Average Rate Of Development Research Articles

Measuring the Degree of Agricultural Development (Cultivation sub-sector) in Rural Areas (Case Study: Dashtroom Dehestan in Boyer-Ahmad County)

Measuring the Degree of Agricultural Development (Cultivation sub-sector) in Rural Areas (Case Study: Dashtroom Dehestan in Boyer-Ahmad County)

Effectiveness of Ginger Root (Zingiber officinale) on Running-Induced Muscle Soreness and Function: A Pilot Study

Context:Analgesics are commonly used by individuals undertaking endurance training; unfortunately, many commonly-used analgesics cause significant adverse effects. Ginger root (Zingiber officinale) has been used effectively as an analgesic in several contexts, but to date, no research is available to evaluate ginger root’s effects in the context of endurance training.Objective:Determine whether ginger root supplementation reduces muscle soreness and prevents impairments in muscle function following a long-distance training run.Design:Randomized, double-blind, placebo-controlled trial.Setting:University marathon training course.Participants:Twenty college students (n = 8 for ginger root group and n = 12 for placebo group).Intervention:Supplementation with 2.2 g·day–1 of ginger root or placebo for three days before, the day of, and the day after a 20–22 mile training run.Main Outcome Measures:Four days before and 24-hr postrun, participants rated soreness on a 100-mm visual analog scale, while vertical jump (VJ), peak force, and average rate of force development (RFD) were assessed during a squat jump. Quade’s rank analysis of covariance was used to assess between-group differences.Results:Median (range) soreness during jogging at 24-hr postrun was lower with ginger root supplementation (37 mm, 15–58) compared with placebo (62 mm, 6–85) (F = 4.6, p = .04). No significant differences for VJ, peak force, and RFD were found between groups.Conclusions:Ginger root may modestly reduce muscle soreness stemming from long-distance running, although it may have little to no effect on measures of muscle function during a VJ. Future studies should explore the mechanisms responsible for reductions in running-induced muscle soreness, as well as evaluate the benefit-to-risk profile of ginger root in the context of endurance training.

Influence of Familiarization and Competitive Level on the Reliability of Countermovement Vertical Jump Kinetic and Kinematic Variables.

Understanding typical variation of vertical jump (VJ) performance and confounding sources of its typical variability (i.e., familiarization and competitive level) is pertinent in the routine monitoring of athletes. We evaluated the presence of systematic error (learning effect) and nonuniformity of error (heteroscedasticity) across VJ performances of athletes that differ in competitive level and quantified the reliability of VJ kinetic and kinematic variables relative to the smallest worthwhile change (SWC). One hundred thirteen high school athletes, 30 college athletes, and 35 professional athletes completed repeat VJ trials. Average eccentric rate of force development (RFD), average concentric (CON) force, CON impulse, and jump height measurements were obtained from vertical ground reaction force (VGRF) data. Systematic error was assessed by evaluating changes in the mean of repeat trials. Heteroscedasticity was evaluated by plotting the difference score (trial 2 - trial 1) against the mean of the trials. Variability of jump variables was calculated as the typical error (TE) and coefficient of variation (%CV). No substantial systematic error (effect size range: -0.07 to 0.11) or heteroscedasticity was present for any of the VJ variables. Vertical jump can be performed without the need for familiarization trials, and the variability can be conveyed as either the raw TE or the %CV. Assessment of VGRF variables is an effective and reliable means of assessing VJ performance. Average CON force and CON impulse are highly reliable (%CV: 2.7% ×/÷ 1.10), although jump height was the only variable to display a %CV ≤SWC. Eccentric RFD is highly variable yet should not be discounted from VJ assessments on this factor alone because it may be sensitive to changes in response to training or fatigue that exceed the TE.

