Concurrent validity of the Microsoft Kinect for assessment of spatiotemporal gait variables

Spatiotemporal characteristics of gait such as step time and length are often associated with overall physical function in clinical populations, but can be difficult, time consuming and obtrusive to measure. This study assessed the concurrent validity of overground walking spatiotemporal data recorded using a criterion reference – a marker-based three-dimensional motion analysis (3DMA) system – and a low-cost, markerless alternative, the automated skeleton tracking output from the Microsoft Kinect™ (Kinect). Twenty-one healthy adults performed normal walking trials while being monitored using both systems. The outcome measures of gait speed, step length and time, stride length and time and peak foot swing velocity were derived using supervised automated analysis. To assess the agreement between the Kinect and 3DMA devices, Bland–Altman 95% bias and limits of agreement, percentage error, relative agreement (Pearson's correlation coefficients: r) overall agreement (concordance correlation coefficients: r_c) and landmark location linearity as a function of distance from the sensor were determined. Gait speed, step length and stride length from the two devices possessed excellent agreement (r and r_c values >0.90). Foot swing velocity possessed excellent relative (r=0.93) but only modest overall (r_c=0.54) agreement. Step time (r=0.82 and r_c=0.23) and stride time (r=0.69 and r_c=0.14) possessed excellent and modest relative agreement respectively but poor overall agreement. Landmark location linearity was excellent (R²=0.991). This widely available, low-cost and portable system could provide clinicians with significant advantages for assessing some spatiotemporal gait parameters. However, caution must be taken when choosing outcome variables as some commonly reported variables cannot be accurately measured.     

Adaptive control of center of mass (global) motion and its joint (local) origin in gait

Dynamic gait stability can be quantified by the relationship of the motion state (i.e. the position and velocity) between the body center of mass (COM) and its base of support (BOS). Humans learn how to adaptively control stability by regulating the absolute COM motion state (i.e. its position and velocity) and/or by controlling the BOS (through stepping) in a predictable manner, or by doing both simultaneously following an external perturbation that disrupts their regular relationship. Post repeated-slip perturbation training, for instance, older adults learned to forward shift their COM position while walking with a reduced step length, hence reduced their likelihood of slip-induced falls. How and to what extent each individual joint influences such adaptive alterations is mostly unknown. A three-dimensional individualized human kinematic model was established. Based on the human model, sensitivity analysis was used to systematically quantify the influence of each lower limb joint on the COM position relative to the BOS and the step length during gait. It was found that the leading foot had the greatest effect on regulating the COM position relative to the BOS; and both hips bear the most influence on the step length. These findings could guide cost-effective but efficient fall-reduction training paradigm among older population.     

Influence of gait speed on the control of mediolateral dynamic stability during gait initiation

This study investigated the influence of gait speed on the control of mediolateral dynamic stability during gait initiation. Thirteen healthy young adults initiated gait at three self-selected speeds: Slow, Normal and Fast. The results indicated that the duration of anticipatory postural adjustments (APA) decreased from Slow to Fast, i.e. the time allocated to propel the centre of mass (COM) towards the stance-leg side was shortened. Likely as an attempt at compensation, the peak of the anticipatory centre of pressure (COP) shift increased. However, COP compensation was not fully efficient since the results indicated that the mediolateral COM shift towards the stance-leg side at swing foot-off decreased with gait speed. Consequently, the COM shift towards the swing-leg side at swing heel-contact increased from Slow to Fast, indicating that the mediolateral COM fall during step execution increased as gait speed rose. However, this increased COM fall was compensated by greater step width so that the margin of stability (the distance between the base-of-support boundary and the mediolateral component of the “extrapolated centre of mass”) at heel-contact remained unchanged across the speed conditions. Furthermore, a positive correlation between the mediolateral extrapolated COM position at heel-contact and step width was found, indicating that the greater the mediolateral COM fall, the greater the step width. Globally, these results suggest that mediolateral APA and step width are modulated with gait speed so as to maintain equivalent mediolateral dynamical stability at the time of swing heel-contact.     

