搜索结果：Journal of applied biomechanics

Given the strong ties to data sharing and the responsible use of resources, reproducibility of modeling and simulation practice is of paramount importance in science. Computational models in orthopedics provide insight into healthy and injured joint mechanics and can inform clinical decision-making. The KneeHub project investigated the influence of modelers' decisions and thus their "art" in simulation and modeling; five teams developed and calibrated knee models using the same experimental data. Model benchmarking evaluated the predictive ability of the models under loading scenarios that were not considered in the development and calibration process. The objective of this study was to evaluate the accuracy of predictions of knee-specific joint biomechanics for benchmark scenarios of simulating a resected anterior cruciate ligament (ACL) using models of one knee and a combined pivot shift loading using models of another knee. The models predicted the major trends in kinematics and kinetics; however, differences were observed in comparison to experimental data and between teams. Model-to-experiment root-mean-square (RMS) errors were up to 6.6±2.4 mm in anterior-posterior (AP) translation, 13.5±12.9 deg in internal-external (IE) rotation, and 5.3±3.4 deg in varus-valgus (VV) rotation; errors were largest in internal-external rotation, and standard deviations reflected differences between teams. While calibrated models were tuned to a similar set of conditions (albeit with different decisions), the optimized stiffness and reference length/strain of ligament structures may not fully reproduce the contributions of these structures to joint kinematics that were measured experimentally in the benchmark scenarios. As researchers often extend models beyond the conditions used to calibrate them, quantifying model accuracy and limitations with benchmarking represents a crucial step toward reproducibility and can help establish best practices for credible modeling in our community.

Alterations in the contributions of paraspinal soft tissues can influence the geometric profile of the spine. This study investigated the effects of passively modeled paraspinal soft tissues (i.e., paraspinal muscles and the thoracolumbar fascia (TLF)), on lumbar segmental mobility and geometric compensation, using a credible and previously validated finite element model (FEM) of the thoracolumbar spine. The model included the vertebrae, rib cage, intervertebral discs (IVDs), pelvis, ligaments, spinal and abdominal muscles, and the TLF. The model was subjected to 30 deg and 60 deg flexion rotation with a fixed pelvic support, and an applied follower load of 1175 N, increasing by 2.4% at each segmental level. Changes in lumbar L2-S1 intervertebral rotation (IVR), lumbar and thoracic range of motion (RoM), and curvature were analyzed for cases involving removal and increased stiffening of the paraspinal muscles and the TLF. Increasing TLF stiffness reduced lumbar RoM (5.1 deg) at 60 deg flexion relative to the validated model, with compensatory increases of 3.6 deg in thoracic RoM. Increases in lumbar lordosis (3.6 deg) were proportional to increases in thoracic kyphosis (3.3 deg). Similar effects of reduced magnitude were observed in 30 deg flexion. Inverse effects were observed following TLF removal. However, no changes were observed with changes in paraspinal muscle contribution. These findings suggest that changes in TLF stiffness influence lumbar segmental mobility and drive compensatory adjustments in the spinal geometric profile.

