Postural and trunk responses to unexpected perturbations depend on the velocity and direction of platform motion.

This study compares postural and trunk responses to translating platform perturbations of varied velocities and directions. A group of 18 young and physically active subjects were exposed to a set of postural perturbations at varied velocities (5, 10, 15, and 20 cm/s) and directions of platform movement (forward, backward, left-lateral, and right-lateral). The center of pressure (CoP) displacement measurement, in addition to the trunk motion (representing the center of mass (CoM) displacement), were both monitored. Results identified that the CoP displacement increased from slow to faster velocities of platform motion more widely in both anterior and posterior directions (50.4 % and 48.4 %) as compared to the CoM displacement (17.8 % and 14.9 %). However a greater increase in the peak CoM velocity (70.3 % and 69.6 %) and the peak CoM acceleration (60.5 % and 53.1 %) was observed. The values in the anterior and posterior direction only differed significantly at the highest velocity of platform motion (i.e. 20 cm/s). A similar tendency was observed in the medio-lateral direction, but there were no significant differences in any parameter in the left-lateral and right-lateral direction. The velocity of the platform motion highly correlated with peak velocity (r=0.92-0.97, P<0.01) and moderately with amplitude of trunk displacement (r=0.56-0.63, P<0.05). These findings indicate that the velocity of perturbation alters peak CoM velocity rather than the magnitude of CoM displacement. The effect of the direction of perturbations on the trunk response emerges only at a high velocity of platform motion, such that the peak CoM velocity and peak CoM acceleration are significantly greater in anterior than posterior direction.

Load release balance test under unstable conditions effectively discriminates between physically active and sedentary young adults.

This study investigates test-retest reliability and diagnostic accuracy of the load release balance test under four varied conditions. Young, early and late middle-aged physically active and sedentary subjects performed the test over 2 testing sessions spaced 1week apart while standing on either (1) a stable or (2) an unstable surface with (3) eyes open (EO) and (4) eyes closed (EC), respectively. Results identified that test-retest reliability of parameters of the load release balance test was good to excellent, with high values of ICC (0.78-0.92) and low SEM (7.1%-10.7%). The peak and the time to peak posterior center of pressure (CoP) displacement were significantly lower in physically active as compared to sedentary young adults (21.6% and 21.0%) and early middle-aged adults (22.0% and 20.9%) while standing on a foam surface with EO, and in late middle-aged adults on both unstable (25.6% and 24.5%) and stable support surfaces with EO (20.4% and 20.0%). The area under the ROC curve >0.80 for these variables indicates good discriminatory accuracy. Thus, these variables of the load release balance test measured under unstable conditions have the ability to differentiate between groups of physically active and sedentary adults as early as from 19years of age.

Effects of Stable and Unstable Resistance Training in an Altered-G Environment on Muscle Power.

The study evaluated the effect of 4 weeks of combined resistance-balance training and resistance training alone in a 90° tilted environment on muscle power. Two groups of healthy young subjects performed leg extensions while in a supine position, either on a firm surface along a linear track or on an unstable surface requiring mediolateral balancing movements. Power and force during squats were measured at isokinetic velocities of 10 and 35 deg/s. Results showed significantly greater gains in peak force (44.1%; F(1,21)=8.876, p=0.026), mean force (58.6%; F(1,21)=16.136, p=0.013), peak power (58.7%; F(1,21)=18.754, p=0.009), and mean power (59.2%; F(1,21)=23.114, p=0.007) at the velocity of 35 deg/s after stable than unstable resistance training. However, there were no significant between-groups differences in pre-post training gains in peak force (10.4%; F(1,21)=1.965, p=0.74), mean force (10.3%; F(1,21)=1.889, p=0.80), peak power (12.9%; F(1,21)=2.980, p=0.49), and mean power (19.1%; F(1,21)=3.454, p=0.36) during squats at the velocity of 10 deg/s. Resistance exercises under stable conditions performed in a 90° tilted environment are more effective in the improvement of high velocity muscle power than their use in combination with balance exercises. Such training may be applicable in pre- and in-flight exercise regimens for astronauts and in functional rehabilitation of bed-ridden patients.

