A NON-LiNEAR CAMERA CALIBRATION ALGORITHM: DIRECT SOLUTION METHOD

Direct Linear Transfonnation (DLT) method suffers from an intrinsic hortcoming: non-orthogonal camera calibration and object space reconstruction. This is due to the fact that the eleven DLT parameters are basically deriVed from a set of ten independent camera parameters and thus are mutually dependent. Alternative algorithms such as MDLT have failed to gain popularity due to the complexity and inconsistency in performance. The purpose of this study Is to develop a non-linear orthogonal camera calibration algorithm with the capability to correct the optical distortion errors

KINEMATIC ANALYSIS OF SPORTS MOVEMENTS: GOLF SWING PLANE ANALYSIS

INTRODUCTION: Kinematics is an area of biomechanics dealing with measurement and description of the human body motion. Quantitative measurement of the motion of interest and subsequent analysis based on the computed kinematic quantities allow investigators an in-depth understanding of the motion itself and the common motion patterns. The human body is a mechanical system with a large number of degrees of freedom and isolating a set of key performance characteristics/components is of crucial importance for effective performance enhancement in complex 3-dimensional (3-D) body motions such as the golf swing. Golf is one of the most popular sports in the modern world with 35 million participants worldwide (Geisler, 2001; Theriault & Lachance, 1998). The sole objective in a golf competition is to minimize the total number of shots taken to finish an 18-hole course using a variety of clubs and shots. The two most important elements of the performance in golf are accuracy (direction and distance) and consistency and one must develop a consistent fundamental swing pattern to secure these qualities. The direction of a shot and the ball carry distance are essentially determined by the clubhead trajectory around the impact position and the impact conditions such as the clubhead velocity, clubface orientation, impact location on the clubface, coefficient of restitution, and the effective mass involved in the impact. The ‘swing plane’, which affects the impact conditions directly, is one of the most frequently used terms in golf coaching lately and is also one of the most controversial and misleading concepts. Since Hogan and Wind (1957) used this term in their book titled “Ben Hogan’s five lessons: the modern fundamentals of golf”, different swing theories have emerged in the popular literature (e.g. Haney & Huggan, 1999; Hardy & Andrisani, 2005). None of these, however, has truly grasped the essence of the swing plane due to the lack of understanding of the complex nature of the actual 3-D swing motion. Moreover, for last four decades, the majority of biomechanical studies on swing mechanics have been conducted based on the planar double-pendulum model (e.g. Budney & Bellow, 1979; Milburn, 1982; Milne & Davis, 1992; Pickering & Vickers, 1999; Sanders & Owens, 1992), originally proposed by Cochran and Stobbs (1968), or the triple-pendulum model (Sprigings & Mackenzie, 2002; Sprigings & Neal, 2000), a variation of the double-pendulum model. Although Vaughan (1981) and Neal and Wilson (1985) pointed out that the swing plane was not planar, it is only recently that scientists have critically investigated the swing plane (Coleman & Anderson, 2007; Coleman & Rankin, 2005; Nesbit, 2005; Shin, Casebolt, Lambert, Kim, & Kwon, 2008). The purpose of this paper is to provide a comprehensive review of both the scientific and the popular golf literature on golf swing mechanics in regards to the concept of swing plane

FLEXIBILITY OF THE EXPERIMENTAL SIMULATION APPROACH TO THE ANALYSIS OF HUMAN AIRBORNE MOVEMENTS: BODY SEGMENT PARAMETER ESTIMATION

The experimental simulation approach to the analysis of human airborne movements provides athletes, coaches, and investigators with unique advantages. However, its potential is not fully utilized due to the complex simulation procedures and it is essential to simplify the simulation procedures to improve its flexibility and applicability. One area that needs improvement & simplification is the body segment parameter (BSP) estimation. In this paper, some recent findings on the effects of the method of BSP estimation on the experimental simulation of complex human airborne movements, and the applicability of selected BSP estimation methods in the experimental simulation of these movements are presented

GAIT STABILITY DURING DIRECTION CHANGE WALKING WITH T-POLES IN THE ELDERLY

INTRODUCTION: Falls are the leading cause of injury deaths for the elderly and typically occur when this population is forced into an unbalanced condition, such as changing a direction during gait. It is widely accepted that the elderly are more vulnerable to falls due to age-related declines in balance and gait stability (Hahn & Chou, 2003). Therefore, a better understanding of gait stability mechanics during direction changes would be critical in reducing the incidence of falls among the elderly. One of the most insightful ways to assess gait stability is to use the instantaneous orientation of the line that connects the center of pressure (COP) and whole body center of mass (COM). The angles made by the line with respect to horizontal line (COM-COP inclination angles) are characterized by the whole body position with respect to the supporting foot during gait (Chou, 2006). Recently, telescopestyle walking poles (T-poles) were deemed effective in reducing elderly fall risk factors (Yoon, 2007); however, the effect of T-poles on gait stability is still unknown. The purpose of this study was to investigate the effects of T-poles on elderly gait stability using COM-COP inclination angles in both straight and direction change during gait

