Brian Horsak

Accuracy of the LPM tracking system considering dynamic position changes

Abstract This study investigates the accuracy of the tracking system LPM (Local Position Measurement). The goal was to determine detailed error values of the system in the context of sports performance analyses. Six moderately trained male soccer players (amateur level) performed 276 runs on three different courses at six different speeds. Additionally, ten small-sided game plays were carried out. All runs and game plays were recorded with the LPM tracking system and the motion capture system VICON simultaneously. VICON served as the reference system. The absolute error of all LPM position estimations was on average 23.4±20.7 cm. The estimation for average velocities varied between 0.01 km h−1 and 0.23 km h−1, the maximum speed estimations differed by up to 2.71 km h−1. In addition, the results showed that the accuracy of the LPM system is highly dependent on the instantaneous dynamics of the player and decreases in the margins of the observation field. These dependencies were quantified. Considering commonly used applications of position tracking systems in sports (Leser, Ogris, & Baca, 2011), the accuracy of LPM is acceptable for position and velocity estimations. The system provides valuable results for average velocities but seems to be far less reliable when dealing with high dynamic movements and measuring instantaneous velocities.

Muscle co-contraction around the knee when walking with unstable shoes

Walking with unstable shoes has been discussed to decrease joint loading. Typical estimates of joint loading using an inverse dynamic approach only account for net joint moments, not considering the potential role of muscular co-contraction. Therefore, the purpose of this study was to compare muscular co-contraction levels when walking with two different unstable shoe constructions (rocker-bottom and toning shoes) compared to walking with regular shoes. For each shoe condition, 12 healthy subjects walked with both, a regular shoe and with an unstable shoe at self-selected walking speed at a 10-m walkway. Surface EMG data of selected muscles were recorded and time normalized for calculating co-contraction indices (CCI) for opposing muscle groups. Results showed an increase of co-contraction primarily for vastii and gastrocnemius muscles for the first and second half of stance when walking with an unstable shoe construction. Therefore, when using an inverse dynamic approach to analyze joint loading differences between regular shoes and unstable shoes, one should be cautious in interpreting the data, as these methods base their estimates of joint moments upon the net joint torque.

A mobile music concept as support for achieving target heart rate in preventive and recreational endurance training

A concept of a mobile phone based system which takes advantage of the influence of listened music during endurance training on running pace, will be presented in this paper. The main goal of the system relies in the support of athletes to achieve their correct target heart rate (THR) during endurance training in the field of recreational and preventive sports. Therefore, a mobile receiver will be developed which should be capable of collecting heart rate data from a standard Polar heart rate chest belt and transmit data via a Bluetooth connection to any mobile device. A feedback algorithm will be developed which will continuously monitor the athletes heart rate and compare it to the individual THR predicted by a prediction equation. If the athletes THR is too low or too high, the algorithm will provide music files featuring that amount of beats per minute (BPM), which will help the user to speed up, slow down or keep the pace to be on track with the predicted THR.

Within-assessor reliability and minimal detectable change of gait kinematics in a young obese demographic

INTRODUCTION Three-dimensional gait analysis (3DGA) in obese populations is a difficult task due to a great amount of subcutaneous fat. This makes it more challenging to identify anatomical landmarks, thus leading to inconsistent marker placement. Therefore, the purpose of this study was to investigate the test-retest reliability for kinematic measurements of obese children and adolescents. METHODS Nine males and two females with an age-based BMI above the 97th percentile (age: 14.6±2.6years, BMI: 33.4±4.4kg/m2) were administered to two 3DGA sessions. To quantify reliability of discrete parameters the intraclass correlation coefficient (ICC2,k), standard error of measurement (SEM) and minimal detectable change (MDC) were calculated. To quantify waveform similarity, the coefficient of multiple correlation (CMC) and the linear fit method (LFM) were used. RESULTS From 28 kinematic parameters, 23 showed acceptable ICCs (≥0.70) and the remaining parameters demonstrated moderate values. These were peak hip extension during stance (0.58), mean pelvis rotation (0.60), mean anterior pelvic tilt (0.64), peak knee flexion during swing (0.67) and peak hip abduction during swing (0.69). The SEM was below 5° for all parameters. The MDC for the sagittal, frontal, and transversal plane were on average 7.5°±2.2, 4.6°±1.3 and 6.0°±0.9 respectively. Both the LFM and CMC showed, in general, moderate to good reliability except for pelvis tilt and hip rotation. CONCLUSION Data demonstrated acceptable error margins especially for the sagittal and frontal plane. Low reliability for the pelvis tilt indicates that great effort is necessary to position the pelvic markers consistently during repeated sessions.

