An Objective Measure of the Subjective Pain Response Resulting from Lumbar Muscle Fatigue Due to Lifting

Abstract

Pain is one of the body's least understood biological responses. Pain measurement often relies on the perception of the individual without any link to known objective responses within the body. The objective of the study was to relate a quantitative measurement of pain obtained by Magnetic Resonance Spectroscopy (MRS), which analyzes chemical shifts in the brain, to perceived pain responses, as measured by ratings of pain. A lifting task was performed to achieve lumbar musculature fatigue, and induce muscle pain. Prior to, immediately following, and 24-hours post, MRS scans were recorded to document chemicals in the brain. All of the participants elicited significant fatigue during the lifting task that resulted in significant pain immediately following and 24-hrs after fatiguing exertions. However, for the majority of brain chemical responses, there was not a significant pattern. The exception was the significant difference in brain response between males and females. Although the results were not completely conclusive in establishing a pain pathway, several key conclusions can be drawn: 1) pain processing appears to be different between males and females, 2) pain pathway to the brain is complex and maybe the underlying reason why low back pain is so elusive, and 3) chemical response may be different, depending upon the location in the brain. Future work will need to better delineate the latency period for muscle pain and changes in the neurosensory system in the brain.