Latest research in football - week 23 - 2018

#1 The Occurrence of Repeated High Acceleration Ability (RHAA) in Elite Youth Football
Reference: Int J Sports Med. 2018 Jun 5. doi: 10.1055/a-0608-4738. [Epub ahead of print]
Authors: Serpiello FR, Duthie GM, Moran C, Kovacevic D, Selimi E, Varley MC
Summary: The aim of the present study was to investigate the occurrence of Repeated High-Acceleration Ability (RHAA) bouts in elite youth football games using 10-Hz GPS devices and two relative thresholds derived from players' actual maximal acceleration. Thirty-six outfield soccer players (age 14.9±0.6 years) participated in the study. Players wore 10-Hz GPS units during 41 official games. High accelerations were defined as efforts commencing above a threshold corresponding to 70% (T70%) or 80% (T80%) of the average 5-m acceleration obtained during a 40-m sprint test; RHAA bouts were defined as ≥3 efforts with ≤45 s recovery between efforts. Results were analysed via generalised linear mixed model and magnitude-based inferential statistics. On average, 8.0±4.6 and 5.1±3.5 bouts were detected in an entire game using T70% and T80%, respectively. When all positions were analysed together, there was a very-likely small difference in the number of RHAA bouts between first and second half for T70% and T80%, respectively. RHAA bouts occur frequently in elite youth football, with small differences between halves and between playing positions within the first or second half in most variables assessed.


#2 Importance of Reactive Agility and Change of Direction Speed in Differentiating Performance Levels in Junior Soccer Players: Reliability and Validity of Newly Developed Soccer-Specific Tests
Reference: Front Physiol. 2018 May 15;9:506. doi: 10.3389/fphys.2018.00506. eCollection 2018.
Authors: Pojskic H, Aslin E, Krolo A, Jukic I, Uljevic O, Spasic M, Sekulic D
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962722/pdf/fphys-09-00506.pdf
Summary: Agility is a significant determinant of success in soccer; however, studies have rarely presented and evaluated soccer-specific tests of reactive agility (S_RAG) and non-reactive agility (change of direction speed - S_CODS) or their applicability in this sport. The aim of this study was to define the reliability and validity of newly developed tests of the S_RAG and S_CODS to discriminate between the performance levels of junior soccer players. The study consisted of 20 players who were involved at the highest national competitive rank (all males; age: 17.0 ± 0.9 years), divided into three playing positions (defenders, midfielders, and forwards) and two performance levels (U17 and U19). Variables included body mass (BM), body height, body fat percentage, 20-m sprint, squat jump, countermovement jump, reactive-strength-index, unilateral jump, 1RM-back-squat, S_CODS, and three protocols of S_RAG. The reliabilities of the S_RAG and S_CODS were appropriate to high (ICC: 0.70 to 0.92), with the strongest reliability evidenced for the S_CODS. The S_CODS and S_RAG shared 25-40% of the common variance. Playing positions significantly differed in BM (large effect-size differences [ES]; midfielders were lightest) and 1RM-back-squat (large ES; lowest results in midfielders). The performance levels significantly differed in age and experience in soccer; U19 achieved better results in the S_CODS (t-test: 3.61, p < 0.05, large ES) and two S_RAG protocols (t-test: 2.14 and 2.41, p < 0.05, moderate ES). Newly developed tests of soccer-specific agility are applicable to differentiate U17 and U19 players. Coaches who work with young soccer athletes should be informed that the development of soccer-specific CODS and RAG in this age is mostly dependent on training of the specific motor proficiency.


