I believe the problem you are encountering is due to the fact that that
action of tibialis anterior is oblique to the anatomical reference
planes. You are forcing the measurement of muscle activity to occur
along an artificial, and arbitrary, geometry. Inasmuch as tibialis
anterior is primarily a foot inverter, I doubt that you would ever be
able to obtain realistic and meaningful measured values if your
perspective is limited to the sagittal plane.

Thomas M. Greiner, Ph.D.
Anatomist and Physical Anthropologist
Dept. of Health Professions
University of Wisconsin - La Crosse
1725 State Street
La Crosse, WI 54601 USA

-----Original Message-----
From: * Biomechanics and Movement Science listserver
[mailto:BIOMCH-L@NIC.SURFNET.NL] On Behalf Of Stuart Miller
Sent: Wednesday, May 07, 2008 9:10 AM
Subject: [BIOMCH-L] Locating Tibialis Anterior tendon's action line
using MRI

Hello all,

My colleagues and I have recently started to calculate the moment arm of
the tibialis anterior and Achilles tendon. The method we are using is
the Reuleaux graphical analysis. The images of the ankle are collected
using MRI techniques. The images are collected in the sagittal plane.
This technique has been described in Maganaris et al. (1999); Clinical
Biomechanics 14 pp661-666.

The problem we are experiencing is of locating the action line of the
tibialis anterior. The tibialis anterior tendon crosses the sagittal
plane, so only an oval cross-section can be seen. This does not appear
enough to accurately locate the action line of the tendon.

I am wondering if anyone has experienced this problem whilst using this
technique, and if so, can suggest any solutions.

The action line of the Achilles tendon is easy to see as it acts along
the sagittal plane.

I will forward a summary of the responses in a few weeks.

Thank you in advance.

Stuart C. Miller BSc. (Hons)

Centre for Sports Medicine and Human Performance

Brunel University