nils-herrmann/clean_scirepeval huggingface dataset:
Upper body kinematic differences between maximum front crawl and backstroke swimming.
Venue: Journal of biomechanics

The purpose of this study was to investigate why front crawl is faster than backstroke from a kinematic perspective. Three-dimensional kinematics were obtained from one upper-limb cycle of ten male competitive swimmers performing 50 m front crawl and backstroke trials at maximum speed. Swimmers achieved faster centre of mass velocity in front crawl than backstroke (1.70 ± 0.04 vs 1.54 ± 0.06 m·s-1; p < 0.01) with no difference in stroke length (2.00 ± 0.25 vs 2.07 ± 0.17 m·cycle-1), while stroke frequency in front crawl was higher than that in backstroke (51.67 ± 6.38 vs 44.81 ± 4.68 cycles·min-1; p < 0.01). Maximum shoulder roll angle in front crawl was larger than that in backstroke (52.88 ± 4.89 vs 49.73 ± 5.73°; p < 0.05), while swimmers had smaller maximum hip roll in front crawl than backstroke (33.79 ± 6.07 vs 39.83 ± 7.25°; p < 0.05). Absolute duration of the release phase (from the last backward movement to the exit from the water of the wrist) and relative duration of the recovery phase were shorter in front crawl than backstroke (0.07 ± 0.03 vs 0.26 ± 0.08 s; p < 0.01, and 28.69 ± 2.50 vs 33.21 ± 1.43%; p < 0.01, respectively). In conclusion, front crawl is faster than backstroke because of its higher stroke frequency due to the shorter absolute release phase and relative recovery phase durations.
The effects of rehabilitation on the biomechanics of patients with athletic groin pain.
Venue: Journal of biomechanics

This study sought to investigate the kinematic and kinetic variables that change in patients with athletic groin pain (AGP) after a successful exercise intervention. The kinematic and kinetic measures of subjects with AGP (n = 65) that completed a lateral hurdle hop, pre and post an exercise rehabilitation program were compared to a control group of matched uninjured individuals (n = 50). Analysis of Characterising Phases was used to identify differences in kinematic and kinetic measures between the groups. AGP subjects returned to pain-free participation in sport in a median time of 9.14 weeks (5.14-29.0). In total 18 different biomechanical variables were significantly different between the AGP group and the uninjured group pre-rehabilitation. Of these, seven variables were no longer significantly different between the AGP group post-rehabilitation and the uninjured group. These seven variables may represent the factors most related to return to play in this cohort and are potential targets for rehabilitation.
Biomechanical implications of the fenestration structure after thoracic endovascular aortic repair.
Venue: Journal of biomechanics

The inadequate landing zone during thoracic endovascular aortic repair (TEVAR) could be resolved by fenestration technology. The fenestration structure consists of a main endograft and a left subclavian artery (LSA) stent-graft. The purpose of this study is to assess the biomechanical implications of the protruding segment (PS) of the LSA stent-graft after TEVAR with in situ fenestration (ISF-TEVAR). The PS is characterized by the protruding length and centerline angle between the LSA and PS. An idealized three-dimensional geometric model of the human aorta was constructed as the reference benchmark. We designed nine postoperative aortic geometries with different protruding lengths (5, 10, 15 mm) and centerline angles (-20°, 0°, +20°). The blood was assumed to be non-Newtonian and the three-element Windkessel model was applied to reproduce physiological pressure waveforms. The interaction between the blood and vessel wall was captured by a two-way fluid-structure method. We also considered the impact of the fenestration structure on the vessel wall. Long protruding length (15 mm) and the retrograde angle (+20°) result in a markedly reduced LSA flow ratio (1.3%). There is a pressure difference between the inner and outer walls of the PS. The region around the PS is more prone to thrombosis. The flow stability and turbulence intensity of downstream blood of the PS gradually deteriorate. The largest deformed region moves from the aortic arch to the ascending aorta after ISF-TEVAR. The postoperative hemodynamics largely depends on the protruding length and angle of the LSA stent-graft. The configurations should be carefully controlled during ISF-TEVAR.
How age and surface inclination affect joint moment strategies to accelerate and decelerate individual leg joints during walking.
Venue: Journal of biomechanics