Can sacral marker approximate center of mass during gait and slip-fall recovery among community-dwelling older adults?

Falls are prevalent in older adults. Dynamic stability of body center of mass (COM) is critical for maintaining balance. A simple yet accurate tool to evaluate COM kinematics is essential to examine the COM stability. The purpose of this study was to determine the extent to which the COM position derived from body segmental analysis can be approximated by a single (sacral) marker during unperturbed (regular walking) and perturbed (gait-slip) gait. One hundred eighty seven older adults experienced an unexpected slip after approximately 10 regular walking trials. Two trials, the slip trial and the preceding regular walking trial, monitored with a motion capture system and force plates, were included in the present study. The COM positions were calculated by using the segmental analysis method wherein, the COM of all body segments was calculated to further estimate the body COM position. These body COM positions were then compared with those of the sacral marker placed at the second sacral vertebra for both trials. Results revealed that the COM positions were highly correlated with those of the sacrum׳s over the time intervals investigated for both walking (coefficient of correlation R>0.97) and slip (R>0.90) trials. There were detectable kinematic difference between the COM and the sacral for both trials. Our results indicated that the sacral marker can be used as a simple approximation of body COM for regular walking, and to somewhat a lesser extent, upon a slip. The benefits from the simplicity appear to overweigh the limitations in accuracy.     

Dynamic stability and compensatory stepping responses during anterior gait–slip perturbations in people with chronic hemiparetic stroke

To examine the control of dynamic stability and characteristics of the compensatory stepping responses to an unexpected anterior gait slip induced under the non-involved limb in people with hemi-paretic stroke (PwHS) and to examine any resulting adaptive changes in these on the second slip due to experience from prior slip exposure. Ten PwHS experienced overground slip (S1) during walking on the laboratory walkway after 5–8 regular walking (RW) trials followed by a second consecutive slip trial (S2). The slip outcome (backward loss of balance, BLOB and no loss of balance, NLOB) and COM state (i.e. its COM position and velocity) stability were examined between the RW and S1 and S1 and S2 at touchdown (TD) of non-involved limb and at liftoff (LO) of the contralateral limb. At TD there was no difference in stability between RW and S1, however at LO, subjects demonstrated a lower stability on S1 than RW resulting in a 100% backward loss of balance (BLOB) with compensatory stepping response (recovery step, RS, 4/10 or aborted step, AS, 6/10). On S2, although there was no change in stability at TD, there was a significant improvement in stability at LO with a 40% decrease in BLOB. There was also a change in step strategy with a decrease in AS response (60% to 35%, p<0.05) which was replaced by an increase in the ability to step (increased compensatory step length, p<0.05) either via a recovery step or a walkover step. PwHS have the ability to reactively control COM state stability to decrease fall-risk upon a novel slip; prior exposure to a slip did not significantly alter feedforward control but improved the ability to use such feedback control for improved slip outcomes.     

Does the anthropometric model influence whole-body center of mass calculations in gait?

Examining whole-body center of mass (COM) motion is one of method being used to quantify dynamic balance and energy during gait. One common method for estimating the COM position is to apply an anthropometric model to a marker set and calculate the weighted sum from known segmental COM positions. Several anthropometric models are available to perform such a calculation. However, to date there has been no study of how the anthropometric model affects whole-body COM calculations during gait. This information is pertinent to researchers because the choice of anthropometric model may influence gait research findings and currently the trend is to consistently use a single model. In this study we analyzed a single stride of gait data from 103 young adult participants. We compared the whole-body COM motion calculated from 4 different anthropometric models (Plagenhoef et al., 1983; Winter, 1990; de Leva, 1996; Pavol et al., 2002). We found that anterior-posterior motion calculations are relatively unaffected by the anthropometric model. However, medial-lateral and vertical motions are significantly affected by the use of different anthropometric models. Our findings suggest that the researcher carefully choose an anthropometric model to fit their study populations when interested in medial-lateral or vertical motions of the COM. Our data can provide researchers a priori information on the model determination depending on the particular variable and how conservative they may want to be with COM comparisons between groups.     

