Reliability of Ipsilateral Motor Pathway Excitability Measurements

Recent research highlights the importance of understanding ipsilateral motor pathway excitability in the context of rehabilitation and sports science. These pathways reflect the activity of the cortico-reticulospinal system. While clinicians increasingly use ipsilateral motor-evoked potentials (iMEPs) to assess neural recovery, the reliability of these measures remained largely unverified. Consequently, a new study evaluated the stability of these neural markers during active exercise.

The study recruited fifty-three healthy participants to undergo sessions involving preacher curls. Specifically, researchers measured contralateral and ipsilateral motor-evoked potentials alongside maximal muscle action potentials. Participants performed repetitions at 30% of their one-repetition maximum (1-RM). Meanwhile, the team delivered transcranial magnetic stimulation (TMS) during the concentric phase of the movement. This rigorous approach allowed for a precise analysis of reliability across different days.

Reliability Findings for Ipsilateral Motor Pathway Excitability

Notably, the results demonstrated good-to-excellent reliability for both intra-session and inter-session measurements. The ICCs for iMEP and cMEP amplitudes were particularly impressive, reaching levels above 0.91. Moreover, the presence of iMEP was consistent and stable over time. Thus, researchers can confidently use these metrics to track neural adaptations in both male and female athletes.

However, the study also provided a cautionary note regarding the iMEP/cMEP ratio (ICAR). While individual amplitudes are stable, the ratio exhibited substantial inter-session variability. Specifically, the coefficient of variation reached 56.8%, which suggests that ICAR may not be a reliable longitudinal marker. Furthermore, sex did not influence the reliability scores, making this assessment method widely applicable.

In conclusion, iMEP and cMEP measurements during exercise offer a robust way to evaluate neural excitability. This tool is particularly useful for rehabilitation specialists monitoring recovery. However, professionals should rely on absolute amplitude measures rather than calculated ratios for the most accurate results.

Frequently Asked Questions

How reliable is the measurement of ipsilateral motor pathway excitability?

Current evidence indicates that measurements of ipsilateral motor pathway excitability, specifically iMEP and cMEP amplitudes, show excellent intra-session and inter-session reliability, with ICC values often exceeding 0.90.

Is there a difference in reliability between men and women?

No, the study found that sex does not influence the reliability of iMEP or cMEP measurements. Both groups show consistent results during exercise-based assessments.

Why is caution advised when using the ICAR ratio?

The iMEP/cMEP ratio (ICAR) exhibits high inter-session variability compared to individual amplitude measures. Consequently, it may lead to less accurate conclusions in longitudinal studies compared to using raw iMEP data.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice or a professional relationship. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

1. Zhou J et al. Intra- and inter-session reliability of ipsilateral motor pathway excitability measurements in male and female adults. J Appl Physiol (1985). 2026 Apr 14. doi: 10.1152/japplphysiol.01122.2025. PMID: 41979887.


2. Cavaleri R et al. Reliability of Transcranial Magnetic Stimulation measures of corticospinal excitability in a task-specific context. Journal of Science and Medicine in Sport. 2017.


3. Bawa P et al. Ipsilateral corticospinal and transcallosal pathways to bicipital and tricipital motoneurons in humans. Exp Brain Res. 2004.