How are we representing the trunk? A narrative review on marker sets for kinematics analysis of neurological conditions.

Workers in aeronautics face high risks of low-back disorders (LBDs). Although occupational passive back exoskeletons show preventive potential during trunk flexion tasks, few studies have been conducted in real workplaces. This field study aims to assess the effects of a rigid passive back exoskeleton on back neuromuscular activity, trunk kinematics and perceived discomfort, as well as the user acceptance. Ten male employees from an aeronautics manufacturer performed their routine polishing activity, later segmented into seven representative tasks, with and without the Laevo FLEX exoskeleton. The results showed significant reductions of 7–25% in erector spinae (ES) activity in four tasks. The average trunk flexion angle was only reduced for one task. Perceived discomfort was not significantly impacted by the exoskeleton. Acceptance was mixed but overall positive. This supports the exoskeleton’s beneficial impact in aeronautical polishing tasks and more generally highlights the potential of such devices for trunk-flexion activities in real settings.

Upper body kinematics during walking and their relationship to fall risk after stroke.

Stride time variability (STV) is an important indicator of gait stability and motor control during running, yet its assessment typically depends on laboratory-based systems or distal sensor placement. This study evaluated whether a single waist-mounted inertial measurement unit (IMU) can estimate STV during prolonged treadmill running using machine learning. Eighteen healthy young adults completed 30min of treadmill running at self-selected speeds while IMUs were placed on the right dorsal foot and low back. Stride times were identified from the foot-mounted IMU and used to calculate STV as the coefficient of variation of 50 consecutive strides, which served as the reference outcome. From the waist-mounted IMU, time- and frequency-domain features were extracted from tri-axial acceleration and angular velocity signals. Four regression models, including artificial neural network (ANN), random forest (RF), decision tree (DT), and XGBoost, were developed to estimate STV. Model performance was evaluated using leave-one-subject-out cross-validation with root mean squared error (RMSE), mean absolute error (MAE), and coefficient of determination (R²). All models demonstrated good subject-independent predictive ability, with XGBoost achieving the best overall performance (R² =0.942, MAE = 0.005, RMSE = 0.009). Features related to forward acceleration, particularly mean and dominant frequency in the X direction, were consistently among the most influential predictors. These findings suggest that trunk kinematics recorded from a single waist-mounted IMU contain sufficient information to estimate running STV, supporting the feasibility of unobtrusive gait stability monitoring during endurance running with implications for assessing fall risk and rehabilitation progress.

Background: Adolescent idiopathic scoliosis (AIS) alters postural control and movement coordination. This study investigated the dynamic biomechanical effects of Schroth therapy on AIS kinematics. Methods: Twelve young individuals with AIS completed a standardized Schroth therapy program, while twelve healthy participants served as controls. Three-dimensional gait kinematics were recorded using the Xsens MVN Awinda during walking at a self-selected speed. Pre- and post-intervention assessments were conducted for the analysis of trunk, pelvic, and lower-extremity kinematics. Results: Changes were observed primarily in proximal kinematic parameters. Pelvic obliquity and thorax–head flexion/extension demonstrated the largest differences (p = 0.004 and p = 0.002, respectively; Cohen’s d = 0.82–0.95). Moderate changes were detected in pelvis–thorax axial rotation and shoulder abduction/adduction patterns. Lower-extremity changes were limited and parameter-specific, with moderate changes observed in selected hip and knee rotational parameters, while other variables showed minimal or no change. Post-intervention comparisons with healthy controls showed that several upper-body kinematic patterns showed patterns that were more alike to those observed in the control group, although direct equivalence cannot be assumed. Conclusions: The findings suggest that Schroth therapy may be associated with changes in trunk and pelvic kinematics during gait in individuals with AIS.

