Abstract Resistance training (RT) improves the skeletal muscle’s ability to generate maximal vol untary force and is accompanied by changes in the activation of the antagonist muscle which is not targeted primarily by RT. However, the nature and role of neural adaptation to RT in the an tagonist muscle is paradoxical and not well understood. We compared moments, agonist muscle activation, antagonist activation, agonist-antagonist coactivation, and electromyographic (EMG)model-predicted moments generated by antagonist hamstring muscle coactivation during isokinetic knee extension in leg strength-trained (n = 10) and untrained (n = 11) healthy, younger adults. Trained vs. untrained adults were up to 58% stronger. During knee extension, hamstring activation was 1.6-fold greater in trained vs. untrained adults (p = 0.022). This hamstring activation produced 2.6-fold greater model-predicted antagonist moments during knee extension in the trained (42.7 ± 19.55 Nm) vs. untrained group (16.4 ± 12.18 Nm; p = 0.004), which counteracted (reduced) uadriceps knee extensor moments ~43 Nm (0.54 Nm·kg−1) and by ~16 Nm (0.25 Nm·kg−1) in trained vs. untrained. Antagonist hamstring coactivation correlated with decreases and increases, respectively, in quadri ceps moments in trained and untrained. The EMG model-predicted antagonist moments revealed training history-dependent functional roles in knee extensor moment generation.

Abstract This study investigates the usefulness of a 10 Hz GPS device for tracking scalar performance in canoe slalom through assessing the validity of automated-informed-aerial video tracking (30 fps and 10 fps) and GPS capability in relation to a known track. Additionally, a real-world (canoe-slalom).A comparison between manual-aerial video tracking (10 fps) and the 10 Hz GPS was performed. All three methods of tracking used during the dry-land test (30 fps or 10 fps video and GPS) reported significantly lower distances (−3.2, −5.1 and −8.5%, p < 0.0001) but were deemed useful based on sample rate and body positioning difference. Intra-method reliability was good (CV = 2.5−2.6%) but requires visual inspection for dataset errors. Informed-colour filtered automated tracking on water was not possible, but manual tracking provided fewer dataset errors than dry-land automated tracking. GPS significantly (p < 0.0001) under reports distance travelled at key moments during real-world slalom with a bias ± SD of 2.26 ± 2.07 m compared to 10 fps manual-aerial video tracking.The aerial video combined with manual tracking proved most suitable for tracking canoe slalom athlete trajectory in a real-world setting but needs to be automated into an application-based package to make it useable for coaches. GPS, as presented, provides insight but does not accurately quantify movements critical in determining the performance of canoe slalom.

Abstract The purpose of this study was to assess the relationship between work rate, stroke metrics,and performance in whitewater slalom. Twelve Spanish, nationally competitive whitewater slalom kayakers took part in a simulated competition while using an instrumented kayak paddle to record stroke metrics over a simulated race, total duration and sectional splits. Performance time was highly correlated to overall power output (r2 = 0.511, p < 0.001), where kayakers demonstrated a positive pacing strategy with power output significantly decreasing over successive sectional splits (158 ± 40, 112 ± 32 and 65 ± 33 W, p < 0.001). This resulted in an increased stroke duration (p < 0.001), time to peak force (p < 0.001), a decrease in stroke peak force (p < 0.001), and rate of peak force development (p < 0.001) over elapsed time. As such, work rate is deemed an objective metric to monitor performance, prescribe training, and ascertain optimal pacing strategies in canoe slalom.

Abstract Traditionally, monitoring biomechanics parameters requires a significant amount of sensors to track exercises such as gait. Both research and clinical studies have relied on intricate motion capture studios to yield precise measurements of movement. We propose a method that captures motion independently of optical hardware with the specific goal of identifying the phases of gait using joint angle measurement approaches like IMU (inertial measurement units) sensors. We are proposing a machine learning approach to progressively reduce the feature number (joint angles) required to classify the phases of gait without a significant drop in accuracy. We found that reducing the feature number from six (every joint used) to three reduces the mean classification accuracy by only 4.04%, while reducing the feature number from three to two drops mean classification accuracy by 7.46%. We extended gait phase classification by using the biomechanics simulation package, OpenSim, to generalize a set of required maximum joint moments to transition between phases. We believe this method could be used for applications other than monitoring the phases of gait with direct application to medical and assistive technology fields.

Abstract Background: Artificial turf (AT) has been related to increased injury rates when compared to natural grass (NG). One potential reason for the differences in injury rates is the difference in mechanical characteristics of the surfaces. Over the course of a season on artificial turf, due to heavy use and environmental factors, properties of the surface (such as compliance) may be altered. The purpose was to compare the effects of newly installed versus aged AT on injury risks at the metatarsophalangeal, ankle, and knee joint during soccer-specific movements. Methods: Eleven male soccer players performed three movements on newly installed and ‘aged’ AT. Kinematics and kinetics were collected for the different surfaces. Results: Knee adduction moments were increased during the v-cut (119 Nm vs. 164 Nm, p = 0.02), and knee external rotation joint moments were increased during the circle run (23 Nm vs. 28 Nm, p = 0.04) with the aged surface. No surface effects were seen during the jog-sprint transition. Conclusions: For movements associated with a high risk for non-contact injuries, the age of the AT resulted in greater risk factors for injury potential at the knee joint. Further research comparing injury rates associated with AT should consider mechanical features, specifically surface compliance.