A joint moment also causes motion at other joints of the body. This joint coupling-perspective allows more insight into two age-related phenomena during gait. First, whether increased hip kinetic output compensates for decreased ankle kinetic output during positive joint work. Second, whether preserved joint kinetic patterns during negative joint work in older age have any functional implication. Therefore, we examined how age and surface inclination affect joint moment strategies to accelerate and/or decelerate individual leg joints during walking. Healthy young (age: 22.5 ± 4.1 years, n = 18) and older (age: 76.0 ± 5.7 years, n = 22) adults walked at 1.4 m/s on a split-belt instrumented treadmill at three grades (0%, 10%, -10%). Lower-extremity moment-induced angular accelerations were calculated for the hip (0% and 10%) and knee (0% and -10%) joints. During level and uphill walking, both age groups showed comparable ankle moment-induced ipsilateral (p = 0.774) and contralateral (p = 0.047) hip accelerations, although older adults generated lower ankle moments in late stance. However, ankle moment-induced contralateral hip accelerations were smaller (p = 0.001) in an older adult subgroup (n = 13) who showed larger hip extension moments in early stance than young adults. During level and downhill walking, leg joint moment-induced knee accelerations were unaffected by age (all p > 0.05). These findings suggest that during level and uphill walking increased hip flexor mechanical output in older adults does not arise from reduced ankle moments, contrary to increased hip extensor mechanical output. Additionally, results during level and downhill walking imply that preserved eccentric knee extensor function is important in maintaining knee stabilization in older age.
Ankle and knee moment and power adaptations are elicited through load carriage conditioning in males.
Venue: Journal of biomechanics

Soldiers routinely conduct load carriage and physical training to meet occupational requirements. These tasks are physically arduous and are believed to be the primary cause of musculoskeletal injury. Physical training can help mitigate injury risk when specifically designed to address injury mechanisms and meet task demands. This study aimed to assess lower-limb biomechanics and neuromuscular adaptations during load carriage walking in response to a 10-week evidence-based physical training program. Thirteen male civilian participants donned 23 kg and completed 5 km of load carriage treadmill walking, at 5.5 km h-1 before and after a 10-week physical training program. Three-dimensional motion capture and force plate data were acquired in over-ground walking trials before and after treadmill walking. These data were inputs to a musculoskeletal model which estimated lower-limb joint kinematics and kinetics (i.e., moments and powers) using inverse kinematics and dynamics, respectively. A two-way analysis of variance revealed significant main effect of training for kinematic and kinetics parameters at the knee and ankle joints (p < 0.05). Post-Hoc comparisons demonstrated a significant decrease (4.2%) in total negative knee power between pre- and post-March 5 km measures after training (p < 0.05). Positive power contribution shifted distally after training, increasing at the post-march measure from 39.9% to 43.6% at the ankle joint (p < 0.05). These findings demonstrate that a periodised training program may reduce injury risk through favourable ankle and knee joint adaptations.
Experimental validation of a novel spine model demonstrates the large contribution of passive muscle to the flexion relaxation phenomenon.
Venue: Journal of biomechanics

