Unloaded Condition Research Articles

Reliability of a new loaded rolling wheel system for measuring spinal stiffness in asymptomatic participants

BackgroundFew, if any, patient reported symptoms have been shown to be related to objective measures of spine function. Recently, patient-reported measures of disability following spinal manipulative therapy have been associated with an immediate decrease in spinal stiffness obtained by instrumented L3 indentation. Given this novel relation, we anticipate that stiffness measures obtained from locations in addition to L3 may yield valuable information. As such, our research team has developed a new technique to acquire stiffness data continuously over an entire spinal region. The reliability of stiffness measurements obtained by this new technique has yet to be quantified.MethodsContinuous stiffness testing employs a weighted roller that moves uninterrupted over the spine while measuring the resulting spinal deflection along a subject-specific, laser-defined trajectory. A volunteer sample of asymptomatic participants were assessed in 2 sessions occurring 1 to 4 days apart, with each session scheduled at the same time of day. Each session consisted of 3 trials each beginning at a baseline of ~ 17 N then progressing to a maximally tolerable load as defined from pre-test familiarization trials (~ 61, 72 or 83 N). Reliability was evaluated with the intraclass correlation coefficient, the standard error of measurement and Bland & Altman analysis.ResultsA total of 17 asymptomatic participants (mean age 29.2 +/− 6 years, 53% female) took part in the study. Overall, the within and between-session reliability of lumbar spine stiffness measures at the maximal tolerable load was excellent ranging from 0.95–1.00 and good to excellent ranging from 0.82–0.93, respectively. Trial averaging was found to reduce standard error of measurement by a mean of 35.2% over all measurement conditions compared to a single trial. Bland and Altman plots for agreement in lumbar spine stiffness measurements varied from − 0.3 +/− 1.2 at unloaded condition to − 0.2 +/− 1.2 at loaded condition. Data from two participants were removed due to the development of back pain between two sessions.ConclusionThis study introduced a new technique for measuring spinal stiffness over an entire spinal region in asymptomatic human participants. The new technique produced reliable measurements quantifying the load-displacement values for within-session and between-session assessments.

CO2 and CH4 sorption properties of granular coal briquettes under in situ states

The aim of this work was an experimental research into the sorption properties of coal briquettes under the various states of stress. The present state of knowledge when it comes to the impact of stress on the CO2 and CH4 sorption properties of coal is limited. Hence, in situ sorption capacity or sorption-induced deformation may vary considerably from these specified in the unloaded conditions. As part of this paper, a research device that enables the sorption measurements for coal samples submitted to loads of up to 40 MPa is presented. Sorption experiments with pure CO2 and pure CH4 were carried out by means of the volumetric method, under isobaric-isothermal conditions. Dry coal material in the form of granular coal briquettes was used. Presented results aimed to prove the existence of a relation between the stress state, sorption capacity and volumetric deformation of coal. Gas sorption and desorption processes on coal may be triggered by the action of mechanical factor. The mechanical load applied to the coal sorbent reduces its sorption capacity but has no direct effect on swelling. The sorption or desorption induced volumetric changes of coal occur regardless of the stress state and regardless of the mechanism of the sorption process itself. Deeper coal seams with reduced CO2 and CH4 sorption capacity may not be as useful for ECBM techniques as the shallower coal seams. Reduction of the sorption capacity with depth may also explain the growing threat of coal and methane outbursts in the USCB mines observed in recent years.

A Knowledge-Driven Approach for 3D High Temporal-Spatial Measurement of an Arbitrary Contouring Error of CNC Machine Tools Using Monocular Vision.

Periodic health checks of contouring errors under unloaded conditions are critical for machine performance evaluation and value-added manufacturing. Aiming at breaking the dimension, range and speed measurement limitations of the existing devices, a cost-effective knowledge-driven approach for detecting error motions of arbitrary paths using a single camera is proposed. In combination with the PNP algorithm, the three-dimensional (3D) evaluation of large-scale contouring error in relatively high feed rate conditions can be deduced from a priori geometrical knowledge. The innovations of this paper focus on improving the accuracy, efficiency and ability of the vision measurement. Firstly, a camera calibration method considering distortion partition of the depth-of-field (DOF) is presented to give an accurate description of the distortion behavior in the entire photography domain. Then, to maximize the utilization of the decimal involved in the feature encoding, new high-efficient encoding markers are designed on a cooperative target to characterize motion information of the machine. Accordingly, in the image processing, markers are automatically identified and located by the proposed decoding method based on finding the optimal start bit. Finally, with the selected imaging parameters and the precalibrated position of each marker, the 3D measurement of large-scale contouring error under relatively high dynamic conditions can be realized by comparing the curve that is measured by PNP algorithm with the nominal one. Both detection and verification experiments are conducted for two types of paths (i.e., planar and spatial trajectory), and experimental results validate the measurement accuracy and advantages of the proposed method.

