Biomechanics

Background: Linear methods of analysis of variability are concerned with the magnitude of variability and often consider deviations from a central mean as errors. The utilization of nonlinear tools to examine variability allows for the exploration and measurement of the patterns of variability displayed by the system. This methodology explores the deterministic properties of biological signals, in this case, gait, or how previous iterations within the gait cycle influence subsequent and future iterations. The nonlinear analysis of gait variability of the joint angle time series has not been investigated in developing children. Methods: We collected 3 min of treadmill walking data for 28 children between the ages of 2 and 10 years old and analyzed their joint angle time series using nonlinear methods of analysis (sample entropy, largest Lyapunov exponent, and recurrence quantification analysis). Results: Our results indicate that the nonlinear variability of children’s gait increases as children age. Interestingly, this contrasts with the findings from our previous work that showed a decrease in linear variability as children age. The combination of a decrease in linear variability, or a refined and improved stability of gait, as well as an increase in nonlinear variability, or an increase in the sophistication and quality of movement patterns, suggest an overall maturation of the neuromuscular system. Conclusions: Our study indicate that there is a refining of gait with age and motor maturation. This refining speaks to the overall multifaceted organization of systems that defines the maturation of gait. Full article

Introduction: Management strategies for stage II tibialis posterior tendon dysfunction are centered on tendon transfers and osteotomies. One of the most commonly used tendon transfers is flexor digitorum longus (FDL) tendon to navicular, but its superiority over transfers to other locations or transfers of other tendons, along with the role of spring ligament and tibialis posterior tendons, have not been objectively evaluated. Aims: We aimed to quantify both the location and magnitude of secondary stresses that develop as a consequence of the initial pathology. Methods: In this study, we used a computational model to study flat foot development and evaluate the effects of various tendon transfers and failures of passive structural elements, as well as their effect on the biomechanics of the foot. Results: We found that both FDL and FHL transfers have biomechanical advantages and disadvantages. Neither of these transfers decrease the stress on the tibialis posterior tendon if the underlying pathologies such as spring ligament failure are not addressed. Conclusions: Of the tendon transfers evaluated, FDL transfer to the navicular had the most profound effect on reducing the stresses on the spring ligament. Full article

Background/Objectives: Computational models are increasingly used in orthopedic research, such as in the context of total knee arthroplasty (TKA). However, the models’ actual integration in clinical practice is far from routine. Major limitations include the amount of input data, effort, and time required for personalization and simulation. In this paper, we present and validate a patient-specific multi-body musculoskeletal TKA model based on sparse input data to address these limitations. Methods: The simulation model was individualized based on the patients’ bone and knee implant 3D geometries, predicted bony landmarks, and soft tissue attachments using annotated statistical shape models, a statistical squat motion pattern, and a statistically based load case. For the validation, we used publicly accessible in vivo knee contact forces during squatting from four patients of the Grand Challenge Competitions (GCCs). Results: The prediction accuracy was quantified using several error metrics, including the root mean square error (RSME). For GCC3 and GCC5, both the range and trend of the mean in vivo contact forces were well matched by the simulation (RMSE lateral: 8.2–26.1% of body weight (BW); RMSE medial: 15.9–42.7 %BW). In contrast, there were relevant deviations between the experiment and simulation in the trend of contact forces for patient GCC2, as well as in the range of medial contact forces for patient GCC6 (RMSE medial: 52.6 %BW). The model setup time was at the magnitude of 15 min per patient, and the simulation was completed in less than 4 min. Conclusions: When comparing our results with the literature, we found similar accuracy to state-of-the-art models in predicting knee contact forces. While remaining deviations between in vivo and simulation data still warrant investigation and evaluation for clinical significance, the model has already successfully addressed important limitations of these previous models, which represent significant barriers to clinical application. Full article

Background: Previous literature has demonstrated that footstep sounds can be related to the unique gait pattern of individuals. This paper investigates the potential of using footstep sounds as a diagnostic tool in gait analysis. Methods: Fifteen participants ran on a treadmill at 2.7 m/s (6.0 MPH) while simultaneously recording plantar pressure and acoustic signals. Participants repeated the same recordings after completing an exhaustive fatigue protocol, thereby creating a modified gait pattern. Results: The modified gait was evident in the center-of-force trajectory, contact pressures, and acoustic signatures. Analysis of the peak contact pressure and acoustic amplitude showed a modest, statistically significant correlation (r = 0.42, p = 0.02). A method to measure the gait stance time from features in the acoustic signature was tested. Conclusions: The results show that acoustic signals can be used to characterize gait changes, but additional work is needed to link acoustic signal features to gait events like toe lift. Full article