Background: Children with juvenile idiopathic arthritis (JIA) exhibit gait abnormalities, postural instability, and compensatory movement strategies due to joint pain, inflammation, and reduced neuromuscular control. These alterations negatively affect functional mobility and movement efficiency. Although gait retraining is commonly recommended in rehabilitation, objective evidence on its short-term biomechanical effects remains limited. This study aimed to evaluate the immediate impact of a single-session standardized movement training intervention on gait biomechanics in children with JIA. Methods: Seventeen children with JIA underwent pre–post gait assessments using the Xsens MVN Awinda wearable motion capture system. The intervention focused on step symmetry, stride length, heel–toe progression, and upright trunk posture, delivered by an experienced physiotherapist following a standardized protocol. Scalar kinematic outcomes were analyzed using paired statistical tests, and time-normalized kinematic waveforms were compared with healthy reference data from 25 age-matched participants derived from the COMPWALK-ACL dataset. Results: Significant improvements were observed in multiple gait parameters following the intervention. Trunk lateral lean decreased significantly (p = 0.0002; d = −1.35), indicating enhanced postural stability. Significant changes were also found in ankle dorsiflexion–plantarflexion (p = 0.0081; d = 0.83) and knee flexion–extension (p = 0.0252; d = 0.68). Waveform analyses showed increased similarity to healthy patterns, particularly in trunk and knee kinematics. Spatiotemporal parameters reflected a slower, more controlled gait pattern, with increased stride time and stance duration. Conclusions: A single session of standardized movement training can produce immediate improvements in gait biomechanics in children with JIA, especially in trunk control and lower-limb kinematics. Wearable motion analysis provides a sensitive tool for detecting these short-term adaptations and supports the inclusion of structured movement training in pediatric JIA rehabilitation.

ABSTRACT This study aimed to characterise early flight posture and classify movement strategies in ski jumping of trunk, hip, and knee kinematics. Using a 10-camera markerless motion capture system, three-dimensional motion data were collected from 30 ski jumpers of different competitive levels. During the early flight phase, time-series waveforms of trunk anterior tilt and hip and knee extension angles were extracted and time-normalised. Principal component analysis (PCA) was applied to reduce waveform dimensionality while preserving dominant coordination features. The first two principal components from each variable were subjected to hierarchical clustering. Based on clustering indices, a three-cluster solution was statistically supported, revealing three distinct movement strategies. To evaluate cluster-specific kinematic differences over time, statistical parametric mapping (SPM) one-way ANOVA with post hoc tests was applied to the original waveforms. Significant main effects of cluster were observed for trunk, hip, and knee kinematics. Post hoc analyses showed that trunk and knee differences were mainly driven by contrasts between Clusters 2 and 3, whereas hip kinematics primarily distinguished Cluster 1. Together, these results indicate that PCA-based clustering supported by SPM enables an objective classification of early flight movement strategies and a descriptive interpretation of inter-individual kinematic differences.

Background. Functional Movement Strength Training (FMST) integrates functional, strength, and plyometric exercises to enhance neuromuscular coordination and movement performance. Although these training modalities have been investigated individually in soccer, their combined effects on core muscle activation and trunk kinematics during jumping heading in adolescent players remain unclear. Objectives. This study aimed to examine the effects of an eight-week FMST program on core muscle activation and trunk kinematics during jumping heading in adolescent male soccer players. Materials and Methods. A quasi-experimental pretest–posttest design with a control group was employed. Thirty adolescent soccer players were allocated into an Experimental Group (EG; n = 16), which completed an eight-week FMST program (three sessions per week), and a Control Group (CG; n = 14), which continued regular training. Muscle activity was assessed using surface electromyography, and kinematic variables of the neck, trunk, hip, knee, and ankle were analyzed during the preparation, take-off, and ball-contact phases of jumping heading. Data were analyzed using Linear Mixed Model analysis. Results. A significant Group × Time interaction was observed for rectus abdominis (RA) activation (p < 0.05), with greater increases in the EG compared to the CG. Furthermore, significant interactions were also found for hip angle during the preparation phase, and for neck angle and trunk tilt during the take-off phase (p < 0.05). No significant differences were identified during the ball-contact phase. Conclusions. Using FMST was associated with increased RA activation and phase-specific modifications in trunk-related kinematics during jumping heading. These findings suggest that integrated training approaches may enhance trunk control and neuromuscular coordination in adolescent soccer players.