Estimation of Quasi-Stiffness of the Human Hip in the Stance Phase of Walking

This work presents a framework for selection of subject-specific quasi-stiffness of hip orthoses and exoskeletons, and other devices that are intended to emulate the biological performance of this joint during walking. The hip joint exhibits linear moment-angular excursion behavior in both the extension and flexion stages of the resilient loading-unloading phase that consists of terminal stance and initial swing phases. Here, we establish statistical models that can closely estimate the slope of linear fits to the moment-angle graph of the hip in this phase, termed as the quasi-stiffness of the hip. Employing an inverse dynamics analysis, we identify a series of parameters that can capture the nearly linear hip quasi-stiffnesses in the resilient loading phase. We then employ regression analysis on experimental moment-angle data of 216 gait trials across 26 human adults walking over a wide range of gait speeds (0.75–2.63 m/s) to obtain a set of general-form statistical models that estimate the hip quasi-stiffnesses using body weight and height, gait speed, and hip excursion. We show that the general-form models can closely estimate the hip quasi-stiffness in the extension (R² = 92%) and flexion portions (R² = 89%) of the resilient loading phase of the gait. We further simplify the general-form models and present a set of stature-based models that can estimate the hip quasi-stiffness for the preferred gait speed using only body weight and height with an average error of 27% for the extension stage and 37% for the flexion stage.     

Does adiposity affect muscle function during walking in children?

The biomechanical mechanisms responsible for the altered gait in obese children are not well understood, particularly as they relate to increases in adipose tissue. The purpose of this study was to test the hypotheses that as body-fat percentage (BF%) increased: (1) knee flexion during stance would decrease while pelvic obliquity would increase; (2) peak muscle forces normalized to lean-weight would increase for gluteus medius, gastrocnemius, and soleus, but decrease for the vasti; and (3) the individual muscle contributions to center of mass (COM) acceleration in the direction of their primary function(s) would not change for gluteus medius, gastrocnemius, and soleus, but decrease for the vasti. We scaled a musculoskeletal model to the anthropometrics of each participant (n=14, 8–12 years old, BF%: 16–41%) and estimated individual muscle forces and their contributions to COM acceleration. BF% was correlated with average knee flexion angle during stance (r=−0.54, p=0.024) and pelvic obliquity range of motion (r=0.78, p<0.001), as well as with relative vasti (r=−0.60, p=0.023), gluteus medius (r=0.65, p=0.012) and soleus (r=0.59, p=0.026) force production. Contributions to COM acceleration from the vasti were negatively correlated to BF% (vertical— r=−0.75, p=0.002, posterior— r=−0.68, p=0.008), but there were no correlation between BF% and COM accelerations produced by the gastrocnemius, soleus and gluteus medius. Therefore, we accept our first, partially accept our second, and accept our third hypotheses. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity may contribute to altered gait kinematics.     

Biomechanical impairments and gait adaptations post-stroke: Multi-factorial associations

Understanding the potential causes of both reduced gait speed and compensatory frontal plane kinematics during walking in individuals post-stroke may be useful in developing effective rehabilitation strategies. Multiple linear regression analysis was used to select the combination of paretic limb impairments (frontal and sagittal plane hip strength, sagittal plane knee and ankle strength, and multi-joint knee/hip torque coupling) which best estimate gait speed and compensatory pelvic obliquity velocities at toeoff. Compensatory behaviors were defined as deviations from control subjects’ values. The gait speed model (n=18; p=0.003) revealed that greater hip abduction strength and multi-joint coupling of sagittal plane knee and frontal plane hip torques were associated with decreased velocity; however, gait speed was positively associated with paretic hip extension strength. Multi-joint coupling was the most influential predictor of gait speed. The second model (n=15; p<0.001) revealed that multi-joint coupling was associated with increased compensatory pelvic movement at toeoff; while hip extension and flexion and knee flexion strength were associated with reduced frontal plane pelvic compensations. In this case, hip extension strength had the greatest influence on pelvic behavior. The analyses revealed that different yet overlapping sets of single joint strength and multi-joint coupling measures were associated with gait speed and compensatory pelvic behavior during walking post-stroke. These findings provide insight regarding the potential impact of targeted rehabilitation paradigms on improving speed and compensatory kinematics following stroke.     