Abstract Redistribution of mechanical output from the ankle to the hip during walking occurs with advanced age. Changes to tissues spanning the ankle may limit the joint from performing mechanical functions necessary to walk at fast speeds and older adults may redistribute work proximally to compensate. Older adults with Parkinson’s disease (PD) do not exhibit the distal-to-proximal redistribution and may therefore be limited in reaching fast walking speeds. We tested whether advanced aging, regardless of the presence of PD, limits the ability to increase motor-like behavior of the ankle as walking speed increases. We also tested whether healthy older adults—but not PD patients—would compensate for reduced motor-like behavior at the ankle with disproportionately larger mechanical redistributions at faster speeds. The 16 young, 16 older, and 8 PD-diagnosed adults walked at 0.8, 1.2, and 1.6 ms−1 on a treadmill. We used joint functional indexing to quantify motor-like behavior of the ankle and a hip-to-ankle mechanical work ratio to quantify mechanical redistribution. We found a significant group x speed interaction (p < 0.05) for motor-like behavior of the ankle, with younger adults increasing motor index more than the older and PD groups as walking speed increased. Contrary to our second hypothesis, we found a significant main effect of speed (p < 0.001) on redistribution ratios, indicating that all three groups decreased redistribution ratios as walking speed increased, but not a significant interaction.

Abstract Interface pressure applied by compression bandages is the therapeutic action of the treatment of some venous or lymphatic pathologies. The so-called Static Stiffness Index, which quantifies the pressure increase from supine to standing position, is usually used to differentiate compression bandages. It was hypothesized that this pressure increase was the consequence of a change in leg geometry (blood and muscle falling down) and a change in calf soft tissue mechanical properties (muscles contraction). Calf soft tissue global stiffness of both legs of 25 patients was characterized in a sitting and standing position. This characterization was combined with interface pressure measurements applied by six different bandages. Though soft tissue mechanical properties significantly increased from sitting to standing position, no correlation was observed with the corresponding pressure increase. Thus, presure increase is mainly attributed to a change in leg geometry.

Abstract When lying supine, due to the reaction force from the mattress acting mostly through the heel, an external knee-extension joint-torque is induced that keeps the knee fully extended. This torque becomes zero if the feet are hung over the end of the support. This study investigated, in patients with knee-osteoarthritis (knee-OA) who routinely sleep supine, whether a change to such a sleeping position would ameliorate the knee pain and associated physical problems they suffer. Patients were recruited (General-Practitioners Centre, UK) over a 9-month period; those eligible (51/70) were randomly allocated to an intervention (65% female; age 71.5 [11.3] yrs; BMI, 29.20 [5.54] kg/m2 ; knee-OA severity, 20 mild–mod/3 severe) or control group (63% female; age, 68.3 [9.7] yrs; BMI, 28.69 [5.51] kg/m2 ; knee-OA severity, 17 mild–mod/2 severe). The primary outcome was improvements (0 [worst] to 100 [best]) in knee pain at 3 months and was rated in the Knee-Injuryand-Osteoarthritis- Outcome-Score questionnaire (KOOS). Secondary outcomes were improvements (0–100) in the other four KOOS-subscales. There were no differences between groups in KOOS outcomes at baseline, and there were no changes in KOOS outcomes in the control group at 3 months. Relative to the baseline KOOS values in Knee-Pain (50.1), Symptoms (52.5), Activities-of-Daily-Living (53.8) and Quality-of-Life (31.5), were all seen to improve at 3 months in the intervention group (by between 11.9 and 12.9); however, when comparing to controls, only the improvements in the subscale Activities-of-Daily-Living (which improved by 12.2) were statistically significant. Findings indicate that for those with knee-OA who routinely sleep supine, sleeping with the feet over the end of the mattress (to prevent the knee being pushed into/held in full extension) can help ameliorate the physical problems they suffer.

Abstract Finite element (FE) analysis can predict proximal human femoral strength. Automated meshing and identifying subregions with high relevance for strength prediction could reduce the laborious modeling process. Mesh morphing based on free-form registration provides a high level of automation and inherently creates isotopological meshes. The goals of this study were to investigate if FE models based on free-form transformed meshes predict experimental femoral strength as well as manually created FE models and to identify regions and parameters with highest correlation to femoral strength. Subject-specific meshes and FE models were created from a set of quantitative CT images (QCT) using a B-Spline registration-based algorithm. Correlation of FE-predicted bone strength and local parameters with experimental bone strength were investigated. FE models based on transformed meshes closely resembled manually created counterparts, with equally strong correlations with experimental bone strength (R 2 = 0.81 vs. R2 = 0.80). The regional analysis showed strong correlations (0.6 < R2 < 0.7) of experimental strength with local parameters. No subregion or parameter lead to stronger correlation than FE predicted bone strength. B-spline-transformed meshes can be used to create FE models, able to predict femoral bone strength and simplify FE model generation. They can be used to reveal relations of local parameters with failure load.