Single-leg squat (SLS) performance is widely used to screen functional movement quality, but practical assessment often relies on expert visual grading or laboratory-based motion capture. In addition, conventional SLS criteria mainly focus on isolated joint deviations and may overlook coordination-related, multisegment movement patterns that characterize impaired performance. This study aimed to examine the feasibility of an interpretable machine learning framework for classifying SLS performance into 3 levels (good, moderate, and poor) from single-smartphone, frontal-view videos based on trunk, pelvic, and knee kinematics, and to evaluate coordination-informed features and model explainability using Shapley additive explanations (SHAP) and local interpretable model-agnostic explanations (LIME). A dataset of frontal-view SLS videos was labeled by physiotherapists into 3 functional categories (good, moderate, and poor). Videos were processed using 2D pose estimation, and models were trained on 17 engineered kinematic features derived from trunk, pelvic, and knee angles. Following the feature selection, 7 classifiers were trained and evaluated using the 8 selected features with stratified 5-fold cross-validation and a held-out test set. SHAP and LIME were applied for global and local interpretability. On the held-out test set, adaptive boosting classified SLS performance with an accuracy of 0.84, an F1-score of 0.85, and an area under curve of 0.92. SHAP indicated that the summated angle (trunk + pelvis + knee), coordination-related features (knee × trunk interaction and knee-to-trunk ratio), and knee angle were key contributors to model predictions. LIME provided instance-level explanations that helped interpret individual classifications and decision boundaries. This study presents an interpretable machine learning framework for classifying SLS performance into 3 levels using frontal-view videos acquired with a single smartphone. By leveraging coordination-informed engineered features and explainable artificial intelligence, the framework enables transparent interpretation of movement performance beyond isolated joint deviations. The proposed workflow uses smartphones for standardized video acquisition, while performance screening is achieved through machine learning. Given its lightweight feature design, this framework has potential for future implementation on modern smartphones and may support rehabilitation planning and injury-prevention strategies in sports and clinical settings.

This study evaluated the test-retest reliability of a depth sensor-based Fukuda Stepping Test and examined associations between sensor-derived kinematic parameters and established clinical outcomes in older adults. Eighty-six community-dwelling older adults (mean age 70.3 ± 4.7 years) performed an eyes-closed stepping task monitored by a Microsoft Kinect v2 sensor. Clinical assessments included the Berg Balance Scale, Timed Up and Go test, Five Times Sit-to-Stand, Montreal Cognitive Assessment, International Physical Activity Questionnaire, and WHOQOL-OLD. Test-retest reliability was assessed using intraclass correlation coefficients in a randomly selected subgroup. Reliability estimates varied across parameters, with temporal and displacement-based measures demonstrating more consistent agreement across sessions, whereas selected angular variables showed greater variability. Correlation analyses identified statistically significant associations between trunk kinematic changes and clinical measures, with effect sizes generally ranging from weak to moderate magnitude. Upper trunk rotation was associated with functional mobility measures, while traditional displacement-based metrics demonstrated limited clinical relationships. These findings support the feasibility of markerless depth-sensing technology for objective quantification of movement during the Fukuda Stepping Test and highlight the potential contribution of segmental kinematic parameters to multidimensional functional assessment in older adults.

Exploratory analysis of relationship between trunk and pelvic motion and shoulder motion during throwing in quarterbacks in American football.