High-Sensitivity Microwave Sensor Based on An Interdigital-Capacitor-Shaped Defected Ground Structure for Permittivity Characterization.

This study proposes a high-sensitivity microwave sensor based on an interdigital-capacitor-shaped defected ground structure (IDCS-DGS) in a microstrip transmission line for the dielectric characterization of planar materials. The proposed IDCS-DGS was designed by modifying the straight ridge structure of an H-shaped aperture. The proposed sensor was compared with conventional sensors based on a double-ring complementary split ring resonator (CSRR), a single-ring CSRR, and a rotated single-ring CSRR. All the sensors were designed and fabricated on 0.76-mm-thick RF-35 substrate and operated at 1.5 GHz under unloaded conditions. Five different standard dielectric samples with dielectric constants ranging from 2.17 to 10.2 were tested for the sensitivity comparison. The sensitivity of the proposed sensor was measured by the shift in the resonant frequency of the transmission coefficient, and compared with conventional sensors. The experiment results show that the sensitivity of the proposed sensor was two times higher for a low permittivity of 2.17 and it was 1.42 times higher for a high permittivity of 10.2 when compared with the double-ring CSRR-based sensor.

Utilization of Multi-Axis Positioning Repeatability Performance in Kinematic Modelling

Detailed description of the multi-axis repeatability performance and the modelling of non-systematic variations in the positioning performance of machine tools can support the understanding of root-causes of capability variations in manufacturing processes. Kinematic characterization is implemented through repeated measurements, which include variations related to the performance of the machine tool. This paper addresses the integration of the positional repeatability in kinematic modelling through the employment of direct measurement results. The findings of this research can be used to develop standardized approaches. The statistical population of random errors along the multi-axis travel first requires the proper management of experimental data. In this paper a methodology and its application are presented for the determination of repeatability under static and unloaded conditions as an inhomogeneous parameter in the work space. The proposed approach is demonstrated in a case study, where the component errors of a linear axis are investigated with repeated laser interferometer measurements to quantify the estimated repeatability and express it in the composed repeatability budget. The conclusions of the proposed methodology outline the sensitivity of kinematic models relying on measurement data, as the repeatability of the system can be in the same magnitude as the systematic errors.

Investigating the influence of intermittent and continuous mechanical loading on skin through non-invasive sampling of IL-1α

Pressure ulcers (PUs) are a major burden to both patients, carers and the healthcare system. It is therefore important to identify patients at risk and detect pressure ulcers at an early stage of their development. The pro-inflammatory cytokine IL-1α is a promising indicator of tissue damage. The aim of this study was to compare the temporal skin response, by means of IL-1α expression, to different loading regimens and to investigate the presence of individual variability. The sacrum of eleven healthy volunteers was subjected to two different loading protocols. After a baseline measurement, the left and right side of the sacrum were subjected to continuous and intermittent loading regimen, respectively, at a pressure of 100 mmHg. Data was collected every 20 min, allowing for a total experimental time of 140 min. Sebum, collected at ambient conditions using Sebutape, was analyzed for the pro-inflammatory cytokine IL-1α. Most robust results were obtained using a baseline normalization approach on individual data. The IL-1α level significantly changed upon load application and removal (p<0.05) for both loading regimens. Highest IL-1α ratio increase, 3.7-fold, was observed for 1 h continuous loading. During the refractory periods for both loading regimen the IL-1α levels were still found to be up-regulated compared to baseline (p<0.05). The IL-1α level increased significantly for the two initial loading periods (p<0.05), but stabilized during the final loading period for both loading regimens. Large individual variability in IL-1α ratio was observed in the responses, with median values of 1.91 (range 1.49–3.08), and 2.52 (range 1.96–4.29), for intermittent and continuous loading, respectively, although the differences were not statistically significant. Cluster analysis revealed the presence of two distinct sub-populations, with either a low or high response to the applied loading regimen. The measurement after the first loading period proved to be representative for the subsequent measurements on each site. This study revealed that trends in normalized IL-1α provided an early indicator for tissue status following periods of mechanical loading and refractory unloaded conditions. Additionally, the observed individual variability in the response potentially identifies patients at risk of developing PUs.