What changes over time are measured on pain, activities, quality of life and thickness of the plantar fascia when (ortho)manual therapy of the foot joints is applied to patients with plantar fasciitis (PF). In this observational single-arm cohort study, 50 patients with PF (31 females and 19 males, aged between 27 and 73 years) were recruited over a 22-month period. Of the 50 patients included, 32 completed the 26-week follow up. Eight patients were excluded after T2 because they needed additional spine treatments. 10 dropped out during the remainder of the study. The intervention protocol involved five visits in the first 6-8 weeks for assessments and treatments and one visit after 26 weeks for evaluation. The (ortho)manual therapy consisted of manual manipulations of the foot joints often preceded by the techniques with hammer and thrift. The (ortho)manual therapy was combined with a corrective insole. Primary outcomes were pain intensity numeric pain rating scale (NPRS), and plantar fascia thickness, assessed via ultrasound. Secondary outcomes included the Patient Specific Functional Scale (PSFS), Foot Function Index (FFI), Short Form 12 (SF-12), and EuroQoL 5D (EQ5D). Significant reductions in NPRS scores at rest (2.98 to 1.39, p = 0.004) during activity (6.64 to 2.66, p ≤ .001), and during the first step in the morning (6.79 to 2.69, p ≤ .001) were observed. Plantar fascia thickness in the unilateral group also decreased significantly over time (affected side 5.34 mm to 3.70 mm, p ≤ 0.001). PSFS scores improved significantly, indicating reduced difficulty in performing activities. The FFI showed significant improvements in pain, disability, and activity subscales. Quality of life showed significant improvement in the physical component scores. Dropout during follow-up, variability in therapist experience, missing data in patient-reported outcomes, and the lack of a standardized ultrasound examiner may have influenced reliability. Additionally, the intervention combined two treatments-(ortho)manual therapy and corrective insoles-making it difficult to isolate their individual effects. Despite these limitations, significant improvements in pain and plantar fascia thickness were observed as early as 1-2 weeks after the first treatment session, with clinically relevant changes sustained over 26 weeks. Due to the limitations, the results of this study should be interpreted with caution, but support (ortho)manual therapy as a promising treatment for PF. Further controlled studies are needed to confirm these findings. The results show pain reduction within 6-8 weeks with further improvement at follow up. The treatment has lasting effects, potentially preventing PF recurrence and other lower extremity issues. Ultrasound findings may alter the understanding of PF and tendon problems.

Older individuals (≥65 y old) with and without lower limb loss experience a high prevalence of falls. Minimizing fall risk depends on an individual's ability to maintain dynamic balance. A metric often used to characterize an individual's ability to regulate dynamic balance is angular momenta during steady-state walking. However, a gap exists in the validity of angular momenta as a measure of dynamic balance in these cohorts. The goal of this study was to evaluate the validity of angular momenta in older individuals with and without transtibial amputation during walking through assessments of construct and criterion validity. Construct and criterion validity were evaluated through correlations of momenta with clinical balance measures and prospective fall numbers over 12 months, respectively. For context, falls were categorized by pattern and scenario. Angular momenta of walking demonstrated evidence of construct and criterion validity in both groups through moderate-to-strong correlations with clinical balance measures and prospective falls. These relationships also varied between groups. The most common pattern and scenario of falls in both groups were trips and level-ground walking, respectively. This study contributes evidence that angular momentum during level-ground walking is a valid measure of dynamic balance in older persons with and without transtibial amputation.

The objective of this work was to develop a finite element model of the thoracolumbar spine to assess the effects of passive structures, rib cage, intervertebral disc (IVD), iliolumbar ligament (ILL), and facet cartilage-capsular ligament (FC-FCL), on segmental range of motion (RoM) and thoracolumbar curvature. The model included the vertebrae, rib cage, IVDs, and pelvis, with ligaments and the FC modeled as tension-only and compression-only spring elements, respectively. The model was subjected to 60° of flexion and 55° of extension. A simulated follower load of 1175 N was applied, increasing by 2.4% at each segmental level. Changes in lumbar intervertebral rotations (IVR), lumbar and thoracic RoM and lumbar lordotic (LLA) and thoracic kyphotic angles (TKA) were analyzed for cases involving removal of the ILL and rib cage and removing the L4-L5 and L5-S1 FC-FCL and increasing the elastic moduli of the L4-L5 and L5-S1 IVD, independently. Removing the L5-S1 FC-FCL increased segmental motion (21.7°) in extension with compensatory reductions at L4-L5 (5.5°). Increases in lumbar lordosis (7°) were proportional to increases in thoracic kyphosis (7°). Similar yet smaller effects were observed when removing the rib cage and ILL, with the inverse observed following increasing IVD stiffness. Removal of the rib cage and ligaments or changes in the stiffness of the IVD influence segmental mobility and drives compensatory adjustments in adjacent segments to maintain congruency. Understanding how these tissues affect spinal alignment may inform surgical strategies aimed at preserving or restoring tissue function to maintain spinal stability.