When an individual enters a maximally flexed spine position, their largest extensor muscles become electrically inactive despite a substantial extensor moment demand being placed on the low back; this is termed flexion relaxation. Stresses within intervertebral discs, ligaments, and passive muscles are thought to support this moment thereby allowing the extensor muscles to 'turn off'. While the mechanical behaviour of the intervertebral disc and ligaments have been studied extensively, less is known regarding the moment supported by passive muscle tissue during spine flexion. Here we estimated the L4/L5 moment supported by the passive musculature during spine flexion based on experimentally derived architectural and material properties. We then tested the validity of the passive muscle prediction by determining whether the cumulative passive tissue moment (including passive muscle, intervertebral discs, and ligaments) would support the extensor moment demand-calculated with inverse dynamics-near maximum spine flexion. The model predicted that the passive tissues were able to support the entire extensor moment demand, indicating that muscle activity was not required to support the weight of the upper body, consistent with the mechanism of flexion relaxation. The model further demonstrated that despite being inactive, spine muscles still greatly contribute to flexion relaxation by passively supporting ~47% of the extensor moment demand on the spine. Finally, there was strong agreement between the predicted active muscle moments and the recorded spine muscle activity (EMG); this strong agreement persisted when the external moment was manipulated using a pulley-system. These findings provide additional confidence that the estimated passive muscle moments are reasonably accurate throughout spine flexion.
A musculoskeletal modelling approach to explain sit-to-stand difficulties in older people due to changes in muscle recruitment and movement strategies.
Venue: Journal of biomechanics

By 2050 the proportion of over 65s is predicted to be 20% of the population. The consequences of an age-related reduction in muscle mass have not been fully investigated and, therefore, the aim of the present study was to quantify the muscle and joint contact forces using musculoskeletal modelling, during a sit-to-stand activity, to better explain difficulties in performing everyday activities for older people. A sit-to-stand activity with and without the use of arm rests was observed in ninety-five male participants, placed into groups of young (aged 18-35 years), middle-aged (aged 40-60 years) or older adults (aged 65 years and over). Older participants demonstrated significantly lower knee extensor and joint forces than the young when not using arm rests, compensating through elevated hip extensor and ankle plantarflexor muscle activity. The older group were also found to have higher shoulder joint contact forces whilst using arm rests. This tendency to reorganise muscle recruitment to include neighbouring groups or other parts of the body could make everyday activities more susceptible to age-related functional decline. Reductions in leg strength, via age- or atrophy- related means, creates increased reliance on the upper body and may result in further lower limb atrophy through disuse. The eventual decline of upper body function reduces strength reserves, leading to increased vulnerability, dependence on others and risk of institutionalisation.
Simple method for measuring center of mass work during field running.
Venue: Journal of biomechanics

The purpose of this study was to propose and validate a new simple method for calculation of center of mass work during field running, in order to avoid the use of costly and inconvenient measurement devices. This method relies on spring-mass model and measurements of average horizontal velocity, and contact and flight times during running. Ten male, recreational subjects ran on a dynamometer treadmill at different velocities ranging from 2.22 to 4.44 m·s-1 during 4 min 30 s for each velocity. Twenty consecutive steps were analyzed after 3 min 30 s. The potential (Wpot), forward kinetic (Wkinf) and the total center of mass (Wext) work data obtained with this new method were compared with the reference data calculated from ground reaction force measurements. Wext, Wpot and Wkinf values calculated with the proposed method were respectively +3.39 ± 0.77% higher, -4.14 ± 0.72% lower and +7.34 ± 1.08% higher than values obtained by the reference method. Furthermore, significant linear regressions close to the identity line were obtained between the reference and the proposed method values of works (r = 0.99, p < 0.05 for Wext; r = 0.98, p < 0.05 for Wpot; r = 0.98, p < 0.05 for Wkinf). It was concluded that this new method could provide a good estimate of center of mass work in field running thanks to a few simple mechanical parameters.
Inflation experiments and inverse finite element modelling of posterior human sclera.
Venue: Journal of biomechanics