Effects of Plyometric Training on Lower-Body Muscle Function in Novice Marathon Runners

Improvements in lower-body force production during concurrent endurance and explosive training have been reported in competitive runners, yet few studies investigate the effects of such training on muscle function in novice runners training for distances beyond 10,000 meters. PURPOSE: To investigate the impact of a plyometric training intervention on lower-body force and power production in novice runners training for a Marathon. METHODS: Students were recruited from a marathon training course. Participants were block randomized into two groups: plyometric/explosive speed training (PLYO) or core stability training (CORE). Squat jump (SJ) and counter-movement jump (CMJ) performance were evaluated using a force platform. Data were sampled at 1202Hz and filtered using a fourth-order Butterworth low-pass filter (50Hz). Dependent measures were peak force, average rate of force development (RFD), peak RFD and jump height, which were determined from the average of three jumps at the beginning and end of the 12-week intervention. A one-way analysis of covariance was conducted to discern between-group differences in jumping performance after the intervention. RESULTS: Vertical jump data were available for 20 participants (Mean ± SD: age = 20.4 ± 1.3 yr, height = 172.1 ± 9 cm, weight = 70.3 ± 10 kg, BMI = 23.5 ± 1.9 kg·m-2, 11 female). After adjusting for pre-intervention values, there was no significant difference between PLYO and CORE on post-intervention jump height during either SJ (p = 0.07, partial eta squared = 0.18) or CMJ (p = 0.57, partial eta squared = 0.02). Post-intervention values for peak force, average RFD and peak RFD did not differ between groups for either jump type. CONCLUSION: Jumping performance parameters were not affected by the 12-week PLYO intervention while concurrently training for a marathon. It appears that the high running volume associated with marathon training negatively influences the ability to increase lower-body force and power production in novice marathon runners. It is possible that one exposure per week of plyometric training performed after a 40-minute training run was insufficient to elicit adaptation in jumping performance. Future investigations should increase the frequency of plyometric training exposure and conduct this training before the days training run.

Corrosion Fatigue Crack Propagation Rates for Steam Turbine Blade 13% Cr Steels

Studies of stress corrosion in X12Cr13 and X20Cr13 steels used for rotor blades of steam turbines have been conducted for determining the average rate of corrosion cracking development da / dt. Specimens were exposed to the salt mist environment of 1,2 ppm NaCl concentration in temperature of 60° C. The research environment represents the initial condensate of humidity from 3÷4%. Average rate of corrosion cracking development for specimens of the X12Cr13 is by 0,005 µm/h higher from specimens of the X20Cr13 steel. Course of the corrosion cracking initiation depends to a high degree on metal structure, and probably the close value of cracking propagation rate depends on the similar structure of those steels – high-tempered martensite with carbides at grain boundaries.

Disease progression in plantations of Acacia mangium affected by red root rot (Ganoderma philippii)

SummaryThe rapid emergence of Acacia mangium as the key industrial plantation species in Indonesia has been followed by the equally rapid emergence of red root rot (Ganoderma philippii) as its potential nemesis. As a consequence, and on severely affected mineral soils in equatorial tropical environments in particular, A. mangium may no longer be capable of producing commercial yields after three rotations. In this experiment, 100‐tree plots were established in commercial plantings of A. mangium at five sites which represented the range of growing conditions used for plantation establishment in Indonesia. Repeated monitoring at approximately 6‐month intervals of above‐ and below‐ground variables was used to explore relationships between measures of tree health and root rot. Crown colour and density were poor predictors of either the presence or severity of infections. Tree mortality increased more or less linearly with time and led to the progressive coalescence of initially discrete disease gaps. The average rate of disease development was about 0.3% per month, and average time from infection to tree death was conservatively estimated at around 1 year. Trees with more than four dead/missing neighbours had a >50% chance of being dead by the following monitoring. By the end of the monitoring period >40% of trees were classified as dead/missing, although this value varied from 20 to 70% depending on site, tree age and rotation. Canonical discriminant analysis correctly allocated >90% trees into their correct group on the first monitoring and similarly classified whether trees would be dead or missing in the following monitoring.

Speed, not magnitude, of knee extensor torque production is associated with self-reported knee function early after anterior cruciate ligament reconstruction.

