Strength and activity of the protractor and retractor muscles of the asymptomatic dyskinetic scapula.

The role of scapular dyskinesis as a risk factor of shoulder injury has been largely discussed. However, most studies have focused on symptomatic patients and less is known on the asymptomatic dyskinetic scapula. Removing the confounding effects of the pathologies could contribute to better characterize the scapula dyskinesis. As muscle properties (strength, fatigue, nerve injury …) have been identified as causative factors of scapular dyskinesis, this study focuses specifically on characterizing the protractor and retractor muscles of the dyskinetic scapula. Thirteen asymptomatic dyskinetic volunteers were compared to eleven asymptomatic non-dyskinetic control volunteers. Muscle characteristics were evaluated in terms of maximal strength, fatigue resistance and electromyographic activity during a functional closed-chained task. The results did not identify kinematic or muscle activity significant differences between the dyskinetic and the control group even in fatigue conditions. However, the results demonstrated that protractors vs. retractors fatigue resistance ratios were imbalanced (<0.8) in the dyskinetic group and significantly lower than in the non-dyskinetic one. Our study suggests that that strength imbalances are not necessarily related to the presence of pain at the shoulder joint. These results demonstrated the importance to complete the clinical assessments of the scapula with strength evaluations even for asymptomatic sport practitioners.

Optimizing the performance of convolutional neural network for enhanced gesture recognition using sEMG.

Deep neural networks (DNNs) have demonstrated higher performance results when compared to traditional approaches for implementing robust myoelectric control (MEC) systems. However, the delay induced by optimising a MEC remains a concern for real-time applications. As a result, an optimised DNN architecture based on fine-tuned hyperparameters is required. This study investigates the optimal configuration of convolutional neural network (CNN)-based MEC by proposing an effective data segmentation technique and a generalised set of hyperparameters. Firstly, two segmentation strategies (disjoint and overlap) and various segment and overlap sizes were studied to optimise segmentation parameters. Secondly, to address the challenge of optimising the hyperparameters of a DNN-based MEC system, the problem has been abstracted as an optimisation problem, and Bayesian optimisation has been used to solve it. From 20 healthy people, ten surface electromyography (sEMG) grasping movements abstracted from daily life were chosen as the target gesture set. With an ideal segment size of 200 ms and an overlap size of 80%, the results show that the overlap segmentation technique outperforms the disjoint segmentation technique (p-value < 0.05). In comparison to manual (12.76 ± 4.66), grid (0.10 ± 0.03), and random (0.12 ± 0.05) search hyperparameters optimisation strategies, the proposed optimisation technique resulted in a mean classification error rate (CER) of 0.08 ± 0.03 across all subjects. In addition, a generalised CNN architecture with an optimal set of hyperparameters is proposed. When tested separately on all individuals, the single generalised CNN architecture produced an overall CER of 0.09 ± 0.03. This study's significance lies in its contribution to the field of EMG signal processing by demonstrating the superiority of the overlap segmentation technique, optimizing CNN hyperparameters through Bayesian optimization, and offering practical insights for improving prosthetic control and human-computer interfaces.

Evolution of the trophy position along the tennis serve player's development.

The trophy position is a coaching cue for the tennis serve that usually corresponds to the racquet high point (RHP) during the preparatory action for the stroke. Mastering this position and its time of occurrence seems essential in overarm movements like in the tennis serve. Clinicians and coaches have a real interest in understanding the trophy position and its evolution during the development of the elite players at different ages. A 3D motion system was used to measure the kinematics of the serve. A group of high-level tennis players were selected for three different age groups: 8 adults (ITN 1), 8 teenagers (ITN 3) and 8 children (ITN 5-6). Results show a modified pattern sequence of the tennis serve between children and adult players. RHP appears earlier relative to impact for children (-0.54 ± 0.10 s) than for adults (-0.36 ± 0.11 s) and teenagers (-0.33 ± 0.05 s) (p = 0.007). At RHP, children present lower trunk transverse plane rotation (p < 0.003) and higher shoulder external rotation (p < 0.003). These positions for the child players may represent an increased risk of shoulder and trunk injury than for older players and contribute to a lower racquet resultant velocity at impact.

Tight shoulders: A clinical, kinematic and strength comparison of symptomatic and asymptomatic male overhead athletes before and after stretching.