Background/Objectives: Asymmetries in force production, characterized by vertical ground reaction forces (VGRFs), during lower-limb bilateral movements such as deadlifting and squatting, are considered biomechanical risk factors for injury. Real-time biofeedback has been used to modify lower limb force production but typically implements monitors. The purpose of this study was to determine the effect of wearable visual biofeedback (WVBF) on asymmetries in VGRFs and knee joint angles and the rate of perceived exertion (RPE) during deadlift and body-weight squatting (BWS) exercises in recreational powerlifters. Methods: Thirteen healthy young adults between 18–35 years of age performed three tasks: deadlifting for mixed-grip style (MIX), double-overhand style (DO), and BWS. Each task included two conditions: with and without WVBF. A two-way (Condition X Task) mixed model analysis of variance was performed to compare the bilateral asymmetry index of VGRFs, knee angle, and RPE scores. Results: A main effect of the condition (with versus without WVBF) was detected for VGRF symmetry (F (1,12) = 62.785, p < 0.001). WVBF showed decreased VGRF asymmetry compared to no biofeedback. For knee angle, a significant condition X task interaction (F (2,24) = 3.505, p < 0.05) was observed. For RPE, a main effect of the condition was observed (F (1,12) = 8.995, p < 0.05). WVBF showed greater RPE compared to no biofeedback. Conclusions: These results indicated that WVBF could reduce VGRF asymmetry during deadlifting and squatting. In addition, targeting force production symmetry may not directly yield joint angle symmetry and may increase perceived exertion. These results could provide valuable insight into VGRF modulation during deadlifting and squatting exercises in athletic and potentially clinical settings when targeting VGRF symmetry. Full article

Background/Objectives: Single-leg hops are used to determine return to sport after anterior cruciate ligament reconstruction (ACLR). Adult studies support the use of single-leg vertical hop (SLVH) due to higher power generation from knee extensors compared to single-leg horizontal hop (SLHH). Research in children is lacking. This study examines the differences between SLVH and SLHH in pediatric athletes post-ACLR. Methods: We retrospectively examined patients with ACLR who performed SLHH and SLVH on each limb while kinematics and kinetics were collected with a Vicon motion capture system. The limb symmetry index (LSI) for hop distance/height was used to classify the patients as asymmetric (LSI < 90%) or symmetric (LSI ≥ 90%). Biomechanics were compared between limbs and as a function of group using linear mixed models. Results: Among the 19 patients (15 female; age 16.3 years; 9.2 months post-surgery), approximately half were classified as asymmetric (10/19 = 53% for SLHH; 9/19 = 47% for SLVH). During SLHH, the symmetric patients’ uninjured limb produced less power and a shorter hop. During SLVH, the symmetric patients produced more power and hopped higher bilaterally. Regardless of symmetry, the reconstructed knee was offloaded (p ≤ 0.03) and contributed less to power absorption (p ≤ 0.02). Conclusions: SLVH height symmetry may be a better indicator of knee recovery than SHLH distance in pediatric athletes. However, knee offloading is common even when symmetry is achieved. Full article

Background/Objectives: The movement and vibration of the body’s soft tissues during dynamic exercise are mechanisms that attenuate force from ground impacts. However, repeated exposure to such vibrations over time can contribute to the development of lower-body soreness and/or injuries. The previous literature has established the benefit of compression garments for the minimisation of soft tissue movement during running, though little is known about this mechanism during other forms of dynamic exercise. The current study aimed to investigate the effect of compression tights on lower-body soft tissue movement during jumping, sprinting and change-of-direction tasks typical of those found in team sports. Methods: In a randomised crossover design, twelve recreationally active males (age 26 ± 2 years) completed countermovement jumps, drop jumps from 45 cm, 10 m straight line sprints and change-of-direction tasks wearing either commercially available sports compression tights or regular exercise tights. Marker-based motion capture was used to quantify soft tissue displacement at the thigh and calf and lower-body kinematic variables during the exercise tasks. Results: No significant (p < 0.05) differences were observed between conditions for soft tissue displacement at the thigh and calf and performance variables for all tasks. There were significant (p = 0.003) differences in peak knee flexion and hip flexion during the 10 m sprint and change-of-direction task between conditions; however, effect sizes were unclear. Conclusions: Compression tights do not appear to influence soft tissue movement or performance during sports-specific forms of locomotion but may alter some kinematic aspects of sprinting and change-of-direction tasks compared with regular exercise tights. Full article