Abstract Finite element (FE) modeling is a commonly used method to investigate the influence of medical devices, such as implants and screws, on the biomechanical behavior of the spine. Another simulation method is multibody simulation (MBS), where the model is composed of several nondeformable bodies. MBS solvers generally require a very short computing time for dynamic tasks, compared with an FE analysis. Considering this computational advantage, in this study, we examine whether parameters for which values are not known a priori can be determined with sufficient accuracy using an MBS model. Therefore, we propose a many-at-a-time sensitivity analysis method that allows us to approximate these a priori unknown parameters without requiring long simulation times. This method enables a high degree of MBS model optimization to be achieved in an iterative process. The sensitivity analysis method was applied to a simplified screw–vertebra model, consisting of an anterior anchor implant screw and vertebral body of C4. An experiment described in the literature was used as the basis for developing and assessing the potential of the method for sensitivity analyses and for validating the model’s action. The optimal model parameters for the MBS model were determined to be c = 823,224 N/m for stiffness and d = 488 Ns/m for damping. The presented method of parameter identification can be used in studies including more complex MBS spine models or to set initial parameter values that are not available as initial values for FE models.

Abstract The objective of this paper is to present our findings on the biomechanical aspects of the virgin passive anisotropic hyperelasticity of the porcine colon based on equibiaxial tensile experiments. Firstly, the characterization of the intestine tissues is discussed for a nearly incompressible hyperelastic fiber-reinforced Holzapfel–Gasser–Ogden constitutive model in virgin passive loading conditions. The stability of the evaluated material parameters is checked for the polyconvexity of the adopted strain energy function using positive eigenvalue constraints of the Hessian matrix with MATLAB. The constitutive material description of the intestine with two collagen fibers in the submucosal and muscular layer each has been implemented in the FORTRAN platform of the commercial finite element software LS-DYNA, and two equibiaxial tensile simulations are presented to validate the results with the optical strain images obtained from the experiments. Furthermore, this paper also reviews the existing models of the active smooth muscle cells, but these models have not been computationally studied here. The review part shows that the constitutive models originally developed for the active contraction of skeletal muscle based on Hill’s three-element model, Murphy’s four-state cross-bridge chemical kinetic model and Huxley’s sliding-filament hypothesis, which are mainly used for arteries, are appropriate for numerical contraction numerical analysis of the large intestine.

Abstract Patients with end stage renal disease require some form of vascular access for treatment, with Arterio-Venous Fistulas (AVF) being the preferred form available due to better patency rates. However, they continue to present complications after creation, leading to early or late failure. While many studies are examining the flow in patient-specific fistulas, they often neglect the influence of vessel compliance on its hemodynamics. The objective of this study is to investigate the effect of wall compliance on the complex hemodynamics of a patient-specific brachio-cephalic AVF and how it differs from a rigid fistula. Particle Image Velocimetry (PIV) was used to capture the flow pattern within the fistula for both steady (Re = 1817) and pulsatile (Reav = 1817, Remax = 2232) flow conditions. The results were compared to rigid model measurements performed under the same Reynolds number. The streamline plots and coefficient of variation results did not differ significantly between the models; however, the non-dimensional velocity and directional variability results did vary between the two fistulas. A difference of approximately 8% was seen between the two models for both steady and pulsatile flow. The findings of this study suggest that to determine the bulk flow, a rigid model is adequate, but to capture the finer details of the flow, a compliant model is necessary.

Abstract Low back pain represents a major economic and societal challenge due to its high prevalence.Lumbar orthoses are one of the recommended treatments. Even if previous results showed their clinical effects, the detailed mode of action is still poorly known, making the device design difficult. A renewed instrumentation and experimental protocol should bring better insight into the lumbar brace– trunk mechanical interaction. This instrumentation should give detailed information on the basic physical or geometrical parameters: the pressure applied on the trunk, the body shape and the strain in the belt. The principal objective of this study was to propose and validate a new measurement protocol, based on pressure mapping systems and full-field shape and strain measurement. The feasibility of the protocol was tested along with its validity and repeatability. The influence of various parameters, which could cause changes in the measurements, was tested with six different belt configurations on one subject. Measurements were also performed to study the impact of posture on pressure and strain. Both pressure and strain appeared to be asymmetric from left to right. The pressure applied by the lumbar belt on the back varies with breathing and with posture. This study showed that full-field measurements were necessary to render the high variability of pressure or strain around the trunk, under recommendations of their use to guarantee a satisfying repeatability.