To examine the magnitude and speed of knee extensor torque production at the initiation of advanced anterior cruciate ligament (ACL) reconstruction rehabilitation and the associations with self-reported knee function. Twenty-eight subjects who were 12 weeks post-ACL reconstruction and 28 age- and sex-matched physically active controls participated in this study. Knee extensor torque was assessed bilaterally with an isokinetic dynamometer at 60°/s. The variables of interest were peak torque, average rate of torque development, time to peak torque and quadriceps symmetry index. Knee function was assessed with the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF). Peak torque and average rate of torque development were lower on the surgical side compared to the non-surgical side and controls. Quadriceps symmetry index was lower in subjects with ACL reconstruction compared to controls. On the surgical side, average rate of torque development was positively correlated with IKDC-SKF score (r = 0.379) while time to peak torque was negatively correlated with IKDC-SKF score (r = -0.407). At the initiation of advanced ACL reconstruction rehabilitation, the surgical side displayed deficits in peak torque and average rate of torque development. A higher rate of torque development and shorter time to peak torque were associated with better self-reported knee function. The results suggest that the rate of torque development should be addressed during advanced ACL reconstruction rehabilitation and faster knee extensor torque generation may lead to better knee function. III.

Monitoring cotton bollworm resistance to Cry1Ac in two counties of northern China during 2009-2013.

Transgenic cotton that expresses a gene derived from the bacterium Bacillus thuringiensis (Bt) has been deployed for combating cotton bollworm in China since 1997. As a follow-up on research started in 2002, the quantitative shifts in larval Cry1Ac resistance of field Helicoverpa armigera populations were monitored from 2009-2013 using bioassays of isofemale lines. A total of 2837 lines from Xiajin and 2055 lines from Anci were screened for growth rate on normal artificial diet and on a diet containing 1.0 µg mL(-1) of Cry1A(c) toxin. In 2009-2013, the mean relative average development rates (RADRs) of H. armigera larvae in the Xiajin population were 0.62, 0.59, 0.59, 0.58 and 0.62 respectively, and in the Anci population 0.54, 0.58, 0.60, 0.53 and 0.62 respectively. Compared with previous results in 2002, there was an increase in the RADR of H. armigera during 2009-2013, with ratios of 1.53-1.63 and 1.77-2.07 in the respective Xiajin and Anci populations, suggesting that resistance to Cry1Ac has increased in H. armigera populations in northern China.

Countermovement Jump Height

The goal of this study was to assess (a) the eccentric rate of force development, the concentric force, and selected time variables on vertical performance during countermovement jump, (b) the existence of gender differences in these variables, and (c) the sport-specific differences. The sample was composed of 189 males and 84 females, all elite athletes involved in college and professional sports (primarily football, basketball, baseball, and volleyball). The subjects performed a series of 6 countermovement jumps on a force plate (500 Hz). Average eccentric rate of force development (ECC-RFD), total time (TIME), eccentric time (ECC-T), Ratio between eccentric and total time (ECC-T:T) and average force (CON-F) were extracted from force-time curves and the vertical jumping performance, measured by impulse momentum. Results show that CON-F (r = 0.57; p < 0.001) and ECC-RFD (r = 0.52, p < 0.001) are strongly correlated with the jump height (JH), whereas the time variables are slightly and negatively correlated (r = -0.21-0.23, p < 0.01). Force variables differ between both sexes (p < 0.01), whereas time variables did not differ, showing a similar temporal structure. The best way to jump high is to increase CON-F and ECC-RFD thus minimizing the ECC-T. Principal component analysis (PCA) accounted for 76.8% of the JH variance and revealed that JH is predicted by a temporal and a force component. Furthermore, the PCA comparison made among athletes revealed sport-specific signatures: volleyball players revealed a temporal-prevailing profile, a weak-force with large ECC-T:T for basketball players and explosive and powerful profiles for football and baseball players.

Is climate warming more consequential towards poles? The phenology of Lepidoptera in Finland

The magnitude and direction of phenological shifts from climate warming could be predictably variable across the planet depending upon the nature of physiological controls on phenology, the thermal sensitivity of the developmental processes and global patterns in the climate warming. We tested this with respect to the flight phenology of adult nocturnal moths (3.33 million captures of 334 species) that were sampled at sites in southern and northern Finland during 1993-2012 (with years 2005-2012 treated as an independent model validation data set). We compared eight competing models of physiological controls on flight phenology to each species and found strong support for thermal controls of phenology in 66% of the species generations. Among species with strong thermal control of phenology in both the south and north, the average development rate was higher in northern vs. southern populations at 10°C, but about the same at 15 and 20°C. With a 3°C increase in temperature (approximating A2 scenario of IPPC for 2090-2099 relative to 1980-1999) these species were predicted to advance their phenology on average by 17 (SE±0.3)days in the south vs. 13 (±0.4)days in the north. The higher development rates at low temperatures of poleward populations makes them less sensitive to climate warming, which opposes the tendency for stronger phenological advances in the north from greater increases in temperature.