A tightness of the posterior structures of the throwing shoulder has been hypothesised to be associated with injuries and pain because of alterations of the scapular kinematics and muscular imbalances. The aims of this study were to identify the clinical and biomechanical profile of symptomatic and asymptomatic overhead athletes with a tight shoulder and to evaluate the efficiency of a self-applied stretching program. Twenty male overhead athletes were recruited. Half of them reported a painful shoulder at the beginning of the study. For four weeks, the volunteers performed daily stretching exercises. Before and after the stretching program, gleno-humeral mobility, scapular kinematics, rotator muscles strength and pain were evaluated. Before stretching, the main difference between the groups was more impingement syndrome and rotator cuff tendon lesion positive tests in the symptomatic group (p < 0.027, effect size = 0.51). After the program, pain reported by the symptomatic volunteers was reduced by approximately 40% and the gleno-humeral internal rotation bilateral difference was significantly reduced by 77.6% (p < 0.009, effect size = 0.84). In the symptomatic group, the scapula at rest was significantly more posteriorly tilted (p = 0.027, effect size = 0.69) after the stretching; a position that has been shown to limit the risk of impingement. The absence of significant differences of the profiles of the symptomatic and asymptomatic overhead athletes before stretching may indicate that the initiation of early prevention programs, including self-applied stretching, should not rely solely on biomechanical and clinical parameters and might be recommended to all players with a tight shoulder.

Normalizing gastrocnemius muscle EMG signal: An optimal set of maximum voluntary isometric contraction tests for young adults considering reproducibility.

BACKGROUND: Even though most studies normalize the surface EMG signal of the gastrocnemius muscle using a single position of maximum voluntary isometric contraction (MVIC), several studies tend to indicate that several positions are in fact needed to obtain a maximal voluntary activation (MVA) for most of the subjects. However, no combination of positions has already been described. RESEARCH QUESTION: A combination of MVIC positions to normalize the EMG signal of the gastrocnemius muscle is investigated. the influence of using several positions on the reproducibility of the normalization process is evaluated. METHODS: Twenty healthy volunteers (45 % female - 55 % male, 25.4 years (SD 4.3), 72.6 kg (SD 13.9), 1.78 m (SD 0.12)) were recruited. Six positions for MVIC were compared and the effect of several normalization combinations on a functional task (gait) was evaluated. RESULTS: Several positions are needed to obtain at least 90 % of the MVA for 90 % of the volunteers even though the use of a single well-chosen position (unipodal standing position with knee fully extended and ankle fully plantar-flexed) will lead to no statistically significant differences of the gait evaluation during stance phase. For each position, five repetitions of the MVIC are recommended to obtain a valid MVA. SIGNIFICANCE: This study confirms that using several MVIC positions is recommended when possible to normalize the gastrocnemius muscle EMG signal. However, in the situation of a patient where limited MVIC attempts are possible, using a single well-chosen position should not significantly influence the amplitude and the reproducibility of the measures.

Activation Profile of Scapular Stabilizing Muscles in Asymptomatic People: Does Scapular Dyskinesis Have an Impact on It?

OBJECTIVE: The aim of the study was to assess the activation profile of scapular stabilizing muscles in dyskinetic asymptomatic people. DESIGN: This is a noninterventional observational study. Two groups of 20 people were included in the study. The first group involved asymptomatic athletes with scapular dyskinesis. The second one included athletes without scapular dysfunction. Muscle activation of upper trapezius, lower trapezius, and serratus anterior were recorded by a surface electromyography during shoulder flexion and shoulder abduction, in unloaded and loaded conditions. RESULTS: A significant increase of the activity of the upper trapezius (between 23% and 31%) and a significant decrease of the activity of the lower trapezius (between 32% and 65%) were observed in the dyskinetic group in comparison with the nondyskinetic group in asymptomatic athletes. A significant increase between 17% and 31% of the activity of the serratus anterior was also observed in dyskinetic people. Likewise, a significant increase approximately 24%-61% and 23%-70% was noted respectively in upper trapezius/lower trapezius and upper trapezius/serratus anterior ratio's in the dyskinetic group. CONCLUSIONS: An alteration of periscapular muscular activation exists in dyskinetic asymptomatic people. Future studies will be needed to know whether those alterations increase the risk of shoulder injuries.

Kinesiotaping for scapular dyskinesis: The influence on scapular kinematics and on the activity of scapular stabilizing muscles.

