Ultrasound-based testing of tendon mechanical properties: a critical evaluation.

In the past 20 years, the use of ultrasound-based methods has become a standard approach to measure tendon mechanical properties in vivo. Yet the multitude of methodological approaches adopted by various research groups probably contribute to the large variability of reported values. The technique of obtaining and relating tendon deformation to tensile force in vivo has been applied differently, depending on practical constraints or scientific points of view. Divergence can be seen in 1) methodological considerations, such as the choice of anatomical features to scan and to track, force measurements, or signal synchronization; and 2) in physiological considerations related to the viscoelastic behavior or length measurements of tendons. Hence, the purpose of the present review is to assess and discuss the physiological and technical aspects connected to in vivo testing of tendon mechanical properties. In doing so, our aim is to provide the reader with a qualitative analysis of ultrasound-based techniques. Finally, a list of recommendations is proposed for a number of selected issues.

Assessment of muscle volume and physiological cross-sectional area of the human triceps surae muscle in vivo.

The purpose of the present study was to investigate whether it is possible to predict the individual muscle volumes within the triceps surae (TS) muscle group by means of easily measurable parameters based on a theoretical consideration. A further objective was to verify the use of the available literature data to assess the contribution of each muscle of the group to the entire TS volume or physiological cross-sectional-area (PCSA). Therefore, magnetic resonance images of the right calf of 13 male subjects were acquired and each muscle of the TS was reconstructed. Muscle length (l(m)), the maximum anatomical cross-sectional-area (ACSA(max)) and muscle volume were obtained from the 3D models. To assess the PCSA, fascicle length was determined by ultrasonography. In general, muscle volume can be expressed as a fraction of the product of ACSA(max) and l(m). The size of the fraction depends on muscle shape and its coefficient of variance among the examined population was considerable low (soleus 6%, gastrocnemius 4% and gastrocnemius lateralis 7%) in the present study. The product of ACSA(max) and l(m) was, therefore, suitable to assess muscle volume (root mean squares, RMS 4-7%). Further, the soleus, gastrocnemius medialis and gastrocnemius lateralis accounted on average for about 52+/-3%, 32+/-2% and 16+/-2% of the total TS volume and 62+/-5%, 26+/-3% and 12+/-2% of the entire TS PCSA, respectively. The coefficient of variance of the relative portions were 5-10% for muscle volume and 8-17% for the PCSA.