JMIR Publications

ABSTRACT

Background:

Chronic pain affects over 30% of the global population and remains a major public health issue due to limited treatment efficacy and the need for mechanism-based, personalized approaches. Motor behavior is theorized to play a role in pain persistence through altered movement patterns, muscle recruitment, and proprioception. While motor behavior is linked to chronic pain, empirical evidence on underlying mechanisms, particularly cortical dynamics, remains scarce.

Objective:

The objective of this study is to investigate longitudinal changes in cortical sensorimotor excitability and their relationship with maladaptive motor behaviors.

Methods:

This prospective longitudinal study will follow 150 healthy participants, aged 18–65, recruited from the community, experiencing experimentally induced muscle pain across four visits (Day 0, Day +2, Day +4, and five days after pain resolution). Pain will be induced using intramuscular injections of nerve growth factor into the extensor carpi radialis brevis (ECRB) muscle. The primary outcome is motor variability, assessed during multidimensional wrist movement tasks and quantified using root means square deviation (RMSD) and muscle synergies (derived from EMG recordings of four forearm muscles). Secondary outcomes include cortical mechanisms (EEG peak alpha frequency; TMS mapping, SICI, and ICF), sensorimotor integration (evoked potential), cognitive control (Multisource Interference Task), and endogenous pain modulation (conditioned pain modulation). Self-report questionnaires will assess pain intensity and disability (PRTEE, MPQ-SF, LMSS) as well as psychological factors such as fear of movement, pain-related beliefs, and coping strategies (TSK, PBQ, CSQ-R). This sample size provides 80% power at 5% significance to detect a medium effect size across 23 predictor variables, with Bonferroni correction and 10% loss-to-follow-up allowance. Data will be analyzed using two-level growth curve modeling to characterize interindividual differences in motor behavior, cortical dynamics, and pain processing trajectories.

Results:

All study procedures have been approved by the Western University Health Science Research Ethics Board (review reference: 2025-125757-103291). Funding was provided by the Canadian Institutes of Health Research (CIHR) under grant number 517783 for the period 2024-2029. Recruitment for the study began in April 2025, and all data collection is expected to be completed by 2028. As of April 2026, we have enrolled 26 participants. Results are expected to be published at the end of 2028.

Conclusions:

The findings will advance understanding of motor behaviour in pain and lay the foundation for personalized therapies, moving beyond current generic treatments that offer limited benefits.