Sequence Stratigraphy of Miocene Tide-Influenced Sandstones In the Minas Field, Sumatra, Indonesia

Abstract The Miocene Sihapas Group in the Minas field, Indonesia, is composed of a succession of tens-of-meters-thick, erosionally based, tide-influenced sandstone intervals interbedded with marine shale-dominated intervals. Despite more than 1600 wells drilled into this 12-km-wide by 30-km-long mature super-giant field, complex internal tidal facies architecture within these sandstone intervals makes predicting local connectivity within the reservoirs challenging. Past interpretations of Minas field suggested that reservoir sandstone intervals are incised-valley deposits, based on assumptions that abrupt coarsening at the base of reservoirs reflects river incision into the shelf and tidal reservoir facies formed in coastal embayments during transgression. In this paper a new interpretation is proposed that suggests that shorelines remained strongly tide-influenced throughout regressive–transgressive depositional episodes. Pronounced discontinuity surfaces in these deposits are interpreted to have formed by a variety of mechanisms: (1) tidal erosion of the sea floor in front of regressing shorelines; (2) lowstand fluvial valley incision; and (3) the reworking of deposits during transgression of the shelf. Consideration of a wider variety of regressive and transgressive tidal depositional settings and erosional processes allowed revision of Minas field stratigraphy to better explain the observed complex facies variations that control reservoir production behavior. Minas field is divided into five major reservoir intervals that overlie low-grade metamorphic basement. The older deposits, comprising the S and D reservoir intervals, contain multiple upward-coarsening tide-influenced regressive shoreline successions, locally cut out by tide-influenced channel sandstone bodies, and capped by thin beds of marine shelf transgressive sandstone and overlying marine shale. Seismic images indicate that these deposits filled erosional basement topography during a period of long-term relative sea level rise. The upper three reservoir intervals (B, A2, and A1) are each interpreted to be fourth-order regressive shoreline deposits that were variably reworked by tidal currents during transgression. Successive intervals record progressively lower average rate of accommodation development, more rapid falling-stage regression, deeper lowstand incision, and greater reworking during intervening transgressions. Together, these three intervals comprise a third-order, flooding-surface-defined, forward-stepping sequence set deposited on a low-gradient continental shelf. Paradoxically, because intervals deposited during more rapid progradation tend to be thinner, in most wells more regressive sandstone intervals contain proportionally more open marine shelf deposits. This reflects that valley incision is localized, and regressive deposits that formed in lower long-term accommodation growth rate settings tend to be more completely reworked by tidal currents during subsequent transgression.

Monitoring land-use change-associated land development using multitemporal Landsat data and geoinformatics in Kom Ombo area, South Egypt

Due to the progressive increase in population, sustainable development of desert land in Egypt has become a strategic priority in order to meet the increasing demands of a growing population for food and housing. Such obligations require efficient compilation of accurate land-cover information in addition to detailed analysis of archival land-use changes over an extended time span. In this study, we applied a methodology for mapping land cover and monitoring change in patterns related to agricultural development and urban expansion in the desert of the Kom Ombo area. We utilized the available records of multitemporal Landsat Thematic Mapper and Enhanced Thematic Mapper Plus images to produce three land-use/land-cover maps for 1988, 1999 and 2008. Post-classification change detection analysis shows that agricultural development increased by 39.2% through the study period with an average annual rate of land development of 8.7 km2 year−1. We report a total increase in urbanization over the selected time span of approximately 28.0 km2 with most of this urban growth concentrated to the east of the Nile and occurring through encroachment on the former old cultivated lands. The archival record of the length of irrigation canals showed that their estimated length was 341.5, 461.8 and 580.1 km in the years 1988, 1999 and 2008, respectively, with a 70% increase in canal length from 1988 to 2008. Our results not only accurately quantified the land-cover changes but also delineated their spatial patterns, showing the efficiency of Landsat data in evaluating landscape dynamics over a particular time span. Such information is critical in making effective policies for efficient and sustainable natural resource management.