Effect of step width manipulation on tibial stress during running

Narrow step width has been linked to variables associated with tibial stress fracture. The purpose of this study was to evaluate the effect of step width on bone stresses using a standardized model of the tibia. 15 runners ran at their preferred 5 k running velocity in three running conditions, preferred step width (PSW) and PSW±5% of leg length. 10 successful trials of force and 3-D motion data were collected. A combination of inverse dynamics, musculoskeletal modeling and beam theory was used to estimate stresses applied to the tibia using subject-specific anthropometrics and motion data. The tibia was modeled as a hollow ellipse. Multivariate analysis revealed that tibial stresses at the distal 1/3 of the tibia differed with step width manipulation (p=0.002). Compression on the posterior and medial aspect of the tibia was inversely related to step width such that as step width increased, compression on the surface of tibia decreased (linear trend p=0.036 and 0.003). Similarly, tension on the anterior surface of the tibia decreased as step width increased (linear trend p=0.029). Widening step width linearly reduced shear stress at all 4 sites (p<0.001 for all). The data from this study suggests that stresses experienced by the tibia during running were influenced by step width when using a standardized model of the tibia. Wider step widths were generally associated with reduced loading of the tibia and may benefit runners at risk of or experiencing stress injury at the tibia, especially if they present with a crossover running style.     

Global and Regional Associations of Smaller Cerebral Gray and White Matter Volumes with Gait in Older People

Background

Gait impairments increase with advancing age and can lead to falls and loss of independence. Brain atrophy also occurs in older age and may contribute to gait decline. We aimed to investigate global and regional relationships of cerebral gray and white matter volumes with gait speed, and its determinants step length and cadence, in older people.

Methods

In a population-based study, participants aged >60 years without Parkinson''s disease or brain infarcts underwent magnetic resonance imaging and gait measurements using a computerized walkway. Linear regression was used to study associations of total gray and white matter volumes with gait, adjusting for each other, age, sex, height and white matter hyperintensity volume. Other covariates considered in analyses included weight and vascular disease history. Voxel-based morphometry was used to study regional relationships of gray and white matter with gait.

Results

There were 305 participants, mean age 71.4 (6.9) years, 54% male, mean gait speed 1.16 (0.22) m/s. Smaller total gray matter volume was independently associated with poorer gait speed (p = 0.001) and step length (p<0.001), but not cadence. Smaller volumes of cortical and subcortical gray matter in bilateral regions important for motor control, vision, perception and memory were independently associated with slower gait speed and shorter steps. No global or regional associations were observed between white matter volume and gait independent of gray matter volume, white matter hyperintensity volume and other covariates.

Conclusion

Smaller gray matter volume in bilaterally distributed brain networks serving motor control was associated with slower gait speed and step length, but not cadence.     

Two Independent Contributions to Step Variability during Over-Ground Human Walking