The effects of a strength and neuromuscular exercise programme for the lower extremity on knee load, pain and function in obese children and adolescents: study protocol for a randomised controlled trial

BackgroundChildhood obesity is one of the most critical and accelerating health challenges throughout the world. It is a major risk factor for developing varus/valgus misalignments of the knee joint. The combination of misalignment at the knee and excess body mass may result in increased joint stresses and damage to articular cartilage. A training programme, which aims at developing a more neutral alignment of the trunk and lower limbs during movement tasks may be able to reduce knee loading during locomotion. Despite the large number of guidelines for muscle strength training and neuromuscular exercises that exist, most are not specifically designed to target the obese children and adolescent demographic. Therefore, the aim of this study is to evaluate a training programme which combines strength and neuromuscular exercises specifically designed to the needs and limitations of obese children and adolescents and analyse the effects of the training programme from a biomechanical and clinical point of view.Methods/DesignA single assessor-blinded, pre-test and post-test randomised controlled trial, with one control and one intervention group will be conducted with 48 boys and girls aged between 10 and 18 years. Intervention group participants will receive a 12-week neuromuscular and quadriceps/hip strength training programme. Three-dimensional (3D) gait analyses during level walking and stair climbing will be performed at baseline and follow-up sessions. The primary outcome parameters for this study will be the overall peak external frontal knee moment and impulse during walking. Secondary outcomes include the subscales of the Knee injury and Osteoarthritis Outcome Score (KOOS), frontal and sagittal kinematics and kinetics for the lower extremities during walking and stair climbing, ratings of change in knee-related well-being, pain and function and adherence to the training programme. In addition, the training programme will be evaulated from a clinical and health status perspective by including the following analyses: cardiopulmonary testing to quantify aerobic fitness effects, anthropometric measures, nutritional status and psychological status to characterise the study sample.DiscussionThe findings will help to determine whether a neuromuscular and strength training exercise programme for the obese children population can reduce joint loading during locomotion, and thereby decrease the possible risk of developing degenerative joint diseases later in adulthood.Trial registrationClinicalTrials NCT02545764, Date of registration: 24 September 2015.

Is the reliability of 3D kinematics of young obese participants dependent on the hip joint center localization method used

The aim of this study was to investigate if the test-retest reliability for three-dimensional (3D) gait kinematics in a young obese population is affected by using either a predictive (Davis) or a functional (SCoRE) hip joint center (HJC) localization approach. A secondary goal was to analyze how consistent both methods perform in estimating the HJC position. A convenience sample of ten participants, two females and eight males with an age-based body mass index (BMI) above the 97th percentile (mean±SD: 34.2±3.9kg/m2) was recruited. Participants underwent two 3D gait analysis sessions separated by a minimum of one day and a maximum of seven days. The standard error of measurement (SEM) and the root mean square error (RMSE) of key kinematic parameters along with the root mean square deviation (RMSD) of the entire waveforms were used to analyze the test-retest reliability. To get an estimate of the consistency of both HJC localization methods, the HJC positions determined by both methods were compared to each other. SEM, RMSE, and RMSD results indicate that the HJC position estimations between both methods are not different and demonstrate moderate to good reliability to estimate joint kinematics. With respect to the localization of the HJC, notable inconsistencies ranging from 0 to 5.4cm were observed. In conclusion, both approaches appear equally reliable. However, the inconsistent HJC estimation points out, that accuracy seems to be a big issue in these methods. Future research should attend to this matter.

EFFECTS OF AN UNSTABLE SHOE CONSTRUCTION ON EMG AND LOWER AND UPPER EXTREMITY GAIT BIOMECHANICS

In the last few years, there was a significant increase in promotion of unstable shoe constructions as a foot wear, which is “beneficial” for health. Even though some authors have conducted research in the field of instable shoe constructions, there is still a gap in consistent results, especially for joint loadings (e.g. Nigg et al.,2006; Romkes et al., 2006), and there is still a lack of research for the effect on trunk kinematics. The understanding of the impact of instable shoe constructions on muscle activation, joint loadings and joint kinematics is a very important task, as well for clinicians and therapists, as for people using such shoes in their everyday life. Consistent experimental results are necessary to obtain a reliable understanding of the effect of such shoes on gait biomechanics. Given the present inconsistency of prior published results, the aim of this study was to obtain further results of biomechanical effects on muscle activation patterns, joint kinematics and loadings and on trunk kinematics during gait with the Masai Barefoot Technology – MBT ®.

