Mark S. Cook

Architectural Analysis of Human Abdominal Wall Muscles: Implications for Mechanical Function

Cadaveric analysis of human abdominal muscle architecture. To quantify the architectural properties of rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transverse abdominis (TrA), and model mechanical function in light of these new data. Knowledge of muscle architecture provides the structural basis for predicting muscle function. Abdominal muscles greatly affect spine loading, stability, injury prevention, and rehabilitation; however, their architectural properties are unknown. Abdominal muscles from 11 elderly human cadavers were removed intact, separated into regions, and microdissected for quantification of physiologic cross-sectional area, fascicle length, and sarcomere length. From these data, sarcomere operating length ranges were calculated. IO had the largest physiologic cross-sectional area and RA the smallest, and would thus generate the largest and smallest isometric forces, respectively. RA had the longest fascicle length, followed by EO, and would thus be capable of generating force over the widest range of lengths. Measured sarcomere lengths, in the postmortem neutral spine posture, were significantly longer in RA and EO (3.29 ± 0.07 and 3.18 ± 0.11 μm) compared to IO and TrA (2.61 ± 0.06 and 2.58 ± 0.05 μm) (P < 0.0001). Biomechanical modeling predicted that RA, EO and TrA act at optimal force-generating length in the midrange of lumbar spine flexion, where IO can generate approximately 90% of its maximum force. These data provide clinically relevant insights into the ability of the abdominal wall muscles to generate force and change length throughout the lumbar spine range of motion. This will impact the understanding of potential postures in which the force-generating and spine stabilizing ability of these muscles become compromised, which can guide exercise/rehabilitation development and prescription. Future work should explore the mechanical interactions among these muscles and their relationship to spine health and function.

Human skeletal muscle biochemical diversity

SUMMARY The molecular components largely responsible for muscle attributes such as passive tension development (titin and collagen), active tension development (myosin heavy chain, MHC) and mechanosensitive signaling (titin) have been well studied in animals but less is known about their roles in humans. The purpose of this study was to perform a comprehensive analysis of titin, collagen and MHC isoform distributions in a large number of human muscles, to search for common themes and trends in the muscular organization of the human body. In this study, 599 biopsies were obtained from six human cadaveric donors (mean age 83 years). Three assays were performed on each biopsy – titin molecular mass determination, hydroxyproline content (a surrogate for collagen content) and MHC isoform distribution. Titin molecular mass was increased in more distal muscles of the upper and lower limbs. This trend was also observed for collagen. Percentage MHC-1 data followed a pattern similar to collagen in muscles of the upper extremity but this trend was reversed in the lower extremity. Titin molecular mass was the best predictor of anatomical region and muscle functional group. On average, human muscles had more slow myosin than other mammals. Also, larger titins were generally associated with faster muscles. These trends suggest that distal muscles should have higher passive tension than proximal ones, and that titin size variability may potentially act to ‘tune’ the proteins mechanotransduction capability.

Architectural assessment of rhesus macaque pelvic floor muscles: comparison for use as a human model

Introduction and hypothesisAnimal models are essential to further our understanding of the independent and combined function of human pelvic floor muscles (PFMs), as direct studies in women are limited. To assure suitability of the rhesus macaque (RM), we compared RM and human PFM architecture, the strongest predictor of muscle function. We hypothesized that relative to other models, RM best resembles human PFM.MethodsMajor architectural parameters of cadaveric human coccygeus, iliococcygeus, and pubovisceralis (pubococcygeus + puborectalis) and corresponding RM coccygeus, iliocaudalis, and pubovisceralis (pubovaginalis + pubocaudalis) were compared using 1- and 2-way analysis of variance (ANOVA) with post hoc testing. Architectural difference index (ADI), a combined measure of functionally relevant structural parameters predictive of length-tension, force-generation, and excursional muscle properties was used to compare PFMs across RM, rabbit, rat, and mouse.ResultsRM and human PFMs were similar with respect to architecture. However, the magnitude of similarity varied between individual muscles, with the architecture of the most distinct RM PFM, iliocaudalis, being well suited for quadrupedal locomotion. Except for the pubovaginalis, RM PFMs inserted onto caudal vertebrae, analogous to all tailed animals. Comparison of the PFM complex architecture across species revealed the lowest, thus closest to human, ADI for RM (1.9), followed by rat (2.0), mouse (2.6), and rabbit (4.7).ConclusionsOverall, RM provides the closest architectural representation of human PFM complex among species examined; however, differences between individual PFMs should be taken into consideration. As RM is closely followed by rat with respect to PFM similarity with humans, this less-sentient and substantially cheaper model is a good alternative for PFM studies.

An unembalmed cadaveric preparation for simulating pleural effusion: A pilot study of chest percussion involving medical students

Cadaveric simulations are an effective way to add clinical context to an anatomy course. In this study, unembalmed (fresh) cadavers were uniquely prepared to simulate pleural effusion to teach chest percussion and review thoracic anatomy. Thirty first‐year medical students were assigned to either an intervention (Group A) or control group (Group B). Group A received hands‐on training with the cadaveric simulations. They were instructed on how to palpate bony landmarks for identifying the diaphragm and lobes of the lungs, as well as on how to properly perform chest percussion to detect abnormal fluid in the pleural space. Students in Group B practiced on each other. Students in Group A benefited from the training in several ways. They had more confidence in their percussive technique (A = mean 4.3/5.0, B = 2.9/5.0), ability to count the ribs on an intact body (A = mean 4.0/5.0, B = 3.0/5.0), and ability to identify the lobes of the lungs on an intact body (A = mean 3.8/5.0, B = 2.3/5.0). They also demonstrated a greater ability to locate the diaphragm on an intact body (A = 100%, B = 60%) and detect abnormal pleural fluid (A = 93%, B = 53%) with greater confidence (A = mean 3.7/5.0, B = 2.5/5.0). Finally, the hands‐on training with the unembalmed cadavers created more excitement around learning in Group A compared with Group B. This study shows that simulating pleural effusion in an unembalmed cadaver is a useful way to enhance anatomy education. Anat Sci Educ 10: 160–169.

Erratum to: Architectural design of the pelvic floor is consistent with muscle functional subspecialization

We found a mathematical error in sarcomere length (Ls) measurements in the original publication. Upon detection of the error, sarcomere lengths were re-measured from the original slide-mounted samples, and also in newly dissected fiber bundles from the same specimens to confirm accuracy. Architectural parameters were then recalculated using corrected Ls and all statistical analyses were repeated using corrected data. The revised calculations affected the absolute values only and showed that the pelvic floor muscles (PFMs) do not have sarcomeres shorter than other human skeletal muscles. Importantly, there are no changes in the major conclusion of the article regarding the functional subspecialization of the individual PFMs. A table containing the revised values and the adjusted Figs. 2 and 3 are presented below. Complete data for coccygeus (C), iliococcygeus (IC), and pubovisceralis (PV) muscles, expressed as means±SEM