BRIDGING THE GAP: KEY PRINCIPLES IN BIOMECHANICALLY GOOD GOLF SWINGS

The purpose of this presentation was to provide an overview of key principles of biomechanically good golf swings and focus areas that have received substantial attention lately, such as the footground interaction and the functional swing plane-based kinematic sequence analysis. More field-based research is required to develop a holistic understanding of the mechanics in good golf swings. Employment of realistic swing models and development of meaningful research questions and analysis methods in close consultation with golf practitioners is essential in the process

APPLICABILITY OF FOUR LOCALIZED-CALIBRATION METHODS IN UNDERWATER MOTION ANALYSIS

Four different localized-calibration methods were developed based on the DLT (direct linear transformation) algorithm in an effort to reduce the error due to refraction in underwater motion analysis. Their applicability in underwater motion analysis was assessed based on a simulated 3D calibration trial with 2 cameras and a hexahedral calibration frame. It was concluded from the analysis of the calibration results that (a) all methods substantially reduced the maximum reconstruction error and demonstrated the potential to minimize object space deformation, (b) localization methods based on overlapped control volumes/areas revealed superior performance than those based on distinct volumes/areas, and (c) the 2D DLT-based localization algorithm provided more accurate object space reconstruction than the 3D DLT-based algorithm

A THREE DIMENSIONAL ANALYSIS OF THE WINDMILL SOFTBALL PITCH

The act of periorming the windmill softball pitch encompasses total body activity with activation of body parts through a link system. With the coordinated action of all body segments, ballistic energy is applied to the ball to result in the greatest produced velocity at the time of ball release. In attempt to improve periormance, coaches and educators must understand the motions about the joints involved. Therefore it was the purpose of this study to determine the joint motions and movement patterns of the kinetic chain in the ballistic skill of periorming the windmill pitch in attempt to improve athletic periormance as well as athletic instruction

ACCURACY OF THE SOFTWARE GENLOCK WITH DIGITAL CAMCORDERS

Recently, digital camcorders have gained popularity as a viable means of recording movements in video motion analysis, mainly due to the ease of use and reasonably high image resolution. Digital camcorders, however, suffer from a major drawback, lack of the hardware genlock capability. Camcorders thus operate independently from each other and introduce time offsets among themselves. These time offsets in turn violate the requirement of simultaneous observations from multiple cameras in the 3·D analysis, producing erroneous real-life coordinates of the markers. This is especially true in fast motions, in which a small time offset can be translated into a large spatial error, and the time offsets must be corrected before the 3-D reconstruction. The genlock (synchronization) of the cameras can be potentially achieved by a software-based strategy, the software genlock. The purpose of this stUdy was to investigate the accuracy of the software genlock using digital camcorders

EXAMINATION OF DIFFERENT DOUBLE-PLANE CAMERA CALIBRATION STRATEGIES FOR UNDERWATER MOTION ANALYSIS

The purpose of this study was to evaluate five different double-plane calibration strategies with various localized control area sizes and degrees of overlapping to identify the best strategy to minimize the object-space reconstruction error in underwater motion analysis. The object-space reconstruction errors (RMS and maximum) and the RMS-to- max ratios were computed from a simulated underwater calibration trial. An imaginary experimental setup based on a theoretical refraction model was used for a series of camera calibrations. Different double-plane calibration strategies based on the same experimental setup generated very different RMS and maximum reconstruction errors. It was concluded from the analysis that large overlapping localized control areas can substantially reduce the reconstruction error in the double-plane method

EFFECTS OF A PILATES EXERCISE PROGRAM ON CORE STRENGTH IN FEMALES

The purpose of this study was to investigate the effects of a core stability-training program on core strength in females. Core stability is the strength and control of postural muscles of the back, abdomen, and pelvis. Some researchers have suggested that core stability might partially explain why females are more prone to anterior cruciate ligament (ACL) injury than males. We randomly assigned 17 female volunteer participants to an exercise or control group. We measured maximum isometric strength of the hip abductors, abdominals, and back extensors, before and after ten weeks of Pilates exercise. The exercise group met three times weekly for 40 minute supervised exercise sessions. A repeated measures MANOVA revealed no training effect at the end of the intervention (F = 0.435, p = 0.87