Three-dimensional architecture of macrofibrils in the human scalp hair cortex

Human scalp hairs are comprised of a central cortex enveloped by plate-like cuticle cells. The elongate cortex cells of mature fibres are composed primarily of macrofibrils-bundles of hard-keratin intermediate filaments (IFs) chemically cross-linked within a globular protein matrix. In wool, three cell types (ortho-, meso- and paracortex) contain macrofibrils with distinctly different filament arrangements and matrix fractions, but in human hair macrofibril-cell type relationships are less clear. Here we show that hair macrofibrils all have a similar matrix fraction (∼0.4) and are typically composed of a double-twist architecture in which a central IF is surrounded by concentric rings of tangentially-angled IFs. The defining parameter is the incremental angle increase (IF-increment) between IFs of successive rings. Unlike the wool orthocortex, hair double-twist macrofibrils have considerable inter-macrofibril variation in IF increment (0.05–0.35°/nm), and macrofibril size and IF increment are negatively correlated. Correspondingly, angular difference between central and outer-most IFs is up to 40° in small macrofibrils, but only 5–10° in large macrofibrils. Single cells were observed containing mixtures of macrofibrils with different diameters. These new observations advance our understanding of the nano-level and cell-level organisation of human hair, with implications for interpretation of structure with respect the potential roles of cortex cell types in defining the mechanical properties of hair.     

The three-dimensional arrangement of intermediate filaments in Romney wool cortical cells

The three-dimensional orientation and arrangement of intermediate filaments in Romney wool ortho-, meso-, and paracortical cells has been revealed using single axis high voltage electron tomography. Modelled tomograms confirm that intermediate filaments in orthocortical cells are arranged helically, with the helical angle progressively increasing from the centre to the periphery of macrofibrils. Intermediate filaments in meso- and paracortical cells display parallel arrangements differing mainly in packing density, with the mesocortex packed more tightly than the paracortex. The intermediate filament arrangements observed confirm expectations based on earlier two-dimensional transmission electron microscopy observations by the authors and other researchers. It is expected that these findings will contribute to a better understanding of the biological and structural basis of wool fibre curvature.     

The influence of the crimp and slope grip position on the finger pulley system

In this study the influence of the grip position (crimp grip vs. slope grip position) on the pulley system of the finger was investigated. For this purpose 21 cadaver finger (11 hands, 10 donors) were fixed into an isokinetic loading device. Nine fingers were loaded in the slope grip position and 12 fingers in the crimp grip position. The forces in the flexor tendons and at the fingertip were recorded. A rupture of the A4 pulley occurred most often in the crimp grip position (50%) but did not occur in the slope grip position, in which alternative events were the most common (67%). The forces in the deep flexor tendon (FDP) (slope grip: 371 N, crimp grip: 348 N) and at the fingertip (slope grip: 105 N, crimp grip: 161 N) were not significantly different between the 2 finger positions, but the forces acting on the pulleys were higher in the crimp grip position (A2 pulley: 287 N, A4 pulley: 226 N) than in the slope grip position (A2 pulley: 121 N, A4 pulley: 103 N). The crimp grip position may be the main cause for A4 pulley ruptures but the slope grip position may be hazardous for other injuries as the forces recorded in the flexor tendons and at the fingertip were comparable at the occurrence of a terminal event.     

A concerted polymerization-mesophase separation model for formation of trichocyte intermediate filaments and macrofibril templates. 1: relating phase separation to structural development

The concept that macrofibril templates, the fibrillar precursor to complete macrofibrils incorporating matrix proteins in trichokeratins, are formed by intracellular anisotropic phase separation of intermediate filaments (IFs), is here developed in detail. The factors affecting structural development, including IF length dispersion, and presence of other macromolecular solutes, are discussed in terms of the statistical thermodynamic models presented over 30 years ago by P.J. Flory and co-workers. The crucial role of pendant IF head groups in controlling IF separation and stabilizing the mesophase is emphasised. In particular, a concerted process of polymerization of unit-length IF precursors coupled with continuous transfer of longer IFs to the anisotropic phase is invoked. Observed structures in differentiated cell lines in mature fibres are rationalised in terms of different possible nematic or double-twist liquid crystalline precursor structures, with varying degrees of anisotropic phase coalescence. The occurrence of rarely observed macromolecular double-twist structures is made plausible by qualitative analysis of mesophase mechanics and reference to alternative structures in other macromolecular mesogens. The model is consistent with, and explains, certain well-known features of mature fibre structure, such as filament-matrix ratios in different cell lines. A few comments relating to the infill of the template by keratin intermediate filament associated proteins (IFAPs) are presented.     