Background/Objectives: Three-dimensional motion analysis is often used to evaluate improvements or decrements in movement patterns in athletes. The purpose of this study was to evaluate the reliability of joint flexion/extension angles of the pitching elbow and bilateral knees and hips in softball pitchers. Methods: Fourteen softball pitchers (17.9 ± 2.3 years) were tested in one session consisting of four sets of five consecutive fastballs and a second session of two sets of five fastballs. The magnitude of systematic bias and within-subject variation was calculated between pitches. An iterative intraclass correlation coefficient (ICC) process was used to determine intra- and inter-session reliability, standard error of measurement and minimal detectable change. Results: Reductions in within-subject variation were observed for all variables when the number of pitches used in calculations was increased. Intra-session ICC values ranged from an average of 0.643 for pitching elbow to 0.989 for stride leg knee. Inter-session ICC values ranged from an average of 0.663 for pitching elbow to 0.996 for stride leg knee. Conclusions: Joint flexion/extension angles during the softball windmill pitch can be measured with good to high reliability using three-dimensional motion analysis. Biomechanical analysis can be confidently used to detect changes in the pitching motion over the course of a season or following an intervention. Full article

This study aimed to validate the effectiveness of the Articulation Motion Assessment System (AMAS), a joint kinematic evaluation system, for clinical applications. AMAS enables synchronised measurement using neurophysiological indicators, overcoming laboratory setting limitations. We compared AMAS-based ankle joint kinematic evaluations, particularly the sagittal and frontal plane angles, with two-dimensional (2D) motion analysis to determine the validity and reliability of AMAS. Both AMAS and 2D motion analysis reliably detected significant differences in angles within the sagittal and frontal planes. Correlation analysis revealed a significant moderate-to-strong correlation between the AMAS and the conventional method of 2D motion analysis, proving the measurement validity of the AMAS (ρ = 0.53–0.77 for sagittal plane angles; ρ = 0.46–0.72 for frontal plane angles). The average root mean squared error (RMSE) was significantly lower in AMAS (10.90 ± 2.93° for sagittal plane angles; 13.44 ± 1.09° for frontal plane angles) than in the inertial sensor-based three-dimensional (3D) motion analysis. Reliability analysis revealed high reliability of measurements (intraclass correlation coefficients (ICC) ≥ 0.76). However, the Bland–Altman analysis identified a slightly lower fixed bias, which was observed as a characteristic of each measurement system. The AMAS accurately detects ankle joint angles without being constrained by measurement environment limitations. Synchronised measurements using neurophysiological indicators potentially contribute to understanding ankle joint control mechanisms and developing rehabilitation strategies. Full article

Background/Objectives: To examine the combined effects of sleep quality, dual tasks, and load carriage on postural stability. Methods: Twenty-three university student participants (12 males, ages: 24.6 ± 6.1 year) completed the Pittsburgh Sleep Quality Index (PSQI), then performed quiet standing and a dual task while standing on force plates with and without load carriage. Correlations and repeated measures analysis of variances were used to assess relationships, main effects, and interaction effects of tasks on center of pressure (COP) to assess postural stability. Both a traditional PSQI global score and a sensitivity analysis of the PSQI cut-off were conducted. Results: With the traditional PSQI criteria, a main effect of sleep quality on 95% ellipse area was observed, with good sleepers outperforming bad sleepers (p = 0.016). Additionally, a significant interaction between sleep quality and task (p = 0.049) indicated that COP anterior–posterior velocity was lower during the dual task for good sleepers. No effects on sleep quality or interaction were found for other COP measures. The sensitivity analysis yielded no effect on sleep quality or interaction effects on any COP measure. There were no significant correlations between the PSQI global scores and COP variables. Conclusions: Overall, the results indicate that sleep quality alone had a limited effect and did not significantly interact with dual tasks or load carriage during quiet standing. Practitioners working with individuals who commonly experience poor sleep quality and perform load carriage and dual tasks should consider that common COP screens to assess postural stability may not detect differences due to self-reported sleep quality in healthy, young adults. Full article

