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Horizontal decelerations are frequently performed during team sports and are closely linked to sports performance and injury. This study aims to provide a comprehensive description of the kinetic demands of decelerations at the whole-body, structural, and tissue-specific levels of the musculoskeletal system. Team-sports athletes performed maximal-effort horizontal decelerations whilst full-body kinematics and ground reaction forces (GRFs) were recorded. A musculoskeletal model was used to determine whole-body (GRFs), structural (ankle, knee, and hip joint moments and contact forces), and tissue (twelve lower-limb muscle forces) loads. External GRFs in this study, especially in the horizontal direction, were up to six times those experienced during accelerated or constant-speed running reported in the literature. To cope with these high external forces, large joint moments (hip immediately after touchdown; ankle and knee during mid and late stance) and contact forces (ankle, knee, hip immediately after touchdown) were observed. Furthermore, eccentric force requirements of the tibialis anterior, soleus, quadriceps, and gluteal muscles were particularly high. The presented loading patterns provide the first empirical explanations for why decelerating movements are amongst the most challenging in team sports and can help inform deceleration-specific training prescription to target horizontal deceleration performance, or fatigue and injury resistance in team-sports athletes. [ABSTRACT FROM AUTHOR]

In order to address gaps in the literature, this study assessed the reproducibility (i.e., difference between and within sessions) of joint and muscle forces using wearable sensors during stationary cycling. Seventeen male cyclists performed two sessions on a cycle ergometer cycling at a combination of three power outputs (1.5, 2.5 and 3.5 W/kg) and three pedalling cadences (60, 80 and 100 rpm) in two sessions (2–7 days apart). The first trial from each session was repeated at the end of the session for assessment of within-session reproducibility. Three-dimensional (3D) full-body motion and 3D bilateral pedal forces were collected using an inertial motion tracking system and a pair of instrumented pedals, respectively. Joint angles, muscle forces and knee joint forces were computed using OpenSim. Poor to excellent agreement (ICCs = 0.31–0.99) was observed and differences were trivial to small and non-significant between trials within-session. Poor to excellent agreement (ICCs = 0.05–0.97) was observed and differences were trivial to large between sessions. Variability can be attributed to changes in muscle recruitment strategies (within and between-sessions) and to repositioning of sensors (between-sessions). [ABSTRACT FROM AUTHOR]

The current study aimed to explore the effects of different footwear on kinetics, kinematics and muscle forces during the barbell back squat in both male and female lifters using Bayesian modelling. Twelve male and twelve female lifters completed squats at 70% of their 1 repetition maximum, in four different footwear conditions (Adidas weightlifting shoe, Inov-8 weightlifting shoe, Cross-fit and minimal footwear). Three-dimensional kinematics were measured using an eight-camera motion analysis system, ground reaction forces using a force platform and muscle/joint forces using musculoskeletal modelling techniques. Differences between footwear were examined using Bayesian 4 (FOOTWEAR) * 2 (GENDER) mixed ANOVA's. Peak quadriceps force was greater in the Adidas (male = 89.78/female = 70.56 N/kg), Cross-fit (male = 92.41/female = 70.82 N/kg) and Inov-8 (male = 91.57/female = 68.21 N/kg) conditions compared to minimal footwear (male = 82.61/female = 64.40 N/kg). In addition, peak patellofemoral stress and patellar tendon forces were greater in the Adidas (patellar tendon force: male = 64.67/female = 42.89 N/kg & patellofemoral stress: male = 143.21/female = 118.92 KPa/kg), Cross-fit (patellar tendon force: male = 67.89/female = 43.52 N/kg & patellofemoral stress: male = 146.02/female = 114.73 KPa/kg) and Inov-8 (patellar tendon force: male = 64.08/female = 41.04 N/kg & patellofemoral stress: male = 193.09/female = 169.09 KPa/kg) conditions compared to minimal footwear (patellar tendon force: male = 56.75/female = 39.92 N/kg & patellofemoral stress: male = 134.06/female = 108.91 KPa/kg). Finally, angular ROM was greater in the minimal footwear (male = 28.04/female = 33.75°) compared to the Adidas (male = 26.85/female = 30.73°) and Inov-8 (male = 26.92/female = 32.63°) conditions. The findings from the current investigation therefore indicate that weightlifting footwear may be able to enhance lower extremity muscle development and improve squat biomechanics owing to a reduced trunk angular ROM; however, this is likely to be at the expense of increased knee joint loading. [ABSTRACT FROM AUTHOR]