Search for novel histone deacetylase inhibitors. Part II: Design and synthesis of novel isoferulic acid derivatives

Previously, we described the discovery of potent ferulic acid-based histone deacetylase inhibitors (HDACIs) with halogeno-acetanilide as novel surface recognition moiety (SRM). In order to improve the affinity and activity of these HDACIs, twenty seven isoferulic acid derivatives were described herein. The majority of title compounds displayed potent HDAC inhibitory activity. In particular, IF5 and IF6 exhibited significant enzymatic inhibitory activities, with IC₅₀ values of 0.73 ± 0.08 and 0.57 ± 0.16 μM, respectively. Furthermore, these compounds showed moderate antiproliferative activity against human cancer cells. Especially, IF6 displayed promising profile as an antitumor candidate with IC₅₀ value of 3.91 ± 0.97 μM against HeLa cells. The results indicated that these isoferulic acid derivatives could serve as promising lead compounds for further optimization.     

The effect of surface area digitizations on the prediction of spherical anatomical geometries for computer-assisted applications

Intraoperative digitization of osseous structures is an integral component of computer-assisted orthopaedic surgery. This study determined the repeatability and accuracy of predicting known radii and center locations of spherical objects for different proportions of digitized surface areas and various sphere sizes. Also, we investigated these accuracies for some relevant near-spherical osseous structures where results from full area digitizations were considered to be true. Digitizations were performed using an electromagnetic tracker with a stylus on the total and fractional surfaces of 10 hemispheres, ranging from 10 to 28 mm in radius. Repeatability was quantified by digitizing five trials of the entire surface and various fractional areas of selected hemisphere sizes. Similar trials were conducted on models of a humeral and femoral head, using the full head area as baseline and digitizing 15 and 30 mm diameter areas of the full head. Mean error for the predicted radii and center positions of the hemispheres ranged from 0.39±0.29 to 0.14±0.07 mm and 0.52±0.31 to 0.22±0.12 mm, respectively. Repeatability for the predicted radii and centers produced maximum standard deviations of 0.31 and 0.42 mm, respectively. All errors decreased as fractional area (40%, 60%, 80% and 100%) increased (p<0.05). Radius of curvature and center position errors for the humeral head model were 1.51±2.11 and 2.28±1.51 mm, respectively. These errors for the femoral head model were 3.37±4.14 and 4.25±4.14 mm, respectively. Errors resulting from the prediction of radius and center indicate that non-spherical anatomical structures are more sensitive to the digitized area, and hence digitization of the largest surface possible seems warranted.     

A multi-scale approach to understand the mechanobiology of intermediate filaments

The animal cell cytoskeleton consists of three interconnected filament systems: actin microfilaments, microtubules and the lesser known intermediate filaments (IFs). All mature IF proteins share a common tripartite domain structure and the ability to assemble into 8–12 nm wide filaments. At the time of their discovery in the 1980s, IFs were only considered as passive elements of the cytoskeleton mainly involved in maintaining the mechanical integrity of tissues. Since then, our knowledge of IFs structure, assembly plan and functions has improved dramatically. Especially, single IFs show a unique combination of extensibility, flexibility and toughness that is a direct consequence of their unique assembly plan. In this review we will first discuss the mechanical design of IFs by combining the experimental data with recent multi-scale modeling results. Then we will discuss how mechanical forces may interact with IFs in vivo both directly and through the activation of other proteins such as kinases.     