ABSTRACT Timing and coordination of body kinematics are crucial for drag-flick performance in field hockey. This study aimed to clarify how coordination between the lower limbs and trunk contributes to effective energy transfer by (1) comparing lower body and trunk kinematic patterns between senior and junior national-level players, (2) examining whether peak kinematic values and keypoints occur in temporal synchrony, and (3) determining whether lower body peak kinematics predict trunk deceleration and ball speed. Kinematic data and ball speed were collected from 57 players (9 senior, 48 junior) from the Royal Dutch Hockey Federation using a 3D motion capture suit (240 Hz) and radar gun. Senior players achieved significantly higher ball speeds and shorter flick phases, associated with more synchronised timing of peak movements and keypoints. Specifically, left foot touchdown (LFT) aligned with trunk acceleration onset, while onset of right wrist flexion (ORWF) corresponded with trunk deceleration onset. The lead leg acted as a braking mechanism converting linear to angular momentum of the trunk, while the trail leg contributed to propulsion and trunk deceleration. Junior players showed delayed peak kinematics and reduced synchronisation. These findings highlight the role of lower limb and trunk mechanics in optimising drag-flick performance through targeted training.

Objectives: While Pilates exercise is commonly prescribed for chronic low back pain (CLBP), its effect on normalizing the lumbar flexion–relaxation ratio (FRR) remains unclear. This trial examined whether an 8-week Pilates exercise program (PEP) modifies FRR magnitude and side-to-side asymmetry in women with CLBP and explored associations with trunk kinematics, pain, and functional capacity. Methods: In a randomized controlled pre-test–post-test training design, ninety-six women with CLBP (55.8 ± 5.4 y) were allocated to a PEP group (n = 49) or a usual-care control group (n = 47). The PEP included two supervised 60-minute mat sessions per week over eight weeks. Surface electromyography of the right and left erector spinae and trunk flexion range of motion (TFRoM), measured via inertial sensors, were recorded during the standardized flexion–extension task pre- and post-intervention. Pain intensity (Visual Analog Scale) and functional capacity (Low Back Outcome Score, LBOS) were assessed concurrently. Results: Two-way repeated-measures ANOVA revealed no group × time interaction for global FRR (p = 0.454) or TFRoM (p = 0.745). FRR asymmetry increased by 11% in the PEP group (p = 0.033), with no change observed in the controls (p = 0.143). Compared to the controls, the PEP group exhibited a 30% reduction in pain (p = 0.003) and a 13.4% improvement in LBOS (p < 0.001) compared to the control group (all ps > 0.228). Conclusions: An 8-week Pilates intervention reduces pain and improves functional capacity in women with CLBP but does not restore lumbar extensor relaxation. The observed increase in FRR asymmetry may reflect compensatory or maladaptive redistribution.

This study examined the effects of velocity-based training (VBT) on free-weight barbell back squat technique compared with traditional resistance training (TR). Ten experienced participants completed anthropometric assessments, one-repetition maximum (1RM) testing, and VBT familiarisation, followed by randomised squat sessions using both methods. During VBT, participants received real-time velocity feedback and lifted with maximal concentric intent; during TR, participants used their habitual technique without feedback. Statistical significance was set at p ≤ 0.05. No significant differences were found in peak joint angles or trunk inclination ( p &gt; 0.05), although small to moderate effects were observed (Hedges’ g ). Mean resultant barbell velocity, the vector sum of horizontal and vertical velocity components, was higher during VBT (0.48 ± 0.05 m·s −1 ) than TR (0.43 ± 0.04 m·s −1 ; p &lt; 0.001), with a large effect; however, the vertical velocity component was greater during TR (94.7 ± 2.1%) than VBT (92.3 ± 3.1%; p = 0.016). The 95% confidence ellipse area of center of pressure (CoP) was larger during VBT (106.7 ± 26.9 cm 2 ) than TR (58.4 ± 16.1 cm 2 ; p &lt; 0.001), with a large effect. Coefficients of variation were comparable across all variables. Collectively, these results indicate that VBT did not significantly alter joint or trunk kinematics, and any observed differences were small and unlikely to be practically meaningful. However, whilst resultant velocity was greater during VBT, this was accompanied by larger CoP perturbations, suggesting greater instability. Practitioners should monitor technique and consider athlete experience, training objectives, and injury risk when implementing VBT.

