Assessment of the contamination of riparian soil and vegetation by trace metals--A Danube River case study.

The aim of this study was to assess the spatial distribution of arsenic and heavy metals (Cd, Cr, Cu Hg, Ni, Pb and Zn) in a riparian area influenced by periodical flooding along a considerable stretch of the Danube River. This screening was undertaken on soil and plant samples collected from 43 sites along 2386 km of the river, collected during the international Joint Danube Survey 3 expedition (ICPDR, 2015). In addition, data on the concentration of these elements in river sediment was used in order to describe the relationship between sediment, riparian soil and riparian plants. A significant positive correlation (Spearman r, for p<0.05) was found for trace metal concentrations in river sediment and soil (r=0.817). A significant correlation between soil and plants (r=0.438) and sediment and plants (r=0.412) was also found for trace metal concentrations. Elevated levels of Cd, Cr, Cu, and Ni were found at certain sites along the Serbian stretch, while elevated concentrations of Hg were also detected in Hungary, of Pb along the Romanian stretch and of As along the Bulgarian stretch (the Lower Danube). These results point to the presence of naturally-occurring metals derived from ore deposits in the Danube River Basin and anthropogenic metals, released by mining and processing of metal ores and other industrial facilities, which are responsible for the entry of metals such as Cu, Ni and Zn. Our results also indicated toxic Cd and Zn levels in plant samples, measured at the Hercegsznato site (Middle Danube, Hungary), which highlighted these elements as a potential limiting factor for riparian vegetation in that area. The distribution of the analysed elements in plant material also indicates the species-specific accumulation of trace metals. Based on our results, the Lower and Middle Danube were found to be more polluted in terms of the analysed elements.

Force-velocity Relationship of Muscles Performing Multi-joint Maximum Performance Tasks.

Manipulation of external loads typically provides a range of force, velocity, and power data that allows for modeling muscle mechanical characteristics. While a typical force-velocity relationship obtained from either in vitro muscles or isolated muscle groups can be described by a hyperbolic equation, the present review paper reveals the evidence that the same relationship obtained from maximum-performance multi-joint movements could be approximately linear. As a consequence, this pattern also results in a relatively simple shape of the power-velocity relationship. The parameters of the linear force-velocity relationship reveal the maximum force, velocity and power. Recent studies conducted on various functional movement tasks reveal that these parameters could be reliable, on average moderately valid, and typically sensitive enough to detect differences among populations of different physical abilities. Therefore, the linear force-velocity relationship together with the associated parabolic power-velocity relationship could provide both a new and simplified approach to studies of the design and function of human muscular system and its modeling. Regarding the practical applications, the reviewed findings also suggest that the loaded multi-joint movements could be developed into relatively simple routine tests of the force-, velocity- and power-generating capacity of the neuromuscular system.

Optimum load in various vertical jumps support the maximum dynamic output hypothesis.

The aim was to generalize the maximum dynamic output (MDO) hypothesis [i. e., the muscle power output in vertical jumps (VJ) is maximized when loaded with one's own body mass] to variety of VJ. We hypothesized that the subjects' own body (a) would be the optimal load for maximizing the power output (i. e., the no-load condition) and also (b) reveal the maximum benefits of stretch-shortening cycle (SSC). 13 participants performed the maximum squat and various counter-movement jumps when loaded by approximately constant external force ranging from -40% to + 40% of their body weight (BW). Regarding the first hypothesis, the differences in both the peak and mean power recorded under different load magnitudes revealed maxima close to no-load condition (i. e., from -3% BW to + 8% BW; R2=0.65-0.96; all P<0.01). Regarding the second hypothesis, the differences in performance between VJ executed with and without SSC also revealed maxima close to no-load conditions (0-2% BW), while the same differences in the power output were observed under relatively low positive loads (14-25% BW; R² = 0.56-0.95; all P<0.01). The findings support the concept that maximal power output occurs close to one's own body mass during VJ with and without SSC, thereby providing additional support to MDO hypothesis.

Selective effects of weight and inertia on maximum lifting.

A novel loading method (loading ranged from 20% to 80% of 1RM) was applied to explore the selective effects of externally added simulated weight (exerted by stretched rubber bands pulling downward), weight+inertia (external weights added), and inertia (covariation of the weights and the rubber bands pulling upward) on maximum bench press throws. 14 skilled participants revealed a load associated decrease in peak velocity that was the least associated with an increase in weight (42%) and the most associated with weight+inertia (66%). However, the peak lifting force increased markedly with an increase in both weight (151%) and weight+inertia (160%), but not with inertia (13%). As a consequence, the peak power output increased most with weight (59%), weight+inertia revealed a maximum at intermediate loads (23%), while inertia was associated with a gradual decrease in the peak power output (42%). The obtained findings could be of importance for our understanding of mechanical properties of human muscular system when acting against different types of external resistance. Regarding the possible application in standard athletic training and rehabilitation procedures, the results speak in favor of applying extended elastic bands which provide higher movement velocity and muscle power output than the usually applied weights.

