Kinetics of crimp and slope grip in rock climbing

The aim was to investigate differences of the kinetics of the crimp and the slope grip used in rock climbing. Nine cadaver fingers were prepared and fixated with the proximal phalanx in a frame. The superficial (FDS) and deep (FDP) flexor tendons were loaded selectively and together with 40 N in the crimp grip (PIP joint flexed 90°/DIP joint hyperextended) and the slope grip position (<25° flexed/50° flexed respectively). Five different grip sizes were tested and the flexion force which was generated to the grip was measured. In the crimp grip the FDP generated more flexion force in small sized holds whereas the FDS generated more force in the larger holds. During the slope grip the FDP was more effective than the FDS. While both tendons were loaded, the flexion force was always greater during crimp grip compared with the slope grip. The FDP seems to be most important for very small holds using the crimp grip but also during slope grip holds whereas the FDS is more important for larger flat holds.     

Prediction of indoor climbing performance in women rock climbers

In an attempt to more clearly understand the strength characteristics of female rock climbers and whether those variables affect and predict climbing performance, 2 indoor climbing performance tests (route and bouldering) were compared to a series of muscular strength tests performed by moderate (n = 6), intermediate (n = 6), and expert (n = 6) female rock climbers. Significant differences (p < 0.05) were found between the expert group and the moderate and intermediate groups for climbing specific hand strength, as well as 1-arm lock-off strength when expressed as a strength-to-weight ratio. Multiple correlations showed that these variables (r > 0.426) as well as a questionnaire of past climbing performance (r > 0.86) significantly correlated to the tests of indoor climbing performance. In conclusion, climbing-specific tests of hand strength and of one arm lock-off strength reliably and sensitively measured 2 significant variables in the performance of indoor rock climbing, and a questionnaire of past best performance may be an accurate tool for the prediction of indoor climbing performance.     

Genetic structure and effective population size of Sydney rock oysters in eastern Australia

Oyster reef habitats are critical to coastal biodiversity and their decline has prompted restoration efforts in Australia. Knowledge gaps exist regarding the population structure and diversity of key species in these habitats. This may be critical information for the design of effective restoration programs. Sydney rock oysters (Saccostrea glomerata) are the dominant reef-forming bivalve in eastern Australia. Wild populations of S. glomerata have declined due to overharvesting, disease outbreaks, coastal development and reduced water quality. Here, we use genetic markers identified by genome-wide sequencing to investigate the genetic structure and diversity of wild Sydney rock oysters throughout their distribution in eastern Australia. We examine evidence for past population bottlenecks and spatial genetic structure associated with the East Australian Current. Analysis of 3, 400 neutral single-nucleotide polymorphisms (SNPs) revealed a single population, and an overlap with two other Saccostrea sp. at the northernmost boundary of the distribution. We detected signals of asymmetric gene flow consistent with the direction of the East Australian Current, and spatial structure patterns of limited genetic isolation by distance and spatial autocorrelation in the northern region (which experiences stronger effects of the East Australian Current) but not in the southern region of the distribution. We found no evidence of significant recent bottlenecks, with high effective population size throughout the species’ range. This information will provide a baseline against which to assess the impact of restoration projects, and guide strategies for sourcing stock for the enhancement of wild oyster populations. Our results provide a positive outlook for the resilience and adaptive capacity of Sydney rock oysters, and highlight wild populations as valuable resources for aquaculture and restoration initiatives.

     

The effect of a repetitive, fatiguing lifting task on horizontal ground reaction forces

There are many outdoor work environments that involve the combination of repetitive, fatiguing lifting tasks and less-than-optimal footing (muddy/slippery ground surfaces). The focus of the current research was to evaluate the effects of lifting-induced fatigue of the low back extensors on lifting kinematics and ground reaction forces. Ten participants performed a repetitive lifting task over a period of 8 minutes. As they performed this task, the ground reaction forces and whole body kinematics were captured using a force platform and magnetic motion tracking system, respectively. Fatigue was verified in this experiment by documenting a decrease in the median frequency of the bilateral erector spinae muscles (pretest-posttest). Results indicate significant (p < 0.05) increases in the magnitude of the peak anterior/posterior (increased by an average of 18.3%) and peak lateral shear forces (increased by an average of 24.3%) with increasing time into the lifting bout. These results have implications for work environments such as agriculture and construction, where poor footing conditions and requirements for considerable manual materials handling may interact to create an occupational scenario with an exceptionally high risk of a slip and fall.     

