An Innovative Compact System to Measure Skiing Ground Reaction Forces and Flexural Angles of Alpine and Touring Ski Boots.

Skiing is a popular winter activity spanning various subdisciplines. Key hardware are ski boots, bindings, and skis, which are designed to withstand loads generated during skiing. Obtaining service forces and moments has always been challenging to researchers in the past. The goal of the present study is to develop and test a lightweight and compact measurement system to obtain the Ground Reaction Forces and the kinematics for ski touring and alpine ski. To do so, we adapted two six-axis load cells to fit into ski touring and alpine skis adding 20 mm height and 500 g weight to the original ski. To measure kinematics, we created custom angular sensors from rotary potentiometers. The system was tested indoors using a force platform and motion capture system before a first set of field tests in which the sensors were used to measure ski touring and alpine skis kinetics and kinematics. Validation trials showed maximum errors of 10% for kinetics and 5% for kinematics. Field tests showed data in agreement with previous findings on the topic. The results of this study show the possibility of using our system to study biomechanics and equipment performances for ski touring, alpine skiing, and possibly other disciplines.

Neural correlates of user learning during long-term BCI training for the Cybathlon competition.

BACKGROUND: Brain-computer interfaces (BCIs) are systems capable of translating human brain patterns, measured through electroencephalography (EEG), into commands for an external device. Despite the great advances in machine learning solutions to enhance the performance of BCI decoders, the translational impact of this technology remains elusive. The reliability of BCIs is often unsatisfactory for end-users, limiting their application outside a laboratory environment. METHODS: We present the analysis on the data acquired from an end-user during the preparation for two Cybathlon competitions, where our pilot won the gold medal twice in a row. These data are of particular interest given the mutual learning approach adopted during the longitudinal training phase (8 months), the long training break in between the two events (1 year) and the demanding evaluation scenario. A multifaceted perspective on long-term user learning is proposed: we enriched the information gathered through conventional metrics (e.g., accuracy, application performances) by investigating novel neural correlates of learning in different neural domains. RESULTS: First, we showed that by focusing the training on user learning, the pilot was capable of significantly improving his performance over time even with infrequent decoder re-calibrations. Second, we revealed that the analysis of the within-class modifications of the pilot's neural patterns in the Riemannian domain is more effective in tracking the acquisition and the stabilization of BCI skills, especially after the 1-year break. These results further confirmed the key role of mutual learning in the acquisition of BCI skills, and particularly highlighted the importance of user learning as a key to enhance BCI reliability. CONCLUSION: We firmly believe that our work may open new perspectives and fuel discussions in the BCI field to shift the focus of future research: not only to the machine learning of the decoder, but also in investigating novel training procedures to boost the user learning and the stability of the BCI skills in the long-term. To this end, the analyses and the metrics proposed could be used to monitor the user learning during training and provide a marker guiding the decoder re-calibration to maximize the mutual adaptation of the user to the BCI system.

Optimising classification of proximal arm strength impairment in wheelchair rugby: A proof of concept study.

This study examined the relationship between proximal arm strength and mobility performance in wheelchair rugby (WR) athletes and examined whether a valid structure for classifying proximal arm strength impairment could be determined. Fifty-seven trained WR athletes with strength impaired arms and no trunk function performed six upper body isometric strength tests and three 10 m sprints in their rugby wheelchair. All strength measures correlated with 2 m and 10 m sprint times (r ≥ -0.43; p ≤ 0.0005) and were entered into k-means cluster analyses with 4-clusters (to mirror the current International Wheelchair Rugby Federation [IWRF] system) and 3-clusters. The 3-cluster structure provided a more valid structure than both the 4-cluster and existing IWRF system, as evidenced by clearer differences in strength (Effect sizes [ES] ≥ 1.0) and performance (ES ≥ 1.1) between adjacent clusters and stronger mean silhouette coefficient (0.64). Subsequently, the 3-cluster structure for classifying proximal arm strength impairment would result in less overlap between athletes from adjacent classes and reduce the likelihood of athletes being disadvantaged due to their impairment. This study demonstrated that the current battery of isometric strength tests and cluster analyses could facilitate the evidence-based development of classifying proximal arm strength impairment in WR.

