ISB recommendations on the reporting of intersegmental forces and moments during human motion analysis

Decreased Mechanical Work Demand in the Chopart Joint After Total Ankle Replacement

BACKGROUND

The success of total ankle replacement (TAR) must be based on restoring reasonable mechanical balance with anatomical structures that can produce mechanical joint work through elastic (eg, tendons, fascia) or viscoelastic (eg, heel pad) mechanisms, or by active muscle contractions. Yet, quantifying the work distribution across the affected joint and the neighboring foot joints after TAR is lacking. Therefore, the objective of this study was to investigate if there is a change in the joint work distribution across the Ankle, Chopart, Lisfranc and Metatarsophalangeal joints during level walking before and after patients undergo TAR.

METHODS

Fifteen patients with end-stage ankle osteoarthritis scheduled for primary TAR for pain relief were recruited and peer-matched with a sample of 15 control subjects. All patients underwent a 3D gait analysis before and after surgery, during which a kinetic multisegment foot model was used to quantify intersegmental joint work.

RESULTS

The contribution of the Ankle joint (P = .007) to the total foot and ankle positive work increased significantly after TAR. In contrast, a significant decrease in the contribution to the total foot and ankle joint positive work (P < .001) were found at the Chopart joint after TAR. The foot joints combined produced a significant increase in a net mechanical work from +0.01 J/kg before surgery to +0.05 J/kg after TAR (P = .006).

CONCLUSION

The findings of this study corroborate the theoretical rationale that TAR reduces significantly the compensatory strategy in the Chopart joint in patients with end-stage ankle osteoarthritis after TAR. However, the findings also showed that the contribution of the ankle joint of patients after TAR to the total foot and ankle joint positive work remained impaired compared to the control group.

Effects of Changing Center of Pressure Position on Knee and Ankle Extensor Moments During Double-Leg Squatting

The effects of changes in the anterior-posterior center of pressure (AP-COP) position on the lower limb joint moments during double-leg squatting remain unclear. The purpose of this study was to determine the effects of AP-COP positional changes on the hip, knee, and ankle extensor moments during double-leg squatting. Sixteen male participants (22.1 ± 1.5 years) performed double-leg squatting under two conditions (anterior and posterior COP conditions) with visual feedback on their COP positions. Kinematics and kinetics were analyzed using a three-dimensional motion analysis system and force plates. The hip, knee and ankle flexion angles and extensor moments at peak vertical ground reaction force were compared between the two conditions using paired t tests. The COP position was 53.5 ± 2.4% of the foot length, starting from the heel, under the anterior condition and 44.4 ± 2.1% under the posterior condition (P < 0.001). The knee extensor moment was significantly smaller under the anterior than the posterior COP condition (P = 0.003, 95% confidence interval (CI) -0.087 to -0.021 Nm/kg/m), while the ankle extensor moment significantly larger under the anterior COP condition than under the posterior COP condition (P < 0.001, 95% CI 0.113 to 0.147 Nm/kg/m). There was no significant difference in hip extensor moment (P = 0.431). The ankle dorsiflexion angle was significantly larger under the anterior than the posterior COP condition (P = 0.003, 95% CI 0.6 to 2.6°), while there was no difference in trunk, hip, or knee flexion angle. The present results indicate that changes in the AP-COP position mainly affect the ankle and knee extensor moments during double-leg squatting, while the effect on the lower limb joint and trunk flexion angles was limited. Visual feedback on the AP-COP position could be useful for modifying the ankle and knee extensor moments during double-leg squatting.

Biomechanical adaptations following a music-based biofeedback gait retraining program to reduce peak tibial accelerations

PURPOSE

The present study aimed to determine whether runners can reduce impact measures after a six-session in-the-field gait retraining program with real-time musical biofeedback on axial peak tibial acceleration (PTA_a ) and identify the associated biomechanical adaptations.

METHODS

Twenty trained high-impact runners were assigned to either the biofeedback or the music-only condition. The biofeedback group received real-time feedback on the PTA_a during the gait retraining program, whereas the music-only condition received a sham treatment. Three-dimensional gait analysis was conducted in the laboratory before (PRE) and within one week after completing the gait retraining program (POST). Subjects were instructed to replicate the running style from the last gait retraining session without receiving feedback while running overground at a constant speed of 2.9 m∙s^-1 .

RESULTS

Only the biofeedback group showed significant reductions in both PTA_a (∆x̅ = -26.9%, p = 0.006) and vertical instantaneous loading rate (∆x̅ = -29.2%, p = 0.003) from PRE to POST. In terms of biomechanical adaptations, two strategies were identified. Two subjects transitioned toward a more forefoot strike. The remaining eight subjects used a pronounced rearfoot strike and posteriorly inclined shank at initial contact combined with less knee extension at toe-off while reducing vertical excursion of the center of mass.

CONCLUSIONS

After completing a music-based biofeedback gait retraining program, runners can reduce impact while running overground in a laboratory. We identified two distinct self-selected strategies used by the participants to achieve reductions in impact.

Estimation of Joint Moments During Turning Maneuvers in Alpine Skiing Using a Three Dimensional Musculoskeletal Skier Model and a Forward Dynamics Optimization Framework

In alpine skiing, estimation of the joint moments acting onto the skier is essential to quantify the loading of the skier during turning maneuvers. In the present study, a novel forward dynamics optimization framework is presented to estimate the joint moments acting onto the skier incorporating a three dimensional musculoskeletal model (53 kinematic degrees of freedom, 94 muscles). Kinematic data of a professional skier performing a turning maneuver were captured and used as input data to the optimization framework. In the optimization framework, the musculoskeletal model of the skier was applied to track the experimental data of a skier and to estimate the underlying joint moments of the skier at the hip, knee and ankle joints of the outside and inside leg as well as the lumbar joint. During the turning maneuver the speed of the skier was about 14 m/s with a minimum turn radius of about 16 m. The highest joint moments were observed at the lumbar joint with a maximum of 1.88 Nm/kg for lumbar extension. At the outside leg, the highest joint moments corresponded to the hip extension moment with 1.27 Nm/kg, the knee extension moment with 1.02 Nm/kg and the ankle plantarflexion moment with 0.85 Nm/kg. Compared to the classical inverse dynamics analysis, the present framework has four major advantages. First, using a forward dynamic optimization framework the underlying kinematics of the skier as well as the corresponding ground reaction forces are dynamically consistent. Second, the present framework can cope with incomplete data (i.e., without ground reaction force data). Third, the computation of the joint moments is less sensitive to errors in the measurement data. Fourth, the computed joint moments are constrained to stay within the physiological limits defined by the musculoskeletal model.

Manual wheelchair biomechanics while overcoming various environmental barriers: A systematic review

During manual wheelchair (MWC) locomotion, the user’s upper limbs are subject to heavy stresses and fatigue because the upper body is permanently engaged to propel the MWC. These stresses and fatigue vary according to the environmental barriers encountered outdoors along a given path. This study aimed at conducting a systematic review of the literature assessing the biomechanics of MWC users crossing various situations, which represent physical environmental barriers. Through a systematic search on PubMed, 34 articles were selected and classified according to the investigated environmental barriers: slope; cross-slope; curb; and ground type. For each barrier, biomechanical parameters were divided into four categories: spatiotemporal parameters; kinematics; kinetics; and muscle activity. All results from the different studies were gathered, including numerical data, and assessed with respect to the methodology used in each study. This review sheds light on the fact that certain situations (cross-slopes and curbs) or parameters (kinematics) have scarcely been studied, and that a wider set of situations should be studied. Five recommendations were made at the end of this review process to standardize the procedure when reporting materials, methods, and results for the study of biomechanics of any environmental barrier encountered in MWC locomotion: (i) effectively reporting barriers’ lengths, grades, or heights; (ii) striving for standardization or a report of the approach conditions of the barrier, such as velocity, especially on curbs; (iii) reporting the configuration of the used MWC, and if it was fitted to the subject’s morphology; (iv) reporting rotation sequences for the expression of moments and kinematics, and when used, the definition of the musculoskeletal model; lastly (v) when possible, reporting measurement uncertainties and model reconstruction errors.