The lumbopelvic-hip musculature plays a critical role in controlling trunk movement during pitching. Training interventions targeting these muscles have been shown to enhance muscle function and increase ball speed. However, evidence linking improvements in lumbopelvic-hip strength and power to changes in trunk kinematics and joint moments during pitching is lacking. To investigate the effects of an 8-week strength-training intervention targeting the lumbopelvic-hip muscles on muscle function and pitching biomechanics in adolescent pitchers. Controlled laboratory study. Research laboratory/training facility. A total of 54 high school pitchers were enrolled into an intervention (age = 15.6 ± 1.5 years, height = 1.76 ± 0.07 m, mass = 72.0 ± 14.3 kg) or a control (age = 16.0 ± 1.0 years, height = 1.76 ± 0.12 m, mass = 76.4 ± 11.4 kg) group. All participants performed an 8-week training targeting the lumbopelvic-hip muscles. Changes in lumbopelvic-hip muscle function, trunk kinematics during pitching, joint loading, and ball speed were measured. The intervention resulted in greater improvements in trunk-rotation strength and power (F 1,44 range, 6.12-11.44; P range, .002-.02) and increases in elbow-varus moment (t 45 = 2.06, P = .046) and ball speed (t 45 = 2.37, P = .014). Although no between-groups differences were observed in pitching kinematic changes, improvements in trunk-rotation strength and power within the intervention group were correlated with a smaller pelvis rotation (a more "closed" pelvis) at lead-foot contact, smaller trunk-separation angle at lead-foot contact, and later timing of peak upper torso-rotation velocity (|r| = 0.436-0.566). The intervention effectively improved trunk-rotation strength and power and ball speed but increased elbow stress. This finding underscores the importance of reducing pitch counts or extending rest periods as ball speed increases. The intervention produced only limited changes in pitching kinematics. Enhanced trunk-rotation strength and power in the intervention group were associated with positive changes in trunk kinematics but no other kinematic adjustments. Combining strength training with technical feedback and extending the intervention duration may lead to greater biomechanical adaptations.

Fatigue-related changes in running technique may depend on a runner’s preferred style. Understanding these changes can inform targeted training to enhance performance. In previous work, we identified two technique-based clusters of runners: the “neutral pelvis” and the “tilted pelvis” clusters. This follow-up study examined whether fatigue induces cluster-specific technique adaptations. Sixty runners (neutral pelvis, n = 32; tilted pelvis, n = 28) completed a treadmill run to exhaustion at 5% above their individual lactate threshold speed. Stride frequency, duty factor, trunk and lower limb kinematics were compared between clusters at the start, middle, and end of the run using a 2-way repeated measures analysis of variance (ANOVA). All runners reached exhaustion in ∼20 minutes, covering ∼5 km. Runners from the tilted pelvis cluster consistently showed greater trunk-to-pelvis extension, more pelvic anterior tilt and greater hip flexion, and a smaller duty factor compared with the neutral pelvis cluster throughout the run. Fatigue-related adaptations were similar across clusters: reduced stride frequency, increased duty factor, greater trunk flexion during stance, increased plantar flexion, and higher coordination variability (trunk-to-pelvis–hip, hip–knee, knee–ankle) during swing. Although fatigue affected both groups similarly, the underlying technique differences suggest these adaptations may have distinct mechanical or performance consequences. Understanding such cluster-specific responses can help coaches tailor training and fatigue management strategies to individual running styles.

Translating biomechanics to clinic: validating a spine-specific wearable for remote functional assessment.