The complexity of inverse finite element modelling methods used in ocular biomechanics research has significantly increased in recent years in order to produce material parameters that capture microscale tissue behaviour. This study presents a more accessible method for researchers to optimise sclera material parameters for use in finite element studies where macroscale sclera displacements are required. Five human donor sclerae aged between 36 and 72 years were subjected to cycles of internal pressure up to 61 mmHg using a custom-built inflation rig. Displacements were measured using a laser beam and two cameras through a digital image correlation algorithm. Specimen-specific finite element models incorporating regional thickness variation and sclera surface topography were divided into six circumferential regions. An inverse finite element procedure was used to optimise Ogden material parameters for each region. The maximum root mean squared (RMS) error between the numerical and experimental displacements within individual specimens was 17.5 µm. The optimised material parameters indicate a gradual reduction in material stiffness (as measured by the tangent modulus) from the equator to the posterior region at low-stress levels up to 0.005 MPa. The variation in stiffness between adjacent regions became gradually less apparent and statistically insignificant at higher stresses. The study demonstrated how inflation testing combined with inverse modelling could be used to effectively characterise regional material properties capable of reproducing global sclera displacements. The material properties were found to vary between specimens, and it is expected that age could be a contributing factor behind this variation.
Implementation of physiological functional spinal units in a rigid-body model of the thoracolumbar spine.
Venue: Journal of biomechanics

Most of the current rigid-body models of the complete thoracolumbar spine do not properly model the intervertebral joint as the highly nonlinear stiffness is not incorporated comprehensively and the effects of compressive load on stiffness is commonly being neglected. Based on published in vitro data of individual intervertebral joint flexibility, multi-level six degree-of-freedom nonlinear stiffness of functional spinal units was modelled and incorporated in a rigid-body model of the thoracolumbar spine. To estimate physiological in vivo conditions of the entire spine, stiffening effects caused by directly applied compressive loads, and contributions to mono-segmental stiffness from the rib cage as well as multi-segmental interactions in the thoracic spine were analysed and implemented. Forward dynamic simulations were performed to simulate in vitro tests that measured the load-displacement response of the spine under various loading conditions. The predicted kinematic responses of the model were in agreement with in vitro measurements, with correlations between simulated and measured segmental displacements varying between 0.66 and 0.97 (p < 0.05) and average deviations below 1.6°. Coupling relationships were found between lateral bending and axial rotation. Under compressive loads, the model behaved stiffer and showed a decreased range of motion: The flexion/extension response of the full thoracolumbar spine under compressive loads up to 800 N was found to strongly correlate with the literature (r = 0.99, p < 0.0001). The implementation of physiological functional spinal units with nonlinear stiffness properties into rigid-body models can enhance accuracy of biomechanical simulations, and enable detailed analysis of spinal kinematics under complex loading conditions seen in vivo.
A quantitative method for evaluation of 6 degree of freedom virtual reality systems.
Venue: Journal of biomechanics

Modern virtual reality systems such as the HTC Vive enable users to be immersed in a virtual world. Validation of the HTC Vive and other contemporaneous systems for use in clinic, research, and industry applications will assure users and developers that games and applications made for these systems are accurate representations of the real world. The purpose of this study was to develop a standardized method for testing the translational and rotational capabilities of VR systems such as the HTC Vive. The translational and rotational capabilities of the HTC Vive were investigated using an industry grade robot arm and a gold standard motion capture system. It was found that the average difference between reported translational distances traveled was 0.74 ± 0.42 mm for all room-scale calibration trials and 0.63 ± 0.27 mm for all standing calibration trials. The mean difference in angle rotated was 0.46 ± 0.46° for all room-scale calibration trials and 0.66 ± 0.40° for all standing calibration trials. When tested using human movement, the average difference in distance traveled was 3.97 ± 3.37 mm. Overall, the HTC Vive shows promise as a tool for clinic, research, and industry and its controllers can be accurately tracked in a variety of situations. The methodology used for this study can easily be replicated for other VR systems so that direct comparisons can be made as new systems become available.
Can shank acceleration provide a clinically feasible surrogate for individual limb propulsion during walking?
Venue: Journal of biomechanics