Entry angle during jump landing changes biomechanical risk factors for ACL injury

ACL injuries are common among athletes. The injury usually occurs during sport movements involving sudden direction changes when landing and cutting. Twenty-one healthy females performed a series of jump-land-jump movements. They jumped from a 28 cm box onto two in-ground force platforms, followed by a maximal vertical jump. The direction of the first jump was tested with seven entry angles, jumping to the right (90 R, 60 R and 30 R), straight forward (0), and jumping to the left (90 L, 60 L and 30 L). Kinematic and kinetic data were recorded for data analysis. During the first 100 ms of landing, participants had significantly smaller peak knee flexion angles, larger initial knee valgus angles and larger peak knee joint external valgus moments when jumping to the right (90 R, 60 R and 30 R) compared to straight forward (0), and jumping to the left (90 L, 60 L and 30 L). Thus, entry angles to the right may increase the risk of ACL injury in the right knee. We suggest that these types of jumps should be used with caution during ACL rehabilitation, but may be useful for testing ACL risk factors in healthy individuals.

Comparison of Existing Methods for Characterizing Bi-Linear Natural Ankle Quasi-Stiffness

Natural ankle quasi-stiffness (NAS) is a mechanical property of the ankle joint during motion. NAS has been historically calculated as the average slope (linear regression) of the net ankle moment vs. ankle angle during discrete phases of stance. However, recent work has shown that NAS is nonlinear during stance. Specifically, during the loading phase (~10-60% of stance), plantarflexion moment increases at an accelerating rate compared to dorsiflexion angle. Updated models have been developed to better capture this inherent nonlinearity. One type of model is called bi-linear NAS (BL-NAS) divides the loading phase of stance into two sub-phases, called early loading (EL) and late loading (LL) NAS. Two papers, written by Crenna & Frigo in 2011 and Shamaei et al. in 2013, outline different BL-NAS models. Both models fit measured data better (lower RMSE) than standard single linear NAS (SL-NAS) models, but have not been widely adopted, possibly because of methodological discrepancies and lack of applicability to physical devices at the time. This paper compares these existing BL-NAS models and translate those findings to possible orthotic device designs. Results showed that both BL-NAS models had lower RMSE than SL-NAS, EL-NAS was not significantly different across walking speeds, and LL-NAS increased significantly at faster walking speeds. These improved NAS models better approximate natural human movement than commonly used SL-NAS models, and provide a basis to design ankle-foot devices with multiple stiffness properties to emulate and facilitate natural human motion.

Golf Swing Biomechanics: A Systematic Review and Methodological Recommendations for Kinematics

Numerous studies have been conducted to investigate golf swing performance in both preventing injury and injury occurrence. The objective of this review was to describe state-of-the-art golf swing biomechanics, with a specific emphasis on movement kinematics, and when possible, to suggest recommendations for research methodologies. Keywords related to biomechanics and golf swings were used in scientific databases. Only articles that focused on golf-swing kinematics were considered. In this review, 92 articles were considered and categorized into the following domains: X-factor, crunch factor, swing plane and clubhead trajectory, kinematic sequence, and joint angular kinematics. The main subjects of focus were male golfers. Performance parameters were searched for, but the lack of methodological consensus prevented generalization of the results and led to contradictory results. Currently, three-dimensional approaches are commonly used for joint angular kinematic investigations. However, recommendations by the International Society of Biomechanics are rarely considered.

Increased Femoral Anteversion Does Not Lead to Increased Joint Forces During Gait in a Cohort of Adolescent Patients

Orthopedic complications were previously reported for patients with increased femoral anteversion. A more comprehensive analysis of the influence of increased femoral anteversion on joint loading in these patients is required to better understand the pathology and its clinical management. Therefore, the aim was to investigate lower-limb kinematics, joint moments and forces during gait in adolescent patients with increased, isolated femoral anteversion compared to typically developing controls. Secondly, relationships between the joint loads experienced by the patients and different morphological and kinematic features were investigated. Patients with increased femoral anteversion (n = 42, 12.8 ± 1.9 years, femoral anteversion: 39.6 ± 6.9°) were compared to typically developing controls (n = 9, 12.0 ± 3.0 years, femoral anteversion: 18.7 ± 4.1°). Hip and knee joint kinematics and kinetics were calculated using subject-specific musculoskeletal models. Differences between patients and controls in the investigated outcome variables (joint kinematics, moments, and forces) were evaluated through statistical parametric mapping with Hotelling T2 and t-tests (α = 0.05). Canonical correlation analyses (CCAs) and regression analyses were used to evaluate within the patients’ cohort the effect of different morphological and kinematic predictors on the outcome variables. Predicted compressive proximo-distal loads in both hip and knee joints were significantly reduced in patients compared to controls. A gait pattern characterized by increased knee flexion during terminal stance (KneeFlex_tSt) was significantly correlated with hip and knee forces, as well as with the resultant force exerted by the quadriceps on the patella. On the other hand, hip internal rotation and in-toeing, did not affect the loads in the joints. Based on the finding of the CCAs and linear regression analyses, patients were further divided into two subgroups based KneeFlex_tSt. Patients with excessive KneeFlex_tSt presented a significantly higher femoral anteversion than those with normal KneeFlex_tSt. Patients with excessive KneeFlex_tSt presented significantly larger quadriceps forces on the patella and a larger posteriorly-oriented shear force at the knee, compared to patients with normal KneeFlex_tSt, but both patients’ subgroups presented only limited differences in terms of joint loading compared to controls. This study showed that an altered femoral morphology does not necessarily lead to an increased risk of joint overloading, but instead patient-specific kinematics should be considered.

One hundred marathons in 100 days: Unique biomechanical signature and the evolution of force characteristics and bone density

BACKGROUND

An extraordinary long-term running performance may benefit from low dynamic loads and a high load-bearing tolerance. An extraordinary runner (age = 55 years, height = 1.81 m, mass = 92 kg) scheduled a marathon a day for 100 consecutive days. His running biomechanics and bone density were investigated to better understand successful long-term running in the master athlete.

METHODS

Overground running gait analysis and bone densitometry were conducted before the marathon-a-day challenge and near its completion. The case's running biomechanics were compared pre-challenge to 31 runners who were matched by a similar foot strike pattern.

RESULTS

The case's peak vertical loading rate (Δx̄ = -61.9 body weight (BW)/s or -57%), peak vertical ground reaction force (Δx̄ = -0.38 BW or -15%), and peak braking force (Δx̄ = -0.118 BW or -31%) were remarkably lower (p < 0.05) than the control group at ∼3.3 m/s. The relatively low loading-related magnitudes were attributed to a remarkably high duty factor (0.41) at the evaluated speed. The foot strike angle of the marathoner (29.5°) was greater than that of the control group, affecting the peak vertical loading rate. Muscle powers in the lower extremity were also remarkably low in the case vs. controls: peak power of knee absorption (Δx̄ = -9.16 watt/kg or -48%) and ankle generation (Δx̄ = -3.17 watt/kg or -30%). The bone mineral density increased to 1.245 g/cm² (+2.98%) near completion of the challenge, whereas the force characteristics showed no statistically significant change.

CONCLUSION

The remarkable pattern of the high-mileage runner may be useful in developing or evaluating load-shifting strategies in distance running.

