Latest research in football - week 39 - 2018

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Examination of Physical Fitness Parameters Between Professional and Amateur Greek Soccer Players During the Transition Period
Reference: J Strength Cond Res. 2018 Oct 4. doi: 10.1519/JSC.0000000000002770. [Epub ahead of print]
Authors: Bekris E, Pidoulas G, Pidoulas P, Gissis I, Katis A, Komsis S
Summary: The aim of the study was to compare physical fitness parameters between professional and amateur soccer players of different levels. The sample consisted of 381 soccer players divided in 4 experimental groups: first division professional players (n = 115), second division professional players (n = 70), third division semiprofessional players (n = 93), and amateur soccer players (n = 103). Players were tested for several physiological parameters at the end of the transition period. Analysis of variance showed significantly lower body fat and increased maximum oxygen consumption (V[Combining Dot Above]O2max) and velocity of maximum oxygen consumption (vV[Combining Dot Above]O2max) values for first division professional players compared with the other experimental groups (p < 0.05). Similarly, first division professional players showed higher performance during squat jump and countermovement jump test compared with the other experimental groups (p < 0.05). Significant differences on flexibility test were observed between amateur players and the other group (p < 0.05). The results of the study indicated that Greek soccer players at the highest level overcome in almost all the underexamination physiological parameters probably because of less absence from training and better implementation of training programs during the transition period.

#2 Individualizing Acceleration in English Premier League Academy Soccer Players
Reference: J Strength Cond Res. 2018 Oct 4. doi: 10.1519/JSC.0000000000002875. [Epub ahead of print]
Authors: Abbott W, Brickley G, Smeeton NJ, Mills S
Summary: Global thresholds are typically used to band acceleration dependent on intensity. However, global thresholds do not account for variation in individual capacities, failing to quantify true intensity of acceleration. Previous research has investigated discrepancies in high-speed distance produced using global and individual speed thresholds, not yet investigated for acceleration. The current aim was to investigate discrepancies between global and individual thresholds when quantifying acceleration tasks. Acceleration data were recorded for 31 professional soccer players, using 10-Hz Global positioning systems devices. Distances traveled performing low-, moderate-, and high-intensity acceleration were calculated for athletes using global and individual thresholds. Global acceleration thresholds for low-, moderate-, and high-intensity acceleration were classified as 1-2, 2-3, and >3 m·s, respectively, with individual thresholds classified as 25-50%, 50-75%, and >75% of maximum acceleration, respectively. Athletes were grouped low (LO), medium (ME), or high (HI) maximum accelerative capacity, determined using 3 maximal 40-m linear sprints. Two-way mixed-design analyses of variance were used to analyze differences in acceleration distances produced between analysis methods and athlete groups. No significant differences were identified between analysis methods for LO. For ME, no significant differences were demonstrated for low intensity. Moderate- and high-intensity acceleration distances were significantly higher for global compared with individual analysis method (p < 0.01). For HI, significantly higher acceleration distances were produced for all acceleration intensities using global thresholds (p < 0.01). Significant differences identified between analysis methods suggest practitioners must apply caution when using global thresholds. Global thresholds do not account for individual capacities and may provide an inaccurate representation of relative intensity of acceleration tasks.

#3 Operative Treatment of Proximal Rectus Femoris Injuries in Professional Soccer Players: A Series of 19 Cases
Reference: Orthop J Sports Med. 2018 Oct 2;6(10):2325967118798827. doi: 10.1177/2325967118798827. eCollection 2018 Oct.
Authors: Lempainen L, Kosola J, Pruna R, Puigdellivol J, Ranne J, Orava S
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Summary: Proximal rectus femoris (PRF) tears are relatively rare injuries among top-level athletes. PRF injuries can be avulsions of both tendon heads (direct and reflected heads) or of a single head, and some have a tendency to progress to recurrent injuries. The purpose was to describe a series of operatively treated PRF ruptures in professional soccer players. Nineteen cases of PRF injuries (18 patients, 1 bilateral) in professional soccer players who were treated surgically were retrospectively reviewed. Perioperative findings with return-to-play data were recorded. Of the PRF injuries, 10 total avulsions (both heads) and 9 single-head tears were seen on magnetic resonance imaging and were later confirmed during surgery. All 18 patients returned to their preinjury level of play (mean follow-up, 2.8 years [range, 1-11 years]). The repair of PRF tears in professional soccer players yielded good results and allowed all patients to return to their preinjury level of play.

