Phosphorus fertilizers as a source of uranium in Serbian soils

Around 1500 t of mineral fertilizers based on phosphorus are applied per annum in Serbia. It is estimated that around 210 kg of uranium (30 g/ha) are in this way introduced into the environment. Due to this fact there is a risk of exposing local population to ionizing radiation. The purpose of this article was to determine whether long-term application of phosphorus fertilizers causes increase of uranium content in arable soils. These investigations were made using field experiments that were set up on three types of soil, chernozem, smonitza and pseudogley, more than 30 years ago. Same variants of mineral nutrition were used in these experiments and all fields had parcels without application of fertilizers (controls). Soil samples were taken from two soil layers (0–30 cm and 30–60 cm) continuously in a period of five years. Statistical analysis of the results obtained indicates that significant differences exist between the control and application of phosphorus fertilizers in the layer from 0–30 cm, while no such differences were found for the layer from 30–60 cm. Physicochemical soil properties change the process of uranium migration and mobilization. Indeed the fixation of uranium by investigated soil types decreases in the following order: chernozem>smonitza>>pseudogley. Since the natural content of uranium in Serbian soils is in the interval from 0.08 to 5.9 ppm, it can be concluded that the results obtained in this investigation are within natural limits. Indeed, the values obtained for total uranium content in the investigated experimental variants were in the range from 0.65 to 1.94 ppm. This finding is of great value from the aspect of environmental protection and prevention of uranium of anthropogenic origin to be incorporated in food chain

Leg stiffness adjustment during hopping at different intensities and frequencies

Understanding leg and joint stiffness adjustment during maximum hopping may provide important information for developing more effective training methods. It has been reported that ankle stiffness has major influence on stable spring-mass dynamics during submaximal hopping, and that knee stiffness is a major determinant for hopping performance during maximal hopping task. Furthermore, there are no reports on how the height of the previous hop could affect overall stiffness modulation of the subsequent maximum one. The purpose of the present study was to determine whether and how the jump height of the previous hop affects leg and joint stiffness for subsequent maximum hop. Ten participants completed trials in which they repeatedly hopped as high as possible (MX task) and trials in which they were instructed to perform several maximum hops with 3 preferred (optimal) height hops between each of them (P3MX task). Both hopping tasks were performed at 2.2 Hz hopping frequency and at the participant's preferred (freely chosen) frequency as well. By comparing results of those hopping tasks, we found that ankle stiffness at 2.2 Hz (p=0.041) and knee stiffness at preferred frequency (p=0.045) was significantly greater for MX versus P3MX tasks. Leg stiffness for 2.2 Hz hopping is greater than for the preferred frequency. Ankle stiffness is greater for 2.2 Hz than for preferred frequencies; opposite stands for knee stiffness. The results of this study suggest that preparatory hop height can be considered as an important factor for modulation of maximum hop

Endurance training protects the heart during maximal exercise in long-distance runners

Introduction Cardiac function (cardiac output) and oxygen extraction (arterio-venous O2 difference) are key physiological determinants of maximal oxygen consumption and endurance performance. Purpose The aim of the study was to determine differences in maximal cardiac function represented by cardiac output and cardiac power output and oxygen extraction represented by arterio-venous O2 difference between long-distance runners and age- and gender-matched healthy individuals. Methods In a prospective observational study, 63 healthy males were recruited: 47 long-distance (half- and full-marathon) runners (aged 32.6 ± 8.6 years, body mass index 23.4 ± 2.2 kg/m²) and 16 healthy untrained individuals (control group, aged 30.9 ± 11.2 years, body mass index 24.8 ± 2.4 kg/m²). All participants underwent maximal graded cardiopulmonary exercise stress seting using an electromagnetic cycle ergometer with simultanous monitoring of metabolic (gas exchange) and hemodynamic (bioreactance) measurements. Cardiac power output, expressed in watts, as a measure of overall function and pumping capability of the heart, was determined as the product between cardiac output and mean arterial blood pressure. Oxygen extraction (arterio-venous O2 difference) was calculated as the ratio between O2 consumption and cardiac output. Results Maximal O2 consumption was significantly lower in the control group compared to runners (absolute values, 3.44 ± 1.12 vs. 3.99 ± 0.52 L/min, p < 0.01; and relative values, 45.3 ± 16.4 vs. 53.6 ± 6.9 ml/kg/min, p < 0.01). However, maximal cardiac output and cardiac power output were significantly higher in the control group compared to runners (21.4 ± 3.9 vs. 18.7 ± 3.0 L/min, p = 0.02; 5.94 ± 1.35 vs. 5.01 ± 1.00 watts, p = 0.01). Maximal stroke volume was significantly higher in control group compared to runners (126 ± 28 vs. 109 ± 21 ml/beat, p = 0.04), whereas maximal heart rate was not significantly different betwen the groups (174 ± 12 vs. 177 ± 22 beats/min, p = 0.70). Arterio-venous O2 difference was significantly higher in runners compared to control group (21.6 ± 3.7 vs. 14.5 ± 3.6 mlO2/100 ml blood, p < 0.01). Conclusion During maximal exercise stress testing long-distance runners demonstrate higher cardiorespiratory fitness and oxygen extraction but lower cardiac output and cardiac power output compared to untrained indivuduals. Ability to extract and utilise more oxygen at lower cardiac output during maximal physiogical stress suggests cardiac protective role of endurance training in long-distance runners

The influence of isometric preload on power expressed during bench press in strength-trained men

The purpose of this study was to compare the power expressed during the bench press exercise in resistance-trained men following different pre-activation conditions. Twenty-two trained men (age 24.1 ± 1.7 years, height 178.6 ± 6.1 cm, body mass 81.1 ± 10.6 kg) completed a maximal effort bench press (1-RM) test (100.0 kg ± 8.1 kg). In a subsequent assessment, each participant performed concentric bench press movements with loads of 20%, 30%, 40% and 50% of their 1-RM preceded by either a concentric contraction (CC), a low isometric preload (LIP; 70% 1-RM) or a high isometric preload (HIP; 100% 1-RM) conditions. All movements were performed in a Smith machine with a settable quick-release device. Participants performed all three conditions in randomized fashion. Results indicated that power outputs during the bench press exercise following HIP were significantly (p \u3c 0.05) greater than CC at 20% 1-RM (+9%), 30% 1-RM (+16%) and 40% 1-RM (+14%), and LIP at 20% 1-RM (+4%), 30% 1-RM (+20%) and 40% 1-RM (+15%). No differences were found between conditions at 50% 1-RM. Area under the force–power curve with HIP was greater (p \u3c 0.05) than with CC and LIP. In conclusion, results of this study indicate that the use of a HIP (100% 1-RM) in trained participants results in significantly greater power output during the concentric phase of a multi-joint exercise when compared to standard concentric movement