Maintaining proper posture is essential for preventing musculoskeletal disorders and reducing injury risks. This study investigates the impact of insoles with ankle dorsiflexion (inverted drop sole) on sagittal posture, spinal curvatures, and core muscle activation. Methods: Fifty-five participants (29 men, 26 women; aged 20–70 years) were evaluated in two conditions: barefoot and with insoles incorporating an inverted drop sole. Kinematic data of trunk, hip, and knee angles, along with spinal curvatures (dorsal kyphosis, lumbar lordosis, and sacral slope), were collected using the Simi Aktysis 3D system and the Medi Mouse IDIAG 360^®. The electromyographic (EMG) activity of the rectus abdominis and rectus femoris muscles was analyzed using the Bioplux^® device. Statistical analyses were conducted using Wilcoxon tests (W) for non-parametric data and Student’s t-tests (T) for parametric data with significance set at p < 0.05. For parametric data, effect size (ES) was used to assess the magnitude of differences based on the Cohen scale. For nonparametric data, the rank biserial correlation (rB) was used, considered an ES equivalent to the correlation coefficient. Results: Significant differences were observed between the barefoot and insole conditions for trunk and knee angles (p = 0.009 and p < 0.001, respectively) with moderate and large magnitude of difference (rB = −0.41 and rB = −0.96, respectively). No significant change in hip angle (p = 0.162) was observed. Spinal curvatures, including dorsal kyphosis, lumbar lordosis, and sacral slope, significantly decreased (p < 0.001), with a large magnitude of difference for dorsal kyphosis, lumbar lordosis, and sacral scope (rB = 0.71, rB = −0.94 and ES = 0.54, respectively). EMG analysis revealed the increased activation of the rectus abdominis and rectus femoris muscles (p < 0.001), with a large magnitude of difference both the rectus abdominis and rectus femoris (rB = −0.82, and ES = −0.82, respectively). Conclusions: Insoles with ankle dorsiflexion significantly improve sagittal posture by reducing spinal curvatures and enhancing core muscle activation. These findings suggest that dorsiflexion technology in footwear may serve as a non-invasive strategy for improving posture, preventing musculoskeletal disorders, and managing low back pain. Full article

Objective: The purpose of this study was to investigate differences in countermovement jump (CMJ) force–time metrics between male and female youth basketball players. Methods: Twenty-two female and seventeen male basketball players (ages 12–16) performed CMJs on a portable force plate system (VALD Performance). The data collected were analyzed for differences in force–time characteristics, specifically during the concentric and eccentric phases of the CMJ. Results: The results showed no statistically significant differences in anthropometric characteristics between the sexes. However, male athletes demonstrated better performance in several force–time metrics during the concentric phase of the CMJ, including concentric impulse, peak velocity, and mean power, ultimately leading to higher vertical jump heights. Sex-specific differences in the eccentric phase were less pronounced, though males exhibited greater relative eccentric mean power. Conclusions: The findings suggest that male players tend to display greater force and power-producing capabilities during the propulsive (concentric) phase of the CMJ. These differences highlight the importance of tailoring training programs to address specific needs, particularly focusing on enhancing concentric force and power production in female basketball players. Full article