#4 Relationship Between Heart Rate Variability and Acute: Chronic Load Ratio Throughout a Season in NCAA D1 Men's Soccer Players
Reference: J Strength Cond Res. 2018 Oct 4. doi: 10.1519/JSC.0000000000002853. [Epub ahead of print]
Authors: Sekiguchi Y, Huggins RA, Curtis RM, Benjamin CL, Adams WM, Looney DP, West CA, Casa DJ
Summary: The purpose of this study was twofold: (a) to examine the relationship between heart rate variability (HRV) and acute:chronic workload ratio (ACWR)-based training load (TL) metrics and (b) to examine relationships across various A:C ratio-based TL metrics. Heart rate variability in 23 male college soccer players (mean ± SD; age, 21 ± 1 years; body mass, 80.3 ± 5.8 kg; height, 181.9 ± 6.5 cm; %body fat, 11.9 ± 2.0%; and V[Combining Dot Above]O2max, 51.9 ± 5.0 ml·kg·min) was measured at 5 time points: week(W)1, W3, W7, W12, and W14 during the 2015 NCAA men's soccer season. Heart rate variability was calculated from beat to beat intervals using a heart rate monitor. Players donned a global position satellite-enabled device that measured the following TL metrics: session time (ST), Player Load (PL), PL·min, and total distance (TD). Acute:chronic workload ratio was calculated for each TL metric: ACWR-based ST (ACWRST), ACWR-based PL (ACWRPL), ACWR-based PL·min (ACWRPLM), and ACWR-based TD (ACWRTD): ACWR = week average TLs/mo average (30 ± 1 days) TLs. Relationships between HRV and ACWR-based each TL metric were evaluated using mixed effects models. Tukey pairwise comparisons were used to examine differences between types of ACWR-based TL metrics. An increase in ACWRST significantly reduced HRV throughout a season (-7.4 ± 3.6 m·s; p = 0.04). There were significant differences between ACWRPLM and ACWRST, ACWRPL and ACWRTD at W1, ACWRPLM and ACWRST at W3 (p < 0.05). In conclusion, ACWRST, ACWRPL, and ACWRTD were significantly different from ACWRPLM. ACWRST was found to significantly predict HRV; higher ACWRST was significantly associated with lower HRV. Therefore, tracking of the ACWR using ST may help to optimize athlete's physiological state throughout a season.

#5 The effects of a calf pump device on second half performance of a simulated soccer match in competitive youth players
Reference: J Sports Sci. 2018 Oct 4:1-9. doi: 10.1080/02640414.2018.1522947. [Epub ahead of print]
Authors: Béliard S, Cassirame J, Ennequin G, Coratella G, Tordi N
Summary: During soccer matches, performance decrements have been reported that relate to both physical abilities and technical skills. To investigate the effects of low-frequency electrical stimulation LFES (VeinoplusSport®, Ad Rem Technology, France) administered during half-time recovery on performance alterations during the second half. Twenty-two highly trained young players undertook a soccer-match simulation (SAFT90). During half-time, they were randomly assigned to LFES group or Placebo group. Each half was split into 3 bouts of 12 minutes. Following each bout, maximal strike speed (MSS), sprint test (ST), maximal sprint accelerations (MA) and metabolic power (MP) were determined in both groups. Arterial (AF) and venous flows (VF) were measured at rest and at the end of half-time. LEFS group exhibited beneficial effects on performance compared to the Placebo group with a likely effect for MSS, ST, MA, and a possible effect for MP. AF and VF increased statistically more in LEFS group compared to Placebo group. The use of specific calf-pump LFES during half-time of a youth simulated soccer match attenuated the decrease in performance during the second half compared to Placebo group. This effect is most marked at the beginning of the second half with regards to explosive parameters.

#6 Does Early Recruitment Predict Greater Physical Performance in Academy Soccer Players?
Reference: Sports (Basel). 2018 Sep 30;6(4). pii: E108. doi: 10.3390/sports6040108.
Authors: Hertzog M, Paul DJ, Nassis GP, Silva JR
Summary: The purpose of this longitudinal study was to investigate whether recruitment status influences neuromuscular and endurance performances in academy soccer players over a 2-year training period (from Under-16 to Under-18). Thirty-seven male soccer players from an elite academy were selected and divided in two cohorts according to their recruitment status: Early Recruitment group (ER; n = 16), training and competing for the academy since Under-14 and Under-15 age groups, and; Late Recruitment group (LR; n = 21) included in the academy training process at Under-16. Squat (SJ) and countermovement jump with (CMJwA) and without arms swing (CMJ), 10-m sprint time, and Vam-Eval test (MAV) were performed in three successive occasions always pre-season (Under-16, Under-17 and Under-18 age groups, T1, T2, and T3 respectively). A two-way (recruitment status × time) analysis of variance with repeated measurements was performed as well as the magnitude of difference using both effect size and magnitude-based inferences. There was no difference between ER and LR for MAV, 10 m-sprint, and SJ from T1 to T3. However, LR players presented non-significant small and possibly greater improvement in CMJ (ES = 0.4) and CMJwA (ES = 0.4) than ER players at T2. These data indicate that early recruitment is not likely to result in greater physical performance improvement at the age of 18.