Human walking exhibits small variations in both step length and step width, some of which may be related to active balance control. Lateral balance is thought to require integrative sensorimotor control through adjustment of step width rather than length, contributing to greater variability in step width. Here we propose that step length variations are largely explained by the typical human preference for step length to increase with walking speed, which itself normally exhibits some slow and spontaneous fluctuation. In contrast, step width variations should have little relation to speed if they are produced more for lateral balance. As a test, we examined hundreds of overground walking steps by healthy young adults (N = 14, age < 40 yrs.). We found that slow fluctuations in self-selected walking speed (2.3% coefficient of variation) could explain most of the variance in step length (59%, P < 0.01). The residual variability not explained by speed was small (1.5% coefficient of variation), suggesting that step length is actually quite precise if not for the slow speed fluctuations. Step width varied over faster time scales and was independent of speed fluctuations, with variance 4.3 times greater than that for step length (P < 0.01) after accounting for the speed effect. That difference was further magnified by walking with eyes closed, which appears detrimental to control of lateral balance. Humans appear to modulate fore-aft foot placement in precise accordance with slow fluctuations in walking speed, whereas the variability of lateral foot placement appears more closely related to balance. Step variability is separable in both direction and time scale into balance- and speed-related components. The separation of factors not related to balance may reveal which aspects of walking are most critical for the nervous system to control.     

The effects of railroad ballast surface and slope on rearfoot motion in walking

The purpose of this study was to investigate the effects of transversely sloped ballasted walking surface on gait and rearfoot motion (RFM) parameters. Motion analysis was performed with 20 healthy participants (15 male and 5 female) walking in six surface-slope conditions: two surfaces (solid and ballasted) by three slopes (0, 5, and 10 degrees). The gait parameters (walking velocity, step length, step rate, step width, stance time, and toe-out angle) showed significant surface effect (p = .004) and surface-slope interaction (p = .017). The RFM motion parameters (peak everted/inverted position, eversion/inversion velocity, and acceleration) revealed significant surface (p = .004) and slope (p = .024) effects. The ballasted conditions showed more cautious gait patterns with lower walk velocity, step length, and step rate and longer stance time. In the RFM parameters, the slope effect was more notable in the solid conditions due to the gait adaptations in the ballasted conditions. Ballast conditions showed reduced inversion and increased eversion and RFM range. The RFM data were comparable to other typical walking conditions but smaller than those from running.     

Minimal step length necessary for recovery of forward balance loss with a single step

Although the boundary conditions necessary to trigger a step in reaction to a forward balance loss have been predicted in previous research, the relationship between minimal step length needed for balance recovery with this single step and the center of mass (COM) motion state (i.e., its position and velocity) remains unknown. The purpose of this paper was to present a theoretical framework within which the minimal step length needed for balance recovery can be estimated. We therefore developed a simplified four-segment sagittal model of human body stepping for balance recovery. The work-energy principle of the Newtonian mechanics was employed in the simulation to determine the amount of excess mechanical energy that can be absorbed as a function of step length and the corresponding eccentric joint work that can be generated in a single step. We found that an increase in initial forward velocity and a greater forward shift of the COM require a corresponding increase in the minimal step length needed for balance recovery. Furthermore, the minimal step length is also a function of the muscle strength at the ankle: the lower the muscle strength, the greater the minimal step length required. Our theoretical framework reduces the complexity associated with previous studies relying on forward dynamics and iterative optimization processes. This method may also be applied to study aspects of balance control such as the prevention of balance loss in the posterior or mediolateral direction.     

Linkage map construction using InDel and SSR markers and QTL analysis of heading traits in Brassica oleracea var. capitata L.

Cabbage heading traits are important quantitative traits that greatly affect both quality and yield of cabbage. However, the genetic control of these traits remains unclear. To detect quantitative trait loci (QTLs) associated with heading traits, a double haploid (DH) population with 196 lines was created from a cabbage hybrid 01–20 × 96–100. A genetic map with insertion–deletion and simple sequence repeat markers was constructed based on the DH population, with a total length of 934.06 cM and average interval length of 2.3 cM between adjacent markers. Field experiments in three seasons were carried out to evaluate the heading traits, including head mature period (Hm), head weight (Hw), core length (Cl), head vertical diameter (Hvd), and the ratio of Cl to Hvd (Cl/Hvd). Using the map and the trait data, 13 reliable QTLs in total were identified and 5 were found in more than one season based on the adjusted means of three seasons. Major QTLs were identified for Hm (R ² = 40.4, LOD = 14.84), Hw (R ² = 28.6, LOD = 9.83), Cl (R ² = 38.8, LOD = 15.73), Hvd (R ² = 19.2, LOD = 9.26), and Cl/Hvd (R ² = 38.8, LOD = 12.75). The most significant QTLs were Hm3.1, Cl3.1, and Cl/Hvd3.1, which were detected in three seasons with the maximum contribution rate of almost 40 %. Six active regions that harbored more than one QTL were identified on five chromosomes, and one of them contained major QTLs associated with five traits. The QTLs obtained in this study should be useful for marker-assisted selection in cabbage breeding and for understanding the genetic control of these traits.     

