Gregor Kuntze

A biomechanical analysis of common lunge tasks in badminton.

Abstract The lunge is regularly used in badminton and is recognized for the high physical demands it places on the lower limbs. Despite its common occurrence, little information is available on the biomechanics of lunging in the singles game. A video-based pilot study confirmed the relatively high frequency of lunging, ∼15% of all movements, in competitive singles games. The biomechanics and performance characteristics of three badminton-specific lunge tasks (kick, step-in, and hop lunge) were investigated in the laboratory with nine experienced male badminton players. Ground reaction forces and kinematic data were collected and lower limb joint kinetics calculated using an inverse dynamics approach. The step-in lunge was characterized by significantly lower mean horizontal reaction force at drive-off and lower mean peak hip joint power than the kick lunge. The hop lunge resulted in significantly larger mean reaction forces during loading and drive-off phases, as well as significantly larger mean peak ankle joint moments and knee and ankle joint powers than the kick or step-in lunges. These findings indicate that, within the setting of this investigation, the step-in lunge may be beneficial for reducing the muscular demands of lunge recovery and that the hop lunge allows for higher positive power output, thereby presenting an efficient lunging method.

Towards real-time profiling of sprints using wearable pressure sensors

On-body sensor systems for sport are challenging since the sensors must be lightweight and small to avoid discomfort, and yet robust and highly accurate to withstand and capture the fast movements associated with sport. In this work, we detail our experience of building such an on-body system for track athletes. The paper describes the design, implementation and deployment of an on-body sensor system for sprint training sessions. We autonomously profile sprints to derive quantitative metrics to improve training sessions. Inexpensive Force Sensitive Resistors (FSRs) are used to capture foot events that are subsequently analysed and presented back to the coach. We show how to identify periods of sprinting from the FSR data and how to compute metrics such as ground contact time. We evaluate our system using force plates and show that millisecond-level accuracy is achievable when estimating contact times.

A low-cost accurate speed-tracking system for supporting sprint coaching:

Accurate speed and split-time information on sprinters is crucial in coaching support. Furthermore, speed and stride parameters (i.e. contact time, stride frequency, and stride length) are important in research on the biomechanics of running. Existing speed-tracking systems for sprinting are expensive, unable to support multiple competing athletes, involve a complicated set-up procedure, or are not sufficiently accurate. This paper describes the design, evaluation results, and application scenarios of a novel, practical, and cost-effective light-sensor network system (commissioned at the National Indoor Athletics Centre, Cardiff, UK) that is capable of capturing criterion-comparable split-time information on simultaneously competing sprinters for long- and short-term coaching support and for biomechanics and sports science research purposes. This unique system is specifically designed to support coaching activities on a daily basis. It was also shown that the light-sensor network system can be integrated with other body-attached measurement systems to achieve continuous tracking of position, speed, and stride parameters of a race.

Rigorous Geometric Self-Calibrating Bundle Adjustment for a Dual Fluoroscopic Imaging System

High-speed dual fluoroscopy is a noninvasive imaging technology for three-dimensional skeletal kinematics analysis that finds numerous biomechanical applications. Accurate reconstruction of bone translations and rotations from dual-fluoroscopic data requires accurate calibration of the imaging geometry and the many imaging distortions that corrupt the data. Direct linear transformation methods are commonly applied for performing calibration using a two-step process that suffers from a number of potential shortcomings including that each X-ray source and corresponding camera must be calibrated separately. Consequently, the true imaging set-up and the constraints it presents are not incorporated during calibration. A method to overcome such drawbacks is the single-step self-calibrating bundle adjustment method. This procedure, based on the collinearity principle augmented with imaging distortion models and geometric constraints, has been developed and is reported herein. Its efficacy is shown with a carefully controlled experiment comprising 300 image pairs with 48 507 image points. Application of all geometric constraints and a 31 parameter distortion model resulted in up to 91% improvement in terms of precision (model fit) and up to 71% improvement in terms of 3-D point reconstruction accuracy (0.3-0.4 mm). The accuracy of distance reconstruction was improved from 0.3±2.0 mm to 0.2 ±1.1 mm and angle reconstruction accuracy was improved from -0.03±0.55° to 0.01±0.06°. Such positioning accuracy will allow for the accurate quantification of in vivo arthrokinematics crucial for skeletal biomechanics investigations.

