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1.
J Hum Kinet ; 92: 193-202, 2024 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-38736604

RESUMEN

The prevalence of the Relative Age Effect (RAE) was studied among medalists from the World Athletics Championships at U18, U20 and Senior age groups and from the Olympic Games from 2000 to 2022. The specific events examined were the 100, 200, 400, 800, 1500, and 3000/5000 m, the long jump, the triple jump, the high jump and the pole vault. Dates of birth from 1,858 outdoor track and field athletes were analysed and further divided into four groups according to the quartile of birth. The RAE was found to be widespread among athletes of both sexes in U18 and U20 age groups in all examined disciplines. There was no difference between the most successful U18 and U20 athletes (p = 0.52). Among senior athletes of both sexes, this effect was not detected and the number of "late-born" athletes in this age group was higher than athletes born in the first three quarters. The prevalence of the RAE across the four groups of events was found in U18 and U20 age groups. Additionally, within each age group, the difference among events was statistically significant. In most successful track and field athletes, the RAE is only significant in U18 and U20 age groups. In senior athletes, the number of "late-born" athletes is significant while RAE disappears. These data may be considered when assessing the athletic potential of an individual athlete.

3.
Drug Test Anal ; 15(8): 889-895, 2023 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-37069126

RESUMEN

Studies examining the effects of new anti-doping measures on sports performance in elite athletes are scarce. During the last decade, a number of new anti-doping methods for the detection of anabolic androgenic steroids were developed. We hypothesized that the implementation of these methods may cause a decrease of performance in athletic disciplines where given substances are widely used. For this purpose, the performance results for 10 athletic disciplines from country (Country A), which was widely accused of systematic doping use, were gathered and pooled into the 2012-2015 and 2016-2019 periods. These periods were seen as before and following the implementation periods, where the effects of new anti-doping methods could be manifested. Also, the performance results of their rival athletes from Country B were analyzed for comparison. The incidence of anti-doping rule violations for both countries was followed. The analysis revealed a decrease in performance results of Country A athletes in eight of 10 disciplines. The performance results of Country B's athletes in seven of 10 disciplines did not and in three disciplines did demonstrate statistically significant change. The decrease in performance of Country A athletes followed a high incidence of steroid detection cases by means of new anti-doping methods. It is highly likely that the consequent performance decrease is due to the implementation of new anti-doping methods. The results of the study bring new facts on the effects of new anti-doping methods implementation and demonstrate following decrease in performance results in population of athletes from the country widely accused of doping use.


Asunto(s)
Rendimiento Atlético , Doping en los Deportes , Humanos , Femenino , Atletas , Esteroides , Esteroides Anabólicos Androgénicos , Doping en los Deportes/prevención & control
4.
Nutr J ; 22(1): 16, 2023 03 08.
Artículo en Inglés | MEDLINE | ID: mdl-36882800

RESUMEN

BACKGROUND: Currently there are no data examining the relationship between the serum concentration of vitamin D bio-chemical marker 25(OH)D and strength and speed characteristics in elite young track and field athletes. Moreover, there are currently no data examining the correlation of vitamin D status with testosterone concentration in elite young track and field athletes. In studies involving members of the general population and athletes from other sports, conflicting data have been reported. MATERIAL AND METHODS: Athletes (n = 68) from both genders took part in this study. Male athletes (n = 23) with mean ± SD age of 18.2 ± 1.9 years and female athletes (n = 45) with mean ± SD age of 17.3 ± 2.6 years participated. All athletes were ranked in the Top-3 in their respective age group and their corresponding results were listed in the Top-20 European records according to https://www.tilastopaja.eu/ in 2021. RESULTS: The average 25(OH)D concentration was 36.5 ± 10.8 ng/mL and 37.8 ± 14.5 ng/mL in male and female athletes respectively. The prevalence of 25(OH)D deficiency (below 20 ng/ml) in both genders was only 5.8%. In the whole group, only 27.9% of athletes had 25(OH)D concentrations between 20 and 30 ng/ml, while 66.2% of athletes had concentrations above 30 ng/ml. There was no difference in vitamin D status between male and female athletes. There was no statistically significant Kruskal-Wallace test correlation between 25(OH)D concentration and performance in the 20 m and 30 m sprint, counter-movement jump and broad jump. There was no correlation between serum concentrations of 25(OH)D and total testosterone in either male or female athletes. CONCLUSION: In elite young track and field athletes who permanently live and train in an area above 50° north latitude, the prevalence of vitamin D deficiency in the summer months was much lower than in previously published studies examining an athletic population, that may be related to the training process. In this specific group of athletes, no correlation was found between serum 25 (OH) D concentration and strength and speed characteristics or total testosterone concentration.


