Biomechanics, Volume 5, Issue 1 (March 2025) – 18 articles

Background/Objectives: This study aimed to examine how uncertainties in inertial properties and minimal sets of inertial parameters (MSIP) affect inverse-dynamics simulations of high-acceleration sport movements and to demonstrate that applying MSIP identified through the free vibration measurement method improves simulation accuracy. Methods: Monte Carlo simulations were performed for running, side-cutting, vertical jumping, arm swings, and leg swings by introducing uncertainties in inertial properties and MSIP. Results: These uncertainties significantly affect the joint torques and ground reaction forces and moments (GRFs&Ms), especially during large angular acceleration. The mass and longitudinal position of the center of gravity had strong effects. Subsequently, MSIP identified by our methods with free vibration measurement were applied to the same tasks, improving the accuracy of the predicted ground reaction forces compared with the standard regression-based estimates. The root mean square error decreased by up to 148 N. Conclusions: These results highlight that uncertainties in inertial properties and MSIP affected the calculated joint torques and GRFs&Ms, and combining experimentally identified MSIP with dynamics simulations enhances precision. These findings demonstrate that utilizing the MSIP from free vibration measurement in inverse dynamics simulations improves the accuracy of dynamic models in sports biomechanics, thereby providing a robust framework for precise biomechanical analyses. Full article

Adductor strains are prevalent injuries in professional soccer. The purpose of this study is to identify further evidence of characteristics associated with adductor injury. MLS and other worldwide leagues have differing styles of play warranting further investigation of injury mechanisms. A descriptive cohort study was conducted with a single professional team in the MLS. Injury data was collected between the 2016 to 2022 seasons to characterize adductor injury. Player position type, age, previous injury, and mechanism(s) of injury (MOI) were assessed to understand the injured population. Generalized estimating equations (GEEs) were utilized to assess the odds of future injury among the injured and non-injured populations. Adductor strains (n = 30) made up 15.5% of all soft-tissue, lower extremity injuries (n = 194) in a single MLS cohort. These injuries were the second most common defined soft-tissue, non-contact injury after hamstring strains (26.4%) and before quadricep strains (11.9%). Among the position types, 28% of defenders, 25% of goalkeepers, 21.4% of forwards, and 20.5% of midfielders experienced at least one adductor strain. The MOI most responsible for these injuries were overuse (30%), change of direction (26.7%), running (13.3%), and kicking (10%). Athletes with previous adductor injury had 167.2 times the odds of adductor injury in a future half-season compared to non-injured athletes. The findings from this study provide further descriptive evidence of player position types and mechanisms related to adductor strain. Insights into the nature of injury within an MLS team and support of previous evidence shows the prevalence of adductor injuries in elite soccer players. Full article

Background/Objectives: Despite widespread use in clinical and athletic settings, validity of handgrip strength (HGS) as a surrogate for maximal strength remains debated, particularly regarding how testing posture influences its predictive value. Moreover, while HGS is frequently considered a marker of ‘total strength’, this term is often vaguely defined, lacking a clear, performance-based framework. Therefore, this study investigates HGS as a potential surrogate measure for one-repetition maximum (1RM) performances in key compound lifts via back squat (BS), bench press (BP), deadlift (DL), and total (TOT), while accounting for variations in testing posture. Methods: Two distinct testing conditions were used to account for postural influences: Experiment 1 implemented high-output standing HGS (HGS_STAND) in 22 recreationally trained males [Wilks Score: 318.51 ± 44.61 au] vs. Experiment 2, which included low-output seated HGS (HGS_SIT) in 22 competitive powerlifters [409.86 ± 46.76 au], with all testing immediately followed by 1RM assessment. Results: Correlational analyses identified the strongest association between HGS_STAND and 1RM DL (r = 0.693, BF₁₀ = 106.42), whereas HGS_SIT exhibited the strongest relationship with 1RM BP (r = 0.732, BF₁₀ = 291.32). Postural effects had a significant impact on HGS outcomes (p < 0.001, η² = 0.413), with HGS_STAND producing higher outputs than HGS_SIT despite lower absolute strength 1RM capabilities. Conclusions: These findings emphasize the role of biomechanical specificity and neuromuscular engagement in grip strength assessments, indicating that HGS can function as a practical surrogate for maximal strength, though its predictive value depends on posture. Strength practitioners, sport scientists, and clinicians should consider these confounding factors when implementing HGS-based monitoring strategies. Full article

Background/Objectives: Mechanical compression of the median nerve is believed to be responsible for idiopathic carpal tunnel syndrome (CTS) due to fibrosis of the subsynovial connective tissue (SSCT). Vascular consequences have also been observed in structures of the carpal tunnel, raising speculation regarding the role of factors such as ischemia and edema in CTS pathology. Methods: We performed a mega-analysis from our database of over 10 years of studies. Mixed-effects models were used to address the disconnect between mechanical and vascular influences on CTS; the effects of biomechanical factors and CTS status were evaluated on carpal tunnel tissue mechanics and blood flow. Altered blood flow was also induced during tissue motion to draw inferences regarding the cyclical relationship between tissue mechanics and fluid flow changes on CTS pathology. Results: Greater movement speed and flexed wrist postures were found to contribute to greater shear strain. Flexed wrist postures and greater fingertip force were found to increase median nerve blood flow. Greater CTS severity was associated with lower median nerve blood flow. Finally, brachial blood flow restriction as a surrogate for elevated carpal tunnel pressure was found to alter tissue motion and increase carpal tunnel tissue shear strain. Conclusions: Finger movement speed, force application, wrist posture, and altered fluid flow in the carpal tunnel contribute to changes in outcomes associated with the development of CTS. The mechanistic findings from this paper should be incorporated into future research to update the damage model for CTS pathology. Full article

