AN AUTOMATED METHOD FOR THE ESTIMATE OF VERTICAL JUMP POWER THROUGH INERTIAL MEASUREMENT UNITS

Vertical jump performance analysis allows for assessing the ability of the lower limb to generate mechanical power. The analysis performed with inertial measurement units (IMUs) is affected by inertial effects of wobbling masses. To compensate for them, an automated method was developed to estimate peak and mean concentric power based on anthropometric and time-frequency features. IMU data of 47 countermovement- (CMJ) and 50 squat- jumps (SJ) performed by 17 participants were used. Force platform data were used to obtain reference power values. Features were chosen according to the best subset regression method, devising a multiple linear regression for each estimated power parameter and jump. The regressions explained 88% and 96% variation, for CMJ peak and average power respectively, while explaining 75% and 74% of the variation for the SJ

Estimation of temporal parameters during sprint running using a trunk-mounted inertial measurement unit

This research was supported by a grant of the Universit a Italo-Francese (Call Vinci) awarded to E. Bergamini.The purpose of this study was to identify consistent features in the signals supplied by a single inertial measurement unit (IMU), or thereof derived, for the identification of foot-strike and foot-off instants of time and for the estimation of stance and stride duration during the maintenance phase of sprint running. Maximal sprint runs were performed on tartan tracks by five amateur and six elite athletes, and durations derived from the IMU data were validated using force platforms and a high-speed video camera, respectively, for the two groups. The IMU was positioned on the lower back trunk (L1 level) of each athlete. The magnitudes of the acceleration and angular velocity vectors measured by the IMU, as well as their wavelet-mediated first and second derivatives were computed, and features related to foot-strike and foot-off events sought. No consistent features were found on the acceleration signal or on its first and second derivatives. Conversely, the foot-strike and foot-off events could be identified from features exhibited by the second derivative of the angular velocity magnitude. An average absolute difference of 0.005 s was found between IMU and reference estimates, for both stance and stride duration and for both amateur and elite athletes. The 95% limits of agreement of this difference were less than 0.025 s. The results proved that a single, trunk-mounted IMU is suitable to estimate stance and stride duration during sprint running, providing the opportunity to collect information in the field, without constraining or limiting athletes’ and coaches’ activities

Trunk Inclination Estimate During the Sprint Start Using an Inertial Measurement Unit: A Validation Study

The proper execution of the sprint start is crucial in determining the performance during a sprint race. In this respect, when moving from the crouch to the upright position, trunk kinematics is a key element. The purpose of this study was to validate the use of a trunk-mounted inertial measurement unit (IMU) in estimating the trunk inclination and angular velocity in the sagittal plane during the sprint start. In-laboratory sprint starts were performed by five sprinters. The local acceleration and angular velocity components provided by the IMU were processed using an adaptive Kalman filter. The accuracy of the IMU inclination estimate and its consistency with trunk inclination were assessed using reference stereophotogrammetric measurements. A Bland-Altman analysis, carried out using parameters (minimum, maximum, and mean values) extracted from the time histories of the estimated variables, and curve similarity analysis (correlation coefficient > 0.99, root mean square difference < 7 deg) indicated the agreement between reference and IMU estimates, opening a promising scenario for an accurate in-field use of IMUs for sprint start performance assessment

BIOMECHANICAL INVESTIGATION OF THE KIZAMI TSUKI IN KARATE ATHLETES

The purpose of this study was to investigate the kinematics and kinetics characteristics of kizami tsuki karate punch technique. Punching actions represent the most frequently performed attacking techniques in karate combat competitions (75% of total actions, kizami tsuki being the most common). Six athletes were asked to perform three kizami tsuki against a hand-held target at their maximal speed. Punch kinematics and kinetics were recorded by means of stereophotogrammetry and forceplates. Power, lower and upper limb kinematics and their coordinative pattern during the punching actions were assessed to characterize the technique. A multiple linear regression model was devised to correlate punching kinematics and kinetic variables with maximal wrist velocity, considered as performance measure. Maximal net power, transformation time, average continuous relative phase between knee and elbow flexion-extension, and elbow peak flexion were significative predictors of wrist velocity (R2 = 0.84), indicating them as key factors to a proficient-performance of the kizami tsuki

ESTIMATE OF TRUNK INCLINATION DURING FAST MOVEMENTS BY INERTIAL SENSING

The purpose of this study was to identify a reliable algorithm to estimate the inclination of a trunk-mounted inertial measurement unit (IMU) during fast movements and to test its subject- and task-specificity. Ten amateur football players performed three times the approach phase of the drive block technique and a fast sit-to-stand-to-sit task. IMU data were processed using an ad hoc adaptive Kaman filter, and pitch angular displacements were obtained and compared to stereophotogrammetric reference estimates. Tuning of the algorithm parameters was performed and relevant accuracy was tested in terms of root mean squared difference (RMSD) and correlation coefficient. Strong correlation (>0.978) were observed for both motor tasks, together with RMSD smaller than 4.4±1.7 deg. The tuned algorithm proved to be neither subject- nor task-specific (p>0.05)

A functional calibration protocol for ankle plantar-dorsiflexion estimate using magnetic and inertial measurement units: Repeatability and reliability assessment

