Document Type


Date of Degree

Fall 2016

Degree Name

PhD (Doctor of Philosophy)

Degree In

Physical Rehabilitation Science

First Advisor

Frey Law, Laura A

First Committee Member

Rakel, Barbara A

Second Committee Member

Selby, John C

Third Committee Member

Shields, Richard K

Fourth Committee Member

Sluka, Kathleen A


Pain and movement are intimately connected and nearly universal human experiences. However, our understanding of the extent, significance, and mechanisms of pain-movement relationships is limited. While pain is a normal, protective response to injury and potentially harmful stimuli, prolonged or dysfunctional neuromuscular adaptions in response to pain can contribute to a variety of pain conditions. Alternatively, movement (in the form of global physical activity, individual exercise programs, and/or specific motor learning/functional tasks) is often prescribed to help decrease pain and improve function. While attempts have been made to show an effect of movement on pain or to better understand altered movement strategies in response to pain, much of the research has been limited to animal models or to those with specific persistent or chronic pain conditions limiting generalizability and interpretability. Therefore, this research sought to advance current understanding of the relationships between physical activity and normal variability in centrally- and peripherally-mediated pain in healthy adults. Additionally, we sought to characterize changes in reflexive motor responses in the upper extremity to an endogenous, naturally-occurring, long-lasting acute muscle pain.

The results of these investigations indicate that greater, self-reported intense (i.e. vigorous) and leisure activity are more strongly associated with decreased pain sensitivity than is pain modulation or measured activity (via accelerometry). Future research is needed to determine directionality of these relationships. Further, reflexive motor responses to endogenous, acute muscle pain in the upper extremity were not significantly altered indicating that changes in pain-related, movement strategies may be more strongly influenced by supraspinal adaptations. These results may have value in improving understanding of pain-related, movement sequelae and directing future research in this area.

Public Abstract

We move differently when we are in pain. Despite being able to observe relationships between pain and movement, our understanding of the extent, significance, and mechanisms of these relationships is unclear. For example, although medical professionals often reassure us that changes in movement in response to pain are normal, dysfunctional movement changes can lead to long-term negative consequences. Similarly, while increased movement/activity is often recommended to decrease pain in those with pain conditions, it is not clear whether increased activity is related to decreased pain in healthy, otherwise pain-free adults. Therefore, this research sought to clarify the relationships between physical activity and normal pain responses in healthy adults. Additionally, we wanted to determine whether protective reflexes in the arm changed in response to naturally occurring muscle pain.

The results of these investigations indicate that more time spent in intense physical (e.g. running) and recreational activities is related to decreased pain in healthy adults. In addition, individual reports of physical activity were more strongly related to decreased pain than measured activity (i.e. accelerometer). More research is needed to determine whether more activity results in decreased pain or whether those with less pain engage in more activity. Further, protective arm reflexes only changed their movement behaviors slightly in response to muscle pain. This indicates that movement changes in response to muscle pain may be more due to changes in pain-related brain areas than in the spinal cord. Additional research is needed to confirm this theory.


nociceptive withdrawal reflex, pain modulation, physical activity measurement, pressure pain threshold, quantitative sensory testing, referred pain


xii, 125 pages


Includes bibliographical references (pages 115-125).


Copyright © 2016 Shannon L.M. Merkle