Intercostal muscle oxygenation during expiratory load breathing at rest

BackgroundDuring acute bronchial obstruction, despite a higher work of breathing, blood supply and oxygen availability may be reduced in intercostal muscles because of mechanical constraints. This hypothesis was assessed in healthy subjects breathing with and without expiratory load (ETL). MethodsEleven men (24 ± 2 years) breathed at rest for 5 min in unloaded condition and for 20 min through a 20-cmH2O ETL. Tissue saturation index (TSI) and changes (Δ) in concentration of total and oxy-haemoglobin ([tHb] and [O2Hb]) were measured in the seventh intercostal space by near-infrared spectroscopy. Results[tHb] and [O2Hb] decreased with ETL (-5.16 μM and -3.54 μM; p < 0.05). TSI did not vary. Negative correlations were observed between Δ[O2Hb] and changes in expiratory flow rate (ΔVt/Te) and between ΔTSI and Δ V˙E (r = -0.78 and -0.74; p ≤ 0.01). ConclusionDespite decreases in Hb concentrations, saturation in oxygen was not reduced with ETL in intercostal muscles, suggesting a satisfactory ventilatory and/or hemodynamic arrangement.

Firing properties of muscle spindles supplying the intrinsic foot muscles of humans in unloaded and freestanding conditions

We recently developed an approach for recording from muscle spindles in the intrinsic muscles of the foot in freestanding humans by inserting a tungsten microelectrode into the posterior tibial nerve behind the medial malleolus of the ankle. Here we characterize the behavior of muscle spindles in the small muscles of the foot in 1) seated subjects with the leg horizontal and the foot naturally plantarflexed and 2) standing subjects. In the first study, recordings were made from 26 muscle spindle afferents located within flexor digiti minimi brevis ( n = 4), abductor digiti minimi ( n = 3), quadratus plantae ( n = 3), plantar interossei ( n = 4), flexor digitorum brevis ( n = 3), dorsal interossei ( n = 2), and lumbricals ( n = 2), with one each supplying abductor hallucis, adductor hallucis, and flexor hallucis brevis. The identity of another two muscle afferents was unknown. The majority of the units were silent at rest, only seven (27%) being spontaneously active. Because of the anatomic constraints of the foot, some spindles supplying muscles acting on the toes responded to movements of one or more digits. In the second study, 12 muscle spindle afferents were examined during standing. The ongoing discharge of eight spindle afferents covaried with changes in the center of pressure during postural sway. We conclude that the majority of spindle endings in the small muscles of the foot are silent at rest, which may allow them to encode changes in conformation of the foot when it is loaded during standing. Moreover, these muscle spindle afferents can provide useful proprioceptive information during standing and postural sway. NEW & NOTEWORTHY We have characterized the firing properties of muscle spindles in the intrinsic muscles of the human foot for the first time. The majority of the spindle endings are silent in seated subjects, and most fire tonically during standing, their discharge covarying with center of pressure during postural sway. We conclude that spindle endings in the intrinsic muscles of the foot provide useful proprioceptive information during free standing.

The significant effect of the medial hamstrings on dynamic knee stability.

While hamstring autograft is a popular option for the general population, BTB autograft is still significantly more popular among professional athletes due to concerns of altering knee kinematics with hamstring harvest. This study seeks to quantify the contribution of the medial hamstrings to knee stability. Valgus knee laxity, anterior tibial translation, and rotational motion were measured in eight fresh-frozen cadaveric knees after forces were applied on the tibia in each plane (coronal, sagittal, and axial). Four muscle loading conditions were tested: (1) physiologic fully loaded pes anserinus, (2) semitendinosus only loaded, (3) gracilis only loaded, and (4) unloaded pes anserinus. The protocol was then repeated with the ACL transected. In the ACL intact knee, the neutral position of the tibia with an unloaded pes anserinus was significantly more externally rotated (p < 0.01) and anteriorly translated (p < 0.05) at all knee flexion angles than a tibia with a physiologic loaded pes anserinus. Applying an external rotation torque significantly increased external rotation for the fully unloaded (p < 0.001), gracilis only loaded (p < 0.001), and semitendinosus only loaded (p < 0.01) conditions at all flexion angles. Applying a valgus torque resulted in a significant increase in laxity for the fully unloaded condition only at 30° of flexion (p < 0.05). Applying an anterior tibial force resulted in significant increase in anterior translation for the fully unloaded condition at all flexion angles (p < 0.01), and for the gracilis only loaded condition in 30° and 60° of flexion (p < 0.05). Similar results were seen in the ACL deficient model. The medial hamstrings are involved in rotational, translational, and varus/valgus control of the knee. Applying anterior, external rotation, and valgus forces on the hamstring deficient knee significantly increases motion in those planes. Harvesting the gracilis and semitendinosus tendons alters native knee kinematics and stability. This is clinically relevant and should be a consideration when choosing graft source for ACL reconstruction, especially in the elite athlete population.

