Reference Values of the Forearm Tremor Power Spectra for Youth Athletes.

The aim of the study was to determine reference graphs of power spectral density functions of forearm physiological tremor and to compare their parameters in the male and female population of young athletes from various sports. One hundred fifty-nine (159) female (15.7 ± 2.1 years, 59.8 ± 8.1 kg, 169.1 ± 7.5 cm) and 276 male (16.4 ± 1.9 years 72.7 ± 10.3 kg and 180.9 ± 8.7 cm) youth athletes participated in the study. Forearm tremor was measured accelerometrically in a sitting position. Power spectrum density (PSD) function was calculated for each individual tremor waveform. Because of right skewness of power distribution, the PSD functions were subjected to logarithmic transformation. Average log-powers in low (2-4 Hz) and high (8-14 Hz) frequency ranges and mean frequencies in those ranges were analyzed. Tremor log-powers for male were greater than for female athletes (p < 0.001), while frequencies of spectrum maxima did not differ from each other. Frequencies of spectrum maxima correlated (p < 0.001) with age (r = 0.277 and 0.326 for males and females, respectively). The obtained reference functions may be utilized in order to quantify and assess tremor size and its changes evoked by stress and fatigue, which can be applied for selection and training monitoring in sports, but also in medicine for detection and diagnosis of pathologic tremor in young individuals.

The Influence of Fatigue on the Characteristics of Physiological Tremor and Hoffmann Reflex in Young Men.

The aim of the study was to determine the relationship between changes in physiological tremor after exercise and changes in the traction properties of the stretch reflex indirectly assessed using the Hoffmann reflex test. The research involved 19 young men practicing canoe sprint (age 16.4 ± 0.7 years, body mass 74.4 ± 6.7 kg, body height 182.1 ± 4.3 cm, training experience 4.8 ± 1.6 years). During resting tests, Hoffmann reflex measurements were performed from the soleus muscle, physiological tremor of the lower limb, and the blood lactate concentration was determined. Then, a graded test was carried out on the kayak/canoe ergometer. Immediately after the exercise and in the 10th and 25th minute following the exercise, Hoffmann's reflex of the soleus muscle was measured. The physiological tremor was measured at 5, 15 and 30 min after exercise. Blood lactate concentrations were determined immediately after physiological tremor. Both the parameters of Hoffmann's reflex and physiological tremor changed significantly after exercise. There were no significant interrelationships between Hoffmann reflex measurements and physiological tremor in resting and post-exercise conditions. No significant correlation was detected between changes in physiological tremor and changes in Hoffmann reflex parameters. It is to be assumed that there is no connection between a stretch reflex and a physiological tremor.

Association between vitamin D status and testosterone and cortisol in ice hockey players.

The identification of the vitamin D receptor in tissues related to testosterone and cortisol production, in conjunction with the observed correlations between vitamin D levels and these hormones in the general population, suggest vitamin D may influence testosterone and cortisol concentrations in athletes. A cross-sectional study design was used to evaluate the association between 25(OH)D and testosterone and cortisol concentrations in young male ice hockey players (n = 50). All athletes were recruited during October from the Sosnowiec area, Poland (50° N). Commercially available ELISA kits were used to determine total serum 25(OH)D, testosterone and cortisol concentrations. Serum 25(OH)D concentration was analyzed as both a continuous and dichotomous variable, binned at the criteria for deficiency (< 20 ng·ml-1), to investigate a threshold effect. Neither continuous (r = 0.18, p = 0.20) nor dichotomous (r = 0.16, p = 0.27) 25(OH)D concentration was significantly correlated with testosterone concentration. A small, inverse correlation (r = -0.30, p = 0.04) was detected between 25(OH)D and cortisol concentrations when analyzed as a dichotomous variable only. Serum 25(OH)D concentration was neither associated with testosterone (p = 0.09) nor cortisol concentrations (p = 0.11) after adjusting for age, fat free mass and fat mass in sequential linear regression. The inability of vitamin D status to independently predict testosterone and cortisol concentrations suggests that any performance-enhancing effects of vitamin D in athletes are unlikely to be mediated primarily through these hormones, at least amongst young male ice-hockey players.

Changes of Strength and Maximum Power of Lower Extremities in Adolescent Handball Players During a Two-year Training Cycle.