A wearable and flexible Bracelet computer for on-body sensing

Small-size, light-weight, flexible and programmable, yet low-cost sensor node is one of the keys to enable Wireless Sensor Network (WSN) research and a wide range of user applications. In this paper, the Bracelet computer is presented. The system is designed to be flexible and wearable that it supports a range of daughter boards of users choice, and provides different ways for the boards to be connected to the main processor board. Despite a range of features, the monetary cost of the system is kept low. An application of the system — which uses the same wireless board as the Bracelet computer for localising a running athlete — is presented in this paper to demonstrate the applicability of the system. The localisation results show that the system achieves an average positional error of 28.945cm.

Profiling sprints using on-body sensors

This paper describes the design, implementation and deployment of a wireless sensor system for athletes. The system is designed to profile sprints based on input from on-body sensors that are wirelessly connected to a nearby infrastructure. We discuss the choice and use of inexpensive Force Sensitive Resistors (FSRs) to measure foot event timings and provide a detailed analysis of the profiling method used to represent high-level information to the coaches and athletes. In this profiling method, we detect sprinting intervals from high-resolution sensor data, and compute the ground contact times for sprinting performances. We validate our results using force plates and show that the system achieves comparable accuracy in measuring the foot contact times (millisecond accuracy) without the limitations of one or few steps.

Exercise Therapy in Juvenile Idiopathic Arthritis: A Systematic Review and Meta-Analysis

OBJECTIVE To conduct a systematic review to evaluate the efficacy of exercise interventions in improving outcomes across domains of functioning and disability in children and adolescents with juvenile idiopathic arthritis (JIA). DATA SOURCES Seven electronic databases were systematically searched up to November 16, 2016. STUDY SELECTION Original data, analytic prospective design, physical therapy-led exercise intervention evaluation, children and adolescents with JIA, and assessment of functional, structural, activity, participation, or quality of life outcomes. DATA EXTRACTION Two authors screened search results, and discrepancies were resolved by consensus. Of 5037 potentially relevant studies, 9 randomized controlled trials and 1 cohort study were included and scored. DATA SYNTHESIS Study quality (Downs and Black quality assessment tool) and level of evidence (Oxford Centre of Evidence-Based Medicine model) were assessed and meta-analysis conducted where appropriate. Alternatively, a descriptive summary approach was chosen. All randomized controlled trials were moderate-quality intervention studies (level 2b evidence; median Downs and Black score, 20 out of 32; range, 15-27). Interventions included aquatic, strengthening, proprioceptive, aerobic, and Pilates exercises. Pediatric activity capacity (Child Health Assessment Questionnaire) improved with exercise (mean difference, .45; 95% confidence interval, .05-.76). Furthermore, descriptive summaries indicated improved activity capacity, body function and structure (pain and muscle strength), and quality of life outcomes. CONCLUSIONS Exercise therapy appears to be well tolerated and beneficial across clinically relevant outcomes in patients with JIA. The paucity of high-quality evidence and study heterogeneity limited the ability to provide conclusive, generalizing evidence for the efficacy of exercise therapy and to provide specific recommendations for clinical practice at this time. Future research evaluating exercise program implementation using validated outcomes and detailed adherence and safety assessment is needed to optimize clinical decision pathways in patients with JIA.

