Optimal stimulation parameters to detect deficits in quadriceps voluntary activation

Area of Science:

• Neuromuscular physiology
• Exercise science
• Biomedical engineering

Background:

• Estimating quadriceps voluntary activation is crucial for assessing muscle function.
• Current stimulation methods can cause significant participant discomfort, limiting study adherence and data quality.
• Optimizing stimulation parameters is needed to balance accurate activation measurement with participant comfort.

Purpose of the Study:

• To identify optimal electrical stimulation parameters for estimating quadriceps voluntary activation.
• To compare different calculation methods for quadriceps activation.
• To minimize participant discomfort during activation assessments.

Main Methods:

• Twelve healthy adults underwent repeated maximal volitional isometric contractions (MVIC).
• Quadriceps stimulation involved 4 combinations (2 or 10 pulses; 400 or 200 V; variable or standardized current) during resting twitch (RT) and MVIC.
• Quadriceps activation was calculated using central activation ratio and percent activation; discomfort was measured via visual analog scale.

Main Results:

• The central activation ratio method yielded significantly higher quadriceps activation values than the percent activation method (p < 0.009).
• A doublet pulse stimulus (2 pulses) significantly reduced discomfort during both RT (p < 0.04) and MVIC (p < 0.001) compared to a 10-pulse train.
• Estimates of quadriceps activation showed strong correlations (r = 0.85-0.99, p < 0.001) across all methods.

Conclusions:

• A doublet pulse stimulus provides quadriceps activation data equivalent to traditional 10-pulse trains.
• This optimized stimulation approach significantly minimizes participant discomfort.
• The doublet pulse stimulus is recommended for efficient and comfortable assessment of quadriceps voluntary activation.