Mating success in brood-guarding male rock bass,Ambloplites rupestris: the effect of body size

Synopsis The hypothesis that variation in a paternal trait associated with offspring survival will result in female mate choice based on that trait was tested in rock bass,Ambloplites rupestris, a temperate fresh water fish with uniparental male care. The number of eggs acquired by 108 nesting male rock bass, in Cranberry Lake (New York State, U.S.A.), was estimated in two different spawning episodes that differed in the size structure of the nesting male stock. Early breeders (between the 4–7 June 1989) were mainly medium and large males (101–300 g), as compared to late breeders (between the 19–21 June 1989) which were mostly small (50–100 g). Because survival of larvae in rock bass is significantly lower in nests guarded by small males as compared to nests guarded by medium and large males, it was hypothesized that female mate choice should have been (1) size-based, and (2) more intense late in the season when the nesting stock was comprised mostly of small males. The results were consistent with these hypotheses. Variation in egg numbers per nest was significantly higher during the late spawning episode. In addition, egg number per nest were normally distributed during the early spawning episode, but were positively skewed and leptokurtic during the later episode. The correlation between male size and egg number was significant for both spawning episodes. However, during the late episode male size explained 23% of the variation in egg numbers versus only 8% of the variation during the earlier episode.     

The effect of variation of the lingual shape of mandibular complete dentures on lingual resistance to lifting forces

Increasing life expectancy, age related reduction in adaptability and progressive severe mandibular resorption all add to the importance of any factor improving the prosthetic success. Objective : To investigate the effect of two different lingual shapes of lower dentures on patients' ability to resist lifting forces. Design : Tongue pressures on the lingual surface of complete mandibular experimental dentures were recorded from mid-line, premolar and molar transducers. Two experimental prostheses were fabricated for each subject: one conventionally contoured, the other formed by piezography. Setting : A clinical research laboratory. Subjects Five experienced complete denture wearers between age 64 and 82 years. Intervention Lifting forces were applied at the midline, left and right premolar sites in random order. Main outcome measures : Peak resistance to lifting forces and lingual pressures used during these tests. Results : Lingual pressures exerted anteriorly were dramatically higher than those on premolar and molar surfaces. Significantly higher pressures were used to resist lifting forces applied to piezographically than conventionally formed contours; correspondingly, significantly higher lifting peak forces were, on average, resisted. Conclusions : Providing a lower denture with a piezographically produced lingual surface was shown, in this preliminary study, to enhance tongue retentive ability over a conventional design. It seems reasonable to maximise retentive potential with oblique sublingual polished surfaces and minimise the adaptive demand, particularly for older patients, by using a piezographic technique which “customises” the contour and precludes over-extension.     

Measuring dimensions: the regulation of size and shape

Over many years evidence has accumulated that plants and animals can regulate growth with reference to overall size rather than cell number. Thus, organs and organisms grow until they reach their characteristic size and shape and then they stop - they can even compensate for experimental manipulations that change, over several fold, cell number or average cell size. If the cell size is altered, the organism responds with a change in cell number and vice versa. We look at the Drosophila wing in more detail: here, both extracellular and intracellular regulators have been identified that link cell growth, division and cell survival to final organ size. We discuss a hypothesis that the local steepness of a morphogen gradient is a measure of length in one axis, a measure that is used to determine whether there will be net growth or not.     

The effect of design variables of condylar total knees on the joint forces in step climbing based on a computer model.

The ability to climb a steep step or rise from a low chair after total knee replacement may be enhanced if the required force in the quadriceps muscle is reduced. This can potentially be achieved if the total knee produces a large lever arm measured from the femoral-tibial contact point to the patellar ligament. A reduced quadriceps force would also reduce the patello-femoral force and the femoral-tibial contact force. The contact point location is likely to be a function of the geometry of the femoral and tibial components in the sagittal plane, including the relative distal and posterior radii of the femoral profile, the location of the bottom-of-the-dish of the tibial surface, the radius of the tibial surface, and the presence or absence of the posterior cruciate ligament. A three-dimensional model of the knee was developed including the quadriceps and various ligaments. In the study, the motion was confined to flexion extension and displacement in the sagittal plane. The quadriceps was assumed to be the only muscle acting. A standard software package (Pro/Mechanica) was used for the analysis. For a femoral component with a smaller distal radius, there was 12% reduction in the quadriceps muscle force and up to 11% reduction in the patello-femoral force from about 100 up to 60 degrees flexion. However, apart from that, there were less than 10% differences in all the forces as a function of all of the design variables studied. This was attributed to the relatively small changes in the lever arm of the patella tendon, since the tendon moves in an anterior-posterior direction along with the femur. An additional factor explaining the results was the change in the anterior-posterior contact point as controlled by the forces in the patella tendon and in the soft tissues. The results imply that for a standard condylar replacement knee, the muscle and contact forces are not greatly affected by the geometrical design variables.     