Validating Dual Fluoroscopy System Capabilities for Determining In‐Vivo Knee Joint Soft Tissue Deformation: A Strategy for Registration Error Management

Knee osteoarthritis (OA) causes structural and mechanical changes within tibiofemoral (TF) cartilage affecting tissue load deformation behavior. Quantifying in-vivo TF soft tissue deformations in healthy and early OA may provide a novel biomechanical marker, sensitive to alterations occurring prior to radiographic change. Dual Fluoroscopy (DF) allows accurate in-vivo TF soft tissue deformation assessment but requires validation. In-vivo healthy and early OA TF cartilage deforms 0.3-1.2mm during static standing full body-weight loading. Our aim was to establish minimum detectable displacement (MDD) for femoral translation in a DF system using a marker-based and markerless approach with variable image intensifier magnifications. An instrumented frame allowed controlled femur specimen translations. Bone positions were reconstructed from DF data using centroids of affixed steel beads (marker-based) and 2D-3D bone feature registration (markerless). Statistical analyses included independent samples t-tests and reliability analysis. Markerless measurements by three trained operators had large variations making it prudent to have an appropriate error management strategy when performing 2D-3D registration. Marker-based MDD improved with image resolution and was 0.05 mm at 3.2 LP/mm (LP: line pairs). Markerless MDD at 3.2 LP/mm was 0.08 mm. Average femur and tibia 2D-3D registrations yielded excellent reliability (84.4%). Therefore, DF images acquired at resolution greater than 3.2 LP/mm would be capable for determining accurate and reliable in-vivo healthy and early OA TF soft tissue deformation. This study provides a registration error management strategy for in-vivo TF soft tissue deformation assessment that could be applied for future clinical applications to establish non-invasive biomechanical markers for early OA diagnosis.

Sensing for stride information of sprinters

Accurate sprint-related information, such as stride times, stance times, stride lengths, continuous Centre-of-Mass (CoM) displacements and split times of sprinters are important to both sprint coaches and biomechanics researchers. These information are traditionally captured using camera-based systems which are very expensive and time-consuming to setup. This paper investigates - through a series of experiments - whether an integrated sensing system would provide a practical, cost-effective alternative to measuring stride-related information of sprinters. The results show that the system achieves an accuracy within 5ms for stance time and stride time measurements, and ~10cm for localisation-related information such as CoM forward displacement and CoM stride displacement (i.e. stride length).

Alterations in lower limb multimuscle activation patterns during stair climbing in female total knee arthroplasty patients

Total knee arthroplasty (TKA) patients commonly experience neuromuscular adaptations that may affect stair climbing competence. This study identified multimuscle pattern (MMP) changes in postoperative female TKA patients during stair climbing with a support vector machine (SVM). It was hypothesized that TKA patients adopt temporal and spectral muscle activation characteristics indicative of muscle atrophy and cocontraction strategies. Nineteen female subjects [10 unilateral sex-specific TKAs, 62.2 ± 8.6 yr, body mass index (BMI) 28.2 ± 5.4 kg/m(2); 9 healthy control subjects, 61.4 ± 7.4 yr, BMI 25.6 ± 2.4 kg/m(2)] were recruited. Surface electromyograms (EMGs) were obtained for seven lower limb muscles of the affected limb of TKA subjects and a randomly assigned limb for control subjects during stair climbing. Stance phase (±30%) EMG data were wavelet transformed and normalized to total power. Data across all muscles were combined to form MMPs and analyzed with a SVM. Statistical analysis was performed with binomial tests, independent group t-tests, or independent group Mann-Whitney U-tests in SPSS (P < 0.05). SVM results indicated significantly altered muscle activation patterns in the TKA group for biceps femoris (recognition rate 84.2%), semitendinosus (recognition rate 73.7%), gastrocnemius (recognition rate 68.4%), and tibialis anterior (recognition rate 68.4%). Further analysis identified no significant differences in spectral activation characteristics between groups. Temporal adaptations, indicative of cocontraction strategies, were, however, evident in TKA MMPs. This approach may provide a valuable tool for clinical neuromuscular function assessment and rehabilitation monitoring.