Susceptibility of Helicoverpa armigera from different host plants in northern China to Bacillus thuringiensis toxin Cry1Ac

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a serious pest of cotton and many other crops in northern China. To evaluate the contribution of alternative hosts as an effective refuge for transgenic cotton expressing the Bacillus thuringiensis (Bt) Cry1Ac toxin, the susceptibility to this toxin was measured in progeny derived from field-collected H. armigera larvae and pupae from different hosts in the Xiajin’s region of the Shandong Province in northern China. During 2008–2010, progeny from a total of 258,56,184 and 160 single-pair crosses derived from wheat (first-generation), Bt cotton (second-generation), Bt cotton (third-generation), and corn (third-generation) were screened on Cry1Ac diets, respectively. Based on relative average development rates (RADR) of H. armigera larvae in these F 1 tests, the second and third-generation moths emerging from Bt cotton fields were more tolerant to the Bt toxin than the first and third-generation moths emerging from wheat and corn each year. These results suggest that there is significant variation in susceptibility to Bt toxins among H. armigera populations derived from different host crops. Alternate crops, such as corn, that maintain Bt susceptible populations of H. armigera could be used as refugia to minimize the evolution of resistance to Bt cotton.

Frequency of Bt resistance alleles in Helicoverpa armigera in 2007–2009 in the Henan cotton growing region of China

Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) is a key insect pest of cotton in the Henan cotton growing region of China. In this region, cotton is grown on small acreages in rich agricultural landscapes, contrary to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt plants) may be sufficient to prevent H. armigera resistance development to Bt toxins. In order to gain a timely understanding of the evolution of resistance of H. armigera to Bt toxin after continuous cultivation of Bt cotton for c. 10 years, we assessed the frequency of alleles conferring resistance to Cry1Ac toxin in field populations of H. armigera sampled from Xinxiang County in Henan province during 2007–2009. Screening F 1 and F 2 generations from isofemale lines, derived from female moths trapped in the field, were used with a discriminating dose of Cry1Ac diet to estimate the frequency of resistance alleles. Totals of 625, 516 and 488 isofemale lines were screened for the F 1 generation in 2007, 2008 and 2009, respectively. Resistance gene frequency in Xinxiang fluctuated between 0.0000 and 0.0005, and it did not increase significantly from 2007 to 2009. Based on the relative average development rates (RADR) of H. armigera larvae in F 1 tests, no substantial increase in Cry1Ac tolerance was found in the Xinxiang region over the 3-yr period.

Trichostatin A-treated eight-cell bovine embryos had increased histone acetylation and gene expression, with increased cell numbers at the blastocyst stage

The objective was to determine the effects of trichostatin A (TSA), a potent histone deacetylase inhibitor, on eight-cell bovine embryos. That treatment increased histone acetylation was confirmed by immunostaining with anti-AcH4K5 and AcH4K8 antibodies. Embryos treated with TSA (100 nM) for various intervals (4, 8, and 12 h) developed to the blastocyst stage as frequently as untreated embryos (average development rate, 49.5%). Treatment with TSA for 12 h increased (P < 0.05) the numbers of inner cell mass (ICM) cells and total cells (TC), as well as the ICM/TC ratio in the blastocyst, but the number of cells in the trophectoderm decreased (P < 0.05). Treated embryos had increased relative abundance (RA) of OCT3/4 and E-CADHERIN mRNA relative to controls at the morula stage (P < 0.05), however, the RA of CDX2 mRNA was unchanged. In conclusion, TSA-treated eight-cell stage embryos had increased histone acetylation and gene expression, which increased ICM and TC numbers and the ICM/TC ratio, but significantly decreased the number of cells in the trophectoderm of resulting blastocysts.