Altered Muscle Contributions are Required to Support the Stance Limb During Voluntary Toe-Walking

Toe-walking characterizes several neuromuscular conditions and is associated with a reduction in gait stability and efficiency, as well as in life quality. The optimal choice of treatment depends on a correct understanding of the underlying pathology and on the individual biomechanics of walking. The objective of this study was to describe gait deviations occurring in a cohort of healthy adult subjects when mimicking a unilateral toe-walking pattern compared to their normal heel-to-toe gait pattern. The focus was to characterize the functional adaptations of the major lower-limb muscles which are required in order to toe walk. Musculoskeletal modeling was used to estimate the required muscle contributions to the joint sagittal moments. The support moment, defined as the sum of the sagittal extensive moments at the ankle, knee, and hip joints, was used to evaluate the overall muscular effort necessary to maintain stance limb stability and prevent the collapse of the knee. Compared to a normal heel-to-toe gait pattern, toe-walking was characterized by significantly different lower-limb kinematics and kinetics. The altered kinetic demands at each joint translated into different necessary moment contributions from most muscles. In particular, an earlier and prolonged ankle plantarflexion contribution was required from the soleus and gastrocnemius during most of the stance phase. The hip extensors had to provide a higher extensive moment during loading response, while a significantly higher knee extension contribution from the vasti was necessary during mid-stance. Compensatory muscular activations are therefore functionally required at every joint level in order to toe walk. A higher support moment during toe-walking indicates an overall higher muscular effort necessary to maintain stance limb stability and prevent the collapse of the knee. Higher muscular demands during gait may lead to fatigue, pain, and reduced quality of life. Toe-walking is indeed associated with significantly larger muscle forces exerted by the quadriceps to the patella and prolonged force transmission through the Achilles tendon during stance phase. Optimal treatment options should therefore account for muscular demands and potential overloads associated with specific compensatory mechanisms.

Flexor digitorum brevis utilises elastic strain energy to contribute to both work generation and energy absorption at the foot

The central nervous system utilizes tendon compliance of the intrinsic foot muscles to aid the foot's arch spring, storing and returning energy in its tendinous tissues. Recently, the intrinsic foot muscles have been shown to adapt their energetic contributions during a variety of locomotor tasks to fulfil centre of mass work demands. However, the mechanism by which the small intrinsic foot muscles are able to make versatile energetic contributions remains unknown. Therefore, we examined the muscle–tendon dynamics of the flexor digitorum brevis during stepping, jumping and landing tasks to see whether the central nervous system regulates muscle activation magnitude and timing to enable energy storage and return to enhance energetic contributions. In step-ups and jumps, energy was stored in the tendinous tissue during arch compression; during arch recoil, the fascicles shortened at a slower rate than the tendinous tissues while the foot generated energy. In step-downs and landings, the tendinous tissues elongated more and at greater rates than the fascicles during arch compression while the foot absorbed energy. These results indicate that the central nervous system utilizes arch compression to store elastic energy in the tendinous tissues of the intrinsic foot muscles to add or remove mechanical energy when the body accelerates or decelerates. This study provides evidence for an adaptive mechanism to enable the foot's energetic versatility and further indicates the value of tendon compliance in distal lower limb muscle–tendon units in locomotion.

Summary: Demonstration of an adaptive mechanism that enables the intrinsic foot muscles to make versatile contributions to whole-body accelerations and decelerations.

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

Lower-limb Joint Torque Prediction using LSTM Neural Networks and Transfer Learning

Estimation of joint torque during movement provides important information in several settings, such as effect of athletes' training or of a medical intervention, or analysis of the remaining muscle strength in a wearer of an assistive device. The ability to estimate joint torque during daily activities using wearable sensors is increasingly relevant in such settings. In this study, lower limb joint torques during ten daily activities were predicted by long short-term memory (LSTM) neural networks and transfer learning. LSTM models were trained with muscle electromyography signals and lower limb joint angles. Hip flexion/extension, hip abduction/adduction, knee flexion/extension and ankle dorsiflexion/plantarflexion torques were predicted. The LSTM models' performance in predicting torque was investigated in both intra-subject and inter-subject scenarios. Each scenario was further divided into intra-task and inter-task tests. We observed that LSTM models could predict lower limb joint torques during various activities accurately with relatively low error (root mean square error ≤ 0.14 Nm/kg, normalized root mean square error ≤8.7%) either through a uniform model or through ten separate models in intra-subject tests. Furthermore, a transfer learning technique was adopted in the inter-task and inter-subject tests to further improve the generalizability of LSTM models by pre-training a model on multiple subjects and/or tasks and transferring the learned knowledge to a target task/subject. Particularly in the inter-subject tests, we could predict joint torques accurately in several movements after training from only a few movements from new subjects.

Hip torques and the effect of posture in side-stepping with elastic resistance

BACKGROUND

The way movement-based exercises affect targeted muscles is not always obvious. Side stepping with an elastic band around the forefeet is aimed at strengthening hip abductors and lateral rotator muscles, with the premise that it creates an external torque of adduction and medial rotation of the femur around the pelvis that needs to be counteracted by hip muscles. However, hip torques during this exercise have not been previously quantified.

RESEARCH QUESTION

Is the premise that the side-stepping exercise creates an external torque of adduction and medial rotation of the femur around the pelvis correct?

METHODS

Thirty-six adults performed the exercise in an upright and a squat posture while 3D kinetic and kinematic data were collected. Hip muscle torques were calculated using inverse dynamics. The effect of posture and potential interactions with sex, side-stepping phases, and trailing/leading directions were analyzed using Pearson correlation and mixed-model ANOVAs.

RESULT

A hip net muscle torque of extension, abduction and medial rotation was required to perform the exercise, regardless of phase and direction. The net muscle torque towards medial rotation required during the exercise was smaller (P < 0.001) in the upright (0.05-0.12 N m kg^-1 m^-1 across phases) compared to the squat posture (0.10-0.24 N m kg^-1 m^-1). In contrast, hip abductor torque was not affected by posture. When averaged across phases and directions, the normalized hip medial rotator muscle torque was highly correlated with knee flexion (r = 0.93, P < 0.001).

SIGNIFICANCE

The assumption that the side-stepping with the elastic band on the forefeet creates an external hip torque of medial rotation is erroneous. The resistance imposed to the hip during this exercise is consistent with the goal of strengthening the muscles that contribute to hip abduction and hip medial (not lateral) rotation. Changing the knee flexion angle is an effective way to manipulate hip rotator torque when prescribing this exercise in strength training and rehabilitation programs.

Comparison of 5 Normalization Methods for Knee Joint Moments in the Single-Leg Squat

Ratio scaling is the most common magnitude normalization approach for net joint moment (NJM) data. Generally, researchers compute a ratio between NJM and (some combination of) physical body characteristics (eg, mass, height, limb length, etc). However, 3 assumptions must be verified when normalizing NJM data this way. First, the regression line between NJM and the characteristic(s) used passes through the origin. Second, normalizing NJM eliminates its correlation with the characteristic(s). Third, the statistical interpretations following normalization are consistent with adjusted linear models. The study purpose was to assess these assumptions using data collected from 16 males and 16 females who performed a single-leg squat. Standard inverse dynamics analyses were conducted, and ratios were computed between the mediolateral and anteroposterior components of the knee NJM and participant mass, height, leg length, mass × height, and mass × leg length. Normalizing NJM-mediolateral by mass × height and mass × leg length satisfied all 3 assumptions. Normalizing NJM-anteroposterior by height and leg length satisfied all 3 assumptions. Therefore, if normalization of the knee NJM is deemed necessary to address a given research question, it can neither be assumed that using (any combination of) participant mass, height, or leg length as the denominator is appropriate nor consistent across joint axes.