Asunto(s)
Atletismo , Vitamina D , Femenino , Humanos , Masculino , Adolescente , Adulto Joven , Adulto , Testosterona , Vitaminas , Atletas
5.
PLoS One ; 18(3): e0283390, 2023.
Artículo en Inglés | MEDLINE | ID: mdl-36952464

RESUMEN

BACKGROUND: The relative age effect (RAE) is most prevalent in highly competitive youth soccer and persists to a lesser extent in senior soccer. However, it is known that soccer players born in the second half of the year are as successful at senior level, indicating that they are equally talented although under-represented at youth level due to bias during the selection process, in which the emphasis is on more pronounced physical qualities in a specific period of time. Examining the prevalence of the RAE among professional soccer players depending on the level of competition and playing position, as well as analyzing the relationship between the player's birth quarter and market value, are of scientific interest. METHODS: The dates of birth, playing position, and market value of all adult male soccer players included in the final rosters of teams from the top-division of 54 European countries, listed on www.transfermarkt.com on August 15th, 2020, were analyzed (18,429 soccer players in total). All players were categorized into four groups according to the quarter of birth (Q) and playing position. All teams were further sub-divided in groups depending on the soccer clubs' level of representation in the UEFA Champions League. RESULTS: Of 18,429 players, 30.9% were born in Q1, 25.7% in Q2, 23.8% in Q3 and 19.6% in Q4. The number of soccer players born in Q1 was lower in less competitive leagues. The number of players born in Q1 decreased as the level of competition decreased; the highest percentage of these players was observed in clubs that are among the top 50 ranked in UEFA or compete in the most prestigious European championships. The RAE was less pronounced in teams that participate in lower competitive championships. There was no significant difference in market value between players playing position and level of competition when born in different quarters. Although, the most expensive soccer players in the European championships were late-born forwards. Players of various groups differed in their market value. CONCLUSIONS: The RAE is currently prevalent in all the most competitive senior soccer leagues and teams in Europe regardless of playing position. There are no significant differences in market value between players of the same playing position and level of competition when born in different quarters. The most expensive soccer players in the European championships are forwards born in Q4. These findings may indicate that the under-representation of "late-born" soccer players in youth, and then consequently in adult soccer, is not associated with lower talent, but with other factors, possibly based on physiological characteristics and socio-cultural factors. Further measures are needed to mitigate the discriminatory effects of selection bias based on the RAE.


Asunto(s)
Fútbol , Adolescente , Humanos , Masculino , Adulto , Fútbol/fisiología , Factores de Edad , Europa (Continente) , Aptitud , Examen Físico
6.
Front Psychol ; 13: 869637, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35719603

