Sex differences in the centre of buoyancy location of competitive swimmers.

The aims of this study were to identify differences in the centre of buoyancy (CB) and centre of mass (CM) locations of male and female collegiate swimmers, and to assess the influence that buoyancy has on freestyle kicking performance. Sixteen female collegiate swimmers (mean +/- s: age 19.1 +/- 1.2 years) had significantly more adipose tissue (20.2 +/- 4.4%) than 15 male collegiate swimmers (19.9 +/- 1.0 years, 12.6 +/- 3.8%). The ratio of the sum of abdominal and suprailiac skinfolds to the thigh skinfold was significantly greater for the males (2.07 +/- 0.37) than the females (1.31 +/- 0.32), implying that females had proportionately more fatty tissue caudally than males. The distance d between the centres of buoyancy and mass was significantly larger for the males (0.79 +/- 0.43 cm) than the females (0.16 +/- 0.34 cm). Both points were more caudal in the female subjects (59.9 +/- 0.7% and 59.8 +/- 0.7% of body height respectively) than in the male subjects (61.7 +/- 0.8% and 61.2 +/- 0.9% respectively). These data suggest that the difference in d may be attributed to the difference in the location of the centre of buoyancy, because the centre of mass difference was not significant and was characterized by a smaller effect size. The amount and distribution of adipose tissue accounted for a significant proportion of variance in d (R2 = 0.25 and 0.29 respectively). Males had a significantly higher proportional kick time, defined as the ratio of times to complete a 22.9 m sprint when kicking and swimming respectively, than females (1.57 +/- 0.09 and 1.51 +/- 0.13 respectively). This shows that the male swimmers kicked proportionally more slowly than the female swimmers. However, the distance d did not account for a significant proportion of variance in the proportional kick time. Therefore, our results do not support the notion that skilled male swimmers are at a performance disadvantage in terms of natural buoyancy characteristics.

Manipulative treatment of carpal tunnel syndrome: biomechanical and osteopathic intervention to increase the length of the transverse carpal ligament.

To quantify the amount of transverse carpal ligament (TCL) elongation in response to osteopathic manipulation or sustained load bearing (or both), a study involving seven cadaver limbs was conducted. Distances from the trapezium to the hamate (distance A) and from the scaphoid to the pisiform (distance B) were measured in five mounted cadaver limbs during and after the limbs bore the weight (2 newtons [N] to 4 N) for 2 several-hour periods. A several-hour period occurred between the weight bearing to assess recoil. Distances A and B were measured before and after the limbs were manipulated, according to previously described techniques, as well as with a new maneuver, termed the "guywire" technique. Two dissected limbs also were subjected to further weight bearing, this time increased to 8 N. Greater weight loads produced greater lengthening of the TCL, and recoil after removal of weight loads was slower than recoil after manipulation. Manipulation was more effective than weight loading for increasing distance A (distal canal), but weight loading generally was more effective than manipulation for increasing distance B (proximal canal). The guywire manipulation combined with direct transverse extension appeared to have the greatest impact on lengthening the TCL distally. These results show promise for the effective use of manipulation and load bearing for TCL elongation and nonsurgical relief of pressure on the median nerve in patients with carpal tunnel syndrome.

Endpoint error in smoothing and differentiating raw kinematic data: an evaluation of four popular methods.

'Endpoint error' describes the erratic behavior at the beginning and end of the computed acceleration data which is commonly observed after smoothing and differentiating raw displacement data. To evaluate endpoint error produced by four popular smoothing and differentiating techniques, Lanshammar's (1982, J. Biomechanics 15, 99-105) modification of the Pezzack et al. (1977, J. Biomechanics, 10, 377-382) raw angular displacement data set was truncated at three different locations corresponding to the major peaks in the criterion acceleration curve. Also, for each data subset, three padding conditions were applied. Each data subset was smoothed and differentiated using the Butterworth digital filter, cubic spline, quintic spline, and Fourier series to obtain acceleration values. RMS residual errors were calculated between the computed and criterion accelerations in the endpoint regions. Although no method completely eliminated endpoint error, the results demonstrated clear superiority of the quintic spline over the other three methods in producing accurate acceleration values close to the endpoints of the modified Pezzack et al. (1977) data set. In fact, the quintic spline performed best with non-padded data (cumulative error = 48.0 rad s-2). Conversely, when applied to non-padded data, the Butterworth digital filter produced wildly deviating values beginning more than the 10 points from the terminal data point (cumulative error = 226.6 rad s-2). Each of the four methods performed better when applied to data subsets padded by linear extrapolation (average cumulative error = 68.8 rad s-2) than when applied to analogous subsets padded by reflection (average cumulative error = 86.1 rad s-2).

NLT and extrapolated DLT:3-D cinematography alternatives for enlarging the volume of calibration.

This study investigated the accuracy of the direct linear transformation (DLT) and non-linear transformation (NLT) methods of 3-D cinematography/videography. A comparison of standard DLT, extrapolated DLT, and NLT calibrations showed the standard (non-extrapolated) DLT to be the most accurate, especially when a large number of control points (40-60) were used. The NLT was more accurate than the extrapolated DLT when the level of extrapolation exceeded 100%. The results indicated that when possible one should use the DLT with a control object, sufficiently large as to encompass the entire activity being studied. However, in situations where the activity volume exceeds the size of one's DLT control object, the NLT method should be considered.

Adjustments to the segment center of mass proportions of Clauser et al. (1969).

One of the most commonly-referenced studies on body segment masses and centers of mass is by Clauser et al. (AMRL Technical Report 69-70, Wright Patterson Air Force Base, 1969). The Clauser et al. data, however, are difficult to use, because the investigators used certain bony landmarks rather than joint centers as reference points for the center of mass proportions. The purpose of this study was to make adjustments to those proportions so that they could be applied directly to segments having joint centers as endpoints. The segments affected by these adjustments were the trunk, upper arm, forearm, thigh, and calf. These new proportions are markedly different than those originally reported by Clauser et al., especially for the trunk segment. Readers are cautioned against using the original proportions when using joint centers as segment endpoints.

Regression equations to predict segmental moments of inertia from anthropometric measurements: an extension of the data of Chandler et al. (1975).

A set of regression equations was developed to fully utilize the data of Chandler et al. (AMRL Technical Report 74-137, Wright-Patterson Air Force Base, 1975) to estimate segmental moments of inertia in living subjects. Using anthropometric measurements as predictors, moments of inertia can be computed about both transverse and longitudinal axes passing through each segment's center of mass. Symmetry about segment long axes is assumed. Because of the small sample size upon which these equations are based, it is suggested that they be used cautiously, especially to avoid extrapolation to subjects having anthropometric measurements outside the range of sample values.