Tibiofemoral joint contact forces increase with load magnitude and walking speed but remain almost unchanged with different types of carried load.

Musculoskeletal injuries (MSI) in the military reduce soldier capability and impose substantial costs. Characterizing biomechanical surrogates of MSI during commonly performed military tasks (e.g., load carriage) is necessary for evaluating the effectiveness of possible interventions to reduce MSI risk. This study determined the effects of body-borne load distribution, load magnitude, and walking speed on tibiofemoral contact forces. Twenty-one Australian Army Reserve soldiers completed a treadmill walking protocol in an unloaded condition and wearing four armor types (standard-issue and three prototypes) with two load configurations (15 and 30 kg) for a total of 8 armor x load ensembles. In each ensemble, participants completed a 5-minute warm-up, and then walked for 10 minutes at both moderate (1.53 m⋅s-1) and fast (1.81 m⋅s-1) speeds. During treadmill walking, three-dimensional kinematics, ground reaction forces, and muscle activity from nine lower-limb muscles were collected in the final minute of each speed. These data were used as inputs into a neuromusculoskeletal model, which estimated medial, lateral and total tibiofemoral contact forces. Repeated measures analyses of variance revealed no differences for any variables between armor types, but peak medial compartment contact forces increased when progressing from moderate to fast walking and with increased load (p<0.001). Acute exposure to load carriage increased estimated tibiofemoral contact forces 10.1 and 19.9% with 15 and 30kg of carried load, respectively, compared to unloaded walking. These results suggest that soldiers carrying loads in excess of 15 kg for prolonged periods could be at greater risk of knee MSI than those with less exposure.

Weighted Walking Influences Lower Extremity Coordination in Children on the Autism Spectrum.

There is sparse quantitative research regarding gait coordination patterns of children on the autism spectrum, though previous studies, relying only upon observational data, have alluded to characteristically poor movement coordination. This study compared walking with a weighted vest, a backpack carriage, and an unloaded walking condition on lower extremity coordination among 10 male children (aged 8-17 years) on the autism spectrum. All participants completed 15 gait trials in the following three conditions: (a) unloaded, (b) wearing a backpack weighted with 15% body mass, and (c) wearing a vest weighted with 15% body mass. We used continuous relative phase analysis to quantify lower extremity coordination and analyzed data through both group and single-subject comparisons. We used the Model Statistic to test for statistical significance at each of the normalized data points for each segment couple (thigh-leg, leg-foot, and thigh-foot). The first 10 and last 10 stride blocks were tested for possible accommodation strategies. Group comparisons revealed no coordination changes among the three conditions (likely due to insufficient statistical power), while single-subject comparisons exposed significant decreased variability in gait coordination patterns ( p < .05) in both loaded conditions, relative to the unloaded condition. These participants exhibited variable coordination patterns during the unloaded gait. When walking with loads, coordination pattern variability of the lower extremities was decreased. This finding suggests that walking while carrying or wearing heavy objects may reduce the number of potential motor pattern choices and thus decrease the overall variability of lower extremity movement patterns. Additional research with a larger and more diverse participant sample is required to confirm this conclusion.

