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At least 1,315 records · Page 73Linked to original sources
PubMed1988

Energetics of indoor track cycling in trained competitors.

Steady-state track VO2 was estimated by means of the retroextrapolation method in seventeen competitive male cyclists at speeds ranging from 28 to 43 km.h-1. Peak VO2 was also determined using an ergocycle multistage test (80 rev.min-1). Results showed large VO2 variations at similar speeds on the track (SEE greater than 10% Y; n = 17). Third degree regressions were the most accurate to describe the evolution of VO2 with speed, while the units ml.kg-0.667.min-1 showed better correlations and lower dispersions than 1.min-1, ml.kg-1.min-1, and 1.min-1.m-2. When categorized according to the Québec Cycling Federation ranking, (elites: n = 6; nonelites: n = 11), the elites tended to demonstrate to a lower mean VO2 for the range of velocities studied. The difference was, however, not statistically significant (P greater than 0.05). Interindividual variations were reduced by expressing VO2 and speed as relative percentages of maximal values in ten subjects: % MAP = 6.475 e exp [0.0274% MAS] where % MAP = track VO2/laboratory peak VO2, and % MAS = speed/speed associated with peak VO2 on the track. No significant difference was observed between track and ergocycle peak VO2 (P greater than 0.05), indicating the validity of the 80 rev.min-1 protocol for laboratory evaluation of racing cyclists. The concept of cycling economy as a contributing factor to performance and applications of the % MAP-% MAS relationship are discussed.

Adult↗
PubMed1998

Injury and training characteristics of male Elite, Development Squad, and Club triathletes.

Links between overuse injury prevalence in triathletes training for 1.5km, 40km, 10km triathlon and both intrinsic and extrinsic factors were assessed in 12 Elite, 17 Development and 87 male Club triathletes by a five year retrospective questionnaire. Elite, Development and Club triathletes differed in training mileage, duration and number of workouts but not in overall injury prevalence, distribution, and severity. Overuse injury occurred in 75.0% of male Elite Squad, 75.0% of Development Squad and 56.3% of Club athletes with 1.9-2.9 sites affected. The most common injuries - the achilles tendon (10.3-17.9%), lower back (15.8-17.9%) and knee (14.2-21.9% of injuries) - were also among the most severe. Running injuries accounted for more of the total number of injuries than cycling injuries in Elite (62.1 % vs 34.5%, p<0.05), Development (64.3% vs 25.0%, p<0.05) and Club triathletes (58.7% vs 15.9%, p<0.05). The number of running injuries sustained correlated with triathlon training distance, cycling distance (p<0.03), swimming distance (p<0.01), number of triathlon workouts (p<0.03) and number of running sessions (p<0.03) within one weeks race training. The number of overuse injuries sustained during cycling correlated with time spent running and cycling.

Adult↗
PubMed1998

[Injury risk of competitive, handicapped cross-country skiers in training nd competition].

Injuries caused by cross country skiing have been poorly investigated in handicapped athletes. The dynamic sliding shape of motion makes this sport to a suitable discipline for people with a deficit of locomotion. Visual handicapped people with a guide are able to improve their motoric skills, co-ordination, orientation and body self-consciousness in the track. Since handicapped athletes are performing in international competitions the training intensity to fulfill the requirements, but also the risk of overstrain induced injuries got increased, like in other high-performance sports. Our study examined injuries and overuse syndromes of the German National Team Ski Nordic during the Paralympics in Tignes/ Albertville (1992). Lillehammer (1994) and the training period in preparation for the Paralympics in Nagano (March 1998). The incidence and kind of injuries in the competitive handicapped cross country skier was comparable with non-handicapped athletes, but the injury pattern was different.

Adult↗
PubMed1986

Effects of physical training and competition on the iron status of female field hockey players.

Female collegiate field hockey players showed decreases in iron stores (as measured by serum ferritin) in each of 3 successive fall seasons studied. After the 1st season of regular play, a decrease (25-23 ng/ml was observed, but measurements after post-season tournament play for the 2nd and 3rd seasons showed significant (P less than 0.05) decreases of 37% (30-19 ng/ml) and 30% (24-17 ng/ml), respectively. The added stress of tournament play appeared to cause additional loss of reserve iron nearly as great as that experienced during early season training. After several years of play, serum ferritin levels in these athletes were frequently between 10 and 20 ng/ml, with the lowest levels occurring in 3rd- and 4th-year athletes. Those women who participated in all 3 years had progressively declining serum ferritin levels throughout their collegiate careers. Participation in collegiate field hockey jeopardizes body iron stores, and iron reserves tend to become progressively more depleted after successive seasons of competition.

