Muscle activation assessment using ultrasound time-harmonic elastography and tonic vibration reflex

Area of Science:

• Biomechanics
• Musculoskeletal Ultrasound
• Rehabilitation Engineering

Background:

• Muscle activation inherently increases tissue stiffness, a property measurable by elastography.
• Assessing skeletal muscle stiffness is crucial for understanding muscle function and diagnosing conditions.
• Current methods for assessing muscle stiffness often rely on voluntary contractions, which can be subjective.

Purpose of the Study:

• To evaluate whether tonic vibration reflex (TVR) can be utilized as a stimulation method for the functional assessment of skeletal muscle stiffness.
• To compare muscle stiffness changes induced by TVR with those induced by active voluntary contractions (VC).

Main Methods:

• Ultrasound time-harmonic elastography (THE) was applied to the vastus lateralis muscle in 25 asymptomatic volunteers.
• Participants underwent THE during passive TVR (100 Hz frequency; 200 µm and 400 µm amplitudes) and active VC (15 N, 22 N, 37 N loads).
• Shear wave speed (SWS), a proxy for muscle stiffness, was measured and analyzed.

Main Results:

• A significant increase in SWS was observed with increasing VC loads (p < 0.001).
• Similarly, TVR activation led to significant increases in SWS for both low and moderate amplitudes (p < 0.001).
• The increase in SWS during moderate TVR amplitude correlated significantly with the SWS increase at a 37 N VC load (r = 0.67, p < 0.001).

Conclusions:

• TVR-induced muscle stiffness changes, particularly at moderate amplitudes and 100 Hz, show promise as an objective alternative to VC-based loading for functional muscle stiffness assessment in healthy individuals.
• Further research is needed to validate TVR-THE as a standardized clinical tool for assessing activation-related stiffness in patient populations.