nils-herrmann/clean_scirepeval huggingface dataset:
Walking speed changes in response to user-driven treadmill control after stroke.
Venue: Journal of biomechanics

The objective of this study was to determine how individuals poststroke respond to user-driven treadmill (UDTM) controlin terms ofwalking speeds, peak anterior ground reaction forces (AGRF), peak posterior ground reaction forces (PGRF), and trailing limb angles (TLA). Twenty individuals with chronic stroke walked overground during a 10-meter walk test to determine their self-selected (SS) speeds before walking on a treadmill in its fixed-speed (FSTM) and UDTM control modes at their SS and fastest comfortable (Fast) speeds. Paired t-tests were used to compare the walking speeds, peak AGRF, peak PGRF, and TLA among test conditions (α = 0.05). Participants selected similar SS (p > 0.05) and faster Fast walking speeds (p < 0.05) with the UDTM control compared to the FSTM control. There were no changes in their peak AGRF or PGRF for either limb or speed between UDTM and FSTM conditions (p > 0.05). Individuals used greater paretic TLA at SS speeds with UDTM control (p < 0.05). There was no difference in the AGRF required at Fast speeds with FSTM and UDTM control even though participants selected faster speeds with UDTM control. In work with young, healthy adults, we found that the treadmill control condition did not affect the amount of forward propulsion needed. Therefore, it is likely that when walking with UDTM control, individuals poststroke adjust their posture to make better use of their forward propulsion. This means they can reach faster walking speeds without increasing their push-off forces. Future work should assess how to most effectively prescribe UDTM control for gait training programs.
Effect of inward-outward rotation on hip wear simulation.
Venue: Journal of biomechanics

The ISO 14242-1 standard specifies a three-axis motion for the wear testing of prosthetic hips. Multidirectionality of the relative motion and serum-based lubrication are known to be necessary for the reproduction of clinical wear mechanisms. For multidirectionality however, biaxial motion has been shown to be sufficient. To a biaxial hip joint simulator that incorporated flexion-extension (FE, range 46°) and abduction-adduction (AA, range 12°), a third motion component, inward-outward rotation (IOR, range 12°) was added according to the ISO 14242-1 standard. Due to the addition of the IOR, the wear rate of vitamin E stabilized, extensively cross-linked polyethylene (VEXLPE) liners decreased by 50 per cent. This was probably attributable to the increased linearity of the relative motion in the stance phase, caused by the simplified motion waveforms and their relative phases specified in the standard. In order not to underestimate the wear rate, the established biaxial motion is preferred.
Sensitivity analysis of muscle properties and impact parameters on head injury risk in American football.
Venue: Journal of biomechanics

Head injuries frequently occur in American football and other contact sports. Uncertainty on the effects of cervical muscle properties on head injury risk may be due to the limitations of previous observational studies. This simulation study employs a musculoskeletal model of the head and neck to investigate the effect of several factors related to head injury metrics in American Football. These factors include isometric muscle strength, the eccentric multiplier (which is related to the athlete's ability to apply greater muscle force during eccentric contractions), posture, muscle activation patterns, and impact properties. Impact properties were based on the literature and tuned to reproduce peak linear and rotational accelerations of the skull. We hypothesized that active neck muscles significantly reduce head injury metrics. We systematically altered each model parameter to test our hypothesis. We then determined which model parameters affect head injury metrics the most. The results of this study indicate that active neck muscles have a statistically significant effect on head injury metrics. Increasing muscle strength and eccentric multiplier also resulted in a statistically significant reduction of head injury metrics. However, posture prior to impact had a much stronger effect than any other factor on head injury metrics. A comprehensive approach to athlete training protocols is recommended, including exercises aimed at increasing eccentric muscle strength and preparation for impacts. Future studies should investigate how targeted muscle strengthening and impact training (i.e. activation patterns and posture) modifies risk.
Review article on spine kinematics of quadrupeds and bipeds during walking.
Venue: Journal of biomechanics