Dynamometric shoulder strength testing is crucial in clinical, research, and sports settings. Reliable and valid protocols are required to track changes in muscle strength over time. Therefore, this study aims to compare the reliability and validity of portable dynamometer protocols, provide an overview of available protocols and their methodological quality, and develop a checklist to guide the planning and reporting of reliability studies. A systematic search of PubMed, Cochrane Library, Web of Science, and CINAHL databases (up to February 2024) identified 53 studies meeting the inclusion criteria. Methodological quality was assessed using the COSMIN Risk of Bias tool and synthesis of evidence was based on criteria for good measurement properties. In case of consistent results meta-analysis was performed. Relative reliability showed sufficient results, while absolute reliability and validity results were less consistent. Although included studies showed limitations in execution and reporting, portable dynamometers can be used to distinguish between individuals. However, interpreting changes in individual shoulder strength requires caution. Examiners should be aware of the measurement properties within their applied protocols. In protocols, where reliability is unknown, it should be investigated to allow appropriate interpretation of results. To address the persistent methodological limitations observed in literature, we propose the "Muscle Strength Reliability Checklist", a structured instrument intended to enhance methodological transparency and consistency. Based on the findings of this systematic review, future protocols should use devices with external fixation, place participants in standardized, stable body positions, and adhere to a standardized timeline, instructions, and encouragement procedures.

Heavy schoolbags are common among school-aged adolescents, yet biomechanical consequences across developmental stages and between sexes remain poorly defined, especially in low- and middle-income countries. This study investigated the effect of schoolbag carriage on gait in South African adolescents. A total of 186 injury-free adolescents (ages 12-18) completed barefoot walking trials over a pressure platform under unloaded and loaded conditions. Spatiotemporal and kinetic gait parameters were recorded and normalized to body height and weight. Analyses included (1) comparison of schoolbag mass by sex and grade (ie, school year); (2) evaluation of gait by loading condition, grade, and sex; and (3) prediction of loaded-condition gait parameters by relative schoolbag mass. Grades 8 to 11 carried higher absolute loads and grade 8 carried highest relative loads, with 58% exceeding 15% body mass, but no sex differences were found. Load carriage increased stance and double support time; reduced swing phase; and elevated vertical forces, pressures, and loading rates. Females exhibited higher forefoot and midfoot pressures and narrower step width. Relative schoolbag mass predicted greater forefoot/heel loads, lower midfoot loads, and narrower step width. Schoolbag carriage imposes substantial biomechanical demands, particularly in early adolescence and among females, emphasizing need for age- and sex-specific guidelines to mitigate long-term musculoskeletal risk.

Trochanteric soft tissues have significant effects on fall-related hip fracture risk; however, little is known about their composition and spatial distribution. Accordingly, this study determined (1) the influence of sex and anatomical location on muscle thickness, adipose thickness, and total soft tissue thickness surrounding the proximal femur; and (2) the effects of sex- and location-specific soft tissue thickness on predicted fall-related hip impact forces. Ultrasound was used to measure muscle thickness, adipose thickness, and total soft tissue thickness at 12 locations surrounding the proximal femur in 25 young adult participants. Fall-related hip impact forces were predicted with a mass-spring model, accounting for force attenuation by soft tissues, at 2 common impact sites. The data demonstrated that tissue thickness and impact forces were significantly influenced by sex and anatomical location. Males had more muscle, less adipose, less total soft tissues, less force attenuation, and higher impact forces than females. Total soft tissue thickness and muscle thickness were lowest over the lateral femur, while adipose thickness was lowest over the anterolateral femur. Force attenuation was higher while impact forces were lower at the posterolateral impact site. The data support that the accuracy of hip impact models could be improved by incorporating sex-, location-, and composition-specific soft tissue thickness measures.