A Novel Multi-Axial Pressure Sensor Probe for Measuring Triaxial Stress States Inside Soft Materials.

This paper presents the concept, design, construction, and validation of a novel probe based on the hexadic disposition of six pressure sensors suitable for measuring triaxial stress states inside bulky soft materials. The measurement of triaxial stress states inside bulk materials such as brain tissue surrogates is a challenging task needed to investigate internal organs' stress states and validate FE models. The purpose of the work was the development and validation of a 17 × 17 × 17 mm probe containing six pressure sensors. To do so, six piezoresistive pressure sensors of 6 mm diameter were arranged into an hexad at three cartesian axes and bisecting angles, based on the analytical solution of the stress tensor. The resulting probe was embedded in a soft silicone rubber of known characteristics, calibrated under cyclic compression and shear in three orientations, and statically validated with combined loads. A calibration matrix was computed, and validation tests allowed us to estimate Von Mises stress under combined stress with an error below 6%. Hence, the proposed probe design and method can give indications about the complex stress state developing internally to soft materials under triaxial high-strain fields, opening applications in the analysis of biological models or physical surrogates involving parenchyma organs.

Application of Inertial Motion Unit-Based Kinematics to Assess the Effect of Boot Modifications on Ski Jump Landings-A Methodological Study.

Biomechanical studies of winter sports are challenging due to environmental conditions which cannot be mimicked in a laboratory. In this study, a methodological approach was developed merging 2D video recordings with sensor-based motion capture to investigate ski jump landings. A reference measurement was carried out in a laboratory, and subsequently, the method was exemplified in a field study by assessing the effect of a ski boot modification on landing kinematics. Landings of four expert skiers were filmed under field conditions in the jump plane, and full body kinematics were measured with an inertial motion unit (IMU) -based motion capture suit. This exemplary study revealed that the combination of video and IMU data is viable. However, only one skier was able to make use of the added boot flexibility, likely due to an extended training time with the modified boot. In this case, maximum knee flexion changed by 36° and maximum ankle flexion by 13°, whereas the other three skiers changed only marginally. The results confirm that 2D video merged with IMU data are suitable for jump analyses in winter sports, and that the modified boot will allow for alterations in landing technique provided that enough time for training is given.

Development of Instrumented Running Prosthetic Feet for the Collection of Track Loads on Elite Athletes.

Knowledge of loads acting on running specific prostheses (RSP), and in particular on running prosthetic feet (RPF), is crucial for evaluating athletes' technique, designing safe feet, and biomechanical modelling. The aim of this work was to develop a J-shaped and a C-shaped wearable instrumented running prosthetic foot (iRPF) starting from commercial RPF, suitable for load data collection on the track. The sensing elements are strain gauge bridges mounted on the foot in a configuration that allows decoupling loads parallel and normal to the socket-foot clamp during the stance phase. The system records data on lightweight athlete-worn loggers and transmits them via Wi-Fi to a base station for real-time monitoring. iRPF calibration procedure and static and dynamic validation of predicted ground-reaction forces against those measured by a force platform embedded in the track are reported. The potential application of this wearable system in estimating determinants of sprint performance is presented.

Moderate treadmill run worsened static but not dynamic postural stability of healthy individuals.

PURPOSE: Running has been demonstrated to be one of the most relevant exercise in altering static postural stability, while limiting attention has been paid to its effects on dynamic postural stability. The aim of the present study was to investigate if 25 min of moderate running on a treadmill altered static and dynamic postural stability in healthy subjects. METHODS: Eight female and six male participants (age 27.7 ± 8.3 years, height 170.9 ± 12.2 cm, weight 63.9 ± 15.6 kg) took part in the study. Before and after the run static postural stability was evaluated on a stabilometric platform (10 trials of 30 s each), while dynamic postural stability was assessed on an instrumented unstable platform (2 trials of 30 s each). RESULTS: After the treadmill run the area of the confident ellipse (from 67.97 ± 34.56 to 93.08 ± 50.00 mm2), sway path velocity (from 6.92 ± 1.85 to 7.83 ± 2.57 mm/s), sway area velocity (from 6.88 ± 3.27 to 9.54 ± 5.36 mm2/s), and medio-lateral maximal oscillation (from 9.48 ± 2.80 to 11.44 ± 3.64 mm) significantly increased. Stabilogram diffusion analysis showed no statistically significant difference in the diffusion coefficients, both short and long term. No statistically significant differences were reported in all the parameters of the dynamic postural stability test. CONCLUSION: The contrasting results of the static and dynamic postural stability tests raise the question of which are the more selective tests to assess the acute effect of physical exercise on postural stability among healthy individuals. The proper interaction of both static and dynamic postural evaluations could represent the next challenge in the postural stability assessment.