Sheep, pigs and goats are the most commonly used large animals for preclinical spinal applications. However, there is an increasing number of voices challenging the suitability of quadrupeds, as the obvious postural differences give reason to presume significant differences in the spinal kinematics compared to humans. Rather, it is often questioned if primates did not represent the more suitable experimental animals due to their ability to bipedal walking. Both perspectives, however, have never been systematically addressed. Therefore, the present paper reviews the existing literature on in vivo spinal kinematics of quadrupeds, primates and humans during walking and critically discusses the comparability between these species. Surprisingly, no studies were found for sheep, pigs or goats. Instead, the literature search yielded 50 studies on quadrupeds, horses (n = 37) and dogs (n = 13), primates (n = 10) and humans (n = 61). In general, the kinematic data revealed a high level of heterogeneity and often demonstrated methodological deficits, e.g., insufficient number of measured animals. More kinematic variables were comparable between humans and quadrupeds than between humans and primates. Differences in spinal characteristics, however, could also be found amongst quadrupeds themselves (horse vs. dog). In conclusion, using of a particular animal species as a model for spine research requires its characterization. Cross-species extrapolations are ineligible. Furthermore, the review revealed significant differences between the bipedal walk of primates and humans. The gait alone thus does not constitute a valid argument for the superiority of primates over quadrupeds as experimental animal models for human spine research.
Stair negotiation behaviour of older individuals: Do step dimensions matter?
Venue: Journal of biomechanics

Stair falls are a major health problem for older people. Most studies on identification of stair fall risk factors are limited to staircases set in given step dimensions. However, it remains unknown whether the conclusions drawn would still apply if the dimensions had been changed to represent more challenging or easier step dimensions encountered in domestic and public buildings. The purpose was to investigate whether the self-selected biomechanical stepping behaviours are maintained when the dimensions of a staircase are altered. Sixty-eight older adults (>65 years) negotiated a seven-step staircase set in two step dimensions (shallow staircase: rise 15 cm, going 28 cm; steep staircase: rise 20 cm, going 25 cm). Six biomechanical outcome measures indicative of stair fall risk were measured. K-means clustering profiled the overall stair-negotiating behaviour and cluster profiles were calculated. A Cramer's V measured the degree of association in membership between clusters. The cluster profiles revealed that the biomechanically risky and conservative factors that characterized the overall behaviour in the clusters did not differ for the majority of older adults between staircases for ascent and descent. A strong association of membership between the clusters on the shallow staircase and the steep staircase was found for stair ascent (Cramer's V: 0.412, p < 0.001) and descent (Cramer's V: 0.380, p = 0.003). The findings indicate that manipulating the demand of the task would not affect the underpinning mechanism of a potential stair fall. Therefore, for most individuals, detection of stair fall risk might not require testing using a staircase with challenging step dimensions.
Dynamic interactions between lumbar intervertebral motion segments during forward bending and return.
Venue: Journal of biomechanics

Continuous dynamic multi-segmental studies of lumbar motion have added depth to our understanding of the biomechanics of back pain, but few have attempted to continuously measure the proportions of motion accepted by individual levels. This study attempted to compare the motion contributions of adjacent lumbar levels during an active weight bearing flexion and return protocol in chronic, non-specific low back pain (CNSLBP) patients and controls using quantitative fluoroscopy (QF). Eight CNSLBP patients received QF during guided standing lumbar flexion. Dynamic motion sharing of segments from L2 to S1 were calculated and analysed for interactions between levels. Eight asymptomatic controls were then matched to the 8 patients for age and sex and their motion sharing patterns compared. Share of intersegmental motion was found to be consistently highest at L2-L3 and L3-L4 and lowest at L5-S1 throughout the motion in both groups, with the exception of maximum flexion where L4-L5 received the greatest share. Change in motion sharing occurred throughout the flexion and return motion paths in both participant groups but tended to vary more at L4-L5 in patients (p < 0.05). In patients, L5-S1 provided less angular range (p < 0.05) and contributed less at maximum bend (p < 0.05), while L3-L4, on average over the bending sequence, provided a greater share of motion (p < 0.05). Intervertebral motion sharing inequality is therefore a normal feature during lumbar flexion. However, in patients, inequality was more pronounced, and variability of motion share at some levels increased. These effects may result from differences in muscular contraction or in the mechanical properties of the disc.
Direct muscle electrical stimulation as a method for the in vivo assessment of force production in m. abductor hallucis.
Venue: Journal of biomechanics