Effect of weighted sled towing on sprinting effectiveness, power and force-velocity relationship

This study aimed to compare the components of force-velocity (F-V) and power-velocity (P-V) profiles and the mechanical effectiveness of force application (or force ratio–RF) among various sled-towing loads during the entire acceleration phase of a weighted sled sprint. Eighteen sprinters performed four 50-m sprints in various conditions: unloaded; with a load corresponding to 20% of the athlete’s body mass (BM); with a load of 30% BM; and with a load of 40% BM. Data were collected with five video cameras, and the images were digitised to obtain velocity from the derivation of the centre-of-mass position. F-V and P-V components and RF were estimated from sprinting velocity-time data for each load using a validated method that is based on an inverse dynamic approach applied to the sprinter’s centre-of-mass (it models the horizontal antero-posterior and vertical ground reaction force components) and requires only measurement of anthropometric and spatiotemporal variables (body mass, stature and instantaneous position or velocity during the acceleration phase). The theoretical maximal velocity decreased with load compared with the unloaded condition (for 20% BM: -6%, effect size (ES) = 0,38; for 30% BM: -15%, ES = 1.02; for 40% BM: -18%, ES = 1.10). The theoretical maximal horizontal force (F0) and maximal power were not different among conditions. However, power at the end of the acceleration phase increased with load (40% BM vs 0%: 72%; ES = 2.73) as well as the maximal mechanical effectiveness (12%; ES = 0.85). The linear decrease in RF was different between 30 or 40% BM and the unloaded condition (-23%; ES = 0.74 and 0.66). Better effectiveness may be developed with 40% BM load at the beginning of the acceleration and with the various load-induced changes in the components of the F-V and P-V relationships, allowing a more accurate determination of optimal loading conditions for maximizing power.

Design of CSRR-Based Electronically Tunable Compact RF Sensor for Material Testing

A novel concept of designing electronically tunable compact planar RF sensor operating in the S-band (2.7–3.1 GHz) for material testing is presented. The proposed design makes use of the complementary split ring resonator (CSRR) loaded microstrip line coupled to the varactor diode, where the electronic tuning is facilitated by reverse biased varactor diode. Using the improved design topology, proposed structure is able to provide material testing over a wide tunable range using only the single unit of CSRR resonator. The proposed tunable sensor is designed using the CST-MWS, and accordingly various parameters are optimized to obtain the desired performance. Equivalent circuit of the resonant structure is obtained using the advanced design system. The proposed structure is fabricated on a FR-4 substrate, and accordingly the S-parameters are measured under unloaded condition with a biasing voltage range of 0–28 V, using the network analyzer. The testing of the fabricated structure shows a close match between the measured and the simulated scattering parameters. Finally the dielectric properties of various standard test samples are measured over a number of frequency points in S-band using the proposed sensor, where the newly developed empirical formulas are employed to relate the dielectric properties with the corresponding measured resonance frequencies.

Contributions of longitudinal track unevenness and track stiffness variation to railway induced vibration

Dynamic train-track interaction originates from excitation mechanisms such as longitudinal track unevenness, parametric excitation due to track stiffness variation and impact excitation due to wheel flats, wheel out-of-roundness and rail joints. Track stiffness variation can be regarded as longitudinal track unevenness in loaded condition, but for the mitigation of track geometry degradation it is important to distinguish between track unevenness in unloaded condition and track stiffness variation. This paper studies how longitudinal track unevenness and track stiffness variation contribute to railway induced vibration. A case study is performed for a railway line in Furet, Sweden. Based on measured track unevenness and stiffness data from the IMV 100 track recording car, the train-track interaction forces and free field vibrations are computed for each of these two excitation mechanisms separately, as well as for a combination of both. The computed free field vibrations are in good agreement with measured vibrations at the same site. The contribution of the track stiffness variation to the interaction forces and free field vibrations is much lower than the contribution of the longitudinal track unevenness. Track stiffness variation can also be modeled as equivalent track unevenness, leading to results slightly different from those obtained when track unevenness and track stiffness variation are modeled separately, and a poorer agreement with the measured vibrations.

The impact of dyspnea and threat of dyspnea on error processing.

Dyspnea (breathlessness) is a threatening and aversive bodily sensation and a major symptom of various diseases. It has been suggested to impair several aspects of functioning in affected patients, but experimental proof for this assumption is widely absent. Error processing is an important domain of functioning and has intensively been studied using electrophysiological measures. Specifically, the error-related negativity (ERN) has been suggested to reflect early performance monitoring and error detection, while the error positivity (Pe) has been linked to subsequent error awareness. So far, little is known about the effects of anticipated or perceived dyspnea on error processing. Therefore, in 49 healthy participants, we studied the effects of experimentally induced dyspnea and threat of dyspnea on the ERN/Pe and behavioral task performance. Participants performed the arrowhead version of the flanker task during three experimental conditions: an unloaded baseline condition, a dyspnea condition, and a threat of dyspnea condition. Dyspnea was induced by breathing through inspiratory resistive loads, while high-density EEG was continuously measured. No differences in task performance (reaction times, error rates) and ERN mean amplitudes were found between conditions. However, mean amplitudes for the Pe differed between conditions with smaller Pe amplitudes during threat of dyspnea compared to baseline and dyspnea conditions, with the latter two conditions showing no difference. These results may suggest that threat of dyspnea, but not dyspnea itself, reduces error awareness, while both seem to have no impact on early error processing and related behavioral performance.