Reliability and methodological issues of power assessment during chest presses on unstable surface with different weights.

AIM: The study compares the reliability of peak power (Ppeak) and mean power in acceleration (Pmean acc) and entire concentric phase (Pmean total) of chest presses on the bench and unstable Swiss ball with different weights. METHODS: A group of 32 fit men performed over 2 testing sessions 3 trials of barbell chest presses on the bench and Swiss ball, without and with countermovement, with weights of 40, 60 and 80% 1RM. RESULTS: High values of correlation coefficients (above .80) and no significant differences between trials signify stability of measurement under both stable and unstable conditions. When chest presses were performed on the bench, ICC and SEM% values were in range .97 to .98 and 7.6 to 7.7%, respectively for Pmean total, .96 to .98 and 9.1 to 9.6%, respectively for Pmean acc, and .94 to .97 and 9.2 to 10.0%, respectively for Ppeak. Their values during chest presses on a Swiss ball ranged from .93 to .96 and 8.4 to 9.1%, respectively for Pmean total, from .87 to .90 and 11.7 to 12.2%, respectively for Pmean acc, and from .79 to .82 and 12.1 to 13.4%, respectively for Ppeak at weights of 40 and 60% 1RM, and from .70 to .76 and 17.6 to 19.8%, respectively at weight of 80% 1RM. CONCLUSION: Measurement of peak and mean power during unstable chest presses provides reliable data comparable to those obtained during bench presses under all conditions tested. However, peak values of power measured during unstable chest presses with weights ≥80% 1RM should be interpreted with caution.

Concurrent validity of clinical tests for measuring hamstring flexibility in school age children.

The objectives were 1) to evaluate the hamstring muscle flexibility in children and adolescents; 2) to examine the relative contribution of the spinal curvatures, pelvic tilt and hamstring flexibility on the sit-and-reach (SR) score; and 3) to determine the validity of the sit-and-reach test through both active and passive hip flexion tests. 118 children and adolescents (aged 7-18 years; 60 males and 58 females) were tested for sit-and-reach (SR), passive straight leg raise (PSLR) and active straight leg raise (ASLR). The spinal curvatures and pelvic tilt were assessed during the SR test by means of the Spinal Mouse system. Females showed a statistically greater anterior pelvic tilt, distance reached in the SR test and hip flexion in both PSLR and ASLR tests than males. The pelvic tilt independently explained more than 60% of the variance (distance reached in the SR test) and in conjunction with lumbar flexion explained more than 80% of the variance. In conclusion, the pelvic tilt is the main determinant of SR test in school age children. The SR test can be considered an appropriate and valid test for evaluating pelvic tilt and lumbar flexion in school age children, but not to measure hamstring flexibility.

Utilization of elastic energy during weight exercises differs under stable and unstable conditions.

AIM: The study compares the power outputs in concentric phase of chest presses and squats performed without and with countermovement on stable and unstable support surface, respectively. METHODS: A group of 16 physical education students performed randomly in four different days 3 repetitions of: 1) barbell chest presses on the bench and Swiss ball, respectively, and 2) barbell squats on stable support base and Bosu ball, respectively. Exercises were performed without and with countermovement (CM) using maximal effort in concentric phase of lifting. Initial weight of 20 kg increased by 10 kg or 5 kg (at higher loads) up to at least 85% of previously established 1RM under stable conditions. A PC based system FiTRO Dyne Premium was used to monitor force and velocity and to calculate power. As a parameter of the capability to use elastic energy was considered the difference in mean power in concentric phase of weight exercises (ΔP) performed with and without CM. RESULTS: There were higher power outputs in concentric phase of CM chest presses as compared to those performed from quiet position on the chest under both stable and unstable conditions. This enhancement of power due to CM was rather modest at lower weights and become more pronounced with increasing weights reaching a maximum at 57.1% 1RM on stable and at 47.6% 1RM on unstable support surface. Lifting heavier weights not only failed to increase the enhancing effect but led to its decline. Similar trend was observed during squats with maximal enhancement of power in concentric phase of lifting at about 80% 1RM under both conditions. The ΔP was significantly lower during chest presses on Swiss ball than on the bench, however, only at higher weights lifted (≥60% 1RM). On the other hand, the ΔP during squats performed on Bosu ball and on stable support base did not differ significantly across all weights lifted. CONCLUSION: The ability to utilize elastic energy during CM chest presses is more profoundly compromised under unstable than stable conditions, namely at higher weights lifted. On the other hand, there is similar enhancement of power in concentric phase of CM squats on stable and unstable support surface regardless of weights lifted. Besides the type of exercise, this may be ascribed to different degree of instability of devices used (Swiss ball vs. Bosu ball).