Adult↗
PubMed1983

Bone marrow iron depression in competitive distance runners.

Suboptimal hemoglobin and serum iron have been reported in endurance athletes. In the present study peripheral blood, bone marrow cellularity and hemosiderin, serum iron and serum iron binding capacity were observed in 12 competitive distance runners. Hemoglobin, hematocrit, mean corpuscular volume and concentration, serum iron and iron binding capacity were within normal range. Peripheral blood showed mild hypochromia in six runners, bone marrow cellularity was reduced in two, while bone marrow hemosiderin granules were absent in seven and traces were seen in five. These data suggest that a proportion of highly trained distance runners have insufficient iron stores and need supplementation to balance their iron requirements.

Adolescent↗
PubMed2004

Pursuit-evasion predator-prey waves in two spatial dimensions.

We consider a spatially distributed population dynamics model with excitable predator-prey kinetics, where species propagate in space due to their taxis with respect to each other's gradient in addition to, or instead of, their diffusive spread. Earlier, we have described new phenomena in this model in one spatial dimension, not found in analogous systems without taxis: reflecting and self-splitting waves. Here we identify new phenomena in two spatial dimensions: unusual patterns of meander of spirals, partial reflection of waves, swelling wave tips, attachment of free wave ends to wave backs, and as a result, a novel mechanism of self-supporting complicated spatiotemporal activity, unknown in reaction-diffusion population models.

Adaptation, Physiological↗
PubMed2004

Food chain chaos with canard explosion.

The "tea-cup" attractor of a classical prey-predator-superpredator food chain model is studied analytically. Under the assumption that each species has its own time scale, ranging from fast for the prey to intermediate for the predator and to slow for the superpredator, the model is transformed into a singular perturbed system. It is demonstrated that the singular limit of the attractor contains a canard singularity. Singular return maps are constructed for which some subdynamics are shown to be equivalent to chaotic shift maps. Parameter regions in which the described chaotic dynamics exist are explicitly given.

Adaptation, Physiological↗
PubMed2006

Self-organized similarity, the evolutionary emergence of groups of similar species.

Ecologists have long been puzzled by the fact that there are so many similar species in nature. Here we show that self-organized clusters of look-a-likes may emerge spontaneously from coevolution of competitors. The explanation is that there are two alternative ways to survive together: being sufficiently different or being sufficiently similar. Using a model based on classical competition theory, we demonstrate a tendency for evolutionary emergence of regularly spaced lumps of similar species along a niche axis. Indeed, such lumpy patterns are commonly observed in size distributions of organisms ranging from algae, zooplankton, and beetles to birds and mammals, and could not be well explained by earlier theory. Our results suggest that these patterns may represent self-constructed niches emerging from competitive interactions. A corollary of our findings is that, whereas in species-poor communities sympatric speciation and invasion of open niches is possible, species-saturated communities may be characterized by convergent evolution and invasion by look-a-likes.

Animals↗
PubMed2006

The dynamics of Machiavellian intelligence.

The "Machiavellian intelligence" hypothesis (or the "social brain" hypothesis) posits that large brains and distinctive cognitive abilities of humans have evolved via intense social competition in which social competitors developed increasingly sophisticated "Machiavellian" strategies as a means to achieve higher social and reproductive success. Here we build a mathematical model aiming to explore this hypothesis. In the model, genes control brains which invent and learn strategies (memes) which are used by males to gain advantage in competition for mates. We show that the dynamics of intelligence has three distinct phases. During the dormant phase only newly invented memes are present in the population. During the cognitive explosion phase the population's meme count and the learning ability, cerebral capacity (controlling the number of different memes that the brain can learn and use), and Machiavellian fitness of individuals increase in a runaway fashion. During the saturation phase natural selection resulting from the costs of having large brains checks further increases in cognitive abilities. Overall, our results suggest that the mechanisms underlying the "Machiavellian intelligence" hypothesis can indeed result in the evolution of significant cognitive abilities on the time scale of 10 to 20 thousand generations. We show that cerebral capacity evolves faster and to a larger degree than learning ability. Our model suggests that there may be a tendency toward a reduction in cognitive abilities (driven by the costs of having a large brain) as the reproductive advantage of having a large brain decreases and the exposure to memes increases in modern societies.

Biological Evolution↗
PubMed2003

Stress promotes maleness in hermaphroditic modular animals.