Gait analysis before and after achilles tendon surgical suture in a single-subject study: a case report.

Achilles tendon rupture is a disabling injury that requires a long recovery time. We describe a unique case of a 46-year-old male who had undergone gait analysis as part of a personal physical examination and who, 16 months later, ruptured his left Achilles tendon while running. With gait kinematic and kinetic data available both before and after his injury, we determined the residual gait asymmetries on his uninjured side and compared the pre- and postinjury measurements. We analyzed his gait at 1, 4, and 7 weeks after his return to full weightbearing. Compared with the preinjury values, at 7 weeks he had almost complete range of motion in his left ankle (-2%) and a slight increase in gait velocity (+6%) and cadence (+3%). The peak power of his injured ankle was 90% of its preinjury value. In contrast, the unaffected ankle was at 118%. These observations suggest that measuring the asymmetries of the gait cycle, especially at the beginning of rehabilitation, can be used to improve treatment. We had the patient strengthen his ankle using a stationary bicycle before he returned to running. Kinetics also appears to be more powerful than kinematics in detecting functional asymmetries associated with reduced calf strength, even 15 weeks after surgery. Gait analysis could be used to predict the effectiveness of rehabilitation protocols and help calibrate and monitor the return to sports participation while preventing overloading muscle and tendon syndromes.

A digital process to replicate the socket-foot alignment in below-knee running specific prostheses.

A well-fitting socket and a fine-tuned foot alignment are crucial elements in a running-specific prosthesis to allow Paralympic athletes with below-knee amputation to express their full competitive potential. For this reason, once a satisfactory socket-foot configuration is established after dynamic alignment, it is fundamental to reproduce the same conditions when constructing the definitive carbon fiber socket, and when renewing or constructing a back-up prosthesis, without dismantling the original. In addition, to cope with emerging needs of the athlete, it would be beneficial to implement fine-tuning adjustments of the alignment in a very controlled manner. At present, this requires elaborate bench procedures, which tend to be expensive, time consuming, prone to manual errors, cumbersome in use and most often require damaging or disposing of the current socket. In this study, we propose an original CAD/CAM workflow that allows replicating the desired socket-foot configuration for below-knee sprinting prostheses, as well as performing socket adaptations and introducing fine-tuning adjustments to the alignments. The workflow is exemplified with reference to two case studies involving elite Paralympic runners with transtibial and partial foot amputations, respectively.

Digital design and fabrication of multi-material hand orthoses to allow an athlete with scleroderma to play sitting volleyball.

Scleroderma is a chronic and progressive autoimmune disorder of connective tissues often causing lesions and deformities of the hands. Individuals affected by this condition experience daily life limitations and are typically unable to take part in sport activities that involve impacts on the hands. In this article we describe the design and manufacturing of custom-made hand orthoses to play sitting volleyball, for an elite paralympic athlete affected by scleroderma. The devices consist of a carbon fibre shell with an internal silicone padding and an external polymeric multilayer cover. The manufacturing of the orthoses involves digital modelling, 3D printing, composite lamination and an innovative method to create a strong and durable chemical bonding between silicone and carbon fibre. The internal silicone padding proved to be effective in hosting and protecting the hands, whereas the external shell with polymeric multilayer cover allowed to dampen the ball shocks while effectively hitting the ball. Indeed, these devices allowed the athlete to take part in the 2020 Tokyo Paralympic games and were used for two years without showing any damage.

