Delayed-Onset Muscle Soreness Alters Mechanical Sensitivity, but Not Thermal Sensitivity or Pain Modulatory Function

Abstract

Introduction

Many clinical musculoskeletal pain conditions are characterized by chronic inflammation that sensitizes nociceptors. An unresolved issue is whether inflammation affects all nociceptors in a similar manner. Exercise-induced muscle damage (EIMD) has been proposed as a model for simulating clinical inflammatory pain in healthy samples. We sought to test the effect of EIMD on various painful stimuli (pressure and thermal), central pain processing (via the nociceptive flexion reflex) and endogenous pain modulation via conditioned pain modulation and exercise-induced hypoalgesia.

Methods

Eighteen participants (9F, age: 24.6 ± 3.3) were recruited for repeated measures testing and each completed pain sensitivity testing prior to and 48 hours after an eccentric exercise protocol. The participants performed a minimum of 6 rounds of 10 eccentric knee extension exercises to induce muscle damage and localized inflammation in the right quadriceps. Force decrements, knee range-of-motion, and delayed onset muscle soreness (DOMS) were used to quantify EIMD.

Results

There was a significant main effect of time for pressure pain (%diff; −58.9 ± 23.1; p = 0.02, ηp2 = 0.28) but no significant main effect was observed for limb (%diff; −15.5 ± 23.9; p = 0.53, ηp2 = 0.02). In contrast, there was a significant interaction between time and limb (p < 0.001, ηp2 = 0.47) whereby participants had lower pressure pain sensitivity in the right leg only after the damage protocol (%diff; −105.9 ± 29.2; p = 0.002).

Discussion

Individuals with chronic inflammatory pain usually have an increased sensitivity to pressure, thermal, and electrical stimuli, however, our sample, following muscle damage to induce acute inflammation only had sensitivity to mechanical pain. Exercise induced inflammation may reflect a peripheral sensitivity localized to the damaged muscle rather than a global sensitivity like those with chronic pain display.

Keywords:

• pain sensitivity
• exercise induced muscle damage
• acute inflammation
• pain modulation

Acknowledgments

The authors would like to thank the participants for their time and effort throughout the project. An abstract on some of the findings presented in this paper was presented at the American College of Sport Medicine Annual Meeting as a poster presentation with interim findings. The poster’s abstract was published in Medicine and Science in Sport and Exercise. DOI: 10.1249/01.mss.0000878032.71202.7b

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare no conflicts of interest in this work.

Additional information

Funding

Funding for this study was provided by the Department of Health and Exercise Science Helen Riddle Dissertation Award and the College of Arts and Sciences Robberson Research Award to Jessica Peterson.