Precise quantification of the lumbar flexion-relaxation phenomenon can provide a better understanding of the load transfer between active and passive tissues and its implications for spinal stability. This study aimed to compare the precision of instantaneous angles using 1 versus 2 inertial motion sensors to determine the deactivation (electromyography [EMG]-off) and reactivation (EMG-on) of left and right erector spinae muscles during trunk flexion and extension. Electromyography and kinematic data were collected from 12 participants who performed 20 slow, controlled trunk flexion-extension motions. The angle derived from 1 motion sensor was the pitch angle of the T12 sensor, and the angle derived from 2 sensors was the difference between the pitch angles of the T12 and S1 sensors. The EMG-off (or EMG-on) angle was defined as the angle at which unilateral erector spinae muscle activity dropped below (or exceeded) 3 times the muscle activity recorded at full trunk flexion during trunk flexion and extension. Results revealed that absolute and relative variability in 20 EMG-off and EMG-on angles were greater when measured with 1 inertial motion sensor than with 2 sensors (P ≤ .003), suggesting that using 2 sensors can improve the precision of flexion-relaxation phenomenon determination compared with using 1 sensor.

To investigate the biomechanical effects of the IntraSPINE (Cousin Biotech, Wervicq-Sud, France) interlaminar distraction device on both the operated and adjacent spinal segments during unilateral biportal endoscopic (UBE) discectomy for huge lumbar disc herniation (HLDH) in young patients. Based on preoperative and postoperative CT data of a patient with a single-segment, large lumbar disc herniation at the L4-5 segment, a three-dimensional finite element model of the L1-S1 segments was established. Three models were constructed: a preoperative model (M1), a postoperative model without IntraSPINE implantation after unilateral discectomy (M2), and a postoperative model with IntraSPINE implantation (M3). After model validation, a 500 N axial load and a 10 N·m moment were applied to simulate six motion conditions. A comparative analysis was performed on the range of motion (ROM), intradiscal pressure, maximum von Mises stress in the annulus, and maximum shear stress in the annulus at each segment from L3 to S1, as well as the facet joint stress at the L4-5 segment. Compared with the M1 model, the M2 model exhibited a significant increase in mobility at the L4-5 segment, with the most pronounced rise ROM observed during right bending-an increase of 36.8%. Increases of 31.5% and 14.9% were also noted during left bending and left axial rotation, respectively. The intradiscal pressure at this segment increased by 59.7% during flexion, while the maximum von Mises stress in the annulus rose by 82.4% during right axial rotation, and the shear stress increased by 95.2% during extension. Additionally, the stress on the right facet joint (surgical side) peaked at 6.8799 MPa during left bending, which was significantly higher than in the M1 model, indicating reduced segmental stability and marked stress concentration. This was accompanied by compensatory increases in both mobility and stress in adjacent segments. In contrast, the M3 model demonstrated a downward trend in all biomechanical indicators at the L4-5 segment. ROM decreased by 33.2% during flexion, intradiscal pressure decreased by 58.4% during extension, maximum von Mises stress in the annulus decreased by 32.3% during left axial rotation, and shear stress dropped by 88.9% during left axial rotation. The maximum stress on the right facet joint during left bending was reduced to 2.8862 MPa, which was significantly lower than in both M2 and M1 models. No abnormal increase in motion or stress was observed in the adjacent segments. The IntraSPINE dynamic stabilization system combined with UBE discectomy surgery offers significant biomechanical advantages in the treatment of HLDH. Its unique dynamic stabilization properties can effectively maintain intervertebral height, preserve partial mobility of the operated and adjacent segments, and alleviate postoperative stress concentration on the intervertebral disc and facet joints. Therefore, it may serve as a promising treatment option for HLDH patients.

