Quantification of Neuromuscular Fatigue: What Do We Do Wrong and Why?

Area of Science:

• Exercise Physiology
• Neuroscience
• Biomedical Engineering

Background:

• Neuromuscular fatigue (NMF) assessment typically uses non-invasive voluntary and evoked contractions in healthy, athletic, and clinical groups.
• Stimulation and response measurement for NMF quantification appear straightforward but present inherent challenges.

Purpose of the Study:

• To highlight common pitfalls encountered during the quantification of neuromuscular fatigue.
• To discuss potential biases and limitations in NMF assessment methods and data analysis.

Main Methods:

• Review of existing literature on NMF quantification techniques.
• Analysis of potential issues arising from fatigue definitions, measurement delays, stimulation parameters, and data interpretation.

Main Results:

• NMF quantification can be confounded by the choice of fatigue parameters (e.g., power vs. torque).
• The delay between exercise cessation and testing can lead to underestimation of impairments and misinterpretation of fatigue causes.
• Technique-specific biases (e.g., stimulation intensity) and data analysis choices (e.g., M-wave amplitude) can affect results.

Conclusions:

• Researchers and clinicians must be aware of and mitigate the identified pitfalls for accurate NMF assessment.
• Recommendations include careful consideration of testing delays, population-specific methods, and technique limitations.