RESUMEN

Background: Contemporary research has shown that only a small proportion of high achieving young athletes continue to become successful senior athletes. However, there is a lack of empirical literature tracking the success of senior male and female athletes who were considered high achieving as a youth. Hypothesis: Athletes of both sexes who are successful in youth categories (U18 and U20) are more likely to be successful senior athletes. Conclusion: Data from 67,600 athletes were collated from the tilastopaja.org platform. The inclusion criteria for both genders were determined by top-100 ranking in the U18 and U20 age groups and progression to the top-100 as a senior athlete. Only 23.5% of successful track and field athletes (ranked in top-100) at U18 became a successful senior athlete, while 35.4% were from the U20 group. Girls ranked in the top-100 U18 and U20 categories are significantly more likely to be ranked in the top-100 as a senior when compared to boys. Although, being ranked in the top-50 at U18 and U20 significantly increases the probability of becoming a successful senior athlete when compared with less successful athletes at these age groups (p < 0.001). Notably, the majority (68.5%) of the most successful senior athletes were not ranked in the top-100 when in the U18 or U20 age groups. Only a small group of track and field athletes that are successful at U18 and U20 become successful at senior level. The most successful track and field youth athletes are significantly more likely to succeed as a senior athlete than their less successful peers, while girls are more likely to be successful than boys.

7.
PLoS One ; 17(6): e0265019, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35666729

RESUMEN

There are little data on the incidence, and clinical course of COVID-19 among professional soccer players, and the studies examining putative complications of COVID-19 infections are probabilistic. On February 28, the WHO raised the COVID-19 threat assessment to its highest level. The COVID-19 outbreak became a significant challenge for world health. Around 30 million people got infected with COVID-19 since the beginning of this year. More than 900.000 decease. Thus, examining the incidence of COVID-19 and various aspects of its clinical course in a group of adult professional soccer players would be of great practical interest. The incidence, clinical practice, and severity of COVID-19 infection, as well as the duration of treatment and return to play was studied based on a survey of team physicians and medical records assessment in the group of adult professional soccer players representing the clubs of the Russian Premier-League (RPL) during the period of championship resumption from 01.04.2020 until 20.09.2020. COVID-19 infection was detected in 103 soccer players during COVID-19 screening. This number comprises 14.5% of all soccer players on the rosters of RPL soccer teams and is subjected to regular COVID-19 testing. The asymptomatic course was observed in 43.7% of cases (n = 45). These players were isolated, and their clinical condition was monitored closely. In 56.3% of patients (n = 58), fatigue, headache, fever, and anosmia were the most common symptoms. COVID-19 infection was commonly diagnosed among adult professional soccer players in Russia. However, most cases had a mild course and did not impair return to regular exercise. Only two players were hospitalized with lung lesions and returned to regular sports.


Asunto(s)
COVID-19 , Fútbol , Adulto , COVID-19/epidemiología , Prueba de COVID-19 , Humanos , Incidencia , Tamizaje Masivo
8.
Foot Ankle Spec ; 15(1): 62-66, 2022 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-34142576

RESUMEN

Injuries of the metatarsal bones in football are relatively rare and in most cases are localized in the fifth metatarsal. The gold standard of the diagnosis of fractures in this area can be X-rays, which in most cases allows verifying the diagnosis. The treatment tactics depend on the localization of the fracture according to Lawrence and Botte's classification: 3 zones of localization are distinguished. Fractures located in zones 2 and 3 belong to a high-risk group due to delayed consolidation and nonunion and therefore athletes are most often treated with osteosynthesis using intramedullary screws. The minimal recovery time for this type of treatment is at least 8 weeks. This report describes 7 cases of the fifth metatarsal bone fractures, located in zones 2 and 3 in professional football players who were treated with an immobilization boot, cryotherapy, nutritional supplements of calcium and vitamin D, and local injections of platelet-rich plasma, which contains numerous growth factors. The deadline for returning to regular training activities was 43 to 50 days, and there was no relapse of damage within 6 months of follow-up.Levels of Evidence: Level of evidence 4: case report study.