Differences in the proportion of collagen and muscle in the canine lower urinary tract with regard to gonadal status and gender

Gonadectomy not only affects hormonal homeostasis but also alters the turnover of different components of the extracellular matrix in urogenital tissues. Collagen is an important component of the bladder and urethral walls and thus crucial for the mechanical properties of normal lower urinary tract (LUT) functions. This study aimed at investigating the possibility of differences in the proportion of collagen and muscle tissues in the LUT of intact and gonadectomised male and female dogs. Twenty clinically healthy dogs were used including 10 sexually intact dogs (5 males, 5 anoestrus females) and 10 gonadectomised dogs (4 males and 6 females). Four regions of the LUT, i.e. body and neck of the bladder as well as proximal and distal urethra were collected. The tissue sections were stained with Masson's Trichrome. Quantitative evaluation of the blue-stained area for collagen and red-counterstained area for muscle was performed using colour image analysis. The relative proportion of collagen and muscle significantly differed with the gonadal status, the gender and the region. Overall, gonadectomised dogs had a higher (P < 0.001) proportion of collagen and consequently a lower (P < 0.001) proportion of muscle than intact dogs. Regardless of gonadal statuses, females had a higher (P < 0.05) proportion of collagen and a lower (P < 0.05) proportion of muscle tissues than males. Gender differences were found in all four regions of the LUT in intact dogs but only in proximal urethra in gonadectomised dogs where spayed females had a higher (P < 0.05) proportion of collagen and less muscle (P < 0.05). Regional differences were observed in females; a higher proportion of collagen and therefore less muscle were found in the urethra compared with the bladder. Proportional differences in collagen and muscle between intact and gonadectomised animals suggest a relation of different hormonal statuses to structural changes in the canine LUT. Excessive collagen deposits and less muscular volume may impair structural and functional integrity of the LUT which may associate with the development of post-neutering urinary incontinence in the dog.     

Validation of a smart shoe for estimating foot progression angle during walking gait

The foot progression angle is an important measurement related to knee loading, pain, and function for individuals with knee osteoarthritis, however current measurement methods require camera-based motion capture or floor-embedded force plates confining foot progression angle assessment to facilities with specialized equipment. This paper presents the validation of a customized smart shoe for estimating foot progression angle during walking. The smart shoe is composed of an electronic module with inertial and magnetometer sensing inserted into the sole of a standard walking shoe. The smart shoe charges wirelessly, and up to 160 h of continuous data (sampled at 100 Hz) can be stored locally on the shoe. For validation testing, fourteen healthy subjects were recruited and performed treadmill walking trials with small, medium, and large toe-in (internal foot rotation), small, medium, and large toe-out (external foot rotation) and normal foot progression angle at self-selected walking speeds. Foot progression angle calculations from the smart shoe were compared with measurements from a standard motion capture system. In general, foot progression angle values from the smart shoe closely followed motion capture values for all walking conditions with an overall average error of 0.1 ± 1.9 deg and an overall average absolute error of 1.7 ± 1.0 deg. There were no significant differences in foot progression angle accuracy across the seven different walking gait patterns. The presented smart shoe could potentially be used for knee osteoarthritis or other clinical applications requiring foot progression angle assessment in community settings or in clinics without specialized motion capture equipment.     

Sources of variation contributing to production and quality attributes of Kyrgyz cashmere in Osh and Naryn provinces: Implications for industry development