Gastrocnemius is a premier muscle crossing the knee, but its role in knee biomechanics and on the anterior cruciate ligament (ACL) remains less clear when compared to hamstrings and quadriceps. The effect of changes in gastrocnemius force at late stance when it peaks on the knee joint response and ACL force was initially investigated using a lower extremity musculoskeletal model driven by gait kinematics—kinetics. The tibiofemoral joint under isolated isometric contraction of gastrocnemius was subsequently analyzed at different force levels and flexion angles (0°–90°). Changes in gastrocnemius force at late stance markedly influenced hamstrings forces. Gastrocnemius acted as ACL antagonist by substantially increasing its force. Simulations under isolated contraction of gastrocnemius confirmed this role at all flexion angles, in particular, at extreme knee flexion angles (0° and 90°). Constraint on varus/valgus rotations substantially decreased this effect. Although hamstrings and gastrocnemius are both knee joint flexors, they play opposite roles in respectively protecting or loading ACL. Although the quadriceps is also recognized as antagonist of ACL, at larger joint flexion and in contrast to quadriceps, activity in gastrocnemius substantially increased ACL forces (anteromedial bundle). The fact that gastrocnemius is an antagonist of ACL should help in effective prevention and management of ACL injuries. [ABSTRACT FROM PUBLISHER]

Clinical gait analysis provides great contributions to the understanding of gait patterns. However, a complete distribution of muscle forces throughout the gait cycle is a current challenge for many researchers. Two techniques are often used to estimate muscle forces: inverse dynamics with static optimization and computer muscle control that uses forward dynamics to minimize tracking. The first method often involves limitations due to changing muscle dynamics and possible signal artefacts that depend on day-to-day variation in the position of electromyographic (EMG) electrodes. Nevertheless, in clinical gait analysis, the method of inverse dynamics is a fundamental and commonly used computational procedure to calculate the force and torque reactions at various body joints. Our aim was to develop a generic musculoskeletal model that could be able to be applied in the clinical setting. The musculoskeletal model of the lower limb presents a simulation for the EMG data to address the common limitations of these techniques. This model presents a new point of view from the inverse dynamics used on clinical gait analysis, including the EMG information, and shows a similar performance to another model available in the OpenSim software. The main problem of these methods to achieve a correct muscle coordination is the lack of complete EMG data for all muscles modelled. We present a technique that simulates the EMG activity and presents a good correlation with the muscle forces throughout the gait cycle. Also, this method showed great similarities whit the real EMG data recorded from the subjects doing the same movement. [ABSTRACT FROM PUBLISHER]

The estimation of muscle forces in musculoskeletal shoulder models is still controversial. Two different methods are widely used to solve the indeterminacy of the system: electromyography (EMG)-based methods and stress-based methods. The goal of this work was to evaluate the influence of these two methods on the prediction of muscle forces, glenohumeral load and joint stability after total shoulder arthroplasty. An EMG-based and a stress-based method were implemented into the same musculoskeletal shoulder model. The model replicated the glenohumeral joint after total shoulder arthroplasty. It contained the scapula, the humerus, the joint prosthesis, the rotator cuff muscles supraspinatus, subscapularis and infraspinatus and the middle, anterior and posterior deltoid muscles. A movement of abduction was simulated in the plane of the scapula. The EMG-based method replicated muscular activity of experimentally measured EMG. The stress-based method minimised a cost function based on muscle stresses. We compared muscle forces, joint reaction force, articular contact pressure and translation of the humeral head. The stress-based method predicted a lower force of the rotator cuff muscles. This was partly counter-balanced by a higher force of the middle part of the deltoid muscle. As a consequence, the stress-based method predicted a lower joint load (16% reduced) and a higher superior–inferior translation of the humeral head (increased by 1.2 mm). The EMG-based method has the advantage of replicating the observed cocontraction of stabilising muscles of the rotator cuff. This method is, however, limited to available EMG measurements. The stress-based method has thus an advantage of flexibility, but may overestimate glenohumeral subluxation. [ABSTRACT FROM AUTHOR]

The central tenet of this study was to develop, validate and apply various individualised 3D musculoskeletal models of the human body for application to single-leg landings over increasing vertical heights and horizontal distances. While contributing to an understanding of whether gender differences explain the higher rate of non-contact anterior cruciate ligament (ACL) injuries among females, this study also correlated various musculoskeletal variables significantly impacted by gender, height and/or distance and their interactions with two ACL injury-risk predictor variables; peak vertical ground reaction force (VGRF) and peak proximal tibia anterior shear force (PTASF). Kinematic, kinetic and electromyography data of three male and three female subjects were measured. Results revealed no significant gender differences in the musculoskeletal variables tested except peak VGRF (p = 0.039) and hip axial compressive force (p = 0.032). The quadriceps and the gastrocnemius muscle forces had significant correlations with peak PTASF (r = 0.85,p < 0.05 andr = − 0.88,p < 0.05, respectively). Furthermore, hamstring muscle force was significantly correlated with peak VGRF (r = − 0.90,p < 0.05). The ankle flexion angle was significantly correlated with peak PTASF (r = − 0.82,p < 0.05). Our findings indicate that compared to males, females did not exhibit significantly different muscle forces, or ankle, knee and hip flexion angles during single-leg landings that would explain the gender bias in non-contact ACL injury rate. Our results also suggest that higher quadriceps muscle force increases the risk, while higher hamstring and gastrocnemius muscle forces as well as ankle flexion angle reduce the risk of non-contact ACL injury. [ABSTRACT FROM AUTHOR]