Sex-allocation theory developed for hermaphroditic plants predicts that impaired phenotype or reduced parental survivorship caused by environmental stress should induce relatively greater allocation to the male function. We provide experimental evidence of stress-induced maleness, already well documented in flowering plants, in a modular animal. By using cloned copies of replicate genotypes, we show that the marine bryozoan Celleporella hyalina increases the ratio of male to female modules in response to diverse environmental stressors. Mating trials confirmed that paternity is determined by fair-raffle sperm competition, which should obviate local mate competition at characteristic population density and promote the advantage of increased male allocation. The demonstrated similarity to plants transcends specific physiological pathways and suggests that stress-induced bias toward male function is a general response of hermaphroditic modular organisms to impaired prospects for parental productivity or survival.

Animals↗
PubMed2002

Testing neoclassical competitive market theory in the field.

This study presents results from a pilot field experiment that tests predictions of competitive market theory. A major advantage of this particular field experimental design is that my laboratory is the marketplace: subjects are engaged in buying, selling, and trading activities whether I run an exchange experiment or am a passive observer. In this sense, I am gathering data in a natural environment while still maintaining the necessary control to execute a clean comparison between treatments. The main results of the study fall into two categories. First, the competitive model predicts reasonably well in some market treatments: the expected price and quantity levels are approximated in many market rounds. Second, the data suggest that market composition is important: buyer and seller experience levels impact not only the distribution of rents but also the overall level of rents captured. An unexpected result in this regard is that average market efficiency is lowest in markets that match experienced buyers and experienced sellers and highest when experienced buyers engage in bargaining with inexperienced sellers. Together, these results suggest that both market experience and market composition play an important role in the equilibrium discovery process.

Adult↗
PubMed1975

Life games and statistical models.

A set of equations is obtained, which describes the rules of a class of games (life games). These games simulate the processes of growth, death, survival, and competition. The equations are nonlinear difference equations, where the degree of nonlinearity is directly related to the number of interacting neighbors. The time evolution and the development of geometric patterns can be studied starting from these equations. Extensions and generalizations, such as the introduction of stochastic elements, can easily be accommodated in the formalism. Some significant unsolved problems are noted.

Biological Evolution↗
PubMed1976

An experimental analysis of competitive indeterminacy in Tribolium.

This report reexamines experimentally the problem of competitive indeterminacy in mixed-species populations of the flour beetles, Tribolium confusum and T. castaneum. Indeterminacy takes the form of alternative competitive outcomes: in some replicate cultures one species exterminates the other with a probability, say p, whereas in others, the opposing species wins with a complementary probability, 1-p. The conventional explanation for this is the genetic founder effect hypothesis--an explanation based on genetic stochasticity. The experiment reported here partitioned indeterminacy into founder effect and nonfounder effect components. The results implicate demographic stochasticity, not classical genetic founder effect, as a factor influencing the identity of the winning species.

Animals↗
PubMed2003

Structure- and function-based characterization of a new phosphoglycolate phosphatase from Thermoplasma acidophilum.

The protein TA0175 has a large number of sequence homologues, most of which are annotated as unknown and a few as belonging to the haloacid dehalogenase superfamily, but has no known biological function. Using a combination of amino acid sequence analysis, three-dimensional crystal structure information, and kinetic analysis, we have characterized TA0175 as phosphoglycolate phosphatase from Thermoplasma acidophilum. The crystal structure of TA0175 revealed two distinct domains, a larger core domain and a smaller cap domain. The large domain is composed of a centrally located five-stranded parallel beta-sheet with strand order S10, S9, S8, S1, S2 and a small beta-hairpin, strands S3 and S4. This central sheet is flanked by a set of three alpha-helices on one side and two helices on the other. The smaller domain is composed of an open faced beta-sandwich represented by three antiparallel beta-strands, S5, S6, and S7, flanked by two oppositely oriented alpha-helices, H3 and H4. The topology of the large domain is conserved; however, structural variation is observed in the smaller domain among the different functional classes of the haloacid dehalogenase superfamily. Enzymatic assays on TA0175 revealed that this enzyme catalyzed the dephosphorylation of phosphoglycolate in vitro with similar kinetic properties seen for eukaryotic phosphoglycolate phosphatase. Activation by divalent cations, especially Mg2+, and competitive inhibition behavior with Cl- ions are similar between TA0175 and phosphoglycolate phosphatase. The experimental evidence presented for TA0175 is indicative of phosphoglycolate phosphatase.

Amino Acid Sequence↗