Scapular dyskinesis is observed in 61% of overhead athletes (Burn et al., 2016). For most of them, it remains asymptomatic. However, scapular dyskinesis is considered a risk factor for shoulder injury by some authors (Clarsen et al., 2014). The aim of this study is to explore the effectiveness of kinesiotaping in modifying scapular kinematics and peri-scapular muscle activity in dyskinetic athletes. The 3-dimensional position and orientation of the scapula as well as the activation of upper trapezius, lower trapezius and serratus anterior were recorded in twenty asymptomatic athletes during shoulder movements (flexion and abduction), in loaded and unloaded conditions and in three circumstances (standard, kinesiotaping 1, kinesiotaping 2). A significant decrease between 9 and 12% in upper trapezius activity was observed with kinesiotaping 1 and 2. Lower trapezius activity was slightly increased with kinesiotaping 1 while it was significantly decreased about 15-20% with kinesiotaping 2. No change was observed in serratus anterior activity, for either kinesiotaping 1 or 2. Considering scapular kinematics, both kinesiotaping 1 and 2 significantly increased posterior tilt and upward rotation. External rotation was decreased with kinesiotaping 2, in comparison to standard condition. Kinesiotaping, and especially taping 1, seems to be an effective method for changing periscapular muscle activity and scapular kinematics.

A foot/ground contact model for biomechanical inverse dynamics analysis.

The inverse dynamics simulation of the musculoskeletal system is a common method to understand and analyse human motion. The ground reaction forces can be accurately estimated by experimental measurements using force platforms. However, the number of steps is limited by the number of force platforms available in the laboratory. Several numerical methods have been proposed to estimate the ground reaction forces without force platforms, i.e., solely based on kinematic data combined with a model of the foot-ground contact. The purpose of this work is to provide a more efficient method, using a unilaterally constrained model of the foot at the center of pressure to compute the ground reaction forces. The proposed model does not require any data related with the compliance of the foot-ground contact and is kept as simple as possible. The indeterminacy in the force estimation is handled using a least square approach with filtering. The relative root mean square error (rRMSE) between the numerical estimations and experimental measurements are 4.1% for the vertical component of the ground reaction forces (GRF), 11.2% for the anterior component and 5.3% for the ground reaction moment (GRM) in the sagittal plane.

Using supervised learning machine algorithm to identify future fallers based on gait patterns: A two-year longitudinal study.

INTRODUCTION: Given their major health consequences in the elderly, identifying people at risk of fall is a major challenge faced by clinicians. A lot of studies have confirmed the relationships between gait parameters and falls incidence. However, accurate tools to predict individual risk among independent older adults without a history of falls are lacking. OBJECTIVE: This study aimed to apply a supervised learning algorithm to a data set recorded in a two-year longitudinal study, in order to build a classification tree that could discern subsequent fallers based on their gait patterns. METHODS: A total of 105 adults aged >65 years, living independently at home and without a recent fall history were included in a two-year longitudinal study. All underwent physical and functional assessment. Gait speed, stride length, frequency, symmetry and regularity, and minimum toe clearance were recorded in comfortable, fast and dual task walking conditions in a standardized laboratory environment. Fall events were recorded using personal falls diaries. A supervised machine learning algorithm (J48) has been applied to the data recorded at inclusion in order to obtain a classification tree able to identify future fallers. RESULTS: Based on fall information from 96 volunteers, a classification tree correctly identifying 80% of future fallers based on gait patterns, gender, and stiffness, was obtained, with accuracy of 84%, sensitivity of 80%, specificity of 87%, a positive predictive value of 78%, and a negative predictive value of 88%. DISCUSSION: While the performances of the classification tree warrant further confirmation, it is the first predictive tool based on gait parameters that are identified (not clustered) allowing its use by other research teams. CONCLUSION: This original longitudinal pilot study using a supervised machine learning algorithm, shows that gait parameters and clinical data can be used to identify future fallers among independent older adults.

Gait symmetry in the dual task condition as a predictor of future falls among independent older adults: a 2-year longitudinal study.