Vip3Aa Tolerance Response of Helicoverpa armigera Populations From a Cry1Ac Cotton Planting Region

Transgenic cotton, Gossypium hirsutum L., that expresses the Bacillus thuringiensis (Bt) Cry1Ac toxin, holds great promise in controlling target insect pests. Evolution of resistance by target pests is the primary threat to the continued efficacy of Bt cotton. To thwart pest resistance evolution, a transgenic cotton culitvar that produces two different Bt toxins, cry1Ac and vip3A genes, was proposed as a successor of cry1Ac cotton. This article reports on levels of Vip3Aa tolerance in Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) populations from the Cry1Ac cotton planting region in China based on bioassays of the F1 generation of isofemale lines. In total, 80 isofemale families of H. armigera from Xiajin county of Shandong Province (an intensive Bt cotton planting area) and 93 families from Anci county of Hebei Province (a multiple-crop system including corn [Zea mays L.] , soybean [Glycine max (L.) Merr.], peanut (Arachis hypogaea L.), and Bt cotton) were screened with a discriminating concentration of both Cry1Ac- and Vip3A-containing diets in 2009. From data on the relative average development rates and percentage of larval weight inhibition of F1 full-sib families tested simultaneously on Cry1Ac and Vip3Aa, results indicate that responses to Cry1Ac and Vip3Aa were not genetically correlated in field population ofH. armigera. This indicates that the threat of cross-resistance between Cry1Ac and Vip3A is low in field populations of H. armigera. Thus, the introduction of Vip3Aa/Cry1Ac-producing lines could delay resistance evolution in H. armigera in Bt cotton planting area of China.

Frequency ofBtResistance Alleles inHelicoverpa armigerain the Xinjiang Cotton-Planting Region of China

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is a key insect pest of cotton in Xinjiang cotton-planting region of northwest China. In this region, cotton is grown on average ≈ 1.65 million ha (1.53 ≈ 1.80 million ha) annually in largely monoculture agricultural landscapes, similarly to cropping systems in the United States or Australia. Under such cropping regimes, naturally occurring refuges (with non-Bt crops) may be insufficient to prevent H. armigera resistance development to Bt toxins. Therefore, we assessed frequency of alleles conferring resistance to Cry1Ac toxin of F(1) and F(2) offspring of H. armigera isofemale lines from two distinct localities in the region during 2005-2009. More specifically, a total of 224 isofemale lines was collected from Korla County (≈ 70% Bt cotton adoption) and 402 lines from Shache County (≈ 5% Bt cotton planting). Subsequent offspring was screened on Cry1Ac artificial diet. From 2005 to 2009, resistance gene frequency in Korla fluctuated between 0.0000 and 0.0040, while being 0.0000-0.0008 in individuals collected from Shache, and there were no significant increases in both counties from 2005 to 2009. Relative average development rates (RADRs) of larvae in F(1) tests showed significant increases from Korla, but not in Shache. RADR of F(1) larvae is significantly correlated with RADR of F(2) offspring, indicating genetic variation in response to toxin in field H. armigera population. Although the occurrence of Cry1Ac resistance alleles was low in Xinjiang cotton-planting region of China, particular attention should be given to H. armigera resistance development in Korla County.

Changes in Microbial Functional Diversity and Activity in Paddy Soils Irrigated with Industrial Wastewaters in Bandung, West Java Province, Indonesia

Characteristics, such as microbial biomass, basal respiration, and functional diversity of the microbial communities, were investigated in paddy soils located in Bandung, West Java Province, Indonesia, that have been heavily polluted by industrial effluents for 31 years. Paddy soil samples (10–20 cm) were taken from two sites: polluted soils and unpolluted soils (as control sites). The polluted soils contained higher salinity, higher sodicity, higher nutrient contents, and elevated levels of heavy metals (Cr, Mn, Ni, Cu, and Zn) than unpolluted soils. Soil physicochemical properties, such as maximum water holding capacity, exchangeable sodium percentage, sodium adsorption ratio, and swelling factor, in polluted soils were much greater than those in unpolluted soils (P < 0.05). Changes in the physical and chemical soil properties were reflected by changes in the microbial communities and their activities. BIOLOG analysis indicated that the functional diversity of the microbial community of polluted soils increased and differed from that of unpolluted soils. Likewise, the average rate of color development (average well color development), microbial biomass (measured as DNA concentration), and the soil CO2 respiration were higher in polluted soils. These results indicate that major changes in the chemical and physical properties of paddy soils following the application of industrial wastewater effluents have had lasting impacts on the microbial communities of these soils. Thus, the increased activity, biomass, and functional diversity of the microbial communities in polluted soils with elevated salinity, sodicity, and heavy metal contents may be a key factor in enhancing the bioremediation process of these heavily polluted paddy soils.