Relationships of 35 lower limb muscles to height and body mass quantified using MRI

Skeletal muscle is the most abundant tissue in the body and serves various physiological functions including the generation of movement and support. Whole body motor function requires adequate quantity, geometry, and distribution of muscle. This raises the question: how do muscles scale with subject size in order to achieve similar function across humans? While much of the current knowledge of human muscle architecture is based on cadaver dissection, modern medical imaging avoids limitations of old age, poor health, and limited subject pool, allowing for muscle architecture data to be obtained in vivo from healthy subjects ranging in size. The purpose of this study was to use novel fast-acquisition MRI to quantify volumes and lengths of 35 major lower limb muscles in 24 young, healthy subjects and to determine if muscle size correlates with bone geometry and subject parameters of mass and height. It was found that total lower limb muscle volume scales with mass (R²=0.85) and with the height–mass product (R²=0.92). Furthermore, individual muscle volumes scale with total muscle volume (median R²=0.66), with the height–mass product (median R²=0.61), and with mass (median R²=0.52). Muscle volume scales with bone volume (R²=0.75), and muscle length relative to bone length is conserved (median s.d.=2.1% of limb length). These relationships allow for an arbitrary subject's individual muscle volumes to be estimated from mass or mass and height while muscle lengths may be estimated from limb length. The dataset presented here can further be used as a normative standard to compare populations with musculoskeletal pathologies.     

Rapid,Accurate, and Non-Invasive Measurement of Zebrafish Axial Length and Other Eye Dimensions Using SD-OCT Allows Longitudinal Analysis of Myopia and Emmetropization

Refractive errors in vision can be caused by aberrant axial length of the eye, irregular corneal shape, or lens abnormalities. Causes of eye length overgrowth include multiple genetic loci, and visual parameters. We evaluate zebrafish as a potential animal model for studies of the genetic, cellular, and signaling basis of emmetropization and myopia. Axial length and other eye dimensions of zebrafish were measured using spectral domain-optical coherence tomography (SD-OCT). We used ocular lens and body metrics to normalize and compare eye size and relative refractive error (difference between observed retinal radial length and controls) in wild-type and lrp2 zebrafish. Zebrafish were dark-reared to assess effects of visual deprivation on eye size. Two relative measurements, ocular axial length to body length and axial length to lens diameter, were found to accurately normalize comparisons of eye sizes between different sized fish (R² = 0.9548, R² = 0.9921). Ray-traced focal lengths of wild-type zebrafish lenses were equal to their retinal radii, while lrp2 eyes had longer retinal radii than focal lengths. Both genetic mutation (lrp2) and environmental manipulation (dark-rearing) caused elongated eye axes. lrp2 mutants had relative refractive errors of −0.327 compared to wild-types, and dark-reared wild-type fish had relative refractive errors of −0.132 compared to light-reared siblings. Therefore, zebrafish eye anatomy (axial length, lens radius, retinal radius) can be rapidly and accurately measured by SD-OCT, facilitating longitudinal studies of regulated eye growth and emmetropization. Specifically, genes homologous to human myopia candidates may be modified, inactivated or overexpressed in zebrafish, and myopia-sensitizing conditions used to probe gene-environment interactions. Our studies provide foundation for such investigations into genetic contributions that control eye size and impact refractive errors.     