Asunto(s)
Fútbol Americano , Fracturas Óseas , Huesos Metatarsianos , Plasma Rico en Plaquetas , Tornillos Óseos , Tratamiento Conservador , Humanos , Huesos Metatarsianos/diagnóstico por imagen , Huesos Metatarsianos/cirugía , Estudios Retrospectivos
9.
Artículo en Inglés | MEDLINE | ID: mdl-34770213

RESUMEN

There is now compelling evidence of the effectiveness of a range of post-exercise recovery techniques, including extended nights of sleep, cold water immersion, massage, and compression garments. Currently, limited information is available on post-exercise recovery methods used by elite endurance athletes. Therefore, this study investigated the actual methods of recovery used in this group of athletes. Google Forms were used to collect information on the recovery methods used by elite endurance track and field athletes (n = 153, 61.4% men, 38.6% women; average age: 22.7 ± 4.6 years). The most used methods of recovery were sauna bathing (96.7%), massage (86.9%), daytime nap (81.0%), and long night sleep (at least 9h) (61.4%). Recovery methods with proven effectiveness such as cold water immersion and compression garments were rarely used (15.0% and 7.8%, respectively). Overall, recovery methods were used more often when the tiers of the track and field athletes were higher. Massage and sauna bathing were the most used methods of post-exercise recovery among Russian endurance track and field athletes. In most cases, they were used in conjunction with short daytime nap and long night sleep. Higher tier athletes were more likely to use sauna bathing, massage, long night sleep, and daytime nap but not cold water immersion and compression garments as recovery methods; however, all these methods except for cold water immersion were widely used among elite-tier athletes.


Asunto(s)
Atletas , Ejercicio Físico , Adolescente , Adulto , Frío , Femenino , Humanos , Masculino , Masaje , Prevalencia , Sueño , Adulto Joven
10.
Artículo en Inglés | MEDLINE | ID: mdl-34770245

RESUMEN

Religious fasting in the Holy Month of Ramadan is an important element of the Muslim culture during which no eating or drinking is permitted from dawn till dusk. A considerable number of Muslim soccer players abide by these restrictions, which may cause a negative impact on key running performance parameters during competitive matches. Alterations to diet and water intake during the Holy Month of Ramadan may affect various running performance parameters in elite Muslim professional adult soccer players. This study was conducted with two groups of soccer players from the Russian Premier League (RPL): The Exposure Group (EG) consisted of 13 Muslims age 24.0 ± 2.8 years abiding by religious fasting and the Control Group (CG) included 13 non-Muslim age 26.0 ± 4.4 years. Using the Instat system, the running performance of each player was controlled in both groups during matches from the RPL before and in the third week of Ramadan (a total of two matches for every player). None of the measured parameters demonstrated significant changes in any match. In conclusion, restrictions in diet and liquid intake during the Holy Month of Ramadan had no negative influence on the running performance of elite Muslim professional adult soccer players during daytime matches.


Asunto(s)
Fútbol , Adulto , Ingestión de Líquidos , Ayuno , Humanos , Islamismo , Federación de Rusia , Adulto Joven
11.
Front Psychol ; 12: 738807, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-34803819

RESUMEN

Aim: This study was aimed to investigate the influence of age on the motivations of various types of runners, namely, marathoners, ultra-marathoners, and non-starters. Methods: A total of 1,537 runners including 380 women (24.7%) and 1,157 men (75.3%) took part in the diagnostic survey and completed the motivations of marathoners' scales questionnaire (MOMS). The effect sizes were estimated. Results: The article presents several statistically significant differences in the impact of age on the motivations of runners in different categories and compares the motivations of marathon runners, ultramarathon runners, and non-starters. The results show that young non-starters decide to run for personal goal achievement, and for both marathon and ultramarathon runners, recognition and competition are important. However, for older people in all groups (non-starters, marathoners, and ultramarathoners), personal goal achievement is of the least importance. Among the oldest runners, the most important motives were self-esteem for non-starters and health orientation for marathoners and ultramarathoners.

