Studies

Patient A:
During a physical therapy session, a patient with EDS performed a spinal core-strengthening quadruped bird-dog isometric exercise. She did not complain of pain during or immediately after the exercise and expressed hopefulness. However, later that evening, she called, distressed: “I am in extreme pain—my entire back is burning.” Notably, during our initial intake, when I asked if there was anything else I should know, she replied, “I have a high tolerance for pain.”

Patient B:
Another EDS patient completed deep squat flexibility and strengthening exercises with proper form and no reported pain. Post-session, she noted feeling tired but invigorated. The next day, however, she emailed: “Intense, severe, sharp, burning ankle and shin pain. The pain is excruciating when I stand.” When we later discussed this, she said, “My spouse says I’m the opposite of hypersensitive—it takes a lot for me to say something actually hurts, especially with exercise.”

Despite appropriate technique and no immediate pain complaints, both patients experienced delayed, severe pain responses. These cases challenged my assumptions about pain response, pain tolerance, and the mechanisms behind post-exercise discomfort.

Searching for Explanations

Key Questions: - Why does a low level of exercise trigger a disproportionate response to pain? - Why do patients who claim to have high pain tolerance experience such intense delayed pain?

To answer these questions, I reviewed current literature on chronic pain mechanisms. One leading theory is central nervous system (CNS) sensitization.

CNS Sensitization Explained

CNS sensitization occurs when the brain and spinal cord become overly reactive to sensory input, heightening pain perception. It can be compared to a car alarm set too sensitively. Normally, the alarm only sounds when a window is broken. But if the system is altered, even a gust of wind might trigger it. Similarly, in CNS sensitization, the pain alarm may go off from a minor, non-threatening activity like light exercise.

The pain feels very real, but no actual tissue damage has occurred. This can be frustrating for both the patient and the clinician. It is important to understand that this type of pain, while not harmful, is just as severe and distressing as pain from injury.

Interestingly, research indicates that transient increases in pain or other adverse responses to exercise in chronic pain patients are likely underreported. ¹This raises the possibility that such experiences are more common than acknowledged.

Reconciling Pain Tolerance with Observed Behavior

Both patients claimed to have a high pain tolerance, yet they experienced intense pain from activities not expected to cause discomfort. This initially seemed contradictory. I began to wonder if I misunderstood their cues or if they were confusing pain threshold (the point at which something starts to hurt) with tolerance (the ability to endure pain once it starts).

This disconnect may also reflect a phenomenon known as allodynia, when normally non-painful stimuli cause pain due to errors in CNS processing. Think of it like sunburn: even a gentle touch can be agonizing, though it causes no further damage. Similarly, in chronic pain, gentle exercise might trigger intense pain responses without causing harm.

This distinction is critical: hurt does not always equal harm. Pain may be temporary and tolerable, even if intense, and may represent a step toward recovery rather than a setback.

Supporting Evidence from Research

A study led by Mark Bishop at the University of Florida explored this further.² Researchers compared healthy individuals to those with chronic musculoskeletal pain following an exercise protocol designed to induce delayed onset muscle soreness. Both groups experienced pain, but the chronic pain group reported:

• Higher peak pain at rest (46/100 vs. 20.6/100)
• Longer time to peak pain with movement (2.3 days vs. 1.6 days)
• Prolonged resolution time at rest (9.6 days vs. 2.4 days)

Functional MRI scans reveal brain connectivity differences between groups, particularly in areas related to sensory appraisal and emotional regulation.

These findings suggest that individuals with chronic pain: - Require longer recovery time between sessions - Have impaired ability to interpret sensory signals - Struggle with cognitive control and anxiety related to pain

In short, they experience pain that is more intense, longer-lasting, more easily triggered, and emotionally disruptive compared to pain-free individuals. This reinforces the theory that their brains process pain differently.

Moving Forward: A Revised Approach

To better support individuals with chronic musculoskeletal pain, I plan to adjust my clinical approach in the following ways:

1. Communication and Education - Use positive, placebo-enhancing language; avoid nocebo-inducing terms - Reinforce the distinction between hurt and harm - Encourage regular check-ins via text or email to monitor post-exercise symptoms
2. Emotional and Cognitive Support - Incorporate diaphragmatic breathing with positive affirmations - Guide patients through positive mental imagery - Help reframe negative thoughts (e.g., “There is no damage. It will get better.”)
3. Exercise Programming - Begin with lower-intensity exercises than usual - Progress gradually to promote desensitization - Allow ample time for rest and recovery between sessions
4. Redefining Success - Shift focus from eliminating pain to improving function and emotional response - Accept that progress may be slower and require more frequent supervision - Emphasize resilience, self-awareness, and long-term self-management

Understanding the mechanisms behind delayed-onset pain in individuals with chronic pain conditions like EDS helps clinicians develop more compassionate, informed, and effective interventions. By acknowledging the reality of their pain without assuming harm, we can better support patients on their path to improved function and well-being.

References:

1. Leitzelar BN, Koltyn KF. Exercise and Neuropathic Pain: A General Overview of Preclinical and Clinical Research. Sports Med Open. 2021;7(1):21.
2. Bishop MD, Alappattu MJ, Rana P, et al. Delayed Recovery After Exercise-Induced Pain in People with Chronic Widespread Muscle Pain Related to Cortical Connectivity. Brain Sci. 2024;14(11).

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