GROUND REACTION FORCES DURING LONG JUMP TAKE-OFF FOR TRANSTIBIAL AMPUTEES

The purpose of this study was to investigate ground reaction forces during long jump take-off for lower limb amputees. Elite transtibial amputee (n=3) and able-bodied (n=6) athletes performed six running long jumps in an indoor athletics stadium with a force plate sunk into the runway. For each athletes’ longest jump, vertical (Fz) and horizontal (Fy) peak forces and impulses were calculated. The amputees had a shorter braking impulse duration, followed by a longer propulsive impulse duration with greater peak horizontal propulsive force and impulse than the able-bodied athletes. Vertical loading force and rate of force development at take-off was smaller for the amputees. It may be that amputees attempt to conserve as much horizontal velocity as possible by braking briefly, providing a longer duration in which to apply propulsive forces

CONTRASTING BIOMECHANICS OF ACUTE HAMSTRING STRAINS

Hamstring strains are common in sports. Recently, two different types of hamstring strain have been described, one related to sprinting, the other to stretching exercises (Askling et al., 2006). MRI showed that the sprint-related injury was situated in the long head of the biceps femoris muscle (Askling et al. 2007). Biomechanical modelling has been used to explore mechanisms of the sprint-related injury (Thelen et al. 2006). The purpose here was to contrast the stretch-related injury with the sprint-related one, with respect to injury location and biomechanics

CONTRIBUTIONS TO CLUB VELOCITY IN GOLF SWINGS TO SUBMAXIMAL AND MAXIMAL SHOT DISTANCES

The contribution of joint rotations to endpoint velocity was investigated in golf shots to submaximal and maximal shot distances using a 41degrees of freedom (DOF) kinematic model. A subset of 16 DOFs was found to explain 97%-99% of endpoint velocity regulation at club–ball contact. The largest contributors, for both groups at every shot condition, were pelvis and torso twist rotation among the most proximal DOFs, elbow pronation/supination and wrist flexion/extension among DOFs in the left arm, and shoulder internal/external rotation and wrist flexion/extension among DOFs in the right arm. The contributions from pelvis obliquity, left wrist flexion/extension, left wrist ulnar/radial deviation and right shoulder flexion/extension differed significantly between the advanced and intermediate group

WIRELESS VERTICAL DISPLACEMENT MEASURMENT DURING RUNNING USING AN ACCELEROMETER AND A MOBILE PHONE

The purpose of this study was to investigate in the usability of a wireless accelerometer linked to a mobile phone via Bluetooth radio for measuring vertical displacement in running athletes. Five experienced runners were monitored during lactate threshold testing at three to five different velocities. Accelerometer data was received, processed and stored on the phone to be compared to simultaneous position transducer (ground truth) recordings after data collection. A paired t-test and statistical analysis show no significant differences in the reliability of the recordings. While further investigations are encouraged, the accelerometer and algorithm (running in J2ME on the mobile phone) proof as a flexible, easy-to-use tool for out-of-the-lab monitoring and to provide real-time feedback for running technique experiments

Pose estimation of cyclic movement using inertial sensor data

We propose a method for estimating the rotation and displacement of a rigid body from inertial sensor data based on the assumption that the movement is cyclic in nature, meaning that the body returns to the same position and orientation at regular time intervals. The method builds on a parameterization of the movement by sums of sinusoids, and the amplitude and phase of the sinusoids are estimated from the data using measurement models with Gaussian noise. The maximum likelihood estimate is then equivalent to a weighted nonlinear least squares estimate. The performance of the method is demonstrated on simulated data and on experimental data.Mobile human balance assessmen

Robust Tracking of Periodic Motion in the Plane using Inertial Sensor Data

We propose a robust method for estimating the orientation and displacement of an inertial measurement unit undergoing planar periodic motion. Such movements is a common approximation to human gait and running. We formulate the problem introducing a sparse vector of outlier errors and l1-regularization. The problem thus becomes robust to outliers in the data. The problem can be rewritten as a quadratic programming problem which can be solved efficiently using existing software for convex optimization

Differences between Willingness-to-Pay Estimates from Open-Ended and Discrete-Choice Contingent Valuation Methods: The Effects of Heteroscedasticity

Most comparative studies find that the discrete-choice contingent valuation method (DC-CVM) yields higher willingness-to-pay (WTP) estimates than the open-ended (OE) format. In this paper, we discuss and test several hypotheses to explain why WTP estimates from OE and DC-CVM questions differ. We find that WTP estimates from discrete-choice data are very sensitive to assumptions made about the random utility. In particular, violation of the homoscedasticity assumption may lead to biased WTP estimates if the error terms are correlated with the cost. This violation was a main source of difference in WTP estimates in our studies.

A longitudinal study of gait function and characteristics of gait disturbances in individuals with Alzheimer's disease

Walking in daily life places high demands on the interplay between cognitive and motor functions. A well-functioning dual-tasking ability is thus essential for walking safely. The aims were to study longitudinal changes in gait function during single- and dual-tasking over a period of two years among people with initially mild AD (n = 21). Data were collected on three occasions, twelve months apart. An optical motion capture system was used for three-dimensional gait analysis. Gait parameters were examined at comfortable gait speed during single-tasking, dual-tasking naming names, and naming animals. The dual-task cost for gait speed was pronounced at baseline (names 26%, animals 35%), and remained so during the study period. A significant (p < 0.05) longitudinal decline in gait speed and step length during single- and dual-tasking was observed, whereas double support time, step width and step height showed inconsistent results. Systematic visual examination of the motion capture files revealed that dual-tasking frequently resulted in gait disturbances. Three main characteristics of such disturbances were identified: Temporal disturbance, Spatial disturbance and Instability in single stance. These aberrant gait performances may affect gait stability and increase the risk of falling. Furthermore, the observed gait disturbances can contribute to understanding and explaining previous reported gait variability among individuals with AD. However, the role that dual-task testing and aberrant dual-task gait performance play in the identification of individuals with early signs of cognitive impairment and in predicting fall risk in AD remains to be studied