Altered trunk kinematics have been reported in people with knee disorders and may be driven by neuromuscular deficits in the trunk muscles. Yet, no study has synthesized the evidence for trunk neuromuscular function in people with knee disorders compared with those injury-free. To compare trunk neuromuscular function between people with and without knee disorders. We searched 5 databases from inception to September 2024 for observational studies comparing trunk muscle strength, endurance, stability, and electromyography- or ultrasound-derived measures in people with and without knee disorders. Meta-analyses were conducted for each knee disorder when possible. Outcome-level certainty was assessed using Grading of Recommendations Assessment, Development, and Evaluation, and an evidence gap map was created. Twenty-three studies met the inclusion criteria across 4 knee disorders (ie,patellofemoral pain, ACL deficiency and reconstruction and knee osteoarthritis. People with patellofemoral pain presented with lower lateral trunk flexion strength and endurance (standardized mean differences, -0.48 to -0.54; 95% CI, -0.80 to -0.25) and lower anterior flexion and extension endurance (standardized mean differences, -1.19 to -1.47; 95% CI, -2.69 to -0.26), but no differences for erector spinae onset timing and external oblique amplitude activation during stepping and squatting tasks, compared with controls. We identified very limited evidence for studies investigating ACL deficiency/reconstruction and knee osteoarthritis populations. The lower lateral trunk strength and endurance, as well as lower trunk anterior and extension endurance in people with patellofemoral pain are consistent with previously reported alterations in trunk/lower limb frontal plane kinematics in this population. Further studies investigating trunk neuromuscular function are warranted to identify specific targets that may optimize rehabilitation of people with knee injuries or osteoarthritis.

Motor adaptations during stair ascent and descent in individuals with chronic primary low back pain.

Athletes recovering from concussions face lingering cognitive impairments affecting neuromuscular control, movement patterns and reaction times predisposing them to higher risk for lower extremity injuries including anterior cruciate ligament (ACL) tears.3 Current concussion detection methods are limited by observer interpretation and intentional underperforming on baseline testing (sandbagging).4,5 Kinematic evaluation has been proposed as a possible diagnostic adjunct; however, longitudinal studies investigating changes in objective jump landing kinematics from pre-concussion to post-concussion are limited. The purpose of the present study was to investigate changes in lower extremity and trunk kinematics during a drop vertical jump (DVJ) in collegiate varsity athletes from pre-concussion to post-concussion. Twenty collegiate varsity athletes (16 male, 4 female) performed three DVJs at the preseason assessments directly before and after sustaining a concussion. The DVJs were captured using a Kinect V2 device that has previously been validated for DVJ assessment.1,2 Specific DVJ parameters (Table 1), and the inter-jump variability (IJV) of each parameter (defined as the standard deviation across a single participant's 3 DVJ's), were compared between pre-concussion and post-concussion using a paired one-sided t-test. Statistical significance was set at P Peak sagittal angle of left and right knees decreased significantly post-concussion, indicating less knee flexion (105.66° vs 91.74°, P = .011; 105.01° vs 91.30°, P = .013). Similarly, maximum spine sway in the X axis decreased significantly from 4.37° to 3.41° (P = .048). IJV of peak sagittal angle increased significantly in both knees (5.81° vs 15.71°, P &lt; .01; 4.63° vs 15.29°, P &lt; .01). Similarly, IJV of spine sway variability in the Z axis and maximum ankle distance increased significantly post-concussion (0.42° vs 0.72°, P = .024; 0.017 m vs 0.029 m, P = .022). Multiple DVJ parameters change significantly in collegiate varsity athletes post-concussion. Notably, decreased peak sagittal knee angle has been associated with increased risk of ACL tear.1 Decreased peak sagittal angle and spine sway may indicate stiffer landing mechanics post-concussion while increased IJV in peak sagittal angles and maximum ankle distance suggest compromised consistency in landing patterns. The DVJ is a potentially valuable tool for objective concussion detection and guiding post-concussion rehabilitation to reduce the risk of ACL tears. For any figures or tables, please contact the authors directly.