Added value of motion capture technology for occupational health and safety innovations

Ergonomic principles in production assembly and manufacturing operations have become an essential part of comprehensive health and safety innovations. We aim to provide new insights into occupational health and safety innovations and how they utilise biomechanical methods and cutting-edge motion capture technology by assessing movements at a workplace. The practical goal is to quantify a connection between work exposure and ergonomic risk measures to determine biomechanical risk factors of diseases or health-related disorders objectively. The target group consisted of 62 factory employees working in manufacturing (26 participants on 12 devices) or assembly areas (36 participants on 9 devices). Body posture, body parts position, movements, energy cost and workloads were assessed using an inertial motion capture (MC) system. MC technology accurately assesses the operator’s movements. The proposed methodology could complement ergonomic procedures in the design of workstations, which is the added value of the motion capture technology for occupational health and safety innovations.

Reliability and Repeatability of ACL Quick Check®: A Methodology for on Field Lower Limb Joint Kinematics and Kinetics Assessment in Sport Applications

Anterior cruciate ligament (ACL) lesion represents one of the most dramatic sport injuries. Even though clinical screenings aiming at identifying subjects at risk of injuries are gaining popularity, the use of sophisticated equipment still represents a barrier towards their widespread use. This study aimed to test both reliability and repeatability of a new methodology to assess lower limb joints kinematics and kinetics directly on field with the aid of video cameras and plantar pressure insoles. Ten athletes and one case study (post ACL surgery) were assessed in a gait laboratory, while performing double leg squats, through the simultaneous acquisition of stereophotogrammetry, force plates, commercial video cameras and plantar pressure insoles. Different sources of errors were investigated and both reliability and repeatability analysis performed. Minimum and maximum RMSE values of 0.74% (right knee joint center trajectory) and 64.51%, respectively (ankle dorsi-plantarflexion moment), were detected. Excellent to good correlation was found for the majority of the measures, even though very poor and inverse between-trials correlation was found on a restricted number of trials especially for the ankle dorsi-plantarflexion moment. These findings could be used in combination with already available screening tools in order to provide more repeatable results.

A method for measuring in vivo finger kinematics using electromagnetic tracking

Accurate in vivo measurement of finger joint kinematics is important for evaluation of treatment methods, implant designs, and for the development and validation of computer models of the hand. The main objective of this project was to develop a standardized finger kinematic measurement system employing electromagnetic (EM) tracking to measure in vivo finger motion pathways. A landmark digitization protocol was developed and used in vivo, in a biomechanical study using EM trackers secured to the finger segments. In vivo results for finger flexion/extension showed no significant differences between EM and goniometer results, 5°±3°; p = 0.735.

A Method to Compare Heterogeneous Types of Bone and Cartilage Meshes

Accurately capturing the bone and cartilage morphology and generating a mesh remains a critical step in the workflow of computational knee joint modeling. Currently, there is no standardized method to compare meshes of different element types and nodal densities, making comparisons across research teams a significant challenge. The aim of this paper is to describe a method to quantify differences in knee joint bone and cartilages meshes, independent of bone and cartilage mesh topology. Bone mesh-to-mesh distances, subchondral bone boundaries, and cartilage thicknesses from meshes of any type of mesh are obtained using a series of steps involving registration, resampling, and radial basis function fitting after which the comparisons are performed. Subchondral bone boundaries and cartilage thicknesses are calculated and visualized in a common frame of reference for comparison. The established method is applied to models developed by five modeling teams. Our approach to obtain bone mesh-to-mesh distances decreased the divergence seen in selecting a reference mesh (i.e., comparing mesh A-to-B versus mesh B-to-A). In general, the bone morphology was similar across teams. The cartilage thicknesses for all models were calculated and the mean absolute cartilage thickness difference was presented, the articulating areas had the best agreement across teams. The teams showed disagreement on the subchondral bone boundaries. The method presented in this paper allows for objective comparisons of bone and cartilage geometry that is agnostic to mesh type and nodal density.

Effect of Rearfoot Strikes on the Hip and Knee Rotational Kinetic Chain During the Early Phase of Cutting in Female Athletes

BACKGROUND

Biomechanical factors affecting horizontal-plane hip and knee kinetic chain and anterior cruciate ligament (ACL) injury risk during cutting maneuvers remain unclear. This study aimed to examine whether different foot strike patterns alter horizontal-plane hip and knee kinetics and kinematics during a cutting maneuver in female athletes and clarify the individual force contribution for producing high-risk hip and knee loadings. Twenty-five healthy female athletes performed a 60° cutting task with forefoot and rearfoot first strike conditions. Horizontal-plane hip and knee moment components, angles, and angular velocities were calculated using synchronized data of the marker positions on the body landmarks and ground reaction forces (GRFs) during the task. The one-dimensional statistical parametric mapping paired t test was used to identify the significant difference in kinetic and kinematic time-series data between foot strike conditions.

RESULTS

In the rearfoot strike condition, large hip and knee internal rotation loadings were produced during the first 5% of stance due to the application of GRFs, causing a significantly larger hip internal rotation excursion than that of the forefoot strike condition. Dissimilarly, neither initial hip internal rotation displacement nor knee internal rotation GRF loadings were observed in the forefoot strike condition.

CONCLUSIONS

Rearfoot strike during cutting appears to increase noncontact ACL injury risk as the GRF tends to produce combined hip and knee internal rotation moments and the high-risk lower limb configuration. Conversely, forefoot strike during cutting appears to be an ACL-protective strategy that does not tend to produce the ACL-harmful joint loadings and lower extremity configurations. Thus, improving foot strike patterns during cutting should be incorporated in ACL injury prevention programs.

Physics-based guidelines for accepting reasonable dynamic simulations of movement

OBJECTIVE

During dynamic simulations, residuals are nonphysical generalized forces/moments that dynamically balance external and inertial forces/moments, accounting for data processing and modelling errors. Hicks et al. (2015) made the original residual threshold recommendations for an acceptable simulation, but these thresholds are not based on the dynamic, physics-based movement characteristics. In this study, we present three new, physics-based guidelines for accepting dynamic simulations of movement using zero moment point computations and thresholds for forces, center of pressure, and free moment.

METHODS

We formulate new guidelines and evaluate them alongside the original 2015 recommendations using two movements: single-leg jump-landing (SLJL) and walking gait. We also present a MATLAB function for users to test if their simulations meet these guidelines.

RESULTS

We found that on average, only 4.3% (SLJL) and 8.2% (walking gait) of the original 2015 residuals volume met all the new physics-based guidelines. The free-moment guideline was the most restrictive for reasonable simulations, especially for high-velocity movements at times with lower vertical ground reaction forces. Additionally, some of the new recommended residuals volume fell outside of the original 2015 recommendations. Moreover, accepting reasonable simulations using different thresholds leads to different joint torques as high as 24 Nm (SLJL) and 8.2 Nm (walking gait).

CONCLUSION

The physics-based guidelines are overall more restrictive than the original 2015 recommendations and elicit different simulation kinetics.

SIGNIFICANCE

Using different guidelines may lead to different conclusions and clinical interpretations. We advocate for the physics-based guidelines as they are built upon the dynamic, physics-based characteristics of the movement.

Development of a revolute-type kinematic model for human upper limb using a matrix approach

A mathematical model is proposed for a revolute joint mechanism with an n-degree of freedom (DOF). The matrix approach is used for finding the relation between two consecutive links to determine desired link parameters such as position, velocity and acceleration using the forward kinematic approach. The matrix approach was confirmed for a proposed 10 DOF revolute type (R-type) human upper limb model with servo motors at each joint. Two DOFs are considered each at shoulder, elbow and wrist joint, followed by four DOF for the fingers. Two DOFs were considered for metacarpophalangeal (mcp) and one DOF each for proximal interphalangeal (pip) and distal interphalangeal (dip) joints. MATLAB script function was used to evaluate the mathematical model for determining kinematic parameters for all the proposed human upper limb model joints. The simplified method for kinematic analysis proposed in this paper will further simplify the dynamic modeling of any mechanism for determining joint torques and hence, easy to design control system for joint movements.