BACKGROUND: Given the potential consequences of falls among older adults, a major challenge is to identify people at risk before the first event. In this context, gait parameters have been suggested as markers of fall risk. AIM: To examine, among older people, the prospective relationship between gait patterns assessed in comfortable and challenging walking conditions, and future fall(s). METHOD: A total of 105 adults older than 65 years, living independently at home and without a recent fall history were included in a 2-year, longitudinal, observational study. All underwent physical and functional assessment. Gait speed, stride length, frequency, symmetry and regularity and Minimum Toe Clearance (MTC) were recorded in comfortable (CW), fast (FW) and dual task walking (DTW) conditions. Gait parameter changes occurring between CW and FW and between CW and DTW were calculated and expressed in percent. DTW cost was calculated as the change of DTW relative to CW. Fall events were recorded using fall diaries. Comparisons according to fall occurrence were performed by means of univariate analysis and multivariate binary logistic regression analysis. RESULTS: Two-year follow-up was available for 96 participants, of whom 35 (36.5%) fell at least once. Comparative analysis showed that future fallers had shorter FW stride length and higher symmetry DTW cost than non-fallers (p < 0.05). Binary logistic regression analysis showed that each additional percent of stride symmetry cost was associated with an increase in future fall risk (odds ratio 1.018, 95% Confidence Interval (CI) 1.002-1.033; p = 0.027). DISCUSSION: Our results confirm the association between a symmetry decrease in DTW and future fall(s). Indeed in this study, the mean symmetry DTW cost in fallers is almost 20% higher than in non-fallers, meaning a fall risk that is around 36% higher than among non-fallers. CONCLUSION: This exploratory study shows the usefulness of considering gait parameters, particularly symmetry in challenging walking conditions, for early identification of future fallers.

Inter-Session Reliability of the Tennis Serve and Influence of the Laboratory Context.

To meet the demand of a player's entourage (e.g., coaches and medical staff), it is important for the biomechanics specialist to perform repeatable measures. To the best of our knowledge, to date, it has not been demonstrated whether similar results are obtained between two sessions of testing or between laboratory and field sport kinematic protocols with regard to the tennis serve. This study had two primary aims. First, the inter-session repeatability of biomechanical variables of a tennis serve was evaluated. Second, the differences between laboratory and field evaluations were studied. Thirteen national tennis players (ITN 3) performed the same 28 markers' set laboratory test twice two weeks apart, and other thirteen national players (ITN 3) performed two 4 markers' set tests both in the laboratory and on an official tennis court one week apart. A 3D motion system was used to measure lower-limb, pelvis, trunk, dominant arm and racket kinematics. A force plate was used to evaluate kinetics of legs' drive in the laboratory. A personal method based on a point scoring system was developed to evaluate the ball landing location accuracy. We observed that the majority of the studied variables were acceptable for excellent relative reliability for the inter-session analysis. We also showed that the impact of the laboratory versus field context on the player's serve was limited.

Reliability of unipodal and bipodal counter movement jump landings in a recreational male population.

Movement patterns during landing have been suggested to be related to injury risk. The purpose of this study was to determine the inter-session reliability of kinematic variables and ground reaction forces during landing in a population of male recreational athletes after a counter movement jump. Both unipodal and bipodal landings were evaluated. Furthermore, the possibility to improve landing reliability with a verbal instruction was also studied. Twenty-four male volunteers with no history of lower extremity trauma were randomly assigned to two groups (with and without verbal landing instruction). An optoelectronic 3D system and force plates were used to measure the lower limb joint angles and the ground reaction forces during landing. Intraclass correlation values show moderate to excellent inter-session reliability for the bipodal task (ICC average: 0.80, range: 0.46-0.97) and poor to excellent reliability for the unipodal task (ICC average: >0.75, range: 0.20-0.95). However, large standard errors of measurement values at the ankle joint at impact (27.6 ± 11.5°) and for the vertical ground reaction forces (394 ± 1091 N) show that some variables may not be usable in practice. The verbal instruction had a negative effect on the reliability of unipodal landing but improved the reliability of bipodal landing. These findings show that the reliability of a landing task is influenced by its motor complexity as well as the instruction given to the subject.

Normalizing shoulder EMG: An optimal set of maximum isometric voluntary contraction tests considering reproducibility.

Normalization of the electromyography (EMG) signal is often performed relatively to maximal voluntary activations (MVA) obtained during maximum isometric voluntary contraction (MVIC). The first aim was to provide an inter-session reproducible protocol to normalize the signal of eight shoulder muscles. The protocol should also lead to a level of activation >90% of MVA for >90% of the volunteers. The second aim was to evaluate the influence of the method used to extract the MVA from the EMG envelope on the normalized EMG signal. Thirteen volunteers performed 12 MVICs twice (one week interval). Several time constants (100ms to 2s) were compared when extracting the MVA from the EMG envelope. The EMG activity was also acquired during an arm elevation. Our results show that a combination of nine MVIC tests was required to meet our requirements including reproducibility. Both the number of MVIC tests and the size of the time constant influence the normalized EMG signal during the dynamic activity (variations up to 15%). A time constant of 1s was a good compromise to extract the MVA. These findings are valuable to improve the reproducibility of EMG signal normalization.