We aimed to quantify the sources of variation contributing to the production and quality of cashmere produced in five districts in Osh and Naryn provinces of Kyrgyzstan. In early spring 2008 mid-side cashmere samples were taken from 719 cashmere adult females, and 41 cashmere adult males and castrates. Samples came from 53 villages and a total of 156 farmers’ flocks. For 91 goats from 33 farmers in 13 villages of two districts that had been sampled earlier, cashmere was combed from the goat at the time of a second visit (end of April 2008) when the cashmere would normally be harvested. Following standard cashmere objective measurement, data were examined using general linear modelling to quantify the effects of potential determinants. The mean fibre diameter (MFD) of cashmere differed between provinces (Osh 15.7 μm, Naryn 16.7 μm; P = 4.4 × 10⁻²⁰). About 42% of the cashmere was <16 μm, 48% was 16.0–18.0 μm and 9.5% was >18.0 μm. Most of the cashmere samples were coloured (81%), with 63% black and 19% white. The percentage of cashmere samples that were white declined as MFD increased (26% < 14 μm to 11% of >18 μm). The primary determinants of cashmere MFD of individual goats were age of goat (range 1.46 μm, P = 1.8 × 10⁻¹²) and farm (range 6.5 μm, P = 1.7 × 10⁻¹⁴). The lesser effects detected for sex (range 0.9 μm, P = 0.026) and colour of cashmere (range 1.8 μm, P = 0.023) were based on small sample sizes and are unreliable. Age of goat had important affects on fibre diameter variation (up to 1.7% in coefficient of variation, P = 5.8 × 10⁻⁶) and fibre curvature (2.5–5°/mm, P = 2.1 × 10⁻⁴). By far the greatest effect on fibre curvature was cashmere MFD (P = 3.0 × 10⁻¹⁰⁴) with a smaller effect of sex (about 5°/mm, P = 3.0 × 10⁻⁶). Village effects were detected on fibre diameter variability (range 4.5% in coefficient of variation, P = 0.027) and fibre curvature (range 15°/mm, P = 1.6 × 10⁻⁷). There was a strong negative association between increasing MFD and declining fibre curvature (−5.11 ± 0.181°/mm per 1 μm; P = 7.1 × 10⁻¹²¹; r² = 0.51). Average combed cashmere weight was 164 g, the clean cashmere content was 0.661 and median clean cashmere production was 110 g per goat (range 60–351 g). Combed cashmere production increased with altitude of the village, probably related to different moulting times as spring temperatures warmed up later in higher altitude villages up to 3200 masl. Measurements of combed cashmere MFD were coarser than the mid-side samples taken earlier in the year. There are farmers and cashmere goats in the sampled districts of Kyrgyzstan which produce the finest qualities of commercial cashmere as the vast majority of cashmere is fine, has low variation in fibre diameter and has fibre crimping (curvature) typical of Chinese and Mongolian cashmere. There is substantial scope to increase the production and commercial value of cashmere produced by Kyrgyz goats. In particular, some villages and farmers need to change their buck selection practices if they wish to produce acceptable cashmere. Farmers should separate their finer and white cashmere prior to sale.     

Introduction of sheep meat breeds in extensive systems: Lamb carcass characteristics

Genotype effects on lamb carcass traits were investigated in a 4-year study aimed at assessing potential benefits from introducing meat breeds into the wool-oriented extensive sheep systems of northeastern Patagonia, Argentina. Five ram [Corriedale: CO; Border Leicester: BL; Île de France: IF; Texel: TX; and synthetic CRIII (25% Merino, 37.5% IF, 37.5% TX)] and 5 dam (CO; synthetic CRIII; BLCO: BL × CO; IFCO: IF × CO; and TXCO: TX × CO) genotypes were represented in the study. Data were collected from 436 male lambs of 9 genotypes (CO × CO, BL × CO, IF × CO, TX × CO, CRIII × CO, CRIII × BLCO, CRIII × IFCO, CRIII × TXCO, and CRIII × CRIII). Hot carcass weights and dressing yields were determined after slaughtering. Carcasses were given conformation and subcutaneous fat scores using the EUROP system [scale varying from E (best) to P (poorest) for conformation, and from 1 (lean) to 5 (overfat) for subcutaneous fat]. Linear measurements of carcass length and width were recorded and carcass compactness indices were calculated from those. Purebred CO acted as a standard for comparisons. On a constant liveweight basis, genotypes CRIII × IFCO and CRIII × CRIII presented higher (P < 0.05) carcass weight and dressing yield than CO × CO and BL × CO. Crossbred and synthetic genotypes showed higher (P < 0.05) carcass width than CO × CO. With the exception of BL × CO the remaining genotypes showed higher (P < 0.05) carcass width/length ratio than CO × CO. The probability that carcasses of crossbred and synthetic lambs presented better conformation than CO × CO was higher than 84%. Carcasses of CRIII × IFCO lambs were given the best conformation scores. The probability that BL × CO carcasses presented higher subcutaneous fat than the remaining genotypes exceeded 79%. Our results indicate significant improvements in carcass conformation arising from crossing. Sheep farmers in extensive systems could take advantage of the higher fatness of BL crossbred lambs to produce light carcasses with adequate fat cover, a crucial industry requirement. Terminal crossbreeding with Île de France, Texel, and CRIII rams could be implemented to improve carcass conformation thus matching market demand for heavy carcasses with limited fat content. Second cross schemes did not improve carcass commercial traits over the best terminal cross or the synthetic CRIII breed.     

