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Biomedical subjects

D G Kerwin

Publications and source records attributed to D G Kerwin.

11 recordsLinked to original sources
PubMed2001

Strategies for maintaining a handstand in the anterior-posterior direction.

PURPOSE: The purpose of this analysis was to determine the contributions made by wrist, shoulder, and hip joint torques in maintaining a handstand. METHODS: Handstand balances (N = 6) executed on a force plate and recorded with two genlocked video cameras were subjected to inverse dynamics analysis to determine anterior-posterior joint torques at the wrists, shoulders, and hips. Multiple regression analyses were conducted to investigate which of the joint torques were influential in accounting for anterior-posterior whole-body mass center (CM) movement. RESULTS: Results demonstrated that, in general, all calculated joint torques contributed to CM movement. In a number of trials, wrist torque played a dominant role in accounting for CM variance. Ostensibly, superior handstand balances are characterized by important contributions from wrist torques and shoulder torques with little influence from hip torques. In contrast, hip torques were found to be increasingly influential in less successful balances. CONCLUSIONS: It is concluded that multiple joints are utilized in maintaining a handstand balance in the anterior-posterior direction, and there appears to be two joint involvement strategies, which supports similar findings from postural research on normal upright stance.

Adolescent↗
PubMed1999

A two-segment simulation model of long horse vaulting.

The optimum pre-flight characteristics of the Hecht and handspring somersault vaults were determined using a two-segment simulation model. The model consisted of an arm segment and a body segment connected by a frictionless pin joint, simulating the vault from the Reuther board take-off through to landing. During horse contact, shoulder torque was set to zero in the model. Five independent pre-flight variables were varied over realistic ranges and an objective function was maximized to find the optimum pre-flight for each vault. The Hecht vault required a low trajectory of the mass centre during pre-flight, with a low vertical velocity of the mass centre and a low angular velocity of the body at horse contact. In contrast, the optimum handspring somersault required a high pre-flight trajectory, with a high angular velocity of the body and a high vertical velocity at horse contact. Despite the simplicity of the model, the optimum pre-flights were similar to those used in competitive performances.

Biomechanical Phenomena↗
PubMed1999

Measuring running speed using photocells.

Photocell timing systems are used routinely to measure running speeds. In this study, the accuracy of such systems was evaluated using centre of mass speed estimates from three-dimensional video analysis as criteria. One subject ran at five nominal speeds (5-9 m x s(-1)) for each of five separations (1.6-2.4 m) between consecutive photocells. Running speeds were calculated from the photocell data using single beam and double beam systems. For single beam systems, the start of the first break of a beam and the start of the longest break of a beam were used as trigger criteria. For double beam systems, the first occurrence of both beams being broken and the start of the longest double break were used as trigger criteria. Root mean square speed errors were smaller for the double beam systems. The longest break criterion gave smaller root mean square errors than the first break criterion. In general, errors in speed were smaller for greater photocell separations. An error of 0.1 m x s(-1) was achieved using a single beam system set at hip height with a longest break criterion for photocell separations of around two stride lengths. The advantage of using a double beam system is that it achieves this accuracy without the need to adjust photocell separation for different stride lengths.

Biomechanical Phenomena↗
PubMed1996

Quantification of the uncertainties in resultant joint moments computed in a dynamic activity.

Resultant joint moments are an important variable with which to examine human movement, but the uncertainty with which resultant joint moments are calculated is often ignored. This paper presents a procedure for examining the uncertainty with which resultant joint moments are calculated. The uncertainty was calculated by changing the parameters and variables required to compute the resultant joint moments, by amounts relating to their estimated uncertainties, and then quantifying the resulting change in the resultant joint moments. The procedure was applied to the elbow joint during loaded elbow flexion executed at maximum volitional speed. For this activity, the estimated moments were most sensitive to uncertainties in the derivatives of the position data. A number of other sources of error and uncertainty were identified which warrant further investigation. The protocols outlined in this study are applicable to other activities.

Biomechanical Phenomena↗
PubMed1993

Hand placement techniques in long horse vaulting.