Massive rotator cuff tears often lead to superior migration of the humeral head and abnormal shoulder kinematics and function. In an attempt to restore normal joint kinematics, a modular subacromial implant was developed and evaluated in this biomechanical cadaveric study. Eight cadaveric specimens were assessed using a muscle-loading shoulder simulator that applied loads at 0, 30, and 60 degrees of glenohumeral abduction. Testing states included the intact rotator cuff (native), the simulation of a massive rotator cuff tear, and multiple implant states. Two implant thicknesses (5 and 8 mm) and two implant articular surface constraints (low & high) were tested. Humeral head translation in both anterior-posterior and superior-inferior directions was measured using an optical tracking system. The presence of a massive rotator cuff tear resulted in significant superior humeral head migration relative to the native state (P = 0.016). Both low and high constrained 5 mm thick implants restored superior-inferior humeral head position to within 1 ± 2 mm (P = 0.223) and 1 ± 2 mm (P = 0.928) respectively, of the intact position. Significant inferior translation relative to the native state was observed with both 8 mm implant designs (8 mm low constrained: -4 ± 2 mm, P = 0.060; 8 mm high constrained: -4 ± 2 mm, P = 0.060). No significant differences were observed for anterior-posterior translation. These results demonstrate that an implant affixed to the acromion helps to restore the native position of the humeral head in the presence of a massive rotator cuff tear with superior migration. The 5 mm high constrained implant design was most effective at restoring native humeral head position. Basic Science; Biomechanics.

Meniscal injuries are common and can alter knee biomechanics, increasing the risk of osteoarthritis. This study investigated the effects of unilateral meniscal injuries of different Stoller grades on gait kinematics and kinetics. A total of 158 participants were stratified by MRI into three groups: control group(Grade 0, n = 51), Grade I-II (n = 54), and Grade III (n = 53). Three-dimensional motion capture synchronized with force platforms was used to assess peak sagittal-plane joint angles, joint moments, and ground reaction forces. Multivariate analysis of covariance was applied to adjust for body mass index, Lysholm score, and walking speed. Compared with healthy controls, injured participants demonstrated reduced knee flexion, hip extension, and lower extremity joint moments, along with increased ankle dorsiflexion, knee extension, and hip flexion angles; anterior, posterior, and lateral ground reaction forces were also significantly decreased. Although no significant differences in joint moments or ground reaction forces were observed between Grade I-II and Grade III groups, deviations in joint angles increased gradually with the severity of injury. The most pronounced changes were seen in the knee extension angle, which rose by 309.0% in Grade III compared with the control group, and the hip extension angle, which decreased by 53.3% in Grade III compared with the control group. A 16.5% reduction in the knee flexion angle was also observed. These findings indicate that even mild meniscal injuries produce substantial gait kinetic deficits, while kinematic alterations become more pronounced with higher-grade injuries. The study highlights the value of integrating Stoller grading with objective gait analysis to identify functional impairments not captured by patient-reported outcomes. This comprehensive approach provides a biomechanical basis for early assessment and individualized rehabilitation strategies, supporting knee function preservation and potentially slowing long-term degenerative changes.

This study investigated the relationship between neuromuscular (motor unit action potential amplitude [MUAP], firing rate, recruitment threshold), biomechanical (force loss), physiological (skin temperature), and perceptual (delayed onset of muscle soreness) markers following an intense knee exercise protocol. Eleven participants performed 2 maximal isometric and 5 concentric-eccentric knee contractions. Assessments were made immediately postexercise (0 h), at 24 hours and 48 hours after intense knee exercise protocol. Electromyography signal decomposition and skin temperature were measured during the protocol, while delayed onset of muscle soreness was evaluated at 24 and 48 hours. A reduction in force production (isometric, dynamic, and Work) was observed at all postexercise time points. Delayed onset of muscle soreness increased at 24- and 48-hour postexercise compared to Pre-exercise. At 0 hours, a positive, moderate correlation was observed between dynamic force loss and MUAP of the vastus lateralis (VL). Two moderate positive correlations were observed between firing rate of rectus femoris and minimum temperature, and between the recruitment threshold of VL and mean temperature. At 24-hour postexercise, a positive moderate correlation was observed between dynamic peak torque and MUAP of VL. These findings suggest that full recovery of force is not achieved at 48-hour postexercise, with MUAP of VL playing a key role in muscle recovery.