This study investigates the biomechanical differences between typically developed (TD) individuals and those with contralateral hemiplegia (CH) using musculoskeletal modeling in OpenSim. Ten TD participants and ten CH patients were analyzed for joint angles and external joint moments around the three anatomical axes: frontal, sagittal, and transverse. The analysis focused on hip, pelvis, lumbar, knee, ankle, and subtalar joint movements, leveraging MRI-derived bone length data and gait analysis. Significant differences (p < 0.05) were observed in hip flexion, pelvis tilt, lumbar extension, and ankle joint angles, highlighting the impact of hemiplegia on these specific joints. However, parameters like hip adduction and rotation, knee moment, and subtalar joint dynamics did not show significant differences, with p > 0.05. The comparison of joint angle and joint moment correlations between TD and CH participants highlights diverse coordination patterns in CH. Joint angles show significant shifts, such as HF and LR (−0.35 to −0.97) and PR and LR (0.22 to −0.78), reflecting disrupted interactions, while others like HR and LR (0.42 to 0.75) exhibit stronger coupling in CH individuals. Joint moments remain mostly stable, with HF and HA (0.54 to 0.53) and PR and LR (−0.51 to −0.50) showing negligible changes. However, some moments, like KA and HF (0.11 to −0.13) and PT and KA (0.75 to 0.67), reveal weakened or altered relationships. These findings underscore biomechanical adaptations and compensatory strategies in CH patients, affecting joint coordination. Overall, CH individuals exhibit stronger negative correlations, reflecting impaired coordination. These findings provide insight into the musculoskeletal alterations in hemiplegic patients, potentially guiding the development of targeted rehabilitation strategies. Full article

Background: Much of the research conducted on tactical-style boots has evaluated the biomechanical effect of boots in brand-new condition; however, the extent to which changes due to wear influence lower-extremity biomechanics remains uninvestigated. The purpose of this study was to compare lower-extremity biomechanics with worn-in boots and running shoes during both walking and running. Methods: Lower-extremity biomechanical parameters were evaluated during walking and running in 12 individuals with previous tactical experience. Participants were asked to complete one 5 min bout of walking and running at a self-selected pace in both self-selected athletic shoes and their own worn-in standard-issue tactical boots while lower-extremity spatiotemporal, joint kinematic, kinetic, and ground reaction force data were collected. Differences between conditions were evaluated using the Wilcoxon signed-rank test. Results: Spatiotemporal measures of gait, as well as ankle and hip kinematics, were different between shoes and boots during walking. During running, no spatiotemporal differences existed. However, significant differences were found for the ankle, knee, and hip kinematics between shoe and boot conditions during both walking and running. Conclusions: The worn-in boots in our sample performed similarly to running shoes during both walking and running tasks. Though there were several biomechanical differences between boots and shoes during both tasks, small mean differences suggest that these differences may not be large enough to create substantive or relevant changes in performance. This information could aid in developing future tactical boot design strategies to help aid in lower-extremity injury as well as allowing for optimal performance when wearing boots. Full article

Background/Objectives: Three-dimensional accelerometry data from the lower trunk during running is associated with intervertebral disc degeneration. The kinematic function known as the lumbo–pelvic–hip complex involves movements in the sagittal plane during running. If pelvic movement and acceleration in the anteroposterior direction are correlated, improving running mechanics may reduce the load on the intervertebral disc. This study investigated the relationship between the anteroposterior acceleration of the lower lumbar spine and pelvic tilt movements during running. Methods: Sixteen healthy male college students were enrolled and asked to run on a treadmill for 1 min at 16 km/h, and the acceleration data for their lower lumbar region and running motion in the sagittal plane were recorded. The pelvic tilt angle during running was calculated through two-dimensional motion analysis. Subsequently, a simple linear regression analysis was employed to clarify the relationship between the acceleration data of the lower lumbar region and the pelvic tilt angle during running. Results: The simple linear regression analysis indicated that the root mean squares of the anteroposterior acceleration of the lower lumbar spine were associated with the maximum pelvic tilt angle (r  =  0.32, p  =  0.003, adjusted R² = 0.09) and its range (r  =  0.42, p  =  0.0001, adjusted R² = 0.16). Conclusions: However, the adjusted R² value was low, indicating that although the pelvic tilt angle during running may be related to acceleration in the anteroposterior direction, the effect is small. Full article

Static and dynamic foot function can be evaluated using easy-to-implement, low-cost measurements like arch height index (AHI) and navicular drop (ND). Connections between AHI/ND and lower-extremity kinematics/kinetics have largely focused on gait. Some studies exist evaluating basketball players; however, these predominantly focus on men. To our knowledge, few studies evaluate female athletes, and none have investigated connections between AHI/ND and lower-extremity biomechanics in elite female basketball players. Thus, we conducted an IRB-approved observational investigation of 10 female, National Collegiate Athletic Association (NCAA) Division 1 basketball players, evaluating connections between AHI/ND and lower-extremity biomechanics during basketball activities. Participants completed one visit wherein bilateral AHI/ND measurements and kinematics/kinetics were captured via optical motion capture and force-instrumented treadmill during basketball activities (walking, running, vertical/horizontal jumping, side shuffles, 45° cuts). No connections existed between the AHI and any variable during any task. Contrastingly, ND was statistically significantly correlated with medial/lateral force maximum and range during left cutting. This implies that individuals with stiffer feet produced more side-to-side force than those with more foot mobility during cutting. This is the first report connecting ND to lower-extremity biomechanics in elite, female basketball players. This could inform novel interventions and technologies to improve frontal kinematics/kinetics. Full article