Trunk muscle activation levels during eight stabilization exercises used in the functional kinetics concept: A controlled laboratory study

BACKGROUND To ensure accurate implementation of stabilization exercises in rehabilitation, physical therapists need to understand the muscle activation patterns of prescribed exercise. OBJECTIVE Compare muscle activity during eight trunk and lumbar spine stabilization exercises of the Functional Kinetics concept by Klein-Vogelbach. METHODS A controlled laboratory study with a single-group repeated-measures design was utilized to analyze surface electromyographic intensities of 14 female and 6 male young healthy participants performing eight exercises. Data were captured from the rectus abdominis, external/internal oblique and lumbar paraspinalis. The normalized muscle activation levels (maximum voluntary isometric contraction, MVIC) for three repetitions during each exercise and muscle were analyzed. RESULTS Side bridging (28 ± 20%MVIC) and advanced planking (29 ± 20%MVIC) reached the highest activity in the rectus abdominis. For external and internal oblique muscles, side bridging also showed the greatest activity of 99 ± 36%MVIC and 52 ± 25%MVIC, respectively. Apart from side bridging (52 ± 14%MVIC), the supine roll-out (31 ± 12%MVIC) and prone roll-out (31 ± 9%MVIC) showed the greatest activity for the paraspinalis. The advanced quadruped, seated back extension and flexion on chair/Swiss Ball, prone roll-out and advanced one-leg back bridging only yielded negligible muscle activities for the rectus abdominis (< 5%MVIC). CONCLUSION Based on the data obtained, recommendations for selective trunk muscle activation during eight stabilization exercises were established, which will guide physical therapists in the development of exercises tailored to the needs of their patients.

Reliability of joint kinematic calculations based on direct kinematic and inverse kinematic models in obese children

BACKGROUND In recent years, the reliability of inverse (IK) and direct kinematic (DK) models in gait analysis have been assessed intensively, but mainly for lean populations. However, obesity is a growing issue. So far, the sparse results available for the reliability of clinical gait analysis in obese populations are limited to direct kinematic models. Reliability error-margins for inverse kinematic models in obese populations have not been reported yet. RESEARCH QUESTIONS Is there a difference in the reliability of IK models compared with a DK model in obese children? Are there any differences in the joint kinematic output between IK and DK models? METHODS A test-retest study was conducted using three-dimensional gait analysis data from two obese female and eight obese male participants from an earlier study. Data were analyzed using a DK model and two OpenSim-based IK models. Test-retest reliability was compared by calculating the Standard Error of Measurement (SEM) along with similar absolute reliability measures. A Friedman Test was used to assess whether there were any significant differences in the reliability between the models. Kinematic output of the models was compared by using Statistical Parametric Mapping (SPM). RESULTS No significant differences were found in the reliability between the DK and IK models. The SPM analysis indicated several significant differences between both IK models and the DK approach. Most of these differences were continuous offsets. SIGNIFICANCE Reliability values showed clinically acceptable error-margins and were comparable between all models. Therefore, our results support the careful use of IK models in overweight or obese populations, e.g. for musculoskeletal modelling studies. The inconsistent kinematic output can mainly be explained by different model conventions and anatomical segment coordinate frame definitions.

Short-Term Effects of Real-Time Auditory Display (Sonification) on Gait Parameters in People with Parkinsons’ Disease—A Pilot Study

Parkinson’s disease PD patients frequently experience gait impairments. Auditory input has been shown to be an effective measure to benefit critical gait aspects related to the timing and initiation of movement. An instrumented shoe insole device for real-time sonification of gait has been developed for rehabilitation purposes (SONIGait). The objective of the present pilot study was to gain insight about possible effects of SONIGait on gait parameters in PD patients. Five PD patients participated in this pilot study and completed three series of trials with and without sonification. Spatio-temporal gait parameters were recorded during these trials. The outcomes revealed an increase in walking velocity and cadence along with other gait parameters between pre- and posttest. These data indicate that sonification affects gait parameters and fosters (short-term) learning effects in PD patients. Thus, SONIGait may be a suitable measure to promote gait rehabilitation in PD in the future.