Initial conditions influence the characteristics of ballistic contractions in the ankle dorsiflexors

This study investigated the influence of different initial conditions on a subsequent fast (ballistic) isometric contraction of the ankle dorsiflexor muscles. Surface electromyograms (EMGs) of dorsiflexor and plantarflexor muscles were recorded during ballistic contractions performed without any pre-activation (BAL) and in ballistic contractions preceded by a sustained submaximal contraction (20% MVC) that was followed either by a rapid voluntary relaxation of the agonist muscle (VRBAL) or by a rapid antagonist (reversal) contraction (ARBAL). In the latter condition, three different antagonist torque levels were compared (25, 50 and 75% MVC). The results showed that the mean average rate of torque development was significantly (P < 0.001) greater for the ARBAL condition (968.5 ± 183.9% MVC/s) compared with the VRBAL (509.3 ± 78.7% MVC/s) and BAL (461.8 ± 79.9% MVC/s) conditions. Furthermore, the mean value recorded for VRBAL was significantly (P < 0.05) greater than for BAL condition. The faster increases in torque during the VRBAL and ARBAL conditions were associated with a greater agonist EMG activity. Compared with VRBAL, performance during the ARBAL condition was improved by a greater level of antagonist coactivation and, in some trials, by the presence of a silent EMG period between the end of the antagonist activation and the onset of the agonist ballistic contraction. Together, these results indicate that the initial conditions can have a substantial influence on the rate of torque development during ballistic contractions performed in isometric conditions.

Stability Reliability, Precision, And Association Of Measures Of Average Rate Of Dynamic Force Development

Average rate of dynamic force development (ARDFD) may be calculated from direct and indirect measures of force obtained using force platforms (FP) and accelerometers (A), respectively. However, its utility during jump squats has not been established. PURPOSE: To determine the stability reliability and precision of ARDFD during jump squats calculated from FP and A data, and to ascertain the association between them. METHODS: Fifty-two subjects (27 women and 25 men) with squat training experience were recruited from a university population. All performed a back squat to 90° of knee flexion with an external load > body weight. Subjects used maximum acceleration in performing duplicate countermovement jump squats (CMJ) and static jump squats (SJ) at 20, 30, and 40% of their back squat 1RM on two separate days in a counterbalanced sequence. ARDFD was operationally defined as (Δ force from initiation of concentric phase to peak / Δ time). Data were obtained using a single uniaxial FP beneath the lifter's feet and a pair of A's affixed to opposite ends of the barbell. A-derived force was determined via inverse dynamics with mass considered the sum of body and barbell weights. Force data from FP and A systems were synchronized for ARDFD calculations. Stability reliability was assessed using intraclass correlation, precision by coefficient of variation, and association via Pearson correlation. RESULTS: With one exception (SJ @ 40% 1RM for one A), stability reliability for the different measurement systems met the minimum standard for all jump squat conditions (r > 0.71, n ≈ 44). However, with only one exception for the A's (SJ @ 30% 1RM, CV = 13.6%) and two for the FP (SJ @ 20 and 30% 1RM, CV = 12.2 and 14.5%, respectively), the minimum standard for precision was not attained (CV > 15.1%, n ≈ 44). Since precision was generally poor, two sessions were averaged for each of the dynamometers prior to assessing association. Correlations were high overall (r > 0.81, n ≈ 40). CONCLUSIONS: The different measurement systems generally produced reliable but imprecise ARDFD data. When two-day output was averaged, the association between the various measurement systems was high at all three loads for both types of jump squat. As operationally defined, ARDFD lacks sufficient precision to be a useful tool for monitoring small changes in performance.