Within-Session Reliability and Minimum Detectable Differences for Discrete Lower-Extremity Angles and Moments During Walking

Differences in walking biomechanics between groups or conditions should be greater than the measurement error to be considered meaningful. Reliability and minimum detectable differences (MDDs) have not been determined for lower-extremity angles and moments during walking within a session, as needed for interpreting differences in cross-sectional studies. Thus, the purpose of this study was to determine within-session reliability and MDDs for peak ankle, knee, and hip angles and moments during walking. Three-dimensional gait analysis was used to record walking at 1.25 m/s (±5%) in 18 men, 18-50 years of age. Peak angles and moments were calculated for 2 sets of 3 trials. Intraclass correlation coefficients (3, 3) were used to determine within-session reliability. In addition, MDDs were calculated. Within-session reliability was good to excellent for all variables. The MDDs ranged from 0.9° to 3.6° for joint angles and 0.06 to 0.15 N·m/kg for joint moments. Within-session reliability for peak ankle, knee, and hip angles and moments was better than the between-session reliability reported previously. Overall, our MDDs were similar or smaller than those previously reported for between-session reliability. The authors recommend using these MDDs to aid in the interpretation of cross-sectional comparisons of lower-extremity biomechanics during walking in healthy men.

Increased Trunk Kinetics Observed During Dose-Specific Trunk Lean Gait Modification

Trunk modification is associated with knee abduction moment reduction in both healthy groups and individuals with knee osteoarthritis. Ambulatory-related changes in trunk kinematics have been implicated in increased trunk moment. The purpose of this study was to investigate the effect of dose-specific lateral trunk lean on trunk kinetics during ipsilateral and contralateral stance phases. Nineteen healthy participants completed 10 baseline walking trials, followed by 10 trials employing lateral trunk lean. Trunk modification magnitudes were determined based on the average baseline trunk angle. Five trials of both small and large trunk modification magnitudes were completed. Visual real-time biofeedback was projected as a line graph displaying the trunk angle during stance, and a highlighted bandwidth was designated the target range. A 1-factor repeated-measures analysis of variance or Friedman test was used to assess differences between the conditions (P < .05) in trunk dependent measures. Trunk kinetics displayed significant increases, even during modest modifications to the trunk angle. The participants experienced increased peak frontal plane trunk moment and angular impulse during ipsilateral stance. The observed increase in the peak lateral joint reaction force is suggestive of a compromised loading environment at the spine. Implementing trunk modification might result in unintended secondary changes along the kinetic chain, but further investigation is required.

Subject-Specific Modeling of Femoral Torsion Influences the Prediction of Hip Loading During Gait in Asymptomatic Adults

Hip osteoarthritis may be caused by increased or abnormal intra-articular forces, which are known to be related to structural articular cartilage damage. Femoral torsional deformities have previously been correlated with hip pain and labral damage, and they may contribute to the onset of hip osteoarthritis by exacerbating the effects of existing pathoanatomies, such as cam and pincer morphologies. A comprehensive understanding of the influence of femoral morphotypes on hip joint loading requires subject-specific morphometric and biomechanical data on the movement characteristics of individuals exhibiting varying degrees of femoral torsion. The aim of this study was to evaluate hip kinematics and kinetics as well as muscle and joint loads during gait in a group of adult subjects presenting a heterogeneous range of femoral torsion by means of personalized musculoskeletal models. Thirty-seven healthy volunteers underwent a 3D gait analysis at a self-selected walking speed. Femoral torsion was evaluated with low-dosage biplanar radiography. The collected motion capture data were used as input for an inverse dynamics analysis. Personalized musculoskeletal models were created by including femoral geometries that matched each subject’s radiographically measured femoral torsion. Correlations between femoral torsion and hip kinematics and kinetics, hip contact forces (HCFs), and muscle forces were analyzed. Within the investigated cohort, higher femoral antetorsion led to significantly higher anteromedial HCFs during gait (medial during loaded stance phase and anterior during swing phase). Most of the loads during gait are transmitted through the anterior/superolateral quadrant of the acetabulum. Correlations with hip kinematics and muscle forces were also observed. Femoral antetorsion, through altered kinematic strategies and different muscle activations and forces, may therefore lead to altered joint mechanics and pose a risk for articular damage. The method proposed in this study, which accounts for both morphological and kinematic characteristics, might help in identifying in a clinical setting patients who, as a consequence of altered femoral torsional alignment, present more severe functional impairments and altered joint mechanics and are therefore at a higher risk for cartilage damage and early onset of hip osteoarthritis.

Leg and Joint Stiffness Adaptations to Minimalist and Maximalist Running Shoes

The running footwear literature reports a conceptual disconnect between shoe cushioning and external impact loading: footwear or surfaces with greater cushioning tend to result in greater impact force characteristics during running. Increased impact loading with maximalist footwear may reflect an altered lower-extremity gait strategy to adjust for running in compliant footwear. The authors hypothesized that ankle and knee joint stiffness would change to maintain the effective vertical stiffness, as cushioning changed with minimalist, traditional, and maximalist footwear. Eleven participants ran on an instrumental treadmill (3.5 m·s-1) for a 5-minute familiarization in each footwear, plus an additional 110 seconds before data collection. Vertical, leg, ankle, and knee joint stiffness and vertical impact force characteristics were calculated. Mixed model with repeated measures tested differences between footwear conditions. Compared with traditional and maximalist, the minimalist shoes were associated with greater average instantaneous and average vertical loading rates (P < .050), greater vertical stiffness (P ≤ .010), and less change in leg length between initial contact and peak resultant ground reaction force (P < .050). No other differences in stiffness or impact variables were observed. The shoe cushioning paradox did not hold in this study due to a similar musculoskeletal strategy for running in traditional and maximalist footwear and running with a more rigid limb in minimalist footwear.

Effects of an Exercise Therapy Targeting Knee Kinetics on Pain, Function, and Gait Kinetics in Patients With Knee Osteoarthritis: A Randomized Clinical Trial

In this study, the effects of an exercise therapy comprising yoga exercises and medial-thrust gait (YogaMT) on lower-extremity kinetics, pain, and function in patients with medial knee osteoarthritis were investigated. Fifty-nine patients were randomly allocated to three treatment groups: (a) the YogaMT group practiced yoga exercises and medial thrust gait, (b) the knee-strengthening group performed quadriceps- and hamstring-strengthening exercises, and (c) the treadmill walking group practiced normal treadmill walking in 12 supervised sessions. The adduction and flexion moments of the hip, knee, and ankle; pain intensity; and 2-min walking test were assessed before and after treatment and at 1-month follow-up. The YogaMT group experienced a significant reduction in knee adduction moment. All groups showed significant improvement in pain and function. The YogaMT may reduce medial knee load in patients with knee osteoarthritis in the short term. A larger clinical trial is required to investigate the long-term outcomes of this intervention.

The energetic function of the human foot and its muscles during accelerations and decelerations

The human foot is known to aid propulsion by storing and returning elastic energy during steady-state locomotion. While its function during other tasks is less clear, recent evidence suggests the foot and its intrinsic muscles can also generate or dissipate energy based on the energetic requirements of the center of mass during non-steady-state locomotion. In order to examine contributions of the foot and its muscles to non-steady-state locomotion, we compared the energetics of the foot and ankle joint while jumping and landing before and after the application of a tibial nerve block. Under normal conditions, energetic contributions of the foot rose as work demands increased, while the relative contributions of the foot to center of mass work remained constant with increasing work demands. Under the nerve block, foot contributions to both jumping and landing decreased. Additionally, ankle contributions were also decreased under the influence of the block for both tasks. Our results reinforce findings that foot and ankle function mirror the energetic requirements of the center of mass and provide novel evidence that foot contributions remain relatively constant under increasing energetic demands. Also, while the intrinsic muscles can modulate the energetic capacity of the foot, their removal accounted for only a 3% decrement in total center of mass work. Therefore, the small size of intrinsic muscles appears to limit their capacity to contribute to center of mass work. However, their role in contributing to ankle work capacity is likely important for the energetics of movement.

