Power and maximum strength relationships during performance of dynamic and static weighted jumps

The purpose of this study was to investigate the relationship of the 1 repetition maximum (1RM) squat to power output during countermovement and static weighted vertical squat jumps. The training experience of subjects (N = 22, 87.0 +/- 15.3 kg, 14.1 +/- 7.1% fat, 22.2 +/- 3.8 years) ranged from 7 weeks to 15+ years. Based on the 1RM squat, subjects were further divided into the 5 strongest and 5 weakest subjects (p 相似文献   

Genetic and environmental sources on familial transmission in Biscayan families – III. The dynamometric strength

The present research analyses a cross-sectional sample of 284 individuals (86 fathers, 86 mothers, 54 sons and 58 daughters) in 86 nuclear families living in the province of Biscay (Basque Country, Spain), with the aim of estimating both transmissible and non-transmissible components acting on familial resemblance for the maximum dynamometric strength of both hands, by means of a path analysis. Standardised data of each generation and sex were adjusted to a BETA model of path analysis independent of sex effects, allowing nevertheless the possibility to differentiate between transmissible (genetic and cultural) and non-transmissible (environmental) components acting on the observed phenotypic variance in Biscayan offspring. The results supported the full model of familial transmission for the two variables, in addition to other reduced models that gave rise to transmission effects regardless of any influence from the siblings' shared environment on the environmental transmitted component from their parents (b = 0), and without social homogamy between mates (u = 0). The most parsimonious model created, based on the previous ones, was accepted for both traits. The total transmissible variance (t²) explained between 21% (right hand) and 44% (left hand) of the observed phenotypic variation. These values are close to those from the literature (t² = 37%). However, we should take into account that these kinds of estimations are specific for each group or population.     

Investigating the genetic and environmental structure of Cloninger's personality dimensions in adolescence.

In this study we examined the genetic and environmental structure of four dimensions from Cloninger's personality system: novelty-seeking (NS), harm-avoidance (HA), reward-dependence (RD), and persistence (PS). Although adult twin studies suggest that these personality dimensions are moderately heritable, this is the first twin study of Cloninger's personality dimensions in adolescence--a period marked by significant physiological and social changes. Study participants included 1851 adolescent twins between the ages of 11 and 18 years; 878 complete twin pairs and 95 singleton-responding twins. Subjects were participants in two community-based samples of twins residing in the state of Colorado. Results indicated that cross-sectional mean levels for NS, HA and RD tended to show modest increases across the adolescent years, while PS showed modest mean decreases. Consistent sex differences in means were found only for RD. Univariate biometrical twin models were used to decompose trait variance into genetic and environmental sources. Results indicated that for NS, HA and RD additive genetic influences and unique environmental effects were sufficient to explain the data. PS, however, could be explained by unique and common environmental effects only, with different patterns of common environmental effects for males and females. We found moderate heritability estimates for NS, HA and RD ranging from .28 to .36--with no evidence for sex-limitation in those influences.     

Changes in blood lipids and blood pressure during adolescence.

A total of 625 adolescents from three general practices participated in a cross-sectional study of cardiovascular disease risk factors. The girls had higher serum total and high density lipoprotein (HDL) cholesterol concentrations than the boys, while the boys had higher serum triglyceride concentrations. Smoking (equally prevalent in both sexes) was associated with lower HDL cholesterol concentrations, particularly in boys, while in girls use of oral contraceptives was associated with higher total cholesterol and lower HDL cholesterol concentrations showed striking associations with age, height, and sexual maturation in boys, but not in girls. Triglyceride concentrations were associated with age in boys. Systolic blood pressure and serum urate concentrations were higher in boys and rose steeply with age, but no age association was seen for urate concentrations or systolic blood pressure in girls or for diastolic pressures in either sex. Girls, however, had higher diastolic pressures. There was a strong association between urate concentration and the other cardiovascular disease risk factors, especially HDL cholesterol. Adolescence is associated with considerable changes in cardiovascular disease risk factors, and there are striking sex differences in these changes.     

Genetic determination of fragile-site expression.