Forearm wearable resistance effects on sprint kinematics and kinetics

ObjectivesArm swing is a distinctive characteristic of sprint-running with the arms working in a contralateral manner with the legs to propel the body in a horizontal direction. The purpose of this study was to determine the acute changes in kinematics and kinetics when wearable resistance (WR) of 1kg (equivalent to ∼1% body mass) was attached to each forearm during over ground short distance (20m) maximal sprint-running. DesignCross-sectional study. MethodsTwenty-two male amateur rugby athletes (19.4±0.5years; 97.0±4.8kg; 180.4±7.2cm) volunteered to participate in the study. Radar and Optojump were used to examine kinematic and kinetics between WR and unloaded sprint-running conditions. ResultsNo significant (p<0.05) differences were found at 2m or 5m between conditions, however, the WR condition resulted in a significant increase in 10m, 20m and 10–20m split time (all, ∼2%, small effect size) compared to the unloaded condition. Significant decreases were also found in theoretical maximum velocity (V0) (−1.4%, small effect size) and relative peak horizontal power production (Pmax) (−5.5%, small effect size). Step length (2.1%, small effect size) and contact time (6.5%, medium effect size) were significantly increased, while step frequency (−4.1%, small effect size) and flight time (−5.3%, medium effect size) were significantly decreased. ConclusionsWR forearm loading provides a movement specific overload of the arms which significantly alters step kinematics and sprint times ≥10m.

Variations of handheld loads increase the range of motion of the lumbar spine without compromising local dynamic stability during walking

BackgroundWalking is often considered a beneficial management strategy for certain populations of low back pain patients. However, little is known about how simple challenges that people often encounter, such as carrying loads in the hands, affect the low back during walking. Research QuestionHow do variations in hand loading affect arm swing, lumbar spine range of motion (ROM), and lumbar spine local dynamic stability (LDS) during walking? MethodsSixteen young healthy participants (8 female) performed nine treadmill walking trials, each at 1.25 m/s for 3 consecutive minutes. Conditions manipulated the magnitude of hand loads (unloaded, low, high) and location of hand loads (directly in hands, in bags). Kinematic markers were used to measure sagittal plane arm swing, 3D lumbar spine ROM, and lumbar spine LDS during each trial. ResultsArm swing was significantly (p < 0.001) reduced as load increased directly in the hands; however, when held in bags load magnitude had no effect. Further, arm swing was significantly (p < 0.0001) lower when loads were held in bags. Lumbar flexion/extension ROM was greatest with the low load compared to both unloaded (p = 0.012) and high load (p = 0.0717) conditions, and was also greater (p < 0.0001) with loads held directly in the hands compared to loads in bags. Despite these changes in lumbar spine ROM, lumbar spine LDS was not significantly affected by any of the variations in hand loading. SignificanceThe greater lumbar spine cyclic motion, elicited by low hand loads held directly in the hands during walking, may be beneficial to the health of the low back. No changes in lumbar LDS were found, thereby suggesting that the small, likely beneficial, increases in lumbar spine ROM are well controlled by the motor control system and do not create an increased risk of injury.

Impact of Multidirectional Transverse Calf Muscle Loading on Calf Muscle Force in Young Adults.

