Autonomic Nervous System Influences on Cardiovascular Self-Organized Criticality

Cardiovascular self-organized criticality has recently been demonstrated. We studied a model of autonomic nervous system changes to better characterize heart rate variability self-organized criticality. The model included short and long-term autonomic changes associated with body position and physical training, respectively. Twelve professional soccer players took part in a 5-week training session divided into "Warm-up", "Intensive", and "Tapering" periods. A stand test was carried out at the beginning and end of each period. Heart rate variability was recorded beat by beat (Polar Team 2). Bradycardias, defined as successive heart rates with a decreasing value, were counted according to their length in number of heartbeat intervals. We checked whether bradycardias were distributed according to Zipf's law, a feature of self-organized criticality. Zipf's law draws a straight line when the rank of occurrence is plotted against the frequency of occurrence in a log-log graph. Bradycardias were distributed according to Zipf's law, regardless of body position or training. Bradycardias were much longer in the standing position than the supine position and Zipf's law was broken after a delay of four heartbeat intervals. Zipf's law could also be broken in some subjects with curved long bradycardia distributions by training. Zipf's law confirms the self-organized nature of heart rate variability and is strongly linked to autonomic standing adjustment. However, Zipf's law could be broken, the significance of which remains unclear.

Association between ACTN3 R577X genotype and risk of non-contact injury in trained athletes: A systematic review

PURPOSE

The aim of this study was to review, systematically, evidence concerning the link between the ACTN3 R577X polymorphism and the rates and severity of non-contact injuries and exercise-induced muscle damage in athletes and individuals enrolled in exercise training programs.

METHODS

A computerized literature search was performed in the electronic databases PubMed, Web of Science, and SPORTDiscus, from inception until November 2020. All included studies compared the epidemiological characteristics of non-contact injury between the different genotypes of the ACTN3 R577X polymorphism.

RESULTS

Our search identified 492 records. After the screening of titles, abstracts, and full texts, 13 studies examining the association between the ACTN3 genotypes and the rate and severity of non-contact injury were included in the analysis. These studies were performed in 6 different countries (Spain, Japan, Brazil, China, the Republic of Korea, and Italy) and involved a total participant pool of 1093 participants. Of the studies, 2 studies involved only women, 5 studies involved only men, and 6 studies involved both men and women. All the studies included were classified as high-quality studies (≥6 points in the Physiotherapy Evidence Database (PEDro) scale score). Overall, evidence suggests there is an association between the ACTN3 R577X genotype and non-contact injury in 12 investigations. Six studies observed a significant association between ACTN3 R577X polymorphism and exercise induced muscle damage: 2 with non-contact ankle injury, 3 with non-contact muscle injury, and 1 with overall non-contact injury.

CONCLUSION

The present findings support the premise that possessing the ACTN3 XX genotype may predispose athletes to a higher probability of some non-contact injuries, such as muscle injury, ankle sprains, and higher levels of exercise-induced muscle damage.