Comparative evaluation of two skiing simulators as functional training devices for recreational skiers.

The aims of this study were to examine two ski simulators, Skimagic and Skier's Edge, and to evaluate their efficacy as functional training devices for skiers. Vertical ground reaction forces, knee flexion angle kinematics and muscles activity were recorded on these devices and compared with those measured in similar condition while skiing on snow. Five ski instructors performed three randomized testing sessions (snow, Skimagic and Skier's Edge). During the testing sessions, vertical ground reaction forces were recorded by means of pressure insoles in synchronisation with a portable data logger that collected values of knee flexion-extension and EMG activation of rectus femoris and vastus medialis. EMG activations and ground reaction forces measured while skiing on simulators were lower than on snow. Although less overall EMG activation was present on the simulators, the pattern of EMG activity was closer to real snow on Skimagic than on Skiers' Edge. Results of the present study suggested that the two devices are not effectively applicable for strength training. However, based on the recorded EMG patterns, the Skimagic treadmill is potentially suitable to act as a functional training device for recreational skiers provided that an increase of speed and slope on Skimagic could induce a closer matching of the studied biomechanical parameters with the snow skiing conditions. Key pointsEMG activation and ground reaction forces were lower on both simulators with respect to snow.Both simulators were not able to provide an effective contribution to strength development for skiers.In term of functional training Skier's Edge showed a predominance of concentric action over eccentric which is in contrast with competitive skiing.Skimagic treadmill could be potentially suitable to act as a functional training device for recreational skiers only if an increase of speed and slope will induce a closer matching of the studied biomechanical parameters with the snow skiing conditions.

Biomechanical determinants of top running speeds in para-athletes with unilateral transfemoral amputation.

BACKGROUND: An increased understanding of biomechanical determinants that influence the sprint performance of para-athletes with a unilateral transfemoral amputation will provide us with a basis for better evaluating athletes' sprint performance and would be expected to aid in the development of more effective training methods and running-specific prosthesis selection guidelines. OBJECTIVES: The aim of this study was to investigate the relative contributions of mechanical determinants to the top running speeds of para-athletes with unilateral transfemoral amputation wearing a running-specific prosthesis. STUDY DESIGN: Observational study within the subject. METHODS: Nine para-athletes with unilateral transfemoral amputation wearing a running-specific prosthesis were recruited in this study. They were asked to run at their respective constant top speeds on an instrumented treadmill. From the ground reaction force and spatiotemporal parameters, three mechanical variables-step frequency, mass-specific averaged vertical ground-reaction force, and contact length-were determined for both the affected and unaffected limbs. RESULTS: Stepwise regression analysis showed that the contact length of the affected limb was significant and an independent factor of top running speed ( ß = 0.760, P < 0.05), with a coefficient of determination ( R2 ) of 0.577 ( P < 0.05), whereas the other variables were not associated. CONCLUSION: These results suggest that prosthetic components and alignment are crucial to determining the maximal sprinting performance in uTFA.

Static strength of lower-limb prosthetic sockets: An exploratory study on the influence of stratigraphy, distal adapter and lamination resin.

Knowledge about the mechanical properties of lower-limb prosthetic sockets fabricated with resin infusion lamination and composite materials is limited. Therefore, sockets can be subject to mechanical failure and over-dimensioning, both of which can have severe consequences for patients. For this reason, an exploratory study was conducted to analyze the effect of stratigraphy (layup and fibers), matrix (resin) and mechanical connection (socket distal adapter) on socket static strength, with the objectives of: 1) implementing a mechanical testing system for lower-limb prosthetic sockets based on ISO 10328:2016 and provide the mechanical design of the loading plates, 2) apply the testing system to a series of laminated sockets, and 3) for each type of distal adapter, identify the combinations of stratigraphy and matrix with acceptable strength and minimum weight. Twenty-three laminated sockets were produced and tested. Sixteen met the required strength, with ten exhibiting an excessive weight. Among the remaining six, four combinations of stratigraphy and resin were identified as best option, as they all overcame ISO 10328 P6 loading level and weighted less than 600 g. The selected stratigraphies had limited or absent amount of Perlon stockinettes, which seems to increase weight without enhancing the mechanical strength. Sockets based on Ossur MSS braids and connector show the best compromise between strength and weight when the amount of carbon braids is halved.