Digital breast tomosynthesis: Dose and image quality assessment

The aim of this work was to evaluate how different acquisition geometries and reconstruction parameters affect the performance of four digital breast tomosynthesis (DBT) systems (Senographe Essential – GE, Mammomat Inspiration – Siemens, Selenia Dimensions – Hologic and Amulet Innovality – Fujifilm) on the basis of a physical characterization.Average Glandular Dose (AGD) and image quality parameters such as in-plane/in-depth resolution, signal difference to noise ratio (SDNR) and artefact spread function (ASF) were examined.Measured AGD values resulted below EUREF limits for 2D imaging. A large variability was recorded among the investigated systems: the mean dose ratio DBT/2D ranged between 1.1 and 1.9.In-plane resolution was in the range: 2.2 mm⁻¹–3.8 mm⁻¹ in chest wall-nipple direction. A worse resolution was found for all devices in tube travel direction.In-depth resolution improved with increasing scan angle but was also affected by the choice of reconstruction and post-processing algorithms. The highest z-resolution was provided by Siemens (50°, FWHM = 2.3 mm) followed by GE (25°, FWHM = 2.8 mm), while the Fujifilm HR showed the lowest one, despite its wide scan angle (40°, FWHM = 4.1 mm).The ASF was dependent on scan angle: smaller range systems showed wider ASF curves; however a clear relationship was not found between scan angle and ASF, due to the different post processing and reconstruction algorithms.SDNR analysis, performed on Fujifilm system, demonstrated that pixel binning improves detectability for a fixed dose/projection.In conclusion, we provide a performance comparison among four DBT systems under a clinical acquisition mode.     

Location of chlorhexidine in DMPC model membranes: a neutron diffraction study

Chlorhexidine (CHX) is an effective anti-bacterial agent whose mode of action is thought to be the disruption of the cell membrane. It is known to partition into phospholipid bilayers of aqueous model-membrane preparations. Neutron diffraction data taken at 36 °C on the location of CHX in phosphatidylcholine (PC) bilayers is presented. The center of mass of the deuterated hydrocarbon chain of CHX is found to reside 16 Å from the center of the bilayer in 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (14:0–14:0 PC). This places the drug near the glycerol backbone of the lipid, and suggests a mode of action whereby the molecule is bent in half and inserts wedge-like into the lipid matrix. This mechanism is distinct from detergent-like mechanisms of membrane disruption and more similar to some anti-microbial peptide action, where peptides insert obliquely into the bilayer headgroup region to disrupt its structure.     

Effects of dose and adaptation time of a specific blend of essential oil compounds on rumen fermentation