FIFA World Cup Qatar 2022: Solutions to the Physical Fitness Challenge

In 2022, the FIFA World Cup has been scheduled to take place in Qatar in November and December, months which coincide with the in-season period of the European soccer season. This will be challenging for the staff of the participating national teams and the domestic clubs to which participating players are attached. The aim of this letter to the editor is to propose solutions on how to manage the associated challenges. Regular training and competition over the course of a season in European professional soccer is generally characterized by a pre-competition preparation period of five to six weeks, followed by two competition phases, interspersed with a winter break (Eliakim et al., 2018). Certain leagues such as the English Premier League do not typically have a winter break meaning that games are played almost continuously across the season. During World Cup years, there is usually an average of four to five weeks between the end of national domestic championships and the start of the World Cup tournament (Table 1, Figure 1) which traditionally takes place during the off-season period. However, in 2022, the FIFA World Cup has been scheduled to take place in November and December, months which coincide with the in-season period of the European soccer season (Figure 1). With the World Cup being staged during this part of the season, many national team players (notably those in the major European Leagues) will have just one week of preparation between the last match of their domestic leagues and the start of the World Cup tournament (November 20th, 2022). More precisely, the major European soccer leagues will interrupt match schedules between November 9th and 13th with differences in the number of games completed at this time of the season ranging from 14 to 17 across the various leagues (Table 2). The physical and mental demands placed on modern professional players have steadily risen over recent years due to an increase in the number of matches played during congested periods across the season (Anderson et al., 2016). Since the number of matches is not evenly distributed across the typical 40-week season, players can often compete in as many as three matches in a seven-day period. Aside from the physical and mental demands that are imposed during a match, players might experience insufficient recovery between these games; in part due to extensive travelling which can disrupt the sleep/wake cycle (Lastella et al., 2019). Indeed, poor quality of sleep and the stress induced by a match can negatively affect physical fitness and may even increase the risk of sustaining injuries and/or infections (Clemente et al., 2021) in the period leading up to the World Cup. National teams are composed of players from different leagues who have varying levels of exposure to match-play (e.g., starters, non-starters) in terms of the average weekly volume of soccer matches at their clubs (“Rapports - Observatoire du football CIES”). Moreover, both starters and non-starters are exposed to different external match and training loads (Anderson et al., 2016). External loads have previously been defined as the overall volume of activity that a player performs during both training sessions and matches (Ravé et al., 2020). There is evidence that this metric correlates with a player’s physical fitness status (Clemente et al., 2019) and their injury risk (Malone et al., 2017). Accordingly, it will be challenging for national teams to manage the fitness of players such that they are physically ready to play at the World Cup tournament. This is especially applicable to individuals who play in the major European leagues and we note a significant contrast between European match schedules and those on other continents. For example, in Major League Soccer (MLS) in North America, match schedules will be interrupted from November 5th, 15 days before the World Cup tournament begins. Similarly, in the Japanese J-League in Asia, Saudi Pro League and Qatar Star League, matches will be interrupted one month before the World Cup tournament begins, leaving more time for players on these continents to prepare. It is also important to note that the French, Spanish and English domestic championships will resume their match schedules on December 27th which is just ten days after the end of the World Cup (Figure 1). Clubs will clearly want their players to return uninjured and with sufficient fitness levels to resume domestic competition but these goals could be compromised by the aforementioned scheduling of the World Cup tournament.

Internal and External Training Load in Under-19 versus Professional Soccer Players during the In-Season Period

This study aimed to compare the training load of a professional under-19 soccer team (U-19) to that of an elite adult team (EAT), from the same club, during the in-season period. Thirty-nine healthy soccer players were involved (EAT [n = 20]; U-19 [n = 19]) in the study which spanned four weeks. Training load (TL) was monitored as external TL, using a global positioning system (GPS), and internal TL, using a rating of perceived exertion (RPE). TL data were recorded after each training session. During soccer matches, players' RPEs were recorded. The internal TL was quantified daily by means of the session rating of perceived exertion (session-RPE) using Borg's 0-10 scale. For GPS data, the selected running speed intensities (over 0.5 s time intervals) were 12-15.9 km/h; 16-19.9 km/h; 20-24.9 km/h; >25 km/h (sprint). Distances covered between 16 and 19.9 km/h, > 20 km/h and >25 km/h were significantly higher in U-19 compared to EAT over the course of the study (p = 0.023, d = 0.243, small; p = 0.016, d = 0.298, small; and p = 0.001, d = 0.564, small, respectively). EAT players performed significantly fewer sprints per week compared to U-19 players (p = 0.002, d = 0.526, small). RPE was significantly higher in U-19 compared to EAT (p = 0.001, d = 0.188, trivial). The external and internal measures of TL were significantly higher in the U-19 group compared to the EAT soccer players. In conclusion, the results obtained show that the training load is greater in U19 compared to EAT.