Effects of jump training with negative versus positive loading on jumping mechanics.

We examined the effects of jump training with negative (-30% of the subject's body weight (BW)) VS. positive loading (+30% BW) on the mechanical behaviour of leg extensor muscles. 32 men were divided into control (CG), negative loading (NLG), or positive loading training group (PLG). Both training groups performed maximal effort countermovement jumps (CMJ) over a 7-week training period. The impact of training on the mechanical behaviour of leg extensor muscles was assessed through CMJ performed with external loads ranging from -30% BW to +30% BW. Both training groups showed significant ( P≤0.013) increase in BW CMJ height (NLG: 9%, effect size (ES)=0.85, VS. PLG: 3.4%, ES=0.31), peak jumping velocity ( V(peak); NLG: 4.1%; ES=0.80, P=0.011, VS. PLG: 1.4%, ES=0.24; P=0.017), and depth of the countermovement (Δ H(ecc); NLG: 20%; ES=-1.64, P=0.004, VS. PLG: 11.4%; ES=-0.86, P=0.015). Although the increase in both the V(peak) and Δ H(ecc) were expected to reduce the recorded ground reaction force, the indices of force- and power-production characteristics of CMJ remained unchanged. Finally, NLG (but not PLG) suggested load-specific improvement in the movement kinematic and kinetic patterns. Overall, the observed results revealed a rather novel finding regarding the effectiveness of negative loading in enhancing CMJ performance which could be of potential importance for further development of routine training protocols. Although the involved biomechanical and neuromuscular mechanisms need further exploration, the improved performance could be partly based on an altered jumping pattern that utilizes an enhanced ability of leg extensors to provide kinetic and power output during the concentric jump phase.

Tests of muscle power output: the role of body size.

The effect of body size on the output of the tests of directly assessed muscle power has been mainly ignored in the applied research. We hypothesized that the muscle power output would reveal a positive relationship with body size closely in line with the theoretical predictions, as well as that the strength of the studied relationship could justify standardized normalization procedures applied in routine testing. Male physical education students (n = 111) were evaluated in 10 standard tests of direct assessment of muscle power output. A standard allometric relationship P = A SB was applied to assess the relationship between the tested power output P and selected indices of body size S ( B = allometric exponent; A = parameter). The correlation coefficients obtained between the tested power output and body size ranged within 0.21 - 0.56 for body mass and 0.10 - 0.49 for body height. The mean (SD) values of the allometric exponents B obtained with respect to body mass and body height were 0.55 (0.15) and 1.15 (0.62), respectively. This relationship proved to be strong enough to merit applying a standard normalization. The normalization method should be based on body mass as a preferred index of body size, while the allometric exponent could correspond to the theoretically predicted one (i.e., B = 0.67).

Evaluation of tests of maximum kicking performance.

AIM: Despite the important role of kicking in various athletic activities, the reliability of tests of maximum kicking performance has not been evaluated. The aim of the present study was to assess the reproducibility of performance of standing kick, instep kick and drop kick. METHODS: Male physical education students (n=77) were tested on maximum kicking performance by means of a standard Doppler radar gun. RESULTS: The maximal ball speed in the standing kick, instep kick and drop kick (averaged across the subjects and trials) were 19.8+/-1.9 m s(-1), 26.7+/-2.7 m s(-1) and 25.3+/-2.2 m s(-1), respectively. There were no significant differences in the tested performances among the consecutive kicking trials of each test. The intraclass correlation coefficients ranged between 0.94 and 0.96 (95% confidence intervals 0.93-0.97). The limits of agreement for maximum ball speed in all three tests ranged from 0.2+/-1.4 m(-1) to 0.3+/-1.3 m s(-1), suggesting that in 95% of repeated trials the ball speed might be from 1.2 m s(-1) less to 1.6 m s(-1) greater than the original estimate. The coefficients of variation for all kicking tests were between 2.6% and 3.3% (95% confidence intervals; 2.2-3.9%) suggesting a low intra-subject variability. CONCLUSIONS: Due to a high reliability, relative simplicity, and a small number of participants needed to detect worthwhile changes, the evaluated kicking tests could be highly recommended for sport specific profiling and early selection of young athletes, as well as for the assessment of training procedures and other interventions applied on individual teams of elite soccer, rugby or American football players.