In vivo assessment of the force-generating capacity of m. abductor hallucis (AbH) is problematic due to its combined abduction-flexion action and the inability of some individuals to voluntarily activate the muscle. This study investigated direct muscle electrical stimulation as a method to assess isometric force production in AbH about the 1st metatarsal phalangeal joint (1MPJ) at different muscle-tendon lengths, with the aim of identifying an optimal angle for force production. A 7 s stimulation train was delivered at 20 Hz pulse frequency and sub-maximal (150% motor threshold) intensity to the AbH of the left foot in 16 participants whilst seated, and with the Hallux suspended from a force transducer in 0°,5°,10°,15° and 20° 1MPJ dorsal flexion. Reflective markers positioned on the foot and force transducer were tracked with 5 optical cameras to continuously record the force profile and calculate the external 1MPJ joint flexion moment at each joint configuration. A parabolic relationship was found between AbH force production and 1MPJ configuration. The highest 1MPJ joint moments induced by electrical stimulation were found between 10° and 15° of Hallux dorsal flexion. However, the joint angle (p < 0.001; η2 = 0.86) changed significantly across all but one 1MPJ configurations tested during the stimulation-evoked contraction, resulting in a significant change in the corresponding external moment arm (p < 0.001; η2 = 0.83). Therefore, the changes in joint geometry during contraction should be accounted for to prevent an underestimation of the resulting joint moment. We conclude that direct muscle electrical stimulation combined with dynamometry offers a robust method for standardised assessment of AbH sub-maximal isometric force production.
Spinal sagittal alignment goals based on statistical modelling and musculoskeletal simulations.
Venue: Journal of biomechanics

The definition of target alignment for spinal fusion surgery follows anatomical criteria and strongly relies on surgical experience. However, the optimal patient-specific alignment often remains unknown. Statistical models could provide information about physiological alignments, and musculoskeletal models are powerful tools to investigate biomechanics. We aimed to statistically predict alignments and hypothesized they would be biomechanically favorable. A statistical model was trained with 60 annotated radiographs to predict physiological sagittal alignment based on position of femoral heads and sacrum. Predicted alignments for 11 back pain patients were clinically evaluated in terms of balance and compared to Original alignments. The normative ranges for spinal balance parameters were obtained from Surgimap™. Musculoskeletal loads were furthermore simulated in upright standing and 30° forward flexion, using alignment-specific musculoskeletal models. For the majority of Predicted alignments (n = 9) at least two of three investigated balance parameters were within the normative range, as opposed to the minority of the Original alignments (n = 4). Predicted alignments resulted in significantly lowered overall muscle activity and compressive loads (all levels, both postures). Shear force magnitudes in upright standing decreased significantly at levels L1L2 (-68 N) and L2L3 (-69 N) and clearly yet not significantly at L3L4 (-39 N) and L4L5 (-152 N). Shear loads at level L5S1 remained the same. In flexed postures identical trends were observed. The statistical model was able to predict spinal alignments that led to both improved balance and reduced musculoskeletal loads. Further studies are needed to investigate clinical validity of such models.
A foot/ground contact model for biomechanical inverse dynamics analysis.
Venue: Journal of biomechanics