Optimal climbing speed explains the evolution of extreme sexual size dimorphism in spiders

Several hypotheses have been put forward to explain the evolution of extreme sexual size dimorphism (SSD). Among them, the gravity hypothesis (GH) explains that extreme SSD has evolved in spiders because smaller males have a mating or survival advantage by climbing faster. However, few studies have supported this hypothesis thus far. Using a wide span of spider body sizes, we show that there is an optimal body size (7.4 mm) for climbing and that extreme SSD evolves only in spiders that: (1) live in high‐habitat patches and (2) in which females are larger than the optimal size. We report that the evidence for the GH across studies depends on whether the body size of individuals expands beyond the optimal climbing size. We also present an ad hoc biomechanical model that shows how the higher stride frequency of small animals predicts an optimal body size for climbing.     

The effect of sample size in studies of soil microbial community structure

Replicate soil samples of 0.01, 0.1, 0.25, 1.0 and 10.0 g were taken from a single, large, homogenized sample from a field maintained as continuous meadow. The samples were processed for direct enumeration of bacterial cells and community structure assays by DGGE analysis of PCR-amplified 16S-rDNA fragments from whole community extracts. The goal was to determine the sample size or size range that produced the most consistent results (i.e., mean values) and the lowest variance. Enumeration data were analyzed by ANOVA, and the community composition fingerprints were analyzed by discriminant analysis (DA). Acceptable results were obtained for sample sizes from 0.1 to 1.0 g for both enumeration and community fingerprinting, but the size that yielded the best results for both measures was 0.25 g. The results suggest that for well homogenized silt loam soils with moderate organic matter concentrations, this sample size should produce high quality consistent results. For soils that differ in organic concentrations or clay content, a reconnaissance survey similar to the present examination is recommended.     

The effect of school size on the structure and dynamics of minnow schools

Varying the number of fish in schools of minnows (Phoxinus phoxinus) affects their three-dimensional structure and internal dynamics. Previous authors have suggested that single pairs of fish can be considered a school, but internal organization and structure of two-fish schools are quantitatively different from those for larger schools. Time series analyses show that correlations between fishes' instantaneous velocities increase with school size and as interfish distances decrease. Average cross-correlations of fishes' velocities indicate that leader/follower relationships are common in two-fish schools, but they are not seen for schools with more fish in them. Pairs of fish tend to swim one behind another and on the same level, but larger schools take on a more three-dimensional appearance.     

The structure and intermolecular forces of DNA condensates

Spontaneous assembly of DNA molecules into compact structures is ubiquitous in biological systems. Experiment has shown that polycations can turn electrostatic self-repulsion of DNA into attraction, yet the physical mechanism of DNA condensation has remained elusive. Here, we report the results of atomistic molecular dynamics simulations that elucidated the microscopic structure of dense DNA assemblies and the physics of interactions that makes such assemblies possible. Reproducing the setup of the DNA condensation experiments, we measured the internal pressure of DNA arrays as a function of the DNA–DNA distance, showing a quantitative agreement between the results of our simulations and the experimental data. Analysis of the MD trajectories determined the DNA–DNA force in a DNA condensate to be pairwise, the DNA condensation to be driven by electrostatics of polycations and not hydration, and the concentration of bridging cations, not adsorbed cations, to determine the magnitude and the sign of the DNA–DNA force. Finally, our simulations quantitatively characterized the orientational correlations of DNA in DNA arrays as well as diffusive motion of DNA and cations.     

Measuring the lung function in the mouse: the challenge of size

Measurement of the effects of drugs, mediators and infectious agents on various models of lung disease, as well as assessment of lung function in the intact mouse has the potential for significantly advancing our knowledge of lung disease. However, the small size of the mouse presents significant challenges for the assessment of lung function. Because of compromises made between precision and noninvasiveness, data obtained may have an uncertain bearing on the mechanical response of the lung. Nevertheless, considerable recent progress has been made in developing valid and useful measures of mouse lung function. These advances, resulting in our current ability to measure sophisticated indices of lung function in laboratory animals, are likely to lead to important insights into the mechanisms of lung disease.     

The relation of size to climbing, line-crossing and running performances of male crab spiders

Mobile predators employ a variety of locomotor tasks in hunting, avoiding predators and searching for mates. However, few studies have evaluated the performances of a population’s members in all of their major locomotor tasks, even though all of these performances may affect both an individual’s fitness and how members of a population exploit resources. Male crab spiders Misumena vatia, diminutive members of an extremely sexually dimorphic species, regularly run, climb and cross silken lines. For the most part, individuals moved at similar speeds relative to each other in the three tasks: the 15th fastest runner was approximately 15th fastest in the other two moves as well. Thus, these spiders provided little evidence that any individual excelled at one task or another, relative to other members of its population, thereby exhibiting a marked behavioral syndrome. However, large individuals moved faster than small ones in these tasks, especially when climbing. Although the gravity and bridging hypotheses predict that small individuals climb and cross silken lines faster than larger ones, at ca. 4.15 mg (extremes of 2.5–8.0 mg), male Misumena, and most terrestrial invertebrates, fall well below weight constraints currently predicted by either hypothesis. Data on sexual cannibalism, overwintering, and lifespan suggest possible countering advantages of small size, and hence balancing selection, which may contribute to Misumena’s striking sexual size dimorphism and explain the males’ wide size range.     