To explore genetic effects on the expression of chromosomal fragile sites in vitro, we studied the expression of common fragile sites (c-fra) in cultured lymphocytes of a human chimera (Chi46,XX/46,XY). Since the two cell lines in the chimera share the same environment in vitro and in vivo on cell culture preceding chromosome analysis, differences in the expression of c-fra must be due to genetic factors. The peripheral lymphocytes were cultured in medium 199 and in medium RPMI 1640 with and without aphidicolin. All lesions were localized after GTG-banding and mapped to the human idiogram. In the cultures with aphidicolin the XX cells showed, at high (0.4 microM) APC levels, a significantly higher expression of c-fra than did the XY cells. This difference between cell lineages was not confined to certain individual c-fra; rather it was seen for practically all of them. Therefore, we conclude that there are genetic factors which influence the propensity of c-fra to be expressed. Whether sex is one of these factors, or perhaps even the most important one, still has to be elucidated.     

Resistance training vs. static stretching: effects on flexibility and strength

Morton, SK, Whitehead, JR, Brinkert, RH, and Caine, DJ. Resistance training vs. static stretching: Effects on flexibility and strength. J Strength Cond Res 25(12): 3391-3398, 2011-The purpose of this study was to determine how full-range resistance training (RT) affected flexibility and strength compared to static stretching (SS) of the same muscle-joint complexes in untrained adults. Volunteers (n = 25) were randomized to an RT or SS training group. A group of inactive volunteers (n = 12) served as a convenience control group (CON). After pretesting hamstring extension, hip flexion and extension, shoulder extension flexibility, and peak torque of quadriceps and hamstring muscles, subjects completed 5-week SS or RT treatments in which the aim was to stretch or to strength train the same muscle-joint complexes over similar movements and ranges. Posttests of flexibility and strength were then conducted. There was no difference in hamstring flexibility, hip flexion, and hip extension improvement between RT and SS, but both were superior to CON values. There were no differences between groups on shoulder extension flexibility. The RT group was superior to the CON in knee extension peak torque, but there were no differences between groups on knee flexion peak torque. The results of this preliminary study suggest that carefully constructed full-range RT regimens can improve flexibility as well as the typical SS regimens employed in conditioning programs. Because of the potential practical significance of these results to strength and conditioning programs, further studies using true experimental designs, larger sample sizes, and longer training durations should be conducted with the aim of confirming or disproving these results.     

Genetic sex determination mechanisms and evolution.

Different animal groups exhibit a surprisingly diversity of sex determination systems. Moreover, even systems that are superficially similar may utilize different underlying mechanisms. This diversity is illustrated by a comparison of sex determination in three well-studied model organisms: the fruitfly Drosophila melanogaster, the nematode Caenorhabditis elegans, and the mouse. All three animals exhibit male heterogamety, extensive sexual dimorphism and sex chromosome dosage compensation, yet the molecular and cellular processes involved are now known to be quite unrelated. The similarities must have arisen by convergent evolution. Studies of sex determination demonstrate that evolution can produce a variety of solutions to the same basic problems in development.     

Genetic engineering strategies for environmental applications.

Environmental applications of genetically engineered microorganisms are currently hampered not only by legal regulations restricting their release, but also by the frequent dearth of adequate genetic tools for their construction in the laboratory. Recent approaches to strain development include the use of non-antibiotic markers as selection determinants, the use of transposon-vectors for the permanent acquisition of recombinant genes, and the utilization of expression devices based on promoters from promiscuous plasmids and biodegradative pathway genes.     

Emotional and cognitive changes during adolescence

Adolescence is a critical period for maturation of neurobiological processes that underlie higher cognitive functions and social and emotional behavior. Recent studies have applied new advances in magnetic resonance imaging to increase understanding of the neurobiological changes that occur during the transition from childhood to early adulthood. Structural imaging data indicate progressive and regressive changes in the relative volumes of specific brain regions, although total brain volume is not significantly altered. The prefrontal cortex matures later than other regions and its development is paralleled by increased abilities in abstract reasoning, attentional shifting, response inhibition and processing speed. Changes in emotional capacity, including improvements in affective modulation and discrimination of emotional cues, are also seen during adolescence. Functional imaging studies using cognitive and affective challenges have shown that frontal cortical networks undergo developmental changes in processing. In summary, brain regions that underlie attention, reward evaluation, affective discrimination, response inhibition and goal-directed behavior undergo structural and functional re-organization throughout late childhood and early adulthood. Evidence from recent imaging studies supports a model by which the frontal cortex adopts an increasingly regulatory role. These neurobiological changes are believed to contribute, in part, to the range in cognitive and affective behavior seen during adolescence.     