The inverse dynamics simulation of the musculoskeletal system is a common method to understand and analyse human motion. The ground reaction forces can be accurately estimated by experimental measurements using force platforms. However, the number of steps is limited by the number of force platforms available in the laboratory. Several numerical methods have been proposed to estimate the ground reaction forces without force platforms, i.e., solely based on kinematic data combined with a model of the foot-ground contact. The purpose of this work is to provide a more efficient method, using a unilaterally constrained model of the foot at the center of pressure to compute the ground reaction forces. The proposed model does not require any data related with the compliance of the foot-ground contact and is kept as simple as possible. The indeterminacy in the force estimation is handled using a least square approach with filtering. The relative root mean square error (rRMSE) between the numerical estimations and experimental measurements are 4.1% for the vertical component of the ground reaction forces (GRF), 11.2% for the anterior component and 5.3% for the ground reaction moment (GRM) in the sagittal plane.
Non-periodicity of blood flow and its influence on wall shear stress in the carotid artery bifurcation: An in vivo measurement-based computational study.
Venue: Journal of biomechanics

Although arterial blood flow is physiologically non-periodic under resting conditions, periodic flow assumption has been widely adopted in most hemodynamic studies. So far, it remains unclear how the non-periodicity of blood flow would influence local hemodynamic parameters, especially wall shear stress (WSS) that associates closely with endothelial function and vascular disease. In this study, numerical simulations of blood flows in sixteen normal carotid artery bifurcations were performed under measured non-periodic and averaged periodic flow conditions, respectively, with the obtained results being compared in terms of five typical WSS metrics (i.e., mean WSS (MWSS), time-averaged WSS (TAWSS), oscillatory shear index (OSI), transverse WSS (transWSS), and average temporal gradient of WSS (WSSTG)) in the atheroprone low-WSS regions. It was found that simplifying the physiologically non-periodic flow condition into a periodic one did not significantly alter the major features of WSS distribution, but resulted in underestimations of some WSS metrics. Specifically, the degree of underestimation was largest (27.2% ± 8.3%) for WSSTG, smallest (0.5% ± 0.4%) for MWSS, while moderate (5.1% ± 3.2% ~ 9.2% ± 4.1%) for other WSS metrics. Statistical analyses revealed that the cycle-to-cycle variability of flow velocity waveform (var-V) and the planarity of internal carotid artery correlated strongly with the periodic flow assumption-induced underestimations of WSS metrics. These findings suggest that taking the non-periodic characteristic of blood flow into consideration could be important for studying hemodynamics in arteries with a large var-V or specific morphological characteristics, especially when WSSTG is the main hemodynamic parameter of concern.
Comparison of a portable balance board for measures of persistence in postural sway.
Venue: Journal of biomechanics

Measuring postural sway is important for determining functional ability or risk of falling. Gathering postural sway measures outside of controlled environments is desirable for reaching populations with limited mobility. Previous studies have confirmed the accuracy of the magnitude of postural sway using the Nintendo Wii Balance Board (WBB). However, it is unclear if the WBB can accurately measure persistence of postural sway, i.e., the pattern of center-of-pressure fluctuations over time. The purpose of this study was to compare measures of persistence of postural sway (through detrended fluctuation analysis) using WBB and a force platform (FP). Seventeen healthy individuals performed three standing conditions: eyes open, eyes closed, and one-leg standing. The WBB (30 Hz) was placed on top on the FP (600 Hz) to collect data simultaneously, then the FP data were downsampled to 100 Hz and 30 Hz. The agreement between WBB and FP for measures of postural sway were influenced by the sampling rate and postural sway direction. Intraclass correlation coefficient was excellent (range: 0.953-0.998) for long-term scaling regions in the anterior-posterior direction, but lower (range: 0.352-0.877) and inconsistent for medial-lateral direction and short-term scaling regions. The three comparison groups (WBB at 30 Hz, FP at 30 Hz, and FP at 100 Hz) showed dissimilar abilities in detecting differences in persistence of postural sway. In summary, the WBB is accurate for quantifying persistence of postural sway measurements in long-term scaling regions in the AP direction, but has limitations for short-term scaling regions and the ML direction.
Effect of investigator observation on gait parameters in individuals with stroke.
Venue: Journal of biomechanics