Interpersonal synchronization of movement intermittency.

Most animal species group together and coordinate their behavior in quite sophisticated manners for mating, hunting, or defense purposes. In humans, coordination at a macroscopic level (the pacing of movements) is evident both in daily life (e.g., walking) and skilled (e.g., music and dance) behaviors. By examining the fine structure of movement, we here show that interpersonal coordination is established also at a microscopic - submovement - level. Natural movements appear as marked by recurrent (2-3 Hz) speed breaks, i.e., submovements, that are traditionally considered the result of intermittency in (visuo)motor feedback-based control. In a series of interpersonal coordination tasks, we show that submovements produced by interacting partners are not independent but alternate tightly over time, reflecting online mutual adaptation. These findings unveil a potential core mechanism for behavioral coordination that is based on between-persons synchronization of the intrinsic dynamics of action-perception cycles.

The effect of foot setting on kinematic and kinetic skiing parameters during giant slalom: A single subject study on a Paralympic gold medalist sit skier.

OBJECTIVES: Aim was to study the effect of monoski foot adjustment on kinematic and kinetic skiing parameters expressing sit skier's technique. DESIGN: Independent variable was skier position with respect to bindings, acting on position of monoski foot sole clamp. Front (F), Mid (M) and Rear (R) settings changed with intervals of 20mm. Course time, skiing speed, Ground Reaction Forces (GRFs) magnitude and point of application and damper stroke were dependent variables. METHOD: A Paralympic monoski was equipped with a dynamometric binding plate measuring GRFs, roll and pitch moments. A Paralympic gold medalist (LW10-1) was involved. Skier trajectory and gates location were measured by a differential global navigation satellite system (GNSS) in steep and medium steep slope portions. The athlete performed two giant slalom runs for each foot setting the same day. RESULTS: GRFs, center of pressure (COP) and variations with foot settings were measured. Peaks values up to 3.36 times the total weight and damper speed of 675mm/s in compression were found. Fastest runs, highest peak loads and best subjective ratings were recorded with F setting. COP mean values were influenced by foot adjustments. GRFs in left turns were 54% larger than in the right turns with F setting on steep slope. CONCLUSIONS: The monoski foot adjustment influenced kinematic and kinetic skiing, with F setting showing best results. A skier asymmetric behavior between right and left turning was discovered. Findings can support the design of monoskis for a wider dissemination of Paralympic alpine sit skiing.

Innovative alignment of sprinting prostheses for persons with transfemoral amputation: Exploratory study on a gold medal Paralympic athlete.

BACKGROUND: Recommendations for the alignment of the socket and foot in the sprinting prosthesis of athletes with transfemoral amputation are either based on walking biomechanics or lack public scientific evidence. OBJECTIVES: To explore the biomechanical changes and the sensations of a gold medal Paralympic sprinter, while running with three bench alignments: a conventional reference (A0), an innovative alignment based on the biomechanics of elite able-bodied sprinters (A2), and an intermediate alignment (A1). STUDY DESIGN: Single subject with repeated measures. METHODS: A1 and A2 feature a progressively greater socket tilt and a plantar-flexed foot compared to A0. The 30-year-old female athlete trained with three prostheses, one per alignment, for at least 2 months. We administered a questionnaire to collect her impressions. Then, she ran on a treadmill at full speed (5.5 m/s). We measured the kinematics and moments of the prosthetic side, and the ground reaction forces of both sides. RESULTS: A2 reduced the prosthetic side hip extension at foot-off while preserving hip range of motion, decreased the impulse of the hip moment, and increased the horizontal propulsion, leaving sufficient margin to prevent knee buckling without increasing sound side braking forces. Biomechanical outcomes matched well with subjective impressions. CONCLUSIONS: A2 appears promising to improve the performance and comfort of sprinters with transfemoral amputation, without compromising safety. CLINICAL RELEVANCE: Observation of elite able-bodied sprinters led to the definition of a new specific alignment for the sprinting prosthesis of athletes with transfemoral amputation, which appears promising to improve performance and comfort, without compromising safety. This may constitute a major improvement compared to alignments based on walking biomechanics.