Test-retest reliability of entire time-series data from hip, knee and ankle kinematics and kinetics during one-leg hops for distance: Analyses using integrated pointwise indices

Motion capture systems enable in-depth interpretations of human movements based on data from three-dimensional joint angles and moments. Such analyses carry important bearings for evaluation of movement control during for instance hop landings among sports-active individuals from a performance perspective but also in rehabilitation. Recent statistical development allows analysis of entire time-series of angle and moment during hops using functional data analysis, but the reliability of such multifaceted data is not established. We used integrated pointwise indices (intra-class correlation, ICC; standard error of measurement, SEM) to establish the test-retest reliability of three-dimensional hip, knee and ankle angle and moment curves during landings of one-leg hop for distance (OLHD) in 23 asymptomatic individuals aged 18-28. We contrasted these findings to reliability of discrete variables extracted at specific events (initial contact, peak value). We extended the calculations of ICC and SEM to handle unbalanced situations (varying number of repetitions) to include all available data. Hip and knee angle curves proved reliable with stable ICC curves throughout the landing, with integrated ICCs ≥ 0.71 for all planes except for knee internal/external rotation (ICC = 0.57). Hip and knee moment curves and ankle angle and moments were less reliable and less stable, particularly in the first ~ 10-25% of the landing (integrated ICCs 0.44-0.57). Curve data were generally not in agreement with the results for discrete event data, thus advocating analysis of curve data which contains more information. To conclude, hip and knee angle curve data during OLHD landings can reliably be evaluated, while moment curves necessitate careful consideration.

Contribution of passive moments to inter-segmental moments during gait: A systematic review

Inter-segmental moments computed by inverse dynamic during gait come from active moments, due to muscle contraction, but also from passive moments, resulting from the resistance of the periarticular structures to their deformation. The evaluation of the proportion of the inter-segmental moments that can be attributed to passive moments has led to divergent results. Thus, the purpose of this study was to systematically search and synthesize the evidence of the contribution of passive moments to inter-segmental moments during healthy and pathological gait. A broad systematic search was performed including four databases. Thirteen studies met all inclusion criteria. Results showed that passive moments participate to inter-segmental moments during gait in a non-negligible way. For the ankle, the evaluation of the proportion of inter-segmental moment attributed to passive structures is 5-20% around the push-off. For the knee, this proportion is 40-98% during late swing and 10-80% during the single support phase. For the hip, it is 20-50% at push-off. For pathological population, it has been shown that this contribution may sometimes be more important, either due to a smaller inter-segmental moment or a larger passive moment. These results suggest that passive mechanisms can contribute substantially to normal human gait, facilitating the propulsion or the braking of the joint. Passive structures, acting as elastic springs, thus help to reduce the energy cost of gait. For pathological gait, studying the contribution of passive moments to inter-segmental moments can help to better understand the aetiology of the pathology.

Leg Stiffness, Joint Stiffness, and Running-Related Injury: Evidence From a Prospective Cohort Study

Background:

The spring-like behavior of the leg and the joints of the lower body during running are thought to influence a wide range of physiologic and mechanical phenomena, including susceptibility to overuse injury. If leg and joint stiffness are associated with running-related injuries, altering joint or leg stiffness may be a useful avenue for injury rehabilitation and injury prevention programs.

Purpose:

To test the associations between running-related injury and leg stiffness, knee stiffness, and ankle stiffness in a prospective study of recreational runners.

Study Design:

Cohort study; Level of evidence, 2.

Methods:

A total of 49 healthy recreational runners took part in a year-long study. Participants completed a 3-dimensional kinematic and kinetic biomechanical assessment at baseline and reported training volume and injury status in a weekly survey during the follow-up period. Relationships between stiffness and injury were assessed at the level of individual legs (n = 98) using spline terms in Cox proportional hazards models.

Results:

During follow-up, 23 participants (29 legs) sustained injury. The median time to injury was 27 weeks (53.27 hours of training). Relative injury rate as a function of knee stiffness displayed a weak and nonsignificant U-shaped curve (P = .187-.661); ankle and leg stiffness displayed no discernable associations with relative injury rate (leg stiffness, P = .215-.605; ankle stiffness, P = .419-.712).

Conclusion:

Leg and joint stiffness may not be important factors in the development of running-related injuries. Moderate changes in leg and joint stiffness are unlikely to substantially alter injury risk.

Post-sprain versus post-fracture post-traumatic ankle osteoarthritis: Impact on foot and ankle kinematics and kinetics

BACKGROUND

Common etiologies for post-traumatic ankle osteoarthritis are ankle fractures and chronic ankle instability. As the nature of trauma is different for these two etiologies, it might be expected that the two subtypes of post-traumatic ankle osteoarthritis would display different foot mechanics during gait.

RESEARCH QUESTION

The objective of this exploratory cross-sectional study was to compare the foot kinematics and kinetics of patients suffering from post-fracture ankle osteoarthritis with those of patients suffering from post-sprain ankle osteoarthritis.

METHODS

Twenty-nine subjects with end-stage post-traumatic ankle osteoarthritis and fifteen asymptomatic control subjects participated in this study. All patients suffered from post-traumatic ankle osteoarthritis secondary to ankle-related fracture (Group 1; n = 15) or to chronic ankle instability (Group 2; n = 14). A four-segment kinematic and kinetic foot model was used to calculate intrinsic foot joint kinematics and kinetics during gait. Vector field statistical analysis MANOVA was used to assess differences between groups for the entire three-component intrinsic foot joint angles and moments.

RESULTS

MANOVA showed significant differences between the groups. Post-hoc analyses suggested that the differences between post-fracture ankle osteoarthritis group and controls were caused by a combination of less adducted Shank-Calcaneus position and less plantarflexion at this joint. Post-hoc analyses also suggested that both pathological groups exhibited a decreased plantarflexion moment for Shank-Calcaneus, Chopart, Lisfranc joints compared to controls. Analyses of both pathological groups versus controls for power suggested lower Shank-Calcaneus and Lisfranc power generation during pre-swing phase.

SIGNIFICANCE

No significant differences were found between the two pathological groups in this exploratory study. Alterations in foot kinematics and kinetics were mainly found about the dorsi-/plantarflexion axis during the pre-swing phase of the stance phase for both pathological groups compared to controls. Observed differences were not limited to the painful ankle joint, but seem also to have affected the kinetics of the neighbouring foot joints.

The ulnar collateral ligament loading paradox between in-vitro and in-vivo studies on baseball pitching (narrative review)

Ulnar collateral ligament (UCL) weakening or tears occur in 16% of professional baseball pitchers. To prevent players from sustaining a UCL injury, it is important to understand the relationship between the UCL properties and elbow stabilizers with the load on the UCL during pitching. In-vitro studies showed that the ultimate external valgus torque of 34 Nm would rupture the UCL, which is in apparent conflict with the reported peak valgus torques in pitching (40–120 Nm). Assuming both observations are correct, the question rises why ‘only’ 16 out of 100 professional pitchers sustain a UCL rupture. Underestimation of the effect of other structures in in-vivo studies is most likely the explanation of this mismatch because the calculated in-vivo torque also includes possible contributions of functional and structural stabilizers. In-vitro studies show that the flexor-pronator mass has the potential to counteract valgus torque directly, whereas the elbow flexor-extensor muscles combined with the humeroradial joint might have an indirect effect on valgus torque by increasing the joint compression force. Accurate experimental electromyography data and a more detailed (musculoskeletal)mechanical model of the elbow are needed to investigate if and to what extent the structural and functional stabilizers can shield the UCL during pitching.