Combined effects of speed and directional change on postural adjustments during gait initiation

The study of gait initiation (GI) has primarily focused on gait initiated in a forward direction, however, in everyday life, GI is often combined with a directional change. Ten young adults initiated gait with their right foot in four directions (to the left: −15°, straight ahead: 0°, to the right: 15° and 30°) at self-selected and fast gait speeds. The relationship between starting direction of GI and the lateral center of foot pressure displacement for normal (r² = 0.57) and fast gait speed (r² = 0.75) indicated that the lateral component plays an important role with regards to controlling the desired direction of gait. At the first step of the swing limb, the progression velocity of the center of mass (CM) remained slower for the 30° condition only, whereas no difference was found between directions for CM velocity perpendicular to the intended direction. These results suggest that postural adjustments are scaled to initiate gait in a predetermined direction. By the first step, the orientation of CM is toward the intended direction of gait, however, when gait is initiated in combination with a large change in direction, additional adjustments may be required to reach the intended progression velocity.     

Energy cost of balance control during walking decreases with external stabilizer stiffness independent of walking speed

Human walking requires active neuromuscular control to ensure stability in the lateral direction, which inflicts a certain metabolic load. The magnitude of this metabolic load has previously been investigated by means of passive external lateral stabilization via spring-like cords. In the present study, we applied this method to test two hypotheses: (1) the effect of external stabilization on energy cost depends on the stiffness of the stabilizing springs, and (2) the energy cost for balance control, and consequently the effect of external stabilization on energy cost, depends on walking speed. Fourteen healthy young adults walked on a motor driven treadmill without stabilization and with stabilization with four different spring stiffnesses (between 760 and 1820 N m⁻¹) at three walking speeds (70%, 100%, and 130% of preferred speed). Energy cost was calculated from breath-by-breath oxygen consumption. Gait parameters (mean and variability of step width and stride length, and variability of trunk accelerations) were calculated from kinematic data. On average external stabilization led to a decrease in energy cost of 6% (p<0.005) as well as a decrease in step width (24%; p<0.001), step width variability (41%; p<0.001) and variability of medio-lateral trunk acceleration (12.5%; p<0.005). Increasing stabilizer stiffness increased the effects on both energy cost and medio-lateral gait parameters up to a stiffness of 1260 N m⁻¹. Contrary to expectations, the effect of stabilization was independent of walking speed (p=0.111). These results show that active lateral stabilization during walking involves an energetic cost, which is independent of walking speed.     

Modeling gait score of broiler chicken via production and behavioral data

Lameness in broilers may be associated with pain and is considered a major broiler production and welfare concern. Manual gait score assessment in commercial broiler houses is discrete, time-consuming, and laborious. As such, automatic methods for broiler gait score assessment are urgently needed. The objective of this study was to identify the relation of broiler gait score with several productions and behavioral metrics (bird BW, age, activity, and distribution), and establish three gait score prediction models for automatic gait score estimations in broiler farms with automatic weighing systems, camera systems, or both. Sixteen pens were used to rear Cobb 500 and Ross 708 broilers for eight and nine weeks, respectively (eight pens/strain, 12 birds/pen). The gait scores of all birds were assessed weekly by trained assessors following a six-point (0–5) scoring protocol from the third week. The pen’s average BW was measured weekly. Top-view cameras were installed to continuously record videos of broilers in all 16 pens. Images were extracted from video clips (10 min/hour) during a 16-hour light period to determine the activity index and distribution index through image processing. The gait score was positively correlated with BW (R² = 0.97 for Cobb and R² = 0.96 for Ross), while negatively correlated with activity (R² = 0.78 for Cobb and R² = 0.73 for Ross). The three models showed high accuracies in predicting broiler gait score based on variables of BW, age, activity index, and distribution index (R² = 0.90–0.91, RMSE = 0.38–0.41). The findings of this study demonstrated the potential of estimating broiler gait score using bird BW, age, activity index, and distribution index. This information will assist in the development of automated gait score assessment systems in broiler production.