In this study, the effects of two different hand placement techniques used by gymnasts to perform Tsukahara and Kasamatsu long horse vaults were examined. Selected linear and angular flight descriptors were calculated to determine whether those gymnasts making initial hand contact on the end of the horse gained additional lift, range or rotation when compared to those gymnasts making the more traditional initial hand contact on top of the horse. Three-dimensional cine-film analysis using the Direct Linear Transformation (DLT) was used to obtain data on 17 elite gymnasts competing in the 1991 World Student Games at Sheffield, UK. The gymnasts were divided into two groups according to the techniques used: group E in which the first hand contact was made on the vertical surface of the near end and the second on the top of the horse, and group T in which both hands were placed on top of the horse. The vertical and horizontal motion of each gymnast's mass centre and the somersault rotation during pre-flight (board take-off to horse contact) and post-flight (horse take-off to ground landing) were determined. The projections of linear displacements of each gymnast's mass centre onto a vertical plane were determined from the three-dimensional mass centre co-ordinates, and somersault angles were calculated using the line joining the midpoints of each gymnast's shoulders and knees. Whole body mass centre linear velocity and somersault angular velocity were determined using quintic splines.(ABSTRACT TRUNCATED AT 250 WORDS)

Biomechanical Phenomena↗
PubMed1993

An analytical examination of muscle force estimations using optimization techniques.

Muscle forces are often estimated during human movement using optimization procedures. The optimization procedures involve the minimization of an objective function relating to the muscle forces. In this study 15 different objective functions were evaluated by examining the analytical solutions to the objective functions and by comparing their force predictions with the forces estimated using a validated muscle model. The muscle forces estimated by the objective functions were shown to give poor correspondence with the muscle model predicted muscle forces. The objective function estimates were criticized for not taking sufficient account of the physiological properties of the muscles. As a consequence of the analysis of the objective functions an alternative, simpler function was presented with which to estimate muscle forces in vivo. This function required that to satisfy a given joint moment, the force exerted by each of the muscles divided by the maximum force possible by the muscle was constant for all muscles. For this function the maximum muscle force was determined using a muscle model assuming maximal activation.

Biomechanical Phenomena↗
PubMed1992

Accuracy assessment and control point configuration when using the DLT for photogrammetry.

The direct linear transformation (DLT) is a common technique used to calibrate cameras and subsequently reconstruct points filmed with two or more cameras in a three-dimensional object space. The assessment of the accuracy of this technique, and of the influence of the distribution of control points on accuracy were examined. It was concluded that to obtain a true estimation of reconstruction accuracy, an independent assessment criterion is required, and that the use of control points distributed around the outside, rather than within the space to be calibrated, is preferred.

Calibration↗
PubMed1992

Physiological and metabolic responses of men and women to a 5-km treadmill time trial.

Previous studies have reported strong correlations between 5-km performance times and maximal oxygen uptake (VO2 max) and also for running speeds equivalent to blood lactate concentrations of 4 mM. However, there is little information on the physiological responses of individuals during races over this distance. Therefore, the aim of the present study was to measure the physiological and metabolic responses of endurance trained male (n = 8) and female (n = 8) runners during a 5-km time trial using an instrumented treadmill. Performance times were 18.77 +/- 1.27 min for the men and 21.80 +/- 1.98 min for the women (P less than 0.01). The corresponding times on the athletics track were 17.68 +/- 0.39 min for the men (P less than 0.05) and 20.70 +/- 2.16 min for the women (N.S.). During the treadmill time trials, both the men and women were able to utilize approximately 90% VO2 max, 82% VE max, 98% HR max and produce similar concentrations of blood lactate. Although the physiological and metabolic responses of these endurance-trained men and women to 5-km treadmill running were similar, the faster running times recorded by the men in this study were the result of their higher VO2 max values.

Energy Metabolism↗
PubMed1992

Calculating upper limb inertial parameters.

In the kinematic and kinetic analysis of human movement, an accurate assessment of the inertial properties of the body segments under investigation is often essential. Statistical and geometric models of the segments of the upper limb were examined to determine their ability to predict the moments of inertia of these segments. The cadaver data of Chandler et al. (1975) were used as the criteria with which computed values were compared. The regression equations of Hinrichs (1985) gave the most accurate results; the geometric models appeared to offer the greatest flexibility.

Arm↗