Somatotype Hormone Levels and Physical Fitness in Elite Young Soccer Players over a Two-Year Monitoring Period

The effect of two soccer-training seasons on the growth, development and somatotype hormone concentrations of elite youth soccer players were evaluated. Eighteen elite soccer players and 18 age-matched non-athletic control subjects participated in the study. Anthropometric-measurements, aerobic and anaerobic performance tests and serum concentrations of insulin-like growth factor-1 (IGF-1), insulin-like growth factor binding protein-3 (IGFBP-3), and growth hormone (GH) were assessed at 5 time points across two competitive seasons. Soccer players revealed higher GH, IGF-1 and IGFBP-3 than the control group across all-time points. Significant moderate correlations were observed only in soccer players between hormonal concentrations (IGF-1 and IGFBP-3) and the jumping tests (r = 0.45-0.48; p < 0.01). Somatotropic axis hormones, anthropometric and physical parameters increased to a greater degree with growth and soccer training combined compared to growth alone. Results from this investigation revealed that intense training did not impair growth or development in these young soccer players across 2-year period.

Laterality Influences Agility Performance in Elite Soccer Players

Introduction: Laterality (i.e., handedness, footedness, and eyedness) could have an impact on highly repeated soccer movements and thus, could influence performance. The purpose of this study was to examine the laterality of high-level football players and its effects on 180° left and right U-turn movements.

Materials and Methods: Handedness, footedness, and eyedness were determined in 72 elite football players (EFP, 18.2 ± 2.2 years) from the Stade Rennais Football Club (French League 1) and 9 amateur football players (AFP, 19.6 ± 2.1 years). Players performed a visual-motor task on a synthetic pitch consisting of 180° left and right rotations as fast as possible in response to a visual light on a computer screen. Movement times and reactive times for each left and right rotation were recorded with an accelerometer and video display.

Results: Laterality profiles showed a majority (χ² = 9.42, df = 2, p = 0.031) of crossed formulas (i.e., dominant leg or hand is controlateral to the dominant eye) for EFP (53 ± 7%) and a majority of non-crossed formulas for AFP (63 ± 9%). Reaction times were significantly faster (p = 0.028, effect size = 0.148, trivial) in EFP right-eyed (568.2 ± 55.5 ms) than in AFP (610.0 ± 43.9 ms). For the left rotation and for right-footed players, movement times were significantly different (p = 0.043, effect size = 0.413, small) between EFP (1.15 ± 0.07 s) and AFP (1.17 ± 0.07 s). A significant difference (p < 0.033) was observed between footedness and rotation movement times in the EFP.

Conclusion: Our results showed that laterality profiles differed between EFP and AFP. Hence, in EFP, reaction times depended on the side of the visual stimulus. Moreover, leg laterality of EFP influenced 180° left or right rotation speed. Our results indicate the importance of determining laterality in soccer players and identifying deficits in performance when turning.

Heart rate variability in the standing position reflects training adaptation in professional soccer players

PURPOSE

To show that heart rate variability (HRV) in the standing position better reflects the way in which athletes adapt to training in so-called intermittent sports than the indicator of resting parasympathetic tone usually employed in endurance sports.

METHODS

Twenty professional soccer players (intermittent sport) took part in a 5-week training session divided into three successive periods: "Warm-up", "Intensive training" and "Tapering". At the beginning and end of each of the three periods, a stand test was carried out and the heart rate was recorded, beat by beat (Polar Team 2). We analysed HRV to determine the indicator mostly used to demonstrate training adaptation in endurance sports (lnRMSSD supine, natural logarithm of root mean square of the successive differences) as well as indicators obtained by means of spectral analysis in both supine and standing position.

RESULTS

A decrease in heart rate was observed in the supine position at rest during training (-5.2 ± 1.3 bpm) while lnRMSSD and spectral analysis indicators remained unchanged. The "Warm-up" caused an increase in spectral analysis total power in standing position which was further highlighted by "Tapering" (3.39 ± 0.09, 3.61 ± 0.08 and 3.65 ± 0.09 log ms(2), respectively). However, the autonomic changes are probably more complex than a change in autonomic activity or balance since spectral analysis autonomic indicators remained unchanged.

CONCLUSIONS

HRV in the standing position could monitor training adaptation in intermittent sports contrary to the indicator usually employed in endurance sports. However, the significance of the HRV change in the standing position during training remains unclear.