Essential oils can be used as natural additives in animal feeds. The present study evaluated the effects of three different doses and different adaptation times of a specific blend of essential oils (BEO) on rumen microbial fermentation. Eight dual flow continuous culture fermenters (1320 ml) were used in two periods of 9 days each to study the effects of increasing doses of BEO. Treatments were: CTR (no BEO), D5 (5 mg/l of BEO), D50 (50 mg/l of BEO) and D500 (500 mg/l of BEO). During the last 3 days, samples were taken at 0, 2, 4 and 6 h after the morning feeding and analyzed for large peptide (LPep), small peptides plus amino acid (SPep + AA) and ammonia N concentrations, and at 2 h after feeding for volatile fatty acids (VFA) concentration and profile. The D5 increased total VFA concentration, acetate proportion and acetate to propionate ratio, and decreased propionate and valerate proportion, compared with CTR. The concentration of LPep N tended (P=0.08) to be lower for D5 compared with CTR. In the second experiment, eight sheep were used to study the effects of long-term adaptation of rumen fluid to BEO on ruminal fermentation. Four sheep were assigned at random to the CTR treatment (no BEO) and four sheep were adapted to BEO (110 mg/day of BEO) for 4 weeks (ADBEO). After 4 weeks samples of ruminal fluid were obtained at 0 and 3 h after the morning feeding and in 2 consecutive days using an oro-ruminal probe. Samples were analyzed for LPep, SPep + AA and ammonia N concentrations, total and individual VFA, and pH. Treatment ADBEO tended (P<0.10) to increase acetate proportion and decrease valerate proportion, compared with CTR. Ruminal fluid collected from each of CTR and ADBEO sheep was used to study in vitro fermentation profile of soybean meal, corn meal, alfalfa hay and ryegrass hay. Treatments were: Control fluid (CTR without BEO), CTR fluid plus a single dose of BEO (11 mg/l; CTR + BEO) and ADBEO fluid plus a single dose of BEO (11 mg/l; ADBEO + BEO). Acetate proportion and acetate to propionate ratio was higher, and propionate and isovalerate proportion, and BCVFA and ammonia N concentration were lower in ADBEO + BEO fluid compared with CTR fluid. The addition of essential oils can shift the microbial fermentation in the rumen by increasing the acetate to propionate ratio and inhibiting deamination.     

Directional selection by termites at a branching node created by a ballpoint pen

Subterranean termites excavate complex underground tunnels for foraging. Most tunnels comprise primary and secondary tunnels. Tunnels originating from the nest are called primary and those branching from the primary tunnels are named secondary tunnels; tertiary and quaternary tunnels are rarely observed. During foraging, termites may thus encounter a considerable number of tunnel-branching nodes. Directional selection at such a node is likely correlated to tunnel-growth activity because tunnels containing more termites have a higher probability of growth. In this study, we investigated how termites select the direction of movement at an artificially-designed branching node, by making chemical trails on filter paper, drawing lines using a ballpoint pen which contained the chemical substance that induces the termite to follow trails. The trails consisted of two lines: straight and branching. The branching line was drawn from the center of the straight line at an angle θ (10°, 20°,…, 90°). We then calculated the ratio of the directional selection as r = N_s/N_b, where N_s and N_b represent the number of straight and branching tunnels selected, respectively. The values of r were statistically classified into three groups based on the angle of the branching trail, as follows: 10° ≤ θ ≤ 20°, 30° ≤ θ ≤ 60°, and 70° ≤ θ ≤ 90°. Our paper briefly discusses the underlying mechanisms of the experimental results.     

Estimations of relative effort during sit-to-stand increase when accounting for variations in maximum voluntary torque with joint angle and angular velocity

The main purpose of this study was to compare three methods of determining relative effort during sit-to-stand (STS). Fourteen young (mean 19.6 ± SD 1.2 years old) and 17 older (61.7 ± 5.5 years old) adults completed six STS trials at three speeds: slow, normal, and fast. Sagittal plane joint torques at the hip, knee, and ankle were calculated through inverse dynamics. Isometric and isokinetic maximum voluntary contractions (MVC) for the hip, knee, and ankle were collected and used for model parameters to predict the participant-specific maximum voluntary joint torque. Three different measures of relative effort were determined by normalizing STS joint torques to three different estimates of maximum voluntary torque. Relative effort at the hip, knee, and ankle were higher when accounting for variations in maximum voluntary torque with joint angle and angular velocity (hip = 26.3 ± 13.5%, knee = 78.4 ± 32.2%, ankle = 27.9 ± 14.1%) compared to methods which do not account for these variations (hip = 23.5 ± 11.7%, knee = 51.7 ± 15.0%, ankle = 20.7 ± 10.4%). At higher velocities, the difference in calculating relative effort with respect to isometric MVC or incorporating joint angle and angular velocity became more evident. Estimates of relative effort that account for the variations in maximum voluntary torque with joint angle and angular velocity may provide higher levels of accuracy compared to methods based on measurements of maximal isometric torques.     