Vertical posture and head stability in patients with chronic neck pain.

OBJECTIVE: To evaluate postural performance and head stabilization of patients with chronic neck pain. DESIGN: A single-blind comparative group study. SUBJECTS: Patients with work-related chronic neck pain (n = 9), with chronic whiplash associated disorders (n = 9) and healthy subjects (n = 16). METHODS: During quiet standing in different conditions (e.g. 1 and 2 feet standing, tandem standing, and open and closed eyes) the sway areas and the ability to maintain the postures were measured. The maximal peak-to-peak displacement of the centre of pressure and the head translation were analysed during predictable and unpredictable postural perturbations. RESULTS: Patients with chronic neck pain, in particular those with whiplash-associated disorders, showed larger sway areas and reduced ability to successfully execute more challenging balance tasks. They also displayed larger sway areas and reduced head stability during perturbations. CONCLUSION: The results show that disturbances of postural control in chronic neck pain are dependent on the aetiology, and that it is possible to quantify characteristic postural disturbances in different neck pain conditions. It is suggested that the dissimilarities in postural performance are a reflection of different degrees of disturbances of the proprioceptive input to the central nervous system and/or of the central processing of such input.

Evaluation of methods for normalizing muscle strength in elite and young athletes.

BACKGROUND: The following equation has been most often used in order to present recorded muscle strength (F) normalised for various measures of body size (such as body mass m) Fnor = F x m(-b). Since previous studies have provided inconsistent results, the purpose of the present one was to assess the value of the exponential parameter b (b-value) that (a) provides both the normalised strength independent of body mass and (b) demonstrates the highest possible correlation between the normalised strength and standard tests of movement performance. METHODS: Thirteen groups of male and female athletes of both different age and different sport specialisation were tested for maximal isometric force of various leg muscle groups, as well as for vertical and standing long jump. RESULTS: The data obtained on most of the experimental groups suggested that the b-value close to the theoretically predicted b=0.67, but also different from b=0 and b=1, should be used for calculation of the normalised strength independent of body mass. Although the strength normalised using b=0.67 and b=1 demonstrated higher correlation with jumping performance than the non-normalised strength (i.e., b=0), the data also suggested that b>1 could provide the highest prediction of movement performance. CONCLUSIONS: Muscle strength should be calculated as force per kg(2/3) rather than as absolute force or force calculated per kg of body mass in order to assess strength independent of body size in routine testing of muscle function. However, different and probably task specific normalisation methods could be required in order to predict performance of various movement tasks by assessed muscle strength.

Effects of plyometric training on jumping performance in junior basketball players.

BACKGROUND: Although the plyometric training has proved its efficiency, it remains generally unknown whether a limited amount of plyometric training could improve movements in subjects who already demonstrate high level of performance. METHODS: Three different training regimens were performed in order to study effects of plyometric training on elite junior basketball players. While control group (CG) participated only in the regular midseason training activity, another two groups performed a limited amount of plyometric training employing drop jumps from the height of either 50 cm (EG-50) or 100 cm (EG-100). The height of the maximal vertical jump (CMJ), as well as the maximal voluntary force (F) and the rate of force development (RFD) of hip and knee extensors were tested prior to and after the training. RESULTS: An increase in CMJ (4.8 and 5.6 cm in EG-50 and EG-100, respectively), as well as in F of hip extensors and RFD of knee extensors was observed in both experimental groups, while no significant changes were recorded in CG. When the pretest scores were used as a covariate, both experimental groups demonstrated higher increase in CMJ and RFD of knee extensors then CG. However, no differences were observed between EG-50 and EG-100. The multiple correlation between four isometric parameters and CMJ revealed R2=0.29. CONCLUSIONS: A limited amount of plyometric training could improve jumping performance in elite junior basketball players and this improvement could be partly related with an increase in F of hip extensors and RFD of knee extensors. However, neither of the two initial heights of the applied drop jumps proved to be more effective.

Changes in movement variables associated with transient overshoot of the final position.

Transient overshoot (TO), which is assessed as the distance between the movement amplitude and the final position, was measured in a series of rapid, discrete elbow flexion movements performed under different distance and loading conditions by 7 participants. A positive relationship was found between kinematic variables (peak velocity, peak acceleration and deceleration, and the symmetry ratio) and the magnitude of TO, particularly in short movements performed against a light load. The relationships between TO and electromyographic (EMG) variables were low and mainly insignificant. Thus, TO contributes to the variability of rapid, discrete movements and therefore should be taken into account as an additional parameter in studies of the scaling of movement variables with movement mechanical conditions. TO could also represent a consequence of mechanical properties of the single-joint system rather than an independently programmed primary submovement.