A basic task in biomechanics is the precise analysis of human movements and the investigation of muscle forces that are responsible for these movements. When using inverse dynamics with a focus on the lower extremities, the knee model type is of major interest, as it is well known that the calculated muscle forces depend on the knee model type. It is essential to use individually parameterized models for the knee joint as well as for the femoropatellar joint while analysing the correlations between external and internal loads and the efficiency of specific training exercises for the lower extremities. It will be shown that different knee model types and femoropatellar model types have a major influence on calculated muscle forces. Within this study the multi-body system model was applied to leg extension movements performed on a leg press machine. Concerning the adjustment of a leg press machine, the following two questions were considered: How should a leg press machine be adjusted for individual exercises taking into account the minimization of knee strain? Does the muscular strain correspond to the load calculated and applied externally? The results of this application show that the knee strain could be reduced by 10% after simulative variation of the boundary conditions given by the leg press machine. [ABSTRACT FROM AUTHOR]

The goal of this study is to use motion capture data in order to determine muscle forces involved in the flexion/extension of the human elbow. First, we apply an inverse kinematics algorithm to obtain joint angles from marker positions; next we compute an inverse dynamics algorithm to obtain joint torques, with a generic dynamical model of the human arm designed by using Matlab-Simulink™ Simmechanics. These torques are used in an optimization algorithm under nonlinear constraints in order to compute the muscle forces involved in flexion of the elbow. We propose some results for an extension motion of the elbow, and several solutions to improve and extend the model in order to implement it in a real-time application. [ABSTRACT FROM AUTHOR]

Deficits in movement and bite force are common in patients following segmental resection of the mandible consequent to oral cancer or injury. We have previously developed a dynamic model to analyse the biomechanics of an ungrafted segmental jaw resection with unilateral muscle and joint loss and post-surgical scarring. Here, we describe an inverse-modelling algorithm for automatically predicting muscle activations in the model for prescribed jaw movement and bite-force production. We present the results of simulations that postulate combined muscle activation patterns that could theoretically be used by patients to overcome post-surgical deficits. Such predictions could be the basis for future muscle retraining in clinical cases. [ABSTRACT FROM AUTHOR]

Knowledge of musculoskeletal loading conditions in humans is mandatory for the design of endoprosthestic and osteosynthetic devices. Also, new treatment options such as tissue generation and transplantation require knowledge of the mechanical loads under which tissue formation and regeneration takes place. In this manuscript, a database on musculo-skeletal loading of the proximal femur is presented. The data are based on individual patient gait and radiological data. By means of inverse dynamics and optimization techniques, the internal loads acting at the joint and within the muscles have been determined. The calculated hip contact force has been validated by means of in vivo measurements in four patients. The database is freely available and gives an estimate on internal loads acting at the proximal femur for activities like walking and stair climbing. [ABSTRACT FROM AUTHOR]

This study assessed the maximum pushing force that could be exerted by freestanding subjects, using thumbs only, on a small surface located in one of three horizontal positions at nine heights ranging from 13·5 to 169·9 cm above the floor. Each of 102 subjects made nine force exertion trials. Data are given on the cumulative percentages of subjects who could exert various forces at each of the 27 locations. An analysis of variance showed a highly significant effect due to location of the surface and highly significant interactions of location of the surface and trial presentation direction (top-down or bottom-up); of location of the surface and trial presentation pattern; and of location of the surface, trial presentation direction and trial presentation pattern. Maximum forces are exerted at about waist height and are increasingly reduced with increasing distances above and below the optimum location. Right-sided access to pushing surfaces is favoured over left-sided access. [ABSTRACT FROM PUBLISHER]

The article presents a study on the forces that act on masticatory muscles and temporomandibular (TM) joint on mastication. The study utilizes three-dimensional (3D) model of mandible and skull which was experimentally analyzed for chewing force with the use of a 3D force micro sensor. Results show that the calculated TM joint forces are higher on the specimen balance side while smaller on the bolus side, which indicates that the calculated muscle forces are higher on the bolus side.