12.
Artículo en Inglés | MEDLINE | ID: mdl-34682674

RESUMEN

Monitoring the training of amateur long-distance cross-country skiers (XCS) can help athletes' achieve a higher exercise capacity and protect their health. The aim of this study was to assess body composition changes and lipid profiles in middle-aged amateur long-distance XCS after four months of training, including specialized roller ski training. The results of the time-to-exhaustion (TTE) test and blood tests and changes in body composition were analyzed with basic descriptive statistics: the paired Wilcoxon test was used to compare the results (initial and final). Spearman's rank correlation coefficient (R) was used to assess the influence of various variables on maximum oxygen uptake (VO2max). The findings show that training of amateur long-distance XCS improved maximal oxygen uptake (p = 0.008) and had a positive effect on fat reduction, measured in percentages (p = 0.038) and in kilograms (p = 0.023), but did not change blood lipids or other parameters. Further research could focus on other aspects of the annual training cycle: the competition period, and women in a larger group of athletes. Training with roller skis and a cross-country skiing training machine (a specialized machine for strengthening the arms and upper body) can support health and prevent obesity, overweight, and cardiovascular disease.


Asunto(s)
Entrenamiento Aeróbico , Esquí , Composición Corporal , Femenino , Humanos , Lípidos , Persona de Mediana Edad , Oxígeno , Consumo de Oxígeno , Resistencia Física
13.
Front Physiol ; 12: 738665, 2021.
Artículo en Inglés | MEDLINE | ID: mdl-34630159

RESUMEN

Ultramarathons are becoming increasingly popular every year, leading to more and more publications focusing on athletes of these endurance events. This paper summarizes the current state of knowledge on the effects of ultramarathons on the motor system. Various studies have attempted to answer questions about negative and positive effects on the musculoskeletal system, common injuries, optimal strategies, and regeneration. Considering the increasing number of ultramarathon athletes, the discoveries may have practical applications for a multitude of experts in the field of sports medicine, as well as for the athletes themselves. Acute locomotor system changes in runners as assessed by locomotor biomarkers are reversible and may be asymptomatic or painful. Injuries suffered by runners largely allow them to finish the competition and are usually overlooked. Regeneration, including regular massage and the use of supporting techniques, allows for faster convalescence. This publication is meant to be a source of knowledge for people associated with this discipline.

14.
Orthop J Sports Med ; 9(1): 2325967120979994, 2021 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-33614799

RESUMEN

BACKGROUND: Professional soccer players are often evaluated with asymptomatic lesions of the ankle and foot, and such abnormalities may eventually become clinically relevant. PURPOSE: To ascertain the prevalence of foot and ankle abnormalities in elite professional adult soccer players. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Professional adult male elite soccer players (n = 37) underwent magnetic resonance imaging (MRI) scans of both their feet and ankles. All competed for their respective national junior or adult soccer teams. MRI scans were performed with 1.5-T scanners and analyzed independently by 2 experienced radiologists. RESULTS: The MRI scans of 86.5% of the players showed degenerative joint disease (DJD) in at least 1 of the joints of the foot and ankle. Articular cartilage lesions in the joints of the foot and ankle were evident in 42% of the scans. Of all lesions, 17% were grade 3 or 4 (Noyes and Stabler classification) cartilage lesions and accompanied by subchondral bone marrow edema. The greater the age, weight, and height of the players, the greater was the odds ratio of DJD of the ankle joint. Synovitis in at least 1 of the joints of the foot was detected in 64% of the MRI scans. Leg dominance significantly correlated with bone marrow edema of the talus. CONCLUSION: Elite professional soccer players are often evaluated with a high prevalence of asymptomatic osteochondral lesions with subchondral bone marrow edema in the foot and ankle. These osteochondral lesions may remain asymptomatic or, with the continuing high-intensity stresses that modern professional soccer demands of its athletes, may evolve and cause foot and ankle pain. It is unclear whether and which interventions can be implemented to prevent the occurrence of these abnormalities in the first place.