Background/Aims: Asymmetry of the internal (IR) and external (ER) shoulder rotators can increase the risk of injuries in judokas. Discrete analyses are usually performed in time series data, but they can have biases by removing trends, so other approaches have been proposed to avoid these biases such as statistical parametric mapping (SPM) and principal component analysis (PCA). This study analyzed the asymmetry in the shoulder rotators in female judokas, comparing dominant (D) vs. non-dominant (ND) upper limbs. Methods: For this, 11 elite athletes (age: 20.1 ± 2.9 yrs.; experience: 4.0 ± 0.5 yrs.; body mass: 66.0 ± 14.6 kg; height: 1.6 ± 0.1 m; BMI: 24.8 ± 4.3 kg/m²), were evaluated in an isokinetic dynamometer (Cybex^® Humac/Norm Dynamometer CSMI, 502140, Stoughton, MA, USA). All participants performed the concentric (CON/CON) isokinetic evaluations of internal and external rotation of the shoulder in 60°/s and 180°/s angular velocities. Results: There was no significative asymmetry between IR vs. ER at 60°/s; similar results were observed at 180°/s when analyzed by PCA or SPM methods (p > 0.05 for all comparison). There was no difference between peak torque at 60°/s or 180°/s (p > 0.05 for all comparison). Conclusions: no asymmetry was observed in IR and ER in elite female athletes, regardless of the analysis method. Full article

Transcatheter aortic valve replacement (TAVR) has become the preferred treatment for patients with aortic stenosis (AS) at high surgical risk. However, TAVR is challenging in patients with a pre-existing mitral valve prosthesis, such as a transcatheter mitral valve replacement (TMVR), due to the likelihood of device interference. This study explores the feasibility and safety of performing TAVR in a patient with a pre-existing TMVR procedure using 3D printing, augmented reality (AR) and computational simulations to optimize preprocedural planning. Computational modeling allowed predictions of the spatial relationship between the TAVR and TMVR devices. The simulation output was therefore used as input for augmented visualization of the device interference. The 3D printing of an anatomical replica was used to physically simulate the procedure, ensuring that no significant interference would occur during heart function. The results demonstrated a safe distance of 6.4 mm between the TAVR and TMVR devices, and no functional interference was observed during simulated cardiac cycles. The use of AR in the operating room enhanced the understanding of device positioning, offering a new dimension of precision of the complex cardiovascular intervention. This study concludes that integrating AR, 3D printing, and computational simulations into preprocedural planning for high-risk structural intervention can significantly improve procedural outcomes by enhancing accuracy, safety, and operator confidence. Full article

Background/Purpose: Fractal gait patterns have been shown to be modifiable, but the extent to which they are retained and transferred to new contexts is relatively unknown. This study aimed to close those gaps by enrolling participants (N = 23) in a seven-day fractal gait training program. Methods: Building on related work, the fractal gait training occurred on a treadmill over a 10-min period. Before and after the treadmill training, each participant walked for 10 min overground without the fractal stimulus used during training. The daily post-test was used to examine immediate retention and transfer of the fractal gait patterns from the treadmill to overground. The pre-tests in days 2–7 were used to examine the extent to which the fractal gait patterns from the preceding day were retained 24 h later. Inertial measurement units were used to measure stride time so a consistent measurement method could be employed in the treadmill and overground phases of the study. Results: Our results showed that multiple days of treadmill training led to elevated fractal patterns, indicating a positive training effect. However, the positive training effect observed on the treadmill did not transfer to overground walking. Conclusions: Collectively, the data show that fractal patterns in gait are modifiable across multiple days of training, but the transferability of these patterns to new contexts needs to be further explored. Full article