The aim of the study was to investigate changes of strength and power of the lower extremities in adolescent handball players during a two-year training cycle. Thirty-one male handball players (age 16.0 ± 0.2 years, body mass 81.4 ± 9.7 kg, body height 188.2 ± 6.4 cm) took part in this study. All tests were conducted three times at the beginning of a one-year training programme. The maximum joint torque (JT) of flexors and extensors of the elbow, shoulder, hip, knee and trunk was measured under static conditions. Power of lower extremities was assessed with a repeated sprint ability (RSA) test on a cycloergometer and jump tests: akimbo counter-movement jump (ACMJ), counter-movement jump (CMJ) and spike jump tests on a force plate. Peak power (PP) increased from 914.8 ± 93.9 to 970.0 ± 89.2 and 1037.8 ± 114.4 W (p < 0.05) following the RSA test results. Maximum power increased significantly (p < 0.05) in ACMJ (1951.9 ± 359.7 to 2141.9 ± 378.5 and 2268.5 ± 395.9 W) and CMJ tests (2646.3 ± 415.6 to 2831.2 ± 510.8 and 3064.6 ± 444.5 W). Although significant differences in JT (p < 0.05) were observed during the two year period, their values related to body mass for the lower right extremity, sum of the trunk and sum of all muscle groups increased significantly between the first and the second measurement (from 13.7 ± 1.8 to 14.58 ± 1.99 N·m·kg-1, from 9.3 ± 1.5 to 10.39 ± 2.16 N·m·kg-1, from 43.4 ± 5.2 to 46.31 ± 6.83 N·m·kg-1, respectively). The main finding of the study is that PP in the RSA test and maximal power in the ACMJ and CMJ increase in relation to training experience and age in the group of youth handball players.

Leg strength and power in Polish striker soccer players.

PURPOSE: The main goal of the present study was to examine muscle strength and power of dominant and non-dominant leg, knee extensors and flexors, and their correlations with jumping performances in soccer players. A secondary aim was to evaluate muscle sense. METHODS: 31 male professional strikers (age 20.9 ± 2.3 years, body mass 75.1 ± 6.6 kg, body height 179.5 ± 4.7 cm) participated in the study. The power output of lower extremities and the height of rise of the body mass centre during vertical jumps were measured using a force plate. The maximum muscle torque of the flexors and extensors of the knee were measured under isometric conditions using a special isometric torquemeter. Force sense was measured in isometric conditions in two tests: (a) fifty percent of the maximal voluntary contraction was set as a value of target force and the participants were instructed to reproduce the target force, (b) the participants attempted to develop a torque reproducing a sine course within the range of 10 to 50% of MVC performed. RESULTS: A direct relationship was observed between the peak muscle torque in knee extensors developed during isokinetic contraction at all velocities and power and height of three types of vertical jumps ( p <0.05). No correlation was observed between jumping performance and muscle torque under isometric condition. No differences were found in strength and jumping abilities as well as in force sense between dominant and non-dominant legs. CONCLUSIONS: This study offered a comprehensive and complete evaluation of leg muscle strength, sense and power, with the use of using force plate and isokinetic dynamometry.

Vitamin D status and its relation to exercise performance and iron status in young ice hockey players.

OBJECTIVES: The aim was to examine the association between serum vitamin D concentration and isometric strength of various muscle groups, vertical jump performance, and repeated sprint ability in young ice hockey players. The secondary aim was to determine the association between vitamin D deficiency and indices of iron status. METHODS: Fifty male ice hockey players (17.2±0.9 years) participated in this cross-sectional study. Exercise performance was evaluated using isometric strength measures of upper and lower extremities, vertical jump performance and repeated sprint ability (RSA). Blood samples were collected for the determination of serum 25-hydroxyvitamin D (25(OH)D) and multiple indicies of iron status. RESULTS: The mean serum 25(OH)D concentration was 30.4 ng·ml-1 and ranged from 12.5 to 91.4 ng·ml-1. Eleven participants (22%) had vitamin D deficiency and 20 athletes (40%) had vitamin D insufficiency. Serum 25(OH)D concentration was not positively correlated with isometric muscle strength, vertical jump performance, or RSA after adjusting for age, training experience, fat mass, fat free mass and height. Serum 25(OH)D concentration was not associated with indices of iron status. CONCLUSION: Vitamin D insufficiency is highly prevalent in ice hockey players, but 25(OH)D concentration but it is not associated with exercise performance or indices of iron status.

Countermovement depth - a variable which clarifies the relationship between the maximum power output and height of a vertical jump.

PURPOSE: The aim of this study was to identify the determinants of peak power achieved during vertical jumps in order to clarify relationship between the height of jump and the ability to exert maximum power. METHODS: One hundred young (16.8±1.8 years) sportsmen participated in the study (body height 1.861 ± 0.109 m, body weight 80.3 ± 9.2 kg). Each participant performed three jump tests: countermovement jump (CMJ), akimbo countermovement jump (ACMJ), and spike jump (SPJ). A force plate was used to measure ground reaction force and to determine peak power output. The following explanatory variables were included in the model: jump height, body mass, and the lowering of the centre of mass before launch (countermovement depth). A model was created using multiple regression analysis and allometric scaling. RESULTS: The model was used to calculate the expected power value for each participant, which correlated strongly with real values. The value of the coefficient of determination R2 equalled 0.89, 0.90 and 0.98, respectively, for the CMJ, ACMJ, and SPJ jumps. The countermovement depth proved to be a variable strongly affecting the maximum power of jump. If the countermovement depth remains constant, the relative peak power is a simple function of jump height. CONCLUSIONS: The results suggest that the jump height of an individual is an exact indicator of their ability to produce maximum power. The presented model has a potential to be utilized under field condition for estimating the maximum power output of vertical jumps.

Individual and Combined Influence of ACE and ACTN3 Genes on Muscle Phenotypes in Polish Athletes.