15.
Front Public Health ; 8: 581017, 2020.
Artículo en Inglés | MEDLINE | ID: mdl-33313036

RESUMEN

The aim of this study was to investigate the motivations for beginner runners to take part in Parkrun Poznan and City Trail Poznan, Poland, taking into account their socio-demographical variables. A total of 165 (age: 36.33 ± 10.38) inexperienced runners participated in the diagnostic survey and completed the MOMS (Motivations of Marathoner Scale) questionnaire. The sample consisted of 82 men (49.7%) and 83 women (50.3%). The results showed that men were more likely to start running due to competition-related motivations, while the motivations of women were more often related to affiliation, psychological coping, life meaning, and self-esteem. As age increased, the level of motivation due to personal goal achievement, competition, and recognition scales decreased. The Affiliation Scale was especially important for singles who started running, in comparison with runners who were married or in a relationship. These factors should be taken into consideration by event managers and public health specialists. Promoting safe running among people who have no experience with this sport is as important as encouraging them to run. All runners stated that they would like to run a marathon in the future. Moreover, thanks to initiatives such as City Trail and Parkrun, Polish respondents feel motivated to lead an active lifestyle, with an average score of 4.98 on a 7-point Likert scale.


Asunto(s)
Motivación , Carrera , Adaptación Psicológica , Adulto , Femenino , Humanos , Masculino , Persona de Mediana Edad , Polonia , Conducta Sedentaria
16.
Artículo en Inglés | MEDLINE | ID: mdl-33276648

RESUMEN

Cold water swimming (winter or ice swimming) has a long tradition in northern countries. Until a few years ago, ice swimming was practiced by very few extreme athletes. For some years now, ice swimming has been held as competitions in ice-cold water (colder than 5 °C). The aim of this overview is to present the current status of benefits and risks for swimming in cold water. When cold water swimming is practiced by experienced people with good health in a regular, graded and adjusted mode, it appears to bring health benefits. However, there is a risk of death in unfamiliar people, either due to the initial neurogenic cold shock response or due to a progressive decrease in swimming efficiency or hypothermia.


Asunto(s)
Hipotermia , Natación , Frío , Humanos , Estaciones del Año , Agua
17.
J Orthop Surg Res ; 15(1): 440, 2020 Sep 24.
Artículo en Inglés | MEDLINE | ID: mdl-32972434

RESUMEN

BACKGROUND: The present study assessed the prevalence of non-contact muscle injuries of the lower limbs, including hamstring injuries, in professional Russian soccer players who regularly perform Salah, an obligatory Muslim prayer performed 5 times a day. METHODS: Using a retrospective cohort study design, 68 professional male soccer players (excluding goalkeepers), 34 of whom were Muslims regularly performing Salah (exposure group) and 34 were randomly chosen non-Muslim players (control group), were included in the study. The groups were similar in their playing leagues, field positions, age (27 ± 3.1 vs 28 ± 4.2 years), and body mass index (22 ± 1.2 vs 23 ± 0.92 kg/m2). RESULTS: The incidence of hamstring injury was significantly lower in the exposure group (2 vs 14, p = 0.0085). A declining trend for the number of muscle injuries (either hamstring or not) was observed in the exposure group (11 vs 27, p = 0.0562). Two players in the exposure group and 11 in the control group (p = 0.0115, OR 0.1307, 95% CI 0.0276 to 0.5698) suffered a hamstring injury, with no statistically significant difference in the occurrence of other injuries. The total amount of the training and play days missed because of hamstring and other muscle injuries was significantly lower in the exposure group (24 vs 213 days, p = 0.0043, and 200 vs 344 days, p = 0.0066, respectively). CONCLUSION: The prevalence of non-contact muscle injuries, including hamstring injuries, was lower in professional Russian soccer players who regularly performed Salah.