Changes in movement symmetry associated with strengthening and fatigue of agonist and antagonist muscles.

The hypothesis that strengthening or fatiguing procedures applied on active muscles can affect the symmetry of rapid, discrete movements was tested. Subjects (N = 12) performed rapid, consecutive elbow flexions and extensions between 2 targets before and after (a) applying a strength training program, (b) fatiguing elbow flexors, and (c) fatiguing elbow extensors. The results demonstrated that an increase in strength of elbow extensors caused by applied strength training is associated with an increase in the symmetry ratio (i.e., acceleration time divided by deceleration time) of elbow flexion movements. The symmetry ratio also increased and decreased in movements when agonists and antagonists were fatigued, respectively. Because the strength training and fatiguing procedures are both known to affect muscle force, the data are interpreted as changes in muscles' ability to exert the force while acting as agonists or antagonists. Namely, muscles need equal impulses of force (torque multiplied by time) to accelerate and, thereafter, to decelerate the limb while performing a rapid, discrete movement. The symmetry ratio may therefore be changed so that more time will be provided for muscles that become relatively weaker (compared with their antagonists) because a strengthening or fatiguing procedure has been applied, whereas a shorter time period should be sufficient for action of their stronger antagonists. Although, in the literature, the studied phenomenon has been discussed as a predominantly motor control phenomenon, the present data suggest that the movement symmetry could also be related to agonists' and antagonists' ability to exert force, particularly while performing rapid, discrete movements.

Effects of direction and curvature on variable error pattern of reaching movements.

A number of studies have analyzed various indices of the final position variability in order to provide insight into different levels of neuromotor processing during reaching movements. Yet the possible effects of movement kinematics on variability have often been neglected. The present study was designed to test the effects of movement direction and curvature on the pattern of movement variable errors. Subjects performed series of reaching movements over the same distance and into the same target. However, due either to changes in starting position or to applied obstacles, the movements were performed in different directions or along the trajectories of different curvatures. The pattern of movement variable errors was assessed by means of the principal component analysis applied on the 2-D scatter of movement final positions. The orientation of these ellipses demonstrated changes associated with changes in both movement direction and curvature. However, neither movement direction nor movement curvature affected movement variable errors assessed by area of the ellipses. Therefore it was concluded that the end-point variability depends partly, but not exclusively, on movement kinematics.

Changes in movement final position associated with agonist and antagonist muscle fatigue.

We have tested the hypothesis that agonist and antagonist muscle fatigue could affect the final position of rapid, discrete movements. Six subjects performed consecutive elbow flexion and extension movements between two targets, with their eyes closed prior to, and after fatiguing the elbow extensor muscles. The results demonstrate that elbow extension movements performed in the post-test period systematically undershot the final position as compared to pre-test movements. However, attainment of the aimed final position in elbow flexion movements was unaffected by fatiguing of the extensor muscles. Undershoot of the final position obtained in extension movements was associated with agonist muscle fatigue, a result that was expected from the point of view of current motor control theories, and that could be explained by a reduced ability of the shortening muscle to exert force. On the other hand, the absence of the expected overshoot of the final position when the antagonist is fatigued, indicates the involvement of various reflex and/or central mechanisms operating around the stretched muscle that could contribute to returning the limb to the standard final position after a brief prominent overshoot.

Anthropometric, strength, and power predictors of sprinting performance.

BACKGROUND: The purpose of this study was to examine relations between sprinting performance (i.e. average velocity within both the initial acceleration and maximum speed phases of sprint running) and some standard anthropometric, strength, and power tests. METHODS: Twenty-four male students of physical education were timed over the distances of 0.5-15 m and 15-30 m from the sprint start. Several measures of muscle isometric strength (knee extensors, hip extensors and flexors) and power (height of the counter movement jump and the average power of leg extensors during continuous jumping) were also collected, in addition to the lean body mass and the percentage of both muscle and fat tissue. RESULTS: The results obtained demonstrated that, except for the height of the counter movement jump, all correlation coefficients between the selected variables and sprinting performance were low and, therefore, insignificant. As a consequence, multiple correlation coefficients were also low (0.43 and 0.56 for the initial acceleration and maximal speed phase, respectively). CONCLUSIONS: Most of the standard anthropometric, strength and power tests could be poor predictors of sprinting performance. A better assessment of sprinting performance could be based on more specific tests that, unfortunately, require more complex measurements.

The effects of prior antagonist muscle vibration on performance of rapid movements.