Biomechanical analysis of abdominal injury in tennis serves. A case report.

The serve is an important stroke in any high level tennis game. A well-mastered serve is a substantial advantage for players. However, because of its repeatability and its intensity, this stroke is potentially deleterious for upper limbs, lower limbs and trunk. The trunk is a vital link in the production and transfer of energy from the lower limbs to the upper limbs; therefore, kinematic disorder could be a potential source of risk for trunk injury in tennis. This research studies the case of a professional tennis player who has suffered from a medical tear on the left rectus abdominis muscle after tennis serve. The goal of the study is to understand whether the injury could be explained by an inappropriate technique. For this purpose, we analyzed in three dimensions the kinematic and kinetic aspects of the serve. We also performed isokinetic tests of the player's knees. We then compared the player to five other professional players as reference. We observed a possible deficit of energy transfer because of an important anterior pelvis tilt. Some compensation made by the player during the serve could be a possible higher abdominal contraction and a larger shoulder external rotation. These particularities could induce an abdominal overwork that could explain the first injury and may provoke further injuries. Key pointsIn the proximal-distal sequence, energy is transmitted from lower limbs to upper limps via trunk.The 3D analysis tool is an indispensable test for an objective evaluation of the kinematic in the tennis serve.Multiple evaluations techniques are useful for fuller comprehension of the kinematics and contribute to the awareness of the player's staff concerning pathologies and performance.

Development and validation of an accelerometer-based method for quantifying gait events.

An original signal processing algorithm is presented to automatically extract, on a stride-by-stride basis, four consecutive fundamental events of walking, heel strike (HS), toe strike (TS), heel-off (HO), and toe-off (TO), from wireless accelerometers applied to the right and left foot. First, the signals recorded from heel and toe three-axis accelerometers are segmented providing heel and toe flat phases. Then, the four gait events are defined from these flat phases. The accelerometer-based event identification was validated in seven healthy volunteers and a total of 247 trials against reference data provided by a force plate, a kinematic 3D analysis system, and video camera. HS, TS, HO, and TO were detected with a temporal accuracy ± precision of 1.3 ms ± 7.2 ms, -4.2 ms ± 10.9 ms, -3.7 ms ± 14.5 ms, and -1.8 ms ± 11.8 ms, respectively, with the associated 95% confidence intervals ranging from -6.3 ms to 2.2 ms. It is concluded that the developed accelerometer-based method can accurately and precisely detect HS, TS, HO, and TO, and could thus be used for the ambulatory monitoring of gait features computed from these events when measured concurrently in both feet.

Merging multi-camera data to reduce motion analysis instrumental errors using Kalman filters.

In motion capture systems, markers are often seen by multiple cameras. All cameras do not measure the position of the markers with the same reliability because of environmental factors such as the position of the marker in the field of view or the light intensity received by the cameras. Kalman filters offer a general framework to take the reliability of the various cameras into account and consequently improve the estimation of the marker position. The proposed process can be applied to both passive and active systems. Several reliability models of the cameras are compared for the Codamotion active system, which is considered as a specific illustration. The proposed method significantly reduces the noise in the signal, especially at long-range distances. Therefore, it improves the confidence of the positions at the limits of the field of view.

Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations.

BACKGROUND: The contralateral shoulder is often used as a reference when evaluating a pathologic shoulder. However, the literature provides contradictory results regarding the symmetry of the scapular pattern in a healthy population. We assume that several factors including gender and type of motion may influence the bilateral symmetry of the scapulae. MATERIALS AND METHODS: The dominant and nondominant shoulders of 2 populations of men and women comprising 11 subjects each were evaluated for 3 distinct motions: flexion in the sagittal plane, abduction in the frontal plane, and glenohumeral internal/external rotation with the arm abducted at 90°. Posture, kinematics, and range of motion were studied separately. RESULTS: Asymmetries are observed for motions performed in the frontal and sagittal plane but not for internal/external rotation with the arm abducted at 90°. For both male and female populations, multiplanar asymmetries are observed and the dominant scapula has a larger upward rotation. The asymmetries mainly originate in the scapula's kinematics and not in its original posture. CONCLUSION: Small but significant asymmetries exist between the dominant and nondominant shoulders in terms of kinematics. One should be aware of these differences when using the contralateral shoulder as a reference. LEVEL OF EVIDENCE: Basic science study, kinematics