To evaluate the test-retest reliability of a novel laboratory-based protocol for inducing and measuring head acceleration in multiple directions under anticipated and unanticipated conditions. Laboratory-based test-retest reliability study. Thirty physically active adults (50% female) completed standardized head perturbations using a custom-built apparatus. Perturbations were applied in flexion, extension, lateral flexion, and rotation under both anticipated (cervical muscle pre-activation) and unanticipated (no cervical pre-activation) conditions across two sessions conducted within one week. Peak linear head acceleration (g) and rotational head acceleration (rad/s2) were recorded using a motion capture system. Reliability was assessed using intraclass correlation coefficients (ICC3,1), standard error of measurement (SEM%), and Bland-Altman plots. For anticipated perturbations, both linear head acceleration and rotational head acceleration demonstrated good to excellent test-retest reliability (intraclass correlation coefficient 0.75-0.90), with SEM% ranging from 3.52% to 8.54%. For unanticipated perturbations, reliability was within the moderate to good range (intraclass correlation coefficient 0.72-0.85), with SEM% ranging from 3.99% to 11.72%. Bland-Altman plots indicated no systematic differences between sessions and no evidence of heteroscedasticity. Linear and rotational head acceleration showed moderate to excellent reliability across multiple directions and anticipatory conditions, supporting the utility of this laboratory protocol for head impact biomechanics research. Unanticipated perturbations and rotational accelerations were more variable, likely reflecting the complexity of reflexive and asymmetric neuromuscular responses. Together, these findings provide a methodological foundation for future studies on head impact biomechanics and cervical neuromuscular function.

The purpose of this study was to determine the influence of lower extremity joint kinetics and muscle strength on running economy (RE) over level ground, 5% and 10% grades. Twenty-seven recreational runners (14 females, age: 33.7 [12.8] y, mass: 70.2 [12.5] kg, height: 175.9 [9.1] cm) completed laboratory-based RE, biomechanics, and isokinetic dynamometry testing. Linear regression analyses were used to determine the effect of lower extremity joint work, stiffness, and strength on RE for each grade. Greater ankle plantar flexor work was predictive of better economy when running on the 10% grade (β = -3054.56; P = .013), but not the level ground or 5% grade (P > .05). No other joint work, stiffness, or strength factors were related to RE. A secondary analysis explored the relationship of training factors to RE, demonstrating better 10% grade RE (P = .015) and greater ankle work (P = .048) in trail runners compared with road runners. The results of this study suggest that targeting the energy generation capacity of the plantar flexors may be worthwhile for improving uphill RE. Trail running may lead to specific physiological and biomechanical adaptations that are beneficial to performance.

First ray hypermobility is implicated in many forefoot pathologies, yet its quantitative assessment remains challenging. Instrumented methods have traditionally focused on isolated dorsal displacement of the first metatarsal, which may not reflect physiological load sharing within the forefoot. This cadaveric biomechanical study evaluated the reliability and construct validity of two arthrometer-based measures: the first ray absolute (FRAM) and relative (FRRM) mobility, respectively assessed under isolated loading of the first metatarsal and symmetrical loading of the first metatarsal and lesser metatarsals. Ten fresh-frozen cadaveric lower limb segments were tested using an automated forefoot arthrometer. Within-session reliability was quantified using intraclass correlation coefficients, standard error of measurement, and minimal detectable change. Construct validity was assessed by correlating FRAM and FRRM with a biomechanical reference construct defined as the sum of superior-inferior translations at the first tarsometatarsal and medial naviculo-cuneiform joints measured using optical motion capture. Linear mixed-effects models were used to characterise joint-level kinematic behaviour under each loading mode. FRRM demonstrated excellent within-session reliability (ICC&#xa0;=&#xa0;1.00) and a high positive correlation with the reference construct (R&#xa0;=&#xa0;0.70, p&#xa0;<&#xa0;0.001). FRAM also showed excellent reliability (ICC&#xa0;=&#xa0;0.97) but higher absolute measurement error and a moderate positive correlation with the reference construct (R&#xa0;=&#xa0;0.63, p&#xa0;<&#xa0;0.001). Symmetric loading engaged proximal first ray joints more effectively than isolated loading, which predominantly mobilised the first tarsometatarsal joint. These findings indicate that arthrometer-based assessment of the first ray mobility is sensitive to the loading mode and that symmetric loading provides a more biomechanically representative evaluation of the first ray mobility than traditional isolated approaches.