The effects of prior vibration of the antagonist triceps muscle on the performance of rapid discrete elbow flexion movements were studied in healthy volunteers. The subjects performed 520 movements over five experimental sessions. The application of prior vibration resulted in a shift of the initial position, an undershoot of the final position in untrained subjects, and also in trained subjects if not applied during practice. On the contrary, no undershoot occurred in trained subjects when prior vibration was applied during practice. Improvement in movement performance, as judged by a decrease in variability of the final position, was less successful when vibration was applied during practice. It is supposed that the undershoots were due to prior vibration-induced alterations in proprioceptive messages and a consequent erroneous sense of the arm position. These effects seem to be overcome by practice, but also seem to interfere with learning-based movement improvement.

Learning a motor task involving obstacles by a multi-joint, redundant limb: two synergies within one movement.

In this study, we investigated the hypothesis that the problem of motor redundancy could be solved using synergies representing rules for relative joint involvement to ensure a desired endpoint trajectory which may be context-dependent and may change with practice. Subjects practised a planar movement 'as fast as possible' from an initial to a final position, avoiding three round obstacles. The improvement in motor performance included a decrease in movement time and in the error scores. It was accompanied by the emergence of two distinct synergies. The first one involved elbow and shoulder movements and was used to move from the initial position to the first obstacle, and from obstacle to obstacle, whereas the second, involving the wrist, was used while going around the obstacles. The first synergy was seen before practice and showed an increase in joint coupling with practice. The second synergy was not seen prior to practice; it could not be explained by the pseudo-inverse transformation. We concluded that the central nervous system (CNS) has options for solving the redundancy problem, and that the solutions may be chosen based on such considerations as accuracy requirements, inertial properties of segments, and efficacy of particular joints to move the endpoint along a desired trajectory.

Effects of arm and leg loading on sprint performance.

The effects of loading on sprint kinematics were examined in 24 male students. The moment of inertia of either the arms or legs was increased by up to 50% of their unloaded values and the time for distances of 0.5-15 m and 15-30 m from a sprint start was measured. An increase in leg loading was associated with a gradual decrease in velocity of both sprint phases, while the change associated with arm loading was modest and significant only in the second phase. The decrease in sprint velocity was predominantly due to a reduction in stride rate, while the stride length remained almost unchanged. It was concluded that leg loading affected sprint velocity more than arm loading, and also that the velocity was reduced due to a decrease in the stride rate rather than in the stride length.

Changes in the symmetry of rapid movements. Effects of velocity and viscosity.

Five subjects made rapid, discrete elbow flexion movements over different distances, against different inertial loads, as well as under distance and load combinations that kept movement time constant. The results demonstrated that an increase in peak movement velocity was associated with an increase in the temporal symmetry ratio of the movement (acceleration time divided by deceleration time), as well as with an increase in both agonist electromyographic (EMG) burst duration and antagonist EMG latency. Since an increase in peak movement velocity is associated with faster agonist muscle shortening, as well as with faster stretching of the antagonist muscle, we hypothesize that the velocity-related changes in movement symmetry can be viewed as, at least partially, a consequence of muscle viscosity. Viscosity increasingly resists the shortening agonist and assists the lengthening antagonist when movement velocity increases. Therefore, the agonist muscles require more time to produce the required impulse, while the antagonist muscle can brake the movement in a shorter period of time. In order to test the hypothesis that viscosity is responsible for the velocity-associated changes in the symmetry ratio, we performed a second experiment with distance and load combinations identical to those of the first experiment, but with different external viscous loads, which resisted the slower and assisted the faster movements. The results demonstrated that the movements became more symmetrical in the presence of the viscous load. There were also changes in agonist duration and antagonist latency. We conclude that changes in the symmetry associated with changes in movement velocity may be due to the effects of either muscle viscosity or changes in how muscles are activated to account for differences in viscous force.

Learning transfer from flexion to extension movements: importance of the final position.

Nine subjects (experimental group) were tested on rapid elbow flexion and extension movements performed in the same final position, prior to and after extensive practice of the movements. Nine additional subjects (control group) were also tested, but without any practice between the tests. Comparison of the pretest and posttest results suggested that the experimental group decreased their variable error (i.e., standard deviation of the final movement position) in both practiced (elbow flexion) and nonpracticed (elbow extension) movement. The control group, however, did not improve in either of tested movements. The experimental group demonstrated lower variable error in the nonpracticed elbow extensions than the control group, while the same difference for practiced elbow flexion movements was slightly below the significant level. The results support the importance of the final position in programming of rapid, self-terminated movements; however, they do not rule out the role of other kinetic and kinematic variables (such as movement distance).