The ankle joint complex presents a tangled functional anatomy, which understanding is fundamental to effectively estimate its kinematics on the sagittal plane. Protocols based on the use of magnetic and inertial measurement units (MIMUs) currently do not take in due account this factor. To this aim, a joint coordinate system for the ankle joint complex is proposed, along with a protocol to perform its anatomical calibration using MIMUs, consisting in a combination of anatomical functional calibrations of the tibiotalar axis and static acquisitions. Protocol repeatability and reliability were tested according to the metrics proposed in Schwartz et al. (2004) involving three different operators performing the protocol three times on ten participants, undergoing instrumented gait analysis through both stereophotogrammetry and MIMUs. Instrumental reliability was evaluated comparing the MIMU-derived kinematic traces with the stereophotogrammetric ones, obtained with the same protocol, through the linear fit method. A total of 270 gait cycles were considered. Results showed that the protocol was repeatable and reliable for what concerned the operators (0.4 +/- 0.4 deg and 0.8 +/- 0.5 deg, respectively). Instrumental reliability analysis showed a mean RMSD of 3.0 +/- 1.3 deg, a mean offset of 9.4 +/- 8.4 deg and a mean linear relationship strength of R2 = 0.88 +/- 0.08. With due caution, the protocol can be considered both repeatable and reliable. Further studies should pay attention to the other ankle degrees of freedom as well as on the angular convention to compute them

A CALIBRATION PROCEDURE FOR MIMU SENSORS ALLOWING FOR THE CALCULATION OF ELBOW ANGLES

Non-optical wearable sensors such as magnetic and inertial measurement units (MIMUs) are gaining popularity in sport and clinical settings owing to their ease of application, relative affordability and potential for improved ecological validity. We propose a method for the standardised reference calibration of a simple two-sensor MIMU system for the estimation of anatomically meaningful elbow kinematics. The participant poses with the elbow at 90° flexion and neutral (0°) pronation, allowing for the relative orientation of the MIMU on the forearm to be determined with reference to the MIMU located on the arm. Comparisons were with traditional kinematic marker method results. Root mean squared errors of less than 1° in flex/ext and < 2° (pro/sup) found in simple movements. Results with simple movements provide rationale to expand research to complex movements

Hip joint centre position estimation using a dual unscented Kalman filter for computer-assisted orthopaedic surgery

In computer-assisted knee surgery, the accuracy of the localization of the femur centre of rotation relative to the hip-bone (hip joint centre) is affected by the unavoidable and untracked pelvic movements because only the femoral pose is acquired during passive pivoting manoeuvres. We present a dual unscented Kalman filter algorithm that allows the estimation of the hip joint centre also using as input the position of a pelvic reference point that can be acquired with a skin marker placed on the hip, without increasing the invasiveness of the surgical procedure. A comparative assessment of the algorithm was carried out using data provided by in vitro experiments mimicking in vivo surgical conditions. Soft tissue artefacts were simulated and superimposed onto the position of a pelvic landmark. Femoral pivoting made of a sequence of star-like quasi-planar movements followed by a circumduction was performed. The dual unscented Kalman filter method proved to be less sensitive to pelvic displacements, which were shown to be larger during the manoeuvres in which the femur was more adducted. Comparable accuracy between all the analysed methods resulted for hip joint centre displacements smaller than 1 mm (error: 2.2 ± [0.2; 0.3] mm, median ± [inter-quartile range 25%; inter-quartile range 75%]) and between 1 and 6 mm (error: 4.8 ± [0.5; 0.8] mm) during planar movements. When the hip joint centre displacement exceeded 6 mm, the dual unscented Kalman filter proved to be more accurate than the other methods by 30% during multi-planar movements (error: 5.2 ± [1.2; 1] mm)

DOES THE SITTING POSITION INFLUENCE CLAY TARGET SHOOTING PERFORMANCE IN ATHLETES WITH A MOTOR IMPAIRMENT?

Olympic trap clay target shooting (CTS) is currently performed by motor impaired individuals (MII), but not yet included in the International Paralympic Committee endorsement. This study aimed at supporting the development of a classification model that divides athletes competing in standing and sitting postures. Two groups of 5 standing and 5 sitting MII athletes were recruited for an instrumented CTS task execution. During competition, sitting athletes showed a lower rate of success with respect to the standing ones only for targets requiring wider ranges of motion, possibly due to fatigue. Their predominant use of upper body movements implies an adapted technique to reach a good performance, testified by a smoother movement, a lower peak accelerations at the gun tip, a smaller range for all absolute and relative rotations, and a different muscle activity

AN INERTIAL SENSORS-BASED METHOD FOR PHASES AND EVENTS IDENTIFICATION IN PARA-ROWING: TOWARDS AN ON-WATER PERFORMANCE ASSESSMENT

The aim of this study is to propose and validate an inertial sensors-based methodology for the para-rowing stroke cycles segmentation. One non-disabled athlete performed two para-rowing set-ups, simulating PR1 (arms and shoulders-AS) and PR2 (trunk and arms-TA) conditions. Catch and finish events of each stroke cycle were identified on the signals measured by three sensors located on the right forearm (FA), upper arm (UA), and on the trunk (T). Accuracy was quantified by identifying the same events on the 3D trajectory of one right hand-located marker. UA and FA sensors data lead to a more accurate detection of stroke events with respect to the T sensor (average error: 28.8ms, 29.0ms, 56.9ms). The present results open promising scenarios on the application of inertial sensors in para-rowing for real-time performance-related feedback to athletes and coaches