The effect of 6-week combined agility-balance training on neuromuscular performance in basketball players.

AIM: The study evaluates the effect of 6-week combined agility-balance training on neuromuscular performance in basketball players. METHODS: Subjects divided into experimental (EG, n = 17) and control group (CG, n = 17) underwent a combined agility-balance training (in duration of 30 min) for a period of 6 weeks (4-5 sessions/week). Both groups performed reaction tasks similar to game-like situations, however EG on wobble boards and CG on stable surface. Prior to and after the training parameters of agility, balance, speed of step initiation, strength differentiation accuracy, and explosive power of lower limbs were evaluated. Postural stability was assessed under both static and dynamic conditions (wobble board) with eyes open and eyes closed, respectively. The velocity of the centre of pressure (COP) was registered at 100 Hz by means of posturography system FiTRO Sway check based on dynamometric platform. Using FiTRO Reaction check simple and multi-choice reaction times were measured. The same system was applied to evaluate the agility performance including reaction and movement task. Speed of step initiation was measured using FiTRO Dyne Premium. Jumping abilities were evaluated by means of FiTRO Jumper (10-seconds maximal jumps, Countermovement jump, Squat jump, Drop jump). Using the same system, the subject´s ability to match 50 % of their maximal height of the jump was evaluated. RESULTS: Results showed that a combined agility-balance training improved dynamic balance not only under visual control but also in eyes closed conditions. Training also increased run-out speed that likely contributed to better agility performance, reduced ground contact time during drop jump, and improved the ability to differentiate the force of muscle contraction during repeated jumps. However, such training has been found to be insufficient to improve both simple and multi-choice reaction time, and jumping performance. On the other hand, control group failed to show any significant improvement in examined abilities except for enhancement of jumping performance (Pact, Δ CMJ & SJ). CONCLUSION: It may be concluded that balance exercises performed simultaneously with reaction tasks represent an effective means for improvement of neuromuscular performance in elite athletes.

Quantitative changes of dianthrones, hyperforin and flavonoids content in the flower ontogenesis of Hypericum perforatum.

Samples of Hyperici herba were obtained by harvesting Hypericum perforatum L. in different plant development stages. The relation of flower development phases in the drug's flower fraction was examined. The HPLC method was then employed for the analysis of the content of secondary metabolites in different flower ontogenesis phases. The content of dianthrones, derivatives of quercetin and hyperforin increased from the first bud phases (0.29%, 0.80%, and 2.47%, respectively) to flowers just opened (1.04%, 4.23% and 6.60%, respectively). The content of dianthrones and quercetin glycosides then decreased (in unripe fruits 0.11% and 0.08%, respectively), whereas the amounts of hyperforin increased to 8.07% in fruits. The content of I3,II8-biapigenin increased from 0.21% in small buds to 1.04% in buds just before opening and has then decreased gradually to a value of 0.02% in fruits. Rutin was not detected in the samples.

[Somatic and functional profiles of members of the Slovak karate team]. / Somatický a funkcný profil reprezentantov SR v karate.

The exercise load in karate is prevailingly of anaerobic character, the fact of which is evident by the increase in heart frequency and the levels of blood lactate. During competition, the heart frequency achieved the values of 180-199 beats per minute and the level of blood lactate following the competition was 4.5-6.5 mmol/l. The values of lactate were substantially higher during the training unit (at the time of chronometric measurement) when exercise was more intensive 5.8-12.5 mmo/l at the heart frequency of 180-200 or even more beats per minute, than during competition. The aim of this work was to find out the basic morphologic and functional profiles in the representatives of the National Karate Team on the basis of laboratory methods.