It has been demonstrated that unidirectional transversal muscle loading induced by a plunger influences muscle shape and reduces muscle force. The interaction between muscle and transversal forces may depend on specific neuromuscular properties that change during a lifetime. Compression garments, applying forces from all directions in the transverse plane, are widely used in sports for example to improve performance. Differences in the loading direction (unidirectional vs. multidirectional) may have an impact on force generating capacity of muscle and, thus, on muscle performance. The aim of this study was to examine the effect of multidirectional transversal loads, using a sling looped around the calf, on the isometric force during plantarflexions. Young male adults (25.7 ± 1.5 years, n = 15) were placed in a prone position in a calf press apparatus. The posterior tibial nerve was stimulated to obtain the maximal double-twitch force of the calf muscles with (59.4 and 108.4 N) and without multidirectional transverse load. Compared to the unloaded condition, the rate of force development (RFD) was reduced by 5.0 ± 8.1% (p = 0.048) and 6.9 ± 10.7% (p = 0.008) for the 59.4 and 108.4 N load, respectively. No significant reduction (3.2 ± 4.8%, p = 0.141) in maximum muscle force (Fm) was found for the lower load (59.4 N), but application of the higher load (108.4 N) resulted in a significant reduction of Fm by 4.8 ± 7.0% (p = 0.008). Mean pressures induced in this study (14.3 and 26.3 mm Hg corresponding to the 59.4 and 108.4 N loads, respectively) are within the pressure range reported for compression garments. Taking the results of the present study into account, a reduction in maximum muscle force would be expected for compression garments with pressures ≥26.3 mm Hg. However, it should be noted that the loading condition (sling vs. compression garment) differs and that compression garments may influence other mechanisms contributing to force generation. For example, wearing compression garments may enhance sport performance by enhanced proprioception and reduced muscle oscillation. Thus, superposition of several effects should be considered when analyzing the impact of compression garments on more complex sport performance.

Radiofrequency planar surface coil for magnetic resonance: When the use of a circular wire gives a noticeable advantage with respect to a flat strip conductor?

Depending on their cross-sectional shape, commonly used conductors for radiofrequency (RF) Magnetic Resonance (MR) coils can be categorized into circular wires and flat strips. Due to a more symmetrical current distribution inside conductor volume, coils constituted by wire conductors provide better overall performance in unloaded conditions with respect to the ones made of strip conductor, although wire conductors are difficult to handle for coil manufacturing and additional mechanical competencies are required. Nevertheless, the accomplishment of the best coil performance during imaging, i.e. in the presence of a sample, remains the main issue in MRI. It follows that the use of wire conductors instead of strip ones is worthwhile only if the correspondent increase in coil quality factor with sample is substantial: this is related to the ratio between sample and coil resistance.This paper proposes the application of a finite element method (FEM)-based numerical approach for separately estimating the conductor and radiative losses in planar surface loops characterized by different cross-sectional shapes (circular wire and flat strip) in conjunction with a vector potential calculation-based method for sample-induced resistance estimation. Simulation data were acquired from 5.7 to 128 MHz, for four different size loops (from 2 to 15 cm diameters), with the scope of evaluating the region in the frequency-loop diameter plane where the use of a circular wire conductor gives a noticeable advantage with respect to the flat strip in maximizing signal-to-noise ratio (SNR) in MR applications.

Primarily hip-borne load carriage does not alter biomechanical risk factors for overuse injuries in soldiers

ObjectivesTo determine the effects of different body armour types, carried loads, and walking speeds on trunk and lower-limb joint biomechanics. DesignWithin-subjects repeated measures to determine the effects of different body armour types, carried loads, and walking speeds on trunk and lower-limb joint biomechanics. MethodsTwenty soldiers (29.5±7.1yrs) completed a treadmill walking protocol in an unloaded (baseline) condition and wearing a control, Tiered Body Armour System (TBAS) and five different armour types (cARM1-2, pARM1) with two load configurations (15 and 30kg) for a total of eight armour×load ensembles. In each ensemble, participants walked for 10min at 1.53ms−1 and 1.81ms−1 speeds. Whole-body marker kinematics and ground reaction forces were used, along with a scaled anatomic model, to determine peak lower-limb joint angles, net joint moments, and negative knee work. Peak parameters were compared between armour types, walking speeds, and carried loads using repeated measures ANOVAs. ResultsPeak plantarflexion and hip abduction moments were reduced when wearing cARM1 (p=0.040, p=0.045) and cARM2 (p=0.045, p=0.003) compared to TBAS, while carrying 30kg and/or walking fast. This suggests positive benefits of load distribution at higher task demands. Joint moments increased when participants carried greater load and/or walked faster, and the combined effects of carried load and walking speed were mostly additive. ConclusionsPrimarily hip-borne load carriage does not negatively alter joint kinetics, and some positive adaptations occurred during tasks with higher demands. These results can inform equipment design and physical training programs for load carriage.