Aging and many pathologies that affect gait are associated with reduced ankle power output and thus trailing limb propulsion during walking. However, quantifying trailing limb propulsion requires sophisticated measurement equipment at significant expense that fundamentally limits clinical translation for diagnostics or gait rehabilitation. As a component of joint power, our purpose was to determine if shank acceleration estimated via accelerometers during push-off can serve as a clinically feasible surrogate for ankle power output and peak anterior ground reaction forces (GRF) during walking. As hypothesized, we found that young adults modulated walking speed via changes in peak anterior GRF and peak ankle power output that correlated with proportional changes in shank acceleration during push-off, both at the individual subject (R2 ≥ 0.80, p < 0.01) and group average (R2 ≥ 0.74, p < 0.01) levels. In addition, we found that unilateral deficits in trailing limb propulsion induced via a leg bracing elicited unilateral and relatively proportional reductions in peak anterior GRF, peak ankle power, and peak shank acceleration. These unilateral leg bracing effects on peak shank acceleration correlated with those in peak ankle power (braced leg: R2 = 0.43, p = 0.028) but those effects in both peak shank acceleration and peak ankle power were disassociated from those in peak anterior GRF. In conclusion, our findings in young adults provide an early benchmark for the development of affordable and clinically feasible alternatives for assessing and monitoring trailing limb propulsion during walking.
In vivo attachment site to attachment site length and strain of the ACL and its bundles during the full gait cycle measured by MRI and high-speed biplanar radiography.
Venue: Journal of biomechanics

The purpose of this study was to measure in vivo attachment site to attachment site lengths and strains of the anterior cruciate ligament (ACL) and its bundles throughout a full cycle of treadmill gait. To obtain these measurements, models of the femur, tibia, and associated ACL attachment sites were created from magnetic resonance (MR) images in 10 healthy subjects. ACL attachment sites were subdivided into anteromedial (AM) and posterolateral (PL) bundles. High-speed biplanar radiographs were obtained as subjects ambulated at 1 m/s. The bone models were registered to the radiographs, thereby reproducing the in vivo positions of the bones and ACL attachment sites throughout gait. The lengths of the ACL and both bundles were estimated as straight line distances between attachment sites for each knee position. Increased attachment to attachment ACL length and strain were observed during midstance (length = 28.5 ± 2.6 mm, strain = 5 ± 4%, mean ± standard deviation), and heel strike (length = 30.5 ± 3.0 mm, strain = 12 ± 5%) when the knee was positioned at low flexion angles. Significant inverse correlations were observed between mean attachment to attachment ACL lengths and flexion (rho = -0.87, p < 0.001), as well as both bundle lengths and flexion (rho = -0.86, p < 0.001 and rho = -0.82, p < 0.001, respectively). AM and PL bundle attachment to attachment lengths were highly correlated throughout treadmill gait (rho = 0.90, p < 0.001). These data can provide valuable information to inform design criteria for ACL grafts used in reconstructive surgery, and may be useful in the design of rehabilitation and injury prevention protocols.
Influence of osmolarity and hydration on the tear resistance of the human amniotic membrane.
Venue: Journal of biomechanics

The amnion is considered to be the load-bearing part of the fetal membranes. We investigated the influence of osmolarity of the testing medium and hydration on its fracture toughness. Mode I fracture tests revealed that physiological variations in the bath osmolarity do not influence the tear resistance of amnion, while larger changes, i.e. from physiological saline solution to distilled water, lead to a significant reduction of the fracture toughness. Uniaxial tensile tests on collagen hydrogels confirmed the reduction in toughness, suggesting that lower bath osmolarity triggers changes in the failure properties of single collagen fibers. Prenatal surgeries, in particular fetoscopic procedures with partial amniotic carbon dioxide insufflation, might result in dehydration of the amnion. Dehydration induced a brittle behavior; however, subsequent rehydration for 15 min resulted in a similar tear resistance as for the fresh tissue.