Electrode placement over the innervation zone affects the low-, not the high-frequency portion of the EMG frequency spectrum

The purpose of this study was to use a wavelet-based signal processing technique to examine the influence of electrode placement over the innervation zone (IZ) on the shape of the electromyographic (EMG) frequency spectrum. Ten healthy males (mean ± SD age = 23.6 ± 3.0 years) performed isometric muscle actions of the dominant leg extensors at 10%, 40%, 70%, and 100% of the maximum voluntary contraction (MVC). Surface EMG signals were detected simultaneously from the vastus lateralis with two bipolar electrode arrangements. One of the electrode arrangements had its center point located directly over the IZ, while the other arrangement had its center point distal to the IZ (i.e., 20 mm away). All EMG signals were processed with a wavelet-based procedure. The results showed that for all isometric torque levels, the EMG signals from the distal electrode arrangement demonstrated greater total intensity values than those for the IZ arrangement for frequencies ranging from approximately 2 to 110 Hz. There were no consistent differences, however, between the IZ and distal electrode arrangements for total EMG intensity values above 110 Hz. Thus, these findings indicated that electrode placement over the IZ affected primarily the low-, rather than the high-frequency portion of the EMG frequency spectrum.     

Posture-movement changes following repetitive motion-induced shoulder muscle fatigue

Repetitive motion-induced fatigue not only alters local motion characteristics but also provokes global reorganization of movement. However, the three-dimensional (3D) characteristics of these reorganization patterns have never been documented in detail. The goal of this study was to assess the effects of repetitive reaching-induced arm fatigue on the whole-body, 3D biomechanical task characteristics. Healthy subjects (N = 14) stood and performed a continuous reaching task (RRT) between two targets placed at shoulder height to fatigue. Whole-body kinematic (Vicon^©), kinetic (AMTI^© force platforms) and electromyographic (EMG, Noraxon^©) characteristics were recorded. Maximal voluntary isometric efforts (MVIE) of the shoulder and elbow were measured pre- and post-RRT. Post-RRT shoulder elevation MVIE was reduced by 4.9 ± 8.3% and trapezius EMG amplitude recorded during the RRT increased by 46.9 ± 49.9% from the first to last minute of the RRT, indicating that arm fatigue was effectively induced. During fatigued reaching, subjects elevated their shoulder (11.7 ± 10.5 mm) and decreased their average shoulder abduction angle by 8.3 ± 4.4°. These changes were accompanied by a lateral shift of the body’s center of mass towards the non-reaching arm. These findings suggest a compensatory strategy to decrease the load on the fatigued shoulder musculature.     

Ultrasonographic quantification of architectural response in tibialis anterior to neuromuscular electrical stimulation

While muscle contraction in voluntary efforts has been widely investigated, little is known about contraction during neuromuscular electrical stimulation (NMES). The aim of this study was to quantify in vivo muscle architecture of agonist and antagonist muscles at the ankle joint during NMES. Muscle fascicle lengths and pennation angles of the tibialis anterior (TA) and lateral gastrocnemius muscles were assessed via ultrasonography in 8 healthy young males. Measures were obtained during maximal NMES and torque-matched voluntary dorsiflexion contractions. In the TA, NMES induced a shorter fascicle length (67.2 ± 8.1 mm vs 74.6 ± 11.4 mm; p = 0.04) and a greater pennation angle (11.0 ± 2.4° vs 9.3 ± 2.5°; p = 0.03) compared with voluntary torque-matched dorsiflexion contractions. Architectural responses in the antagonist lateral gastrocnemius muscle did not significantly differ from rest or between voluntary and electrically induced contractions (p > 0.05). Contraction of the antagonist muscle was not a contributing factor to a greater fascicle shortening and increased pennation angle in the TA during NMES. TA architectural response during NMES likely arose from the contribution of muscle synergists during voluntary contractions coupled with a potentially localized contractile activity under the stimulation electrodes during NMES induced contractions.