Coping ability at mid-life in relation to genetic and environmental influences at adolescence: a follow-up of Swedish twins from adolescence to mid-life.

From 1964 to 1971, twins and singleton controls were followed from 10 to 16 years of age in Swedish schools. It was a nationally representative sample of 323 twin pairs, and 1193 classmate controls. In 1991 a follow-up was made of this sample with the purpose of investigating genetic influences on experienced family and school environments, as well as coping ability at the age of 35. The follow-up also evaluated the relation between coping ability at mid-life and family environment, as well as coping ability and school environment at adolescence for males and females. Genetic influences on perceived family and school environments, as well as on self-reported coping ability, have been investigated by means of comparisons of MZ and DZ twin pairs. A stepwise linear regression analysis was performed to assess environmental influences on coping ability at mid-life. The findings indicated that coping ability at mid-life is influenced by both genetic and environmental factors. Different environmental factors were operating for males and females, however. The results demonstrate that early environmental factors and genetic disposition have a long-term effect on coping ability.     

Genetic and environmental factors in human osteoporosis

Osteoporosis is a common disorder, with prolongation of the average life span it has become a major public health problem. On the formation of osteoporosis genetic factors and environmental influences could play a role then it is considered as multi-factorial. Because a variety of functions to affect susceptibility to the formation of osteoporosis VDR-F, VDR-B, COL1A1, ESR1X, ESR1P and CTR are thought to be candidate genes. In this study, the aim is to investigate the relationship between these genes polymorphism and bone mineral density (BMD) values of lumbar vertebra and femoral neck in 188 Turkish people. Lumbar spine and femoral neck BMD of the individuals included in the study were measured by the dual X-ray absorptiometry method. The genotyped polymorphisms by simultaneous amplification of five regions of the genome, containing six SNPs of interest and detecting the amplified product, using the kit MetaBone Clinical Arrays^?. Statistical analyses indicated that; VDR-B gene polymorphisms major (P?=?0.013), VDR-F polymorphisms have minor (P?=?0.082) effect on femur BMD. None of the other genes has any significant effect on spinal BMD. Patient age, body mass index and diet has significant effect on femoral and spinal BMD. Osteoporosis is a multi-factorial disease and many genetic and non-genetic risk factors contribute to the development of osteoporosis. Early detection of a genetic predisposition to osteoporosis should allow delay and/or limit unfavorable changes in the bone tissue.     

Genetic caste determination in Pogonomyrmex harvester ants imposes costs during colony founding

Some populations of Pogonomyrmex harvester ants comprise genetically differentiated pairs of interbreeding lineages. Queens mate with males of their own and of the alternate lineage and produce pure-lineage offspring which develop into queens and inter-lineage offspring which develop into workers. Here we tested whether such genetic caste determination is associated with costs in terms of the ability to optimally allocate resources to the production of queens and workers. During the stage of colony founding, when only workers are produced, queens laid a high proportion of pure-lineage eggs but the large majority of these eggs failed to develop. As a consequence, the number of offspring produced by incipient colonies decreased linearly with the proportion of pure-lineage eggs laid by queens. Moreover, queens of the lineage most commonly represented in a given mating flight produced more pure-lineage eggs, in line with the view that they mate randomly with the two types of males and indiscriminately use their sperm. Altogether these results predict frequency-dependent selection on pairs of lineages because queens of the more common lineage will produce more pure-lineage eggs and their colonies be less successful during the stage of colony founding, which may be an important force maintaining the coexistence of pairs of lineages within populations.     

Genetic and environmental causes of variation in basal levels of blood cells.

