# Changes in mechanical properties at the muscle level could be detected by Nakagami imaging during in-vivo fixed-end contractions

## TL;DR

This study shows that Nakagami imaging can detect changes in muscle stiffness during intense contractions, offering a new non-invasive method for muscle analysis.

## Contribution

The study demonstrates the feasibility of using Nakagami imaging to assess muscle stiffness during dynamic contractions in vivo.

## Key findings

- Nakagami parameters and muscle stiffness increased with contraction intensity.
- High intra-trial reliability and low variability were observed for Nakagami parameters.
- Significant positive correlations were found between Nakagami parameters and muscle stiffness.

## Abstract

In this study, we investigated the capability of the Nakagami transformation to detect changes in vastus lateralis muscle-tendon stiffness (k) during dynamic (and intense) contractions. k was evaluated in eleven healthy males using the gold-standard method (a combination of ultrasound and dynamometric measurements) during maximal and sub-maximal voluntary fixed-end contractions of the knee extensors (20, 40, 60, 80, and 100% of maximum voluntary force), while Nakagami parameters were analysed using the Nakagami transformation during the same contractions. Muscle-belly behaviour was investigated by means of B-mode ultrasound analysis, while Nakagami parameters were obtained in post-processing using radiofrequency data. k was calculated as the slope of the force-muscle-belly elongation relationship. Three contractions at each intensity were performed to calculate the intra-trial reliability and the coefficient of variation (CV) of the Nakagami parameters. At all contraction intensities, high values of intra-trial reliability (range: 0.92–0.96) and low CV (<9%) were observed. k and Nakagami parameters increased as a function of contraction intensity, and significant positive correlations were observed between these variables. These data suggest that changes in mechanical properties (e.g., stiffness) at the muscle level could be investigated by means of Nakagami parameters.