Lower extremity joint kinematics of a simulated lateral ankle sprain after drop landings in participants with chronic ankle instability

This study examined lower extremity joint kinematics in individuals with chronic ankle instability (CAI) and controls during unanticipated and anticipated single-leg drop landings onto a laterally inclined platform. Physically active adults with CAI 15 (n = 15) and controls (n = 15) performed an unanticipated and anticipated 30 cm single-leg drop landing onto a 20° laterally inclined platform. Three-dimensional ankle, knee and hip-joint kinematics were recorded 200 ms pre- to 200 post-landing and analysed with a 2 (group) × 2 (landing condition) SPM ANOVA (p < 0.05). Results revealed individuals with CAI displayed significantly greater ankle internal rotation post-landing across both landing conditions. Anticipated landings elicited significantly greater pre-landing ankle inversion and external rotation, knee abduction and hip adduction. Additionally, significantly less ankle inversion, knee and hip flexion, and knee adduction and hip abduction were present during post-landing of the anticipated landing. Greater ankle internal rotation during landing may contribute to the ankle 'giving way' in individuals with CAI. However, preparatory and reactive proximal-joint kinematics were similar in both groups during landing. This highlights the possible role of the knee and hip joints in assisting with ankle-joint stability during anticipated inversion perturbations.

Computational modelling of muscle fibre operating ranges in the hindlimb of a small ground bird (Eudromia elegans), with implications for modelling locomotion in extinct species

The arrangement and physiology of muscle fibres can strongly influence musculoskeletal function and whole-organismal performance. However, experimental investigation of muscle function during in vivo activity is typically limited to relatively few muscles in a given system. Computational models and simulations of the musculoskeletal system can partly overcome these limitations, by exploring the dynamics of muscles, tendons and other tissues in a robust and quantitative fashion. Here, a high-fidelity, 26-degree-of-freedom musculoskeletal model was developed of the hindlimb of a small ground bird, the elegant-crested tinamou (Eudromia elegans, ~550 g), including all the major muscles of the limb (36 actuators per leg). The model was integrated with biplanar fluoroscopy (XROMM) and forceplate data for walking and running, where dynamic optimization was used to estimate muscle excitations and fibre length changes throughout both gaits. Following this, a series of static simulations over the total range of physiological limb postures were performed, to circumscribe the bounds of possible variation in fibre length. During gait, fibre lengths for all muscles remained between 0.5 to 1.21 times optimal fibre length, but operated mostly on the ascending limb and plateau of the active force-length curve, a result that parallels previous experimental findings for birds, humans and other species. However, the ranges of fibre length varied considerably among individual muscles, especially when considered across the total possible range of joint excursion. Net length change of muscle-tendon units was mostly less than optimal fibre length, sometimes markedly so, suggesting that approaches that use muscle-tendon length change to estimate optimal fibre length in extinct species are likely underestimating this important parameter for many muscles. The results of this study clarify and broaden understanding of muscle function in extant animals, and can help refine approaches used to study extinct species.

Three-dimensional data-tracking simulations of sprinting using a direct collocation optimal control approach

Biomechanical simulation and modelling approaches have the possibility to make a meaningful impact within applied sports settings, such as sprinting. However, for this to be realised, such approaches must first undergo a thorough quantitative evaluation against experimental data. We developed a musculoskeletal modelling and simulation framework for sprinting, with the objective to evaluate its ability to reproduce experimental kinematics and kinetics data for different sprinting phases. This was achieved by performing a series of data-tracking calibration (individual and simultaneous) and validation simulations, that also featured the generation of dynamically consistent simulated outputs and the determination of foot-ground contact model parameters. The simulated values from the calibration simulations were found to be in close agreement with the corresponding experimental data, particularly for the kinematics (average root mean squared differences (RMSDs) less than 1.0° and 0.2 cm for the rotational and translational kinematics, respectively) and ground reaction force (highest average percentage RMSD of 8.1%). Minimal differences in tracking performance were observed when concurrently determining the foot-ground contact model parameters from each of the individual or simultaneous calibration simulations. The validation simulation yielded results that were comparable (RMSDs less than 1.0° and 0.3 cm for the rotational and translational kinematics, respectively) to those obtained from the calibration simulations. This study demonstrated the suitability of the proposed framework for performing future predictive simulations of sprinting, and gives confidence in its use to assess the cause-effect relationships of technique modification in relation to performance. Furthermore, this is the first study to provide dynamically consistent three-dimensional muscle-driven simulations of sprinting across different phases.

Impact of foot modeling on the quantification of the effect of total ankle replacement: A pilot study

BACKGROUND

Kinematic and kinetic foot models showed that computing ankle joint angles, moments and power with a one-segment foot modeling approach alters kinematics and tends to overestimate ankle joint power. Nevertheless, gait studies continue to implement one-segment foot models to assess the effect of total ankle replacement.

RESEARCH QUESTION

The objective of this pilot study was to investigate the effect of the foot modeling approach (one-segment versus multi-segment) on how total ankle replacement is estimated to benefit or degrade the patient's biomechanical performance.

METHODS

Ten subjects with post-traumatic ankle osteoarthritis scheduled for total ankle replacement and 10 asymptomatic subjects were recruited. A one-segment and a multi-segment foot model were used to calculate intrinsic foot joints kinematics and kinetics during gait. A linear mixed model was used to investigate the effect of the foot model on ankle joint kinematic and kinetic analysis and the effect of total ankle replacement.

RESULTS

Differences in range of motion due to the foot model effect were significant for all the gait subphases of interest except for midstance. Peak power generation was significantly overestimated when computed with the one-segment foot model. Ankle and shank-calcaneus joint dorsi-/plantarflexion range of motion did not increase post-operatively except during the loading response phase. A significant 'group' effect was found for stance and pre-swing phase range of motion, with total ankle replacement patients showing lower range of motion values than controls for dorsi/plantarflexion.

SIGNIFICANCE

The outcome of this study showed that the 'foot model' had a significant effect on estimates of range of motion and power generation. The findings in our study therefore emphasize the clinical interest of multi-segment foot modeling when assessing the outcome of a therapeutic intervention.

The human foot functions like a spring of adjustable stiffness during running

Like other animals, humans use their legs like springs to save energy during running. One potential contributor to leg stiffness in humans is the longitudinal arch (LA) of the foot. Studies of cadaveric feet have demonstrated that the LA can function like a spring, but it is unknown whether humans can adjust LA stiffness in coordination with more proximal joints to help control leg stiffness during running. Here, we used 3D motion capture to record 27 adult participants running on a forceplate-instrumented treadmill, and calculated LA stiffness using beam bending and midfoot kinematics models of the foot. Because changing stride frequency causes humans to adjust overall leg stiffness, we had participants run at their preferred frequency and frequencies 35% above and 20% below preferred frequency to test for similar adjustments in the LA. Regardless of which foot model we used, we found that participants increased LA quasi-stiffness significantly between low and high frequency runs, mirroring changes at the ankle, knee and leg overall. However, among foot models, we found that the model incorporating triceps surae force into bending force on the foot produced unrealistically high LA work estimates, leading us to discourage this modeling approach. Additionally, we found that there was not a consistent correlation between LA height and quasi-stiffness values among the participants, indicating that static LA height measurements are not good predictors of dynamic function. Overall, our findings support the hypothesis that humans dynamically adjust LA stiffness during running in concert with other structures of the leg.

Functional muscle synergies to support the knee against moment specific loads while weight bearing

OBJECTIVE

Externally applied abduction and rotational loads are major contributors to the knee joint injury mechanism; yet, how muscles work together to stabilize the knee against these loads remains unclear. Our study sought to evaluate lower limb functional muscle synergies in healthy young adults such that muscle activation can be directly related to internal knee joint moments.

