Sarcomere length distribution quantification in whole muscle frozen sections

Abstract

Laser diffraction (LD) is a valuable tool for measuring sarcomere length (L s ), a major determinant of muscle function. However, this method relies on few measurements per sample that are often extrapolated to whole muscle properties. Currently it is not possible to measure L s throughout an entire muscle and determine how L s varies at this scale. To address this issue, we developed an actuated LD scanner for sampling large numbers of sarcomeres in thick whole muscle longitudinal sections. Sections of high optical quality and fixation were produced from tibialis anterior and extensor digitorum longus muscles of Sprague-Dawley rats (N=6). Scans produced twodimensional L s maps, capturing >85% of the muscle area per section. Individual L s measures generated by automatic LD and bright-field microscopy showed excellent agreement over a large L s range (ICC>0.93). Two-dimensional maps also revealed prominent regional L s variations across muscles.

Characterization of three dimensional volumetric strain distribution during passive tension of the human tibialis anterior using Cine Phase Contrast MRI

“…Our previous finite element modelling study, which defined IMP as the hydrostatic component of the Cauchy stress tensor, suggests that both pressure and stress are characterized by regional differences in muscle (Jenkyn et al, 2002). Related modeling work has more directly demonstrated region differences in fiber-direction muscle stress and sarcomere length (recently confirmed experimentally (O’Connor et al, 2016)), concluding that intramuscular force transmission is also non-uniform (Yucesoy et al, 2003a). This and similar studies further found that muscle force at the proximal and distal muscle ends were unequal, providing evidence for inter- and extramuscular myofascial force transmission (Huijing and Baan, 2001; Maas et al, 2001).…”

Dynamic Musculoskeletal Functional Morphology: Integrating diceCT and XROMM

“…A recently developed probe capable of measuring thousands of sarcomeres in vivo (Young et al, 2017) offers a promising alternative to mechanical transducers and may help resolve the problems of modeling single muscle force from sarcomere length during non-isometric and submaximal activity. However, multiple such probes will be necessary given that fiber and sarcomere strain are heterogeneous throughout the muscle (Ahn et al, 2003;Konow et al, 2010;Wentzel et al, 2011;Holman et al, 2012;Moo et al, 2016;O'Connor et al, 2016).…”

“…The whole muscle and whole fiber lengths estimated using our method do not provide information on sarcomere length dynamics, which impairs our ability to estimate muscle force. Fascicles and sarcomeres exhibit strain heterogeneity, the functional consequences of which are unclear (Ahn et al, 2003;Konow et al, 2010;Wentzel et al, 2011;Holman et al, 2012;O'Connor et al, 2016;Moo et al, 2016). Muscle morphology may contribute to strain heterogeneity, as the more peripheral fibers in fusiform muscles may have different strain patterns than more central fibers (Pappas et al, 2002;Blemker et al, 2005;Zatsiorsky and Prilutsky, 2012).…”

Muscle Functional Morphology in Paleobiology: The Past, Present, and Future of “Paleomyology”

“…Furthermore, we seldom know what proportion of maximum force capability is represented by muscle activation during a biologically significant action if that action is not amenable to experimental testing. Additional issues include heterogeneity of fiber activation and fiber length within a muscle which might produce erroneous estimates of muscle force, delay in the signal of activation, and issues related to the relationship between force and velocity (Ahn et al, ; German et al, ; Konow et al, ; Wentzel et al, ; Holman et al, ; O'Connor et al, ; Moo et al, ). Another unknown is the relative contribution of the passive components of muscle tissue (e.g., tendon, aponeurosis, etc.)…”