Background/Objectives: This study compared step-by-step kinematic measurements from an infrared contact mat (IR-mat) and an inertial measurement unit (IMU) system during bounding and single leg jumping for speed, while also evaluating the validity of algorithms originally developed for sprinting and running when applied to horizontal jumps. The aim was to investigate differences in contact times between the systems. Methods: Nineteen female football players (15 ± 0.5 years, 61.0 ± 5.9 kg, 1.70 ± 0.06 m) performed attempts in both jumps over 20 m with maximum speed, of which the first eight steps were analysed. Results: Significant differences were found between the systems, with the IR-mat recording longer contact times than the IMU. The IR-mat began and ended its measurements slightly earlier and later, respectively, compared to the IMU system, likely due to the IMU’s algorithm, which was developed for sprinting with forefoot contact, while more midfoot and heel landing is used during jumps. Conclusions: Both systems provide reliable measurements; however, the IR mat consistently records slightly longer contact times for horizontal jumps. While the IMU is dependable, it exhibits a consistent bias compared to the IR mat. For bounding, the IR mat begins recording 0.018 s earlier at touch down and stops 0.021 s later. For single leg jumps, it starts 0.024 s earlier and ends 0.021 s later, resulting in contact times that are, on average, 0.039–0.045 s longer. These findings provide valuable insights for coaches and researchers in selecting appropriate measurement tools, highlighting the systematic differences between IR mats and IMUs in horizontal jump analysis. Full article

Purpose: This study explores the impact of take-off distance on hurdling and interval running kinematics in sprint hurdles, recognizing its potential to improve performance. While beginners often use shorter take-off distances, a deeper understanding could inform coaching strategies aimed at improving hurdle technique. Methods: Ten male elite and highly trained hurdlers ran 60 m hurdles under original, short, and long take-off distances (OTD, STD, and LTD, respectively). The sagittal plane kinematics of the fourth hurdle and interval running were obtained using two high-speed cameras at a rate of 120 frames per second. Intraindividual step parameters were compared between conditions. Results: Running speed and step frequency were significantly lower in the STD than in the OTD and LTD. Significant interactions were found for step length with a significantly longer recovery step length in the STD than in the LTD. Furthermore, the hurdling distance was significantly longer in the LTD than in the OTD. In addition, the touchdown distance was significantly shorter in the LTD and longer in the STD compared to the OTD. Therefore, an STD is associated with a shorter acceleration distance between hurdles, whereas an LTD is associated with a longer acceleration distance. Therefore, the take-off distance influenced the distance for acceleration between hurdles, and the recovery step was related to the take-off distance. Conclusions: STD has negative effects on hurdling and interval running, even among elite and highly trained hurdlers. Full article

Bone metastases occur when cancer cells from the primary tumor spread to the bones. The incidence of bone metastases is increasing due to the longer survival of patients with primary tumors, driven by advances in cancer treatments. In patients with multiple bone metastases, care is primarily palliative, aiming to improve their quality of life through pain relief. Bone metastases are strongly associated with pathological fractures, particularly in the femur. In these cases, minimally invasive treatments such as percutaneous cementoplasty and internal fixation with intramedullary nails are growing in popularity. Methods: This manuscript focuses on studying these two therapies by developing virtual models using ANSYS^® software. Thermal and thermomechanical analyses were conducted to evaluate the heat effect resulting from the polymerization of different types of bone cement and to assess the benefits of combining it with internal fixation using intramedullary nails made of different materials. Results: The results highlight the advantages of combining these two techniques compared to cementoplasty alone. Furthermore, the use of Gentamicin Bone Cement (CMW 3^®) with an intramedullary nail made of either material has been shown to provide a more significant functional improvement. Conclusions: The combination of cementoplasty with internal fixation is more effective than cementoplasty alone. The use of CMW 3^® cement with an intramedullary nail made of either material provides greater control over the growth of the metastatic lesion. The chosen injection angle results in an excessive volume of cement, causing a high degree of thermal necrosis. Full article

Background/Objectives: One potential risk factor that remains especially contentious in the anterior cruciate ligament (ACL) injury literature is the role of neuromuscular fatigue in ACL injury risk. Therefore, the purposes of this review are (i) to present the research and practical concepts of lower extremity neuromuscular fatigue; and (ii) to review the literature relating to neuromuscular fatigue as an ACL injury risk factor and mechanism. Methods: A structured review was performed in the Medline database using a search strategy that included terms such as “anterior cruciate ligament injury” and “knee injuries” combined with terms such as “injury” and “fatigue”. Articles were included if they included young healthy participants (18–35) and made a comparison between non-fatigued and fatigued states that were assessed with at least one lower extremity biomechanical variable associated with ACL injury risk. Results: Overall, there were 67 studies included, accounting for 1440 participants (627 male and 813 female) across a variety of sports and activities. Of these, 53 (79%) reported a post-fatigue change in the kinematics, kinetics, neuromuscular, and/or other (e.g., proprioceptive) outcomes that indicate that the participants would be at an increased risk of an ACL injury. The most common argument against fatigue as a risk factor is that ACL injuries do not tend to occur later in a game or season, when it is assumed that athletes would be most fatigued. Conclusions: The evidence presented in this review suggests that localized neuromuscular fatigue is a risk factor, among multiple factors, for ACL injuries, providing another modifiable risk factor that should be considered when developing ACL injury risk reduction interventions. Full article

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