METHODS

Concatenated non-negative matrix factorization extracted muscle and moment synergies of 22 participants from electromyographic signals and joint moments elicited during a weight-bearing force matching protocol.

RESULTS

Two synergy sets were extracted: Set 1 included four synergies, each corresponding to a general anterior, posterior, medial, or lateral force direction. Frontal and transverse moments were coupled during medial and lateral force directions. Set 2 included six synergies, each corresponding to a moment type (extension/flexion, ab/adduction, internal/external rotation). Hamstrings and quadriceps dominated synergies associated with respective flexion and extension moments while quadriceps-hamstring co-activation was associated with knee abduction. Rotation moments were associated with notable contributions from hamstrings, quadriceps, gastrocnemius, and hip ab/adductors, corresponding to a general co-activation muscle synergy.

CONCLUSION

Our results highlight the importance of muscular co-activation of all muscles crossing the knee to support it during injury-inducing loading conditions such as externally applied knee abduction and rotation. Functional muscle synergies can provide new insight into the relationship between neuromuscular control and knee joint stability by directly associating biomechanical variables to muscle activation.

Non-extension movements inducing over half the mechanical energy directly contributing to jumping height in human running single-leg jump

The running single-leg jump (RSLJ), including certain non-extension movements (movements not induced by lower-limb extension works), is the highest jumping mode in humans. Here, we show the substantial contributions of non-extension movements, in generating mechanical energy directly contributing to the jumping height (E_vert) in RSLJ. We determined the component of increase in E_vert due to each segment movement in RSLJs by 13 male high-jumpers. The stance-leg shank forward rotation (rotation opposite to the actions of the knee extensors and ankle plantar flexors on the shank), increased E_vert (0.76 ± 0.70 J/kg). E_vert due to the stance-leg thigh forward rotation (4.39 ± 0.57 J/kg) was substantially larger than the inflowing energy into the thigh (difference: 2.36 ± 0.42 J/kg). These results suggest that the forward rotations of the shank and thigh transformed horizontal kinetic energy (E_hori) to E_vert.E_vert was increased by the elevation of the free-leg side of the pelvis (0.53 ± 0.22 J/kg) and rotation of free-leg thigh (1.52 ± 0.26 J/kg). The non-extension movements contributed to over half (59 ± 6%) the increase in E_vert during the take-off phase. Human-specific morphologies are essential for the contributions of non-extension movements; fully extensible knee joints and relatively longer legs with respect to body mass for the transformation from E_hori to E_vert by shank and thigh rotations, and a wide and short pelvis for increasing E_vert by pelvic elevation. This study provides quantifiable evidence to indicate how substantially non-extension movements contribute to higher RSLJ.

An Extensive Set of Kinematic and Kinetic Data for Individuals with Intact Limbs and Transfemoral Prosthesis Users

This paper introduces an extensive human motion data set for typical activities of daily living. These data are crucial for the design and control of prosthetic devices for transfemoral prosthesis users. This data set was collected from seven individuals, including five individuals with intact limbs and two transfemoral prosthesis users. These data include the following types of movements: (1) walking at three different speeds; (2) walking up and down a 5-degree ramp; (3) stepping up and down; (4) sitting down and standing up. We provide full-body marker trajectories and ground reaction forces (GRFs) as well as joint angles, joint velocities, joint torques, and joint powers. This data set is publicly available at the website referenced in this paper. Data from flexion and extension of the hip, knee, and ankle are presented in this paper. However, the data accompanying this paper (available on the internet) include 46 distinct measurements and can be useful for validating or generating mathematical models to simulate the gait of both transfemoral prosthesis users and individuals with intact legs.

Efficient trajectory optimization for curved running using a 3D musculoskeletal model with implicit dynamics

Trajectory optimization with musculoskeletal models can be used to reconstruct measured movements and to predict changes in movements in response to environmental changes. It enables an exhaustive analysis of joint angles, joint moments, ground reaction forces, and muscle forces, among others. However, its application is still limited to simplified problems in two dimensional space or straight motions. The simulation of movements with directional changes, e.g. curved running, requires detailed three dimensional models which lead to a high-dimensional solution space. We extended a full-body three dimensional musculoskeletal model to be specialized for running with directional changes. Model dynamics were implemented implicitly and trajectory optimization problems were solved with direct collocation to enable efficient computation. Standing, straight running, and curved running were simulated starting from a random initial guess to confirm the capabilities of our model and approach: efficacy, tracking and predictive power. Altogether the simulations required 1 h 17 min and corresponded well to the reference data. The prediction of curved running using straight running as tracking data revealed the necessity of avoiding interpenetration of body segments. In summary, the proposed formulation is able to efficiently predict a new motion task while preserving dynamic consistency. Hence, labor-intensive and thus costly experimental studies could be replaced by simulations for movement analysis and virtual product design.

Biomechanical measures of short-term maximal cycling on an ergometer: a test-retest study

An understanding of test-retest reliability is important for biomechanists, such as when assessing the longitudinal effect of training or equipment interventions. Our aim was to quantify the test-retest reliability of biomechanical variables measured during short-term maximal cycling. Fourteen track sprint cyclists performed 3 × 4 s seated sprints at 135 rpm on an isokinetic ergometer, repeating the session 7.6 ± 2.5 days later. Joint moments were calculated via inverse dynamics, using pedal forces and limb kinematics. EMG activity was measured for 9 lower limb muscles. Reliability was explored by quantifying systematic and random differences within- and between-session. Within-session reliability was better than between-sessions reliability. The test-retest reliability level was typically moderate to excellent for the biomechanical variables that describe maximal cycling. However, some variables, such as peak knee flexion moment and maximum hip joint power, demonstrated lower reliability, indicating that care needs to be taken when using these variables to evaluate biomechanical changes. Although measurement error (instrumentation error, anatomical marker misplacement, soft tissue artefacts) can explain some of our reliability observations, we speculate that biological variability may also be a contributor to the lower repeatability observed in several variables including ineffective crank force, ankle kinematics and hamstring muscles' activation patterns.

Estimating the Effects of Awareness on Neck-Muscle Loading in Frontal Impacts with EMG and MC Sensors

Critical traffic situations, such as vehicle collisions and emergency manoeuvres, can cause an occupant to respond with reflex and voluntary actions. These affect the occupant's position and dynamic loading during interactions with the vehicle's restraints, possibly compromising their protective function. Electromyography (EMG) is a commonly used method for measuring active muscle response and can also provide input parameters for computer simulations with models of the human body. The recently introduced muscle-contraction (MC) sensor is a wearable device with a piezo-resistive element for measuring the force of an indenting tip pressing against the surface of the body. The study aimed to compare how data collected simultaneously with EMG, video motion capture, and the novel MC sensor are related to neck-muscle loading. Sled tests with low-severity frontal impacts were conducted, assuming two different awareness conditions for seated volunteers. The activity of the upper trapezius muscle was measured using surface EMG and MC sensors. The neck-muscle load F was estimated from an inverse dynamics analysis of the head's motion captured in the sagittal plane. The volunteers' response to impact was predominantly reflexive, with significantly shorter onset latencies and more bracing observed when the volunteers were aware of the impact. Cross-correlations between the EMG and MC, EMG and F, and F and MC data were not changed significantly by the awareness conditions. The MC signal was strongly correlated (r = 0.89) with the neck-muscle loading F in the aware and unaware conditions, while the mean ΔF-MC delays were 21.0 ± 15.1 ms and 14.6 ± 12.4 ms, respectively. With the MC sensor enabling a consistent measurement-based estimation of the muscle loading, the simultaneous acquisition of EMG and MC signals improves the assessment of the reflex and voluntary responses of a vehicle's occupant subjected to low-severity loading.