Orysiak, J, Mazur-Rózycka, J, Busko, K, Gajewski, J, Szczepanska, B, and Malczewska-Lenczowska, J. Individual and combined influence of ACE and ACTN3 genes on muscle phenotypes in polish athletes. J Strength Cond Res 32(10): 2776-2782, 2018-The aim of this study was to examine the association between angiotensin-converting enzyme (ACE) and α-actinin-3 (ACTN3) genes, independently or in combination, and muscle strength and power in male and female athletes. The study involved 398 young male (n = 266) and female (n = 132) athletes representing various sport disciplines (ice hockey, canoeing, swimming, and volleyball). All were Caucasians. The following measurements were taken: height of jump and mechanical power in countermovement jump (CMJ) and spike jump (SPJ), and muscle strength of 10 muscle groups (flexors and extensors of the elbow, shoulder, hip, knee, and trunk). The insertion-deletion (I/D) polymorphism of ACE and the R577X polymorphism of ACTN3 were typed using polymerase chain reaction (PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), respectively. The genotype distribution of the ACE and ACTN3 genes did not differ significantly between groups of athletes for either sex. There was no association between ACE and ACTN3 genotypes (alone or in combination) and sum of muscle strength, height of jump or mechanical power in both jump tests (CMJ and SPJ) for male and female athletes. These findings do not support an influential role of the ACE and ACTN3 genes in determining power/strength performance of elite athletes.

Measuring the force of punches and kicks among combat sport athletes using a modified punching bag with an embedded accelerometer.

The main aim of the study was to design a new system to measure punching and kicking forces as well as reaction times in combat sport athletes. In addition, the study examined whether there were any intergender differences in the force of punches thrown by boxers and kicking forces delivered by taekwondo athletes. Boxers (male, n = 13; female, n = 7) were examined for the force of single straight punches and taekwondo athletes (male, n = 14; female, n = 14) for force of single Apdolio and Dwit Chagi kicks. The punching bag was equipped with acceleration transducers and gyroscopes embedded in a cylinder covered with a layer to absorb shock as well as a set of colour signal diodes. Value of the punching bag's acceleration was used for calculating: strike force; the punching location on the bag; and time of a strike. The relative error of force calculation was 3%; the relative error in acceleration measurement was less than 1%. The force of a straight rear-hand punch was greater than the force of a lead-hand punch among male and female boxers. The force of Apdolio kick delivered with a rear leg was greater compared to a lead leg among female and male taekwondo athletes. Significant gender differences were noticed in the force in both types of kicks. In boxers, intergender differences were reported only for the force of a punch thrown with the rear hand. Based on these findings, it was concluded that the modified punching bag is a good diagnostic tool for combat sports.

Relationship Between ACTN3 R577X Polymorphism and Physical Abilities in Polish Athletes.

The purpose of this study was to examine the association between α-actinin 3 (ACTN3) R577X polymorphism and physical abilities of male athletes performing various sports (volleyball, ice hockey, canoeing, swimming). One hundred eighty-five subjects were recruited for the study. The following measurements were taken: height of jump and power output in countermovement jump and spike jump (SPJ) and muscle strength of 10 muscle groups. The R577X polymorphism of ACTN3 was typed using polymerase chain reaction restriction fragment length polymorphism. The results showed that RR genotype carriers develop greater power output in SPJ than RX and XX individuals (44.6 ± 11.1, 42.6 ± 11.0, and 38.4 ± 7.9 W·kg(-1) for RR, RX, and XX genotypes, respectively) and height of jump in SPJ (0.537 ± 0.075, 0.523 ± 0.072, and 0.498 ± 0.053 m for RR, RX, and XX genotypes, respectively). Muscle strength did not differ between genotype groups. This suggests that the ACTN3 gene has a greater impact on determining dynamic movements than influencing static muscle strength.

Relationship between ACTN3 R577X polymorphism and maximal power output in elite Polish athletes.

BACKGROUND AND OBJECTIVE: The main purpose of this study was to examine the association between ACTN3 R577X polymorphism and the ability to produce peak power in young male athletes from various sports. Our hypothesis was that the ACTN3 R577X polymorphism is associated with jumping performance and athletes with RR genotype have better scores in tests than athletes with XX or RX genotype independently of the sport discipline. MATERIALS AND METHODS: Two hundred young Polish male participants representing different disciplines were recruited for this study. Genotyping for ACTN3 gene was performed using polymerase chain reaction. The power output of lower extremities and the height of rise of the body mass center during vertical jumps were measured on a force plate. RESULTS: The genotype distribution of the ACTN3 gene did not differ significantly between groups of athletes. The significant difference in height of counter-movement jump was found between athletes with RR and XX genotype (0.446±0.049m vs. 0.421±0.036m, respectively, P=0.026). The ACTN3 RR genotype was associated with greater muscle power and height of jump in young male athletes. CONCLUSIONS: These results suggest that the ACTN3 gene may play a significant role in determining muscle phenotypes. However, this gene is only one of many factors which could contribute to athletes' performance and muscle phenotypes.