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In vivo moment arm determination using B-mode ultrasonography
1Graduate School of Health and Sport Science, Nippon Sport Science University, Setagaya, Tokyo, Japan. itom@nittai.ac.jp
Journal of Biomechanics
|February 1, 2000
Summary
Ultrasonography accurately measured tibialis anterior (TA) muscle moment arms in vivo. Higher muscle forces (30-60% MVC) provided more reliable moment arm estimates than relaxed states (0% MVC).
Area of Science:
- Biomechanics
- Musculoskeletal System
- Medical Imaging
Background:
- The tibialis anterior (TA) muscle plays a crucial role in ankle dorsiflexion.
- Accurate measurement of the TA moment arm is essential for understanding lower limb biomechanics and function.
- Previous methods for determining moment arms have limitations in vivo.
Purpose of the Study:
- To measure the in vivo tendon excursion of the tibialis anterior (TA) muscle.
- To determine the TA moment arm (m) across different force levels.
- To evaluate the reliability of ultrasonography for estimating TA moment arms.
Main Methods:
- In vivo B-mode ultrasonography was used to measure TA tendon excursion in seven subjects.
- Subjects exerted three force levels: 0%, 30%, and 60% maximal voluntary contraction (MVC).
- A dynamometer controlled ankle angle, and a parametric model (m = R sin(a + delta)) was fitted to the data.
Main Results:
- Moment arm (R) values at 0% MVC were significantly smaller than at 30% and 60% MVC.
- Moment arm estimates at 0% MVC were considered inadequate due to potential muscle-tendon unit slackness.
- Moment arm values at 30% and 60% MVC were deemed reliable estimates of the TA moment arm.
Conclusions:
- Ultrasonography provides a functional in vivo assessment of tendon excursion.
- Applying muscle tension (30-60% MVC) minimizes confounding effects of slackness and tendon elongation.
- This ultrasonographic technique offers more significant moment arm estimations compared to other in vivo or cadaver methods.