The genetic and environmental determinants of variation in blood cell size and number were investigated in 392 pairs of 12-year-old twins. The following blood cell indices were measured: haemoglobin, red blood cell count, haematocrit, mean corpuscular volume, platelet number, total white cell count, level of neutrophils, monocytes, eosinophils, total lymphocytes, CD3+ lymphocytes, CD4+ lymphocytes, CD8+ lymphocytes, CD19+ lymphocytes, CD56+ lymphocytes and CD4+/CD8+ ratio. Genetic factors contributed significantly to all blood cell measures accounting for between 61 and 96% of variance. Heritability estimates did not differ significantly between males and females, although the sample size of the present study was not large enough to exclude the possibility of sex-limited gene expression. Common environmental factors were important in determining red blood cell count and haematocrit, but were not important in determining basal levels of any white blood cell type.     

Genetic and environmental influences on self-esteem in a Japanese twin sample.

The purpose of the present study is to clarify the mechanism of Japanese self-esteem (SE) in genetic and environmental influences using twin methodology. Eighty-one pairs of adolescent twins, including 50 pairs of monozygotic (MZ) twins and 31 pairs of dizygotic (DZ) twins, participated in this study. Self-esteem was assessed using the Rosenberg Self-Esteem Scale (RSES), translated into Japanese. As a result of using univariate twin analyses, model comparisons using the Akaike Information Criterion (AIC) indicated that the AE model was the best fit (AIC = -5.35). In the best-fitting AE model, the heritability (a2) of SE was revealed to be moderate, accounting for 49% of the variance; environmental influences (individual-specific environmental factors) explained 51% of the variance. These results are consistent with the findings of some behavioral genetics studies of SE in the West and show that there is no difference between Western and Japanese populations in the mechanism of SE considering genetic and environmental influences. The results also suggest the importance of considering both genetic and environmental factors in studies of Japanese SE.     

Pretesting static and dynamic stretching does not affect maximal strength

The purpose of this study was to determine whether there was a significant difference in static stretching (SS), dynamic stretching (DS), and no stretching (NS) on maximal strength (one-repetition maximum [1RM]) in the bench and leg presses using free weights on 19 college-aged men and 32 women. Most of the participants were moderately to very active and had previous experience with weight training. The design was repeated measures, with each treatment being randomly assigned. Each testing session was separated by 72 hours. Moderate-intensity stretching was defined as stretching as far as possible without any assistance, and subjects were encouraged to do their best. For the SS routine, the chest, shoulder, triceps, quadriceps, and hamstrings were stretched. Three repetitions were performed for 15 seconds, each separated by a 10-second rest. For DS, the upper-body stretch was swinging each arm, one at a time, as far forward and then as far backward as possible in a diagonal plane. For the legs, the same movement was done for each leg, except performed in a sagittal plane. Each forward and backward movement took about 2 seconds. Three 30-second sets were administered, and a 10-second rest was allowed between sets. Next, 1RM was determined for the bench and leg presses in random order. Two warm-up sets were given, followed by several 1RM attempts. The last successful lift was recorded as the 1RM. Data were reported using means +/- SD. A one-way ANOVA with repeated measures was used with alpha set at 0.05. There was no significant difference among the treatments. Moderate-intensity stretching does not seem to adversely affect 1RM in the bench and leg presses.     

Co-contraction during static and dynamic knee extensions in ACL deficient subjects.

Co-contraction of the muscles is proposed in the literature as one of the strategies that anterior cruciate ligament deficient (ACLD) subjects can use to compensate the loss of ACL function. This study examined the response of ACLD and control subjects to different shear forces in isometric and slow-dynamic knee extensions. Twelve chronic ACLD and 10 control subjects performed submaximal positioning and slow-dynamic knee extensions (between 45 degrees and 5 degrees of knee flexion) with two external flexion moments both applied at two distances on the lower leg. The shear force was controlled by changing the moment arm without changing the moment. Electromyographic data were collected from knee flexor and extensor muscles. In the analysis of variance, no significant effect of subject group was found in positioning or slow-dynamic tasks across all muscles. The effect of knee angle was significantly different between the subject groups for biceps femoris in positioning and for rectus femoris in slow-dynamic tasks, but these effects were very small and will not have a great impact on the resulting shear forces. There was no interaction between moment arm and subject group. Therefore, the hypothesis that ACLD subjects increase co-contraction in situations with an increased shear load in positioning and slow-dynamic knee extensions could not be confirmed.