Asunto(s)
Atletas/psicología , Atletas/estadística & datos numéricos , Traumatismos en Atletas/epidemiología , Traumatismos en Atletas/prevención & control , Islamismo , Extremidad Inferior/lesiones , Músculo Esquelético/lesiones , Religión , Fútbol/estadística & datos numéricos , Adulto , Traumatismos en Atletas/psicología , Músculos Isquiosurales/lesiones , Humanos , Masculino , Prevalencia , Estudios Retrospectivos , Federación de Rusia , Adulto Joven
18.
Artículo en Inglés | MEDLINE | ID: mdl-32927832

RESUMEN

The aim of this study was to investigate how family life and marital status influence the motivations of ultramarathoners. Two-hundred-sixty-seven Polish athletes participated in the diagnostic survey during the Karkonosze Winter Ultramarathon. The Polish version of the Motivation of Marathoner Scale was used. The motivations of ultra-runners were investigated among the following groups of respondents: people in a relationship/marriage; singles; people with children vs. childless people; people who run alone and with a partner; people who parted with a partner because of lack of support for running. Research results can be useful for sport managers-e.g., findings show the relative importance of modern sport for singles in the second half of life. Research has also shown how people in relationships and people with children can be realized through demanding long-distance running. We also found that running ultramarathons can pose a threat to a relationship.


Asunto(s)
Relaciones Familiares/psicología , Estado Civil , Motivación , Carrera , Niño , Humanos , Resistencia Física , Polonia
19.
Polymers (Basel) ; 12(8)2020 Jul 28.
Artículo en Inglés | MEDLINE | ID: mdl-32731329

RESUMEN

This research investigated the effect of irradiation with an electron beam energy of 10 MeV in doses of 26-156 kGy on polytetrafluoroethylene (PTFE) with a 15% and 20% graphite additive. The research has shown that mechanical (compression strength, hardness, and Young's modulus) and sclerometric (coefficient of wear micromechanism and coefficient of resistance to wear) properties improve and tribological wear decreases as graphite content increases. Electron beam irradiation increases the degree of crystallinity of both materials to a similar extent. However significant differences in the improvement of all examined properties have been demonstrated for PTFE with higher (20%) graphite content subjected to the electron beam irradiation. This polymer is characterized by higher hardness and Young's modulus, reduced susceptibility to permanent deformation, higher elasticity, compression strength, and above all, a nearly 30% reduction in tribological wear compared to PTFE with a 15% graphite additive. The most advantageous properties can be obtained for both of the examined composites after absorbing a dose of 104 kGy. The obtained results hold promise for the improvement of the operational life of friction couples which do not require lubrication, used for example in air compressors and engines, and for the possibility of application of these modified polymers. In particular PTFE with 20% graphite content, in the nuclear and space industry.

20.
J Strength Cond Res ; 34(9): 2522-2527, 2020 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-32569124

RESUMEN

Bezuglov, E, Shvets, E, Lyubushkina, A, Lazarev, A, Valova, Y, Zholinsky, A, and Waskiewicz, Z. Relative age effect in Russian elite hockey. J Strength Cond Res 34(9): 2522-2527, 2020-A considerable amount of literature has been published on relative age effect (RAE) in many sports; however, only a few studies have investigated this phenomenon in European elite ice hockey. The objective of this research was to study RAE prevalence in Russian elite ice hockey, which for years has been holding leading positions in global ice hockey. To estimate RAE prevalence, birthdates of recruits of leading ice hockey academies, players of the leading junior and adult teams, and most successful Russian-born National Hockey League (worlds' strongest ice hockey league) players were identified (n = 2,285). A high prevalence of RAE was identified. The number of players born in the first half of the year was higher than those born later in the year-65.5 and 34.5%, respectively. The RAE prevalence was high among all age groups of recruits of the leading Russian hockey academies and junior teams. In contrast to junior hockey, more players born in the fourth quarter of the year were identified in elite adult teams. The high prevalence of RAE in Russian hockey might be explained by the fact of a high level of competition among young players during recruitment to hockey academies. Moreover, the coaches aim to achieve immediate progress, thus selecting more mature players who are better physically developed. However, "later-born" are widely present in elite adult ice hockey leagues.


Asunto(s)
Desarrollo del Adolescente/fisiología , Desarrollo Infantil/fisiología , Hockey/fisiología , Logro , Adolescente , Factores de Edad , Atletas , Niño , Estudios Transversales , Humanos , Masculino , Prevalencia , Federación de Rusia , Adulto Joven
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