Influence of different ranges of motion on selective recruitment of shoulder muscles in the sitting military press: an electromyographic study.

Popular fitness literature suggests that varying the elbow range of motion (ROM) during the Military press can lead up to specific muscle isolation especially for deltoid and trapezius muscles. The purpose of the study was to examine the effect of ROM at different loads on the electromyographic (EMG) activity of 8 preselected muscles. Six experienced lifters performed 3 sets of 10 repetitions, each one with a different ROM: the first one with a final elbow angle of 90 degrees (R1); the second with 135 degrees (R2), and the last one with a final elbow angle of 180 degrees (R3). Three resistances were chosen (no load, 30% of one repetition maximum [1-RM], and 70% of 1-RM), and sets were separated by 5 minutes rest. Electromyographic surface electrodes were placed on the clavicular head of pectoralis major, anterior deltoid, medial deltoid (MD), posterior deltoid (PD), upper trapezius, middle trapezius (MT), long head of triceps, and teres minor (TM). Analysis of variance showed a significant increase of rmsEMG activation with the widest ROM for each muscle and for each load condition except in MT and TM and PD with no load. The results showed that the use of the widest ROM increased the EMG activity of all the muscles selected with respect to the closest one, whereas this effect is not totally confirmed with the employment of R2. In addition, the use of intermediate ROMs was able to isolate the activity of the MD with respect to the trapezius only in the condition of the heaviest load. This suggests to coaches that in strength development programs the employment of an incomplete ROM can reduce the involvement of the trapezius without decreasing medium deltoid activation only with heavy loads.

Personalized Tests in Paralympic Athletes: Aerobic and Anaerobic Performance Profile of Elite Wheelchair Rugby Players.

In Paralympic sports, the goal of functional classifications is to minimize the impact of impairment on the outcome of the competition. The present cross-sectional study aimed to investigate aerobic and anaerobic personalized tests in Paralympic athletes and to correlate them with the classification of the international wheelchair rugby federation (IWRF). Sixteen elite players of the Italian wheelchair rugby team volunteered for the study. Aerobic (incremental test to exhaustion) and anaerobic (Wingate 30s all-out test, 5 and 10-meter sprint test, shuttle test, isometric test) sport-performance measurements were correlated singularly or grouped (Z scores) with the classification point. Moreover, a multivariate permutation-based ranking analysis investigated possible differences in the overall level of performance among the adjacent classified groups of players, considering the scores of each test. A statistically significant correlation between the performance parameters and the IWRF functional classification considering both aerobic and anaerobic personalized tests was detected (0.58 ≤ r ≤ 0.88; 0.0260 ≤ p ≤ 0.0001). The multivariate permutation-based ranking analysis showed differences only for the low-pointers versus mid-pointers (p = 0.0195) and high-pointers (p = 0.0075). Although single performance parameters correlated with athletes' classification point, results of the multivariate permutation-based ranking analysis seem to suggest considering only the most significant anaerobic and sport-specific performance parameters among athletes. These should be combined with the physical assessment and the qualitative observation, which are already part of the classification process to improve its effectiveness.

Kinematic bidimensional analysis of the propulsion technique in wheelchair rugby athletes.

Wheelchair rugby is a sport ideated for individuals with cervical spinal cord injury (CSCI) which is extremely important for maintaining their neuromuscular abilities and improving their social and psychological wellbeing. However, due to the frequent changes in direction and speed it considerably stresses the players' upper limbs. 13 athletes have undergone two sports-related tests on an inertial drum bench and several kinematic parameters have been registered. Most athletes use a semi-circular pattern which is considered protective for the upper limb. With increasing speed, range of motion (ROM) increases. Release angles increment and contact angles reduce, displacing the push angle forward to increase speed. Instead, the more anterior late push angle used to increase velocity is a factor which further loads the shoulder joint. However, other factors affecting propulsion technique, such as posture and wheelchair set up should be studied to further reduce loading on the upper limb.