#7 Relationship of Absolute and Relative Lower-Body Strength to Predictors of Athletic Performance in Collegiate Women Soccer Players
Reference: Sports (Basel). 2018 Sep 29;6(4). pii: E106. doi: 10.3390/sports6040106.
Authors: Andersen E, Lockie RG, Dawes JJ
Summary: The purpose of this study was to investigate the relationships between absolute and relative lower-body strength on predictors of athletic performance among Division II collegiate women's soccer players. Archived pre-season testing data for seventeen (n = 17) female National Collegiate Athletics Association (NCAA) Division II soccer players were analyzed, including: vertical jump, 3RM back squat, 505-agility, modified T-test, 10 m and 30 m sprint, and 20 m multistage fitness test (20 m MSFT). Relative strength was calculated based on the estimated 1RM back squat divided by the athlete's body mass. Significant correlations were discovered between absolute lower-body strength and 505-agility (Right: r = -0.51, p < 0.05; Left: r = -0.59, p < 0.05), modified T-test (r = -0.55, p < 0.05), 10 m and 30 m (r = -0.59, p < 0.05; r = -0.54, p < 0.05), and sprint performance. Relative lower-body strength showed significant correlations with vertical jump (r = 0.54, p < 0.05), 505-agility (Right: r = -0.58, p < 0.05; Left: r = -0.67, p < 0.01), modified T-test (r = -0.75, p < 0.01), 10 m and 30 m (r = -0.59 p < 0.05; r = -0.67, p < 0.01), and the 20 m MSFT (r = 0.58, p < 0.05). These results indicate that strength and conditioning coaches should emphasize the development of absolute and relative lower-body strength with their players to improve power, agility, and speed performance.

#8 Effects of the '11+ Kids' injury prevention programme on severe injuries in children's football: a secondary analysis of data from a multicentre cluster-randomised controlled trial
Reference: Br J Sports Med. 2018 Oct 2. pii: bjsports-2018-099062. doi: 10.1136/bjsports-2018-099062. [Epub ahead of print]
Authors: Beaudouin F, Rössler R, Aus der Fünten K, Bizzini M, Chomiak J, Verhagen E, Junge A, Dvorak J, Lichtenstein E, Meyer T, Faude O
Summary: The purpose of the study was to assess the effects of the injury prevention programme '11+ Kids' on reducing severe injuries in 7 to 13 year old football (soccer) players. Football clubs (under-9, under-11 and under-13 age groups) from the Czech Republic, Germany, the Netherlands and Switzerland were cluster-randomised (clubs) into an intervention (INT) and a control group (CON). INT replaced their usual warm-up by '11+ Kids' two times a week. CON followed their regular training regime. Match and training exposure and injury characteristics were recorded and injury incidence rates (IRs) and 95% CIs calculated. For the present analysis, only severe injuries (absence from training/match ≥28 days) were considered. Hazard ratios (HR) were calculated using extended Cox models. The overall IR of severe injuries per 1000 football hours was 0.33 (95% CI 0.25 to 0.43) in CON and 0.15 (95% CI 0.10 to 0.23) in INT. There was a reduction of severe overall (HR 0.42, 95% CI 0.24 to 0.72), match (0.41, 0.17 to 0.95) and training injuries (0.42, 0.21 to 0.86) in INT. The injury types that were prevented the most were: other bone injuries 66%, fractures 49% and sprains and ligament injuries 37%. Severe injuries located at the knee (82%), hip/groin (81%), the foot/toe (80%) and the ankle (65%) were reduced tremendously. '11+ Kids' has a large preventive effect on severe injuries by investing only 15 to 20 min per training session. The present results should motivate coaches to implement effective injury prevention programmes such as the '11+ Kids' in children's football.

#9 Jumping performance based on duration of rehabilitation in female football players after anterior cruciate ligament reconstruction
Reference: Knee Surg Sports Traumatol Arthrosc. 2018 Sep 28. doi: 10.1007/s00167-018-5154-5. [Epub ahead of print]
Authors: Arundale AJH, Kvist J, Hägglund M, Fältström A
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Summary: The purpose was to determine if female football players who had longer durations of rehabilitation, measured in months, after anterior cruciate ligament reconstruction would have lower tuck jump scores (fewer technique flaws) and smaller asymmetries during drop vertical jump landing. One-hundred-and-seventeen female football players, aged 16-25 years, after primary unilateral ACL reconstruction (median 16 months, range 6-39) were included. Athletes reported the duration of rehabilitation they performed after anterior cruciate ligament reconstruction. Athletes also performed the tuck jump and drop vertical jump tests. Outcome variables were: tuck jump score, frontal plane knee motion and probability of peak knee abduction moment during drop vertical jump landing. There was no difference in tuck jump score based on duration of rehabilitation (n.s.). No interaction (n.s.), difference between limbs (n.s.), or duration of rehabilitation (n.s.) was found for peak knee abduction moment during drop vertical jump landing. No interaction (n.s.) or difference between limbs (n.s.) was found for frontal plane knee motion, but there was a difference based on duration of rehabilitation (P = 0.01). Athletes with > 9 months of rehabilitation had more frontal plane knee motion (medial knee displacement) than athletes with < 6 months (P = 0.01) or 6-9 months (P = 0.03). As there was no difference in tuck jump score or peak knee abduction moment based on duration of rehabilitation, the results of this study press upon clinicians the importance of using objective measures to progress rehabilitation and clear athletes for return to sport, rather than time alone.

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