Cell cycle and cell size dependence of susceptibility to hydrodynamic forces

Exposure of animal cells to intense hydrodynamic forces exerted in turbulent capillary flow, and by controiled agitation and aeration, resulted in preferential destruction of S and G(2) cells and the extent of destruction of these cells was dependent upon the intensity of the action. The loss of these cells was possibly due to their larger size. However, the appearance of large numbers of membrane-bound vesicular structures similar to apoptotic bodies as well as cells with low DNA stainability (in a sub-G(1) peak) suggested that the action of adverse hydrodynamic forces on these large cells may at least in part be to induce an apoptotic response. (c) 1995 John Wiley & Sons, Inc.     

Measuring glomerular number and size in perfused kidneys using MRI

The goal of this work was to nondestructively measure glomerular (and thereby nephron) number in the whole kidney. Variations in the number and size of glomeruli have been linked to many renal and systemic diseases. Here, we develop a robust magnetic resonance imaging (MRI) technique based on injection of cationic ferritin (CF) to produce an accurate measurement of number and size of individual glomeruli. High-field (19 Tesla) gradient-echo MR images of perfused rat kidneys after in vivo intravenous injection of CF showed specific labeling of individual glomeruli with CF throughout the kidney. We developed a three-dimensional image-processing algorithm to count every labeled glomerulus. MRI-based counts yielded 33,786 ± 3,753 labeled glomeruli (n = 5 kidneys). Acid maceration counting of contralateral kidneys yielded an estimate of 30,585 ± 2,053 glomeruli (n = 6 kidneys). Disector/fractionator stereology counting yielded an estimate of 34,963 glomeruli (n = 2). MRI-based measurement of apparent glomerular volume of labeled glomeruli was 4.89 × 10(-4) mm(3) (n = 5) compared with the average stereological measurement of 4.99 × 10(-4) mm(3) (n = 2). The MRI-based technique also yielded the intrarenal distribution of apparent glomerular volume, a measurement previously unobtainable in histology. This work makes it possible to nondestructively measure whole-kidney glomerular number and apparent glomerular volumes to study susceptibility to renal diseases and opens the door to similar in vivo measurements in animals and humans.     

The effect of acidification in enclosures on the biomass and population size structure of Bosmina longirostris

An in situ enclosure experiment was performed from June to September, 1982, in Lake O'Woods, West Virginia (pH7.0), to examine the effects of acidification on the Bosmina longirostris population. Treatments were two control enclosures and two enclosures acidified from an initial pH of 7.2 to pH 4.2 over a 44 day period, using H₂SO₄. B. longirostris was not adversely affected by the acidification. In fact, its abundance, biomass, and mean body size increased in the acid treatment, as compared withe control. This positive response was probably not a direct consequence of the altered water chemistry, but instead may have occured due to reduced competition for food, and also reduced predation pressure. Acidification resulted in a decreased abundance of other herbivores, and elimination of the dominant carnivore, Mesocyclops edax.     

Network structure and forces involved in perilla globulin gelation: comparison with sesame globulin

Scanning electron micrographs show that perilla globulin gel had a finer network structure than sesame α-globulin gel. The effects of various reagents on the gel formation and solubility of perilla and sesame gels were compared. The contribution of disulfide bonds to the formation and stability of perilla gel was greater than to sesame gel, despite having the same subunit structure.     

Ions in water: characterizing the forces that control chemical processes and biological structure

The continuum electrostatics model of Debye and Hückel [P. Debye and E. Hückel, On the theory of electrolytes. I. Freezing point depression and related phenomena., Phys. Z. 24 (1923) 185-206.] and its successors utilize a macroscopic dielectric constant and assume that all interactions involving ions are strictly electrostatic, implying that simple ions in water generate electric fields strong enough to orient water dipoles over long distances. However, solution neutron and X-ray diffraction indicate that even di- and tri-valent ions do not significantly alter the density or orientation of water more than two water molecules (5 A) away. Therefore the long range electric fields (generated by simple ions) which can be detected by various resonance techniques such as fluorescence resonance energy transfer over distances of 30 A (about 11 water diameters) or more must be weak relative to the strength of water-water interactions. Two different techniques indicate that the interaction of water with anions is by an approximately linear hydrogen bond, suggesting that the dominant forces on ions in water are short range forces of a chemical nature.