Evidence indicates females may be more susceptible to sports-related concussion with worse and prolonged symptom severity according to menstrual cycle phase. We investigated whether menstrual cycle phases influence non-concussive heading kinematics in elite female footballers, and whether these impacts affect an athlete's cognition. Five eumenorrheic elite female footballers (Mage&#x2009;=&#x2009;23&#x2009;&#xb1;&#x2009;4&#xa0;years) participated in a 16-week proof-of-concept study wherein menstrual cycle phases were tracked, and cognition was monitored. Participants performed a weekly controlled heading drill by heading a ball thrown from 5&#xa0;m away. Head accelerations were measured using custom-moulded PROTECHT instrumented mouthguards. 256 headers revealed no significant differences in head acceleration across the various phases of the menstrual cycle. However, change in cognitive performance was related to heading completion and menstrual phase. Hormonal fluctuations during the menstrual cycle may influence cognition independent of head impact biomechanics among elite female athletes, under controlled conditions. We note that our study also demonstrated the safety and efficacy of the mouthguard equipment employed here, as well as the ease with which the protocol was received by the athletes. These outcomes should be considered when implementing future research with larger cohorts and the inclusion of match-related heading.

Given the widespread adoption of additive manufacturing in dentistry, assessing the dimensional accuracy of printed objects is critical. This study aimed to evaluate the three-dimensional (3D) deviations produced by four printers utilizing SLA, mSLA, and PolyJet technologies, employing three distinct measurement methodologies. Sixty cube specimens with a 15 mm edge length were fabricated (n = 15 per group) using four different 3D printers: Form 3B+, Prusa SL1, Objet 30 Orthodesk and Connex 260. The distance between opposing cube faces was assessed at twelve predefined locations using three measurement methodologies: manual measurement with a digital micrometer, a micro-computed tomography (micro-CT) system, and an optical scanner. Micro-CT and micrometer measurements yielded reliable dimensional data, whereas the optical scanner consistently yielded underestimated values. Micro-CT yielded superior definition of the specimen surface topography Mean micro-CT measurements differed significantly from the nominal reference value (15,000 &#xb5;m) in 15 of 16 instances for X coordinates (p < 0.01), 15 instances for Y coordinates (p < 0.015), and in 12 instances for Z coordinates (p < 0.03). Deviations were significantly higher in the X and Y axes compared to the Z axis. Micro-CT was identified as the most precise measurement method among those evaluated. Of the printers tested, the Connex260 demonstrated superior overall performance, exhibiting the lowest dimensional deviation. Across all devices, the highest accuracy was consistently observed along the Z-axis. Even minor dimensional inaccuracies in additively manufactured components can compromise the fit, marginal integrity, and function of restorations, directly impacting patient comfort and treatment longevity. Consequently, the careful selection of appropriate printing technologies, validated by precise measurement protocols, is critical for ensuring predictable clinical outcomes.

Squatting, a closed-kinetic chain exercise, requires the complex coordination of multiple muscles. However, the differences in muscle coordination patterns between individuals with varying levels of exercise proficiency remain unclear. This study aimed to compare muscle coordination patterns during the squat exercise between trained and untrained individuals. Sixteen participants, classified into trained and untrained groups, performed 20 repetitive squats while both motion capture and electromyography data were recorded. Muscle synergy analysis was employed to identify muscle coordination patterns, and cluster analysis was used to determine preferred muscle synergies within each group. The findings indicate that trained individuals exhibit muscle synergies characterized by the coactivation of trunk and leg muscles near the bottom position of the squat. By contrast, untrained individuals primarily show coactivation of leg muscles only. Motion analysis further revealed that trained participants maintained a more upright posture during this phase compared with untrained participants. The distinct muscle synergies between trained and untrained individuals suggest the importance of coordinated trunk and leg muscle activation in maintaining postural control near the bottom position, where the movement transitions from descent to ascent. These insights can inform training strategies to promote effective trunk-leg coordination and postural control in untrained individuals.