Improvements in gait speed following various training paradigms applied to patients post-stroke does not always lead to changes in walking performance, defined as gains in daily stepping activity. We hypothesized that testing conditions, specifically the presence of an observer, influences patient behaviors and resultant outcomes may overestimate their true walking capacity. This potential Hawthorne effect on spatiotemporal and biomechanical measures of locomotor function in individuals post-stroke has not been assessed previously. Fifteen ambulatory individuals with chronic stroke wore instrumented insoles and performed two separate normal-pace walking assessments, including unobserved conditions during which participants were unattended and unaware of data collection, and observed conditions with an investigator present. Gait analysis was conducted outside of a laboratory setting using instrumented insoles equipped with a 3D accelerometer and pressure sensors which captured the spatiotemporal kinematics, vertical ground reaction forces and foot acceleration. Data were compared using paired comparisons, with subsequent correlation and stepwise regression analyses to explore potential associations between Hawthorne-induced changes in walking strategies, gait speed and locomotor performance (daily stepping). Except for cadence, other measures of spatiotemporal parameters and swing kinematics (acceleration) were not significantly different between observed vs unobserved conditions. However, analyses of ground reaction forces revealed significantly greater paretic limb loading (Δ1st peak = 1.5 ± 1.6 N/kg Δ2nd peak = 1.4 ± 1.8 N/kg; p < 0.01) and increases in weight bearing symmetry (11-24%, p < 0.01) during observed vs unobserved conditions. This potential Hawthorne effect was greater in those with slower walking speeds and shorter stride lengths but was not related to daily stepping. The present findings suggest that biomechanical parameters of walking function may be related to the presence of an observer and highlight the need to separately measure locomotor capacity (gait speed) and performance (daily stepping).
Effects of age and sex on trunk motor control.
Venue: Journal of biomechanics

The goal of the present study was to assess the effects of age and sex on trunk motor control. Fifty healthy adults (aged between 19 and 67 years, 28 males) participated in this study. Trunk motor control was assessed using force-controlled perturbations directly applied to the trunk. Admittance (inverse of lumped intrinsic and reflexive impedance) decreased with age and tended to be lower in females than males. The age effect on admittance was due to increasing intrinsic stiffness and damping with age, while intrinsic damping and position- and velocity feedback gains were lower in females than males. Feedback delays were not dependent on age. The decrease of trunk admittance with age is most likely due to increasing levels of antagonistic co-activation. Trunk admittance was (just) not significantly different between females and males, in spite of lower feedback gains and damping, possibly due to differences in trunk mass between sexes. These results imply that age and sex differences should be considered when assessing the relationship between back pain and trunk motor control.
Modelling muscle recovery from a fatigued state in isometric contractions for the ankle joint.
Venue: Journal of biomechanics

Current models of localized muscular fatigue are capable of predicting performance in isometric tasks with reasonable accuracy. However, they do not account for the effect of continuously-varying task intensities on muscular recovery from a fatigued state. In this work, we propose and evaluate three continuous functions for modelling recovery to replace a dichotomous step-function in the three-compartment controller (3CC-r) model of muscle fatigue (Looft et al., 2018) and validate their predictions with previously collected data in the literature for intermittent and sustained isometric tasks of the ankle joint performed at different intensities. When compared to experimental data the accuracy of one of the three proposed models of recovery is found to be nearly the same as that yielded by the original step-function, but this seemingly-identical accuracy may be a limitation of the dataset used. A superelliptical curve relating recovery factor to task intensity is proposed to be the closest replacement for the step function as it depicts both the elevated value of recovery factor for near-rest activities as well as a nearly-constant value for low-to-high-intensity tasks.