#3 The Betting Odds Rating System: Using soccer forecasts to forecast soccer
Reference: PLoS One. 2018 Jun 5;13(6):e0198668. doi: 10.1371/journal.pone.0198668. eCollection 2018.
Authors: Wunderlich F, Memmert D
Download link: http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0198668&type=printable
Summary: Betting odds are frequently found to outperform mathematical models in sports related forecasting tasks, however the factors contributing to betting odds are not fully traceable and in contrast to rating-based forecasts no straightforward measure of team-specific quality is deducible from the betting odds. The present study investigates the approach of combining the methods of mathematical models and the information included in betting odds. A soccer forecasting model based on the well-known ELO rating system and taking advantage of betting odds as a source of information is presented. Data from almost 15.000 soccer matches (seasons 2007/2008 until 2016/2017) are used, including both domestic matches (English Premier League, German Bundesliga, Spanish Primera Division and Italian Serie A) and international matches (UEFA Champions League, UEFA Europe League). The novel betting odds based ELO model is shown to outperform classic ELO models, thus demonstrating that betting odds prior to a match contain more relevant information than the result of the match itself. It is shown how the novel model can help to gain valuable insights into the quality of soccer teams and its development over time, thus having a practical benefit in performance analysis. Moreover, it is argued that network based approaches might help in further improving rating and forecasting methods.


#4 Data concerning isometric lower limb strength of dominant versus not-dominant leg in young elite soccer players
Reference: Data Brief. 2018 Jan 31;17:414-418. doi: 10.1016/j.dib.2018.01.022. eCollection 2018 Apr.
Authors: Rouissi M, Chtara M, Bragazzi NL, Haddad M, Chamari K
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988318/pdf/main.pdf
Summary: The present data article describes the isometric lower limb strength of dominant leg versus not-dominant leg measured with handheld dynamometer (HHD) in a sample of 31 young elite soccer players (age 16.42 ± 0.45 years; height 169.00 ± 0.50 cm; leg length 94.80 ± 3.32 cm; body-mass 67.04 ± 5.17 kg).


#5 The Construct Validity of the CODA and Repeated Sprint Ability Tests in Football Referees
Reference: Int J Sports Med. 2018 Jun 14. doi: 10.1055/a-0577-4073. [Epub ahead of print]
Authors: Riiser A, Andersen V, Castagna C, Arne Pettersen S, Saeterbakken A, Froyd C, Ylvisaker E, Naess Kjosnes T, Fusche Moe V
Summary: As of 2017, the international football federation introduced the change of direction ability test (CODA) and the 5×30 m sprint test for assistant referees (ARs) and continued the 6×40 m sprint test for field referees (FRs) as mandatory tests. The aim of this study was to evaluate the association between performance in these tests and running performance during matches at the top level in Norway. The study included 9 FRs refereeing 21 matches and 19 ARs observed 53 times by a local positioning system at three stadiums during the 2016 season. Running performance during matches was assessed by high-intensity running (HIR) distance, HIR counts, acceleration distance, and acceleration counts. For the ARs, there was no association between the CODA test with high-intensity running or acceleration (P>0.05). However, the 5×30 m sprint test was associated with HIR count during the entire match (E -12.9, 95% CI -25.4 to -0.4) and the 5-min period with the highest HIR count (E -2.02, 95% CI -3.55 to -0.49). For the FRs, the 6×40 m fitness test was not associated with running performance during matches (P>0.05). In conclusion, performance in these tests had weak or no associations with accelerations or HIR in top Norwegian referees during match play.


#6 The effects of an enrichment training program for youth football attackers
Reference: PLoS One. 2018 Jun 13;13(6):e0199008. doi: 10.1371/journal.pone.0199008. eCollection 2018.
Authors: Coutinho D, Santos S, Goncalves B, Travassos B, Wong DP, Schollhorn W, Sampaio J
Download link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999098/pdf/pone.0199008.pdf
Summary: The aim of this study was to identify the effects of a complementary training program based on differential learning approach in the physical, technical, creative and positioning performance of youth football attackers. Fifteen players were allocated into the control (U15C = 9, age: 13.9±0.5 years; U17C = 6, age: 16.1±0.7 years) and the experimental (U15E = 9, age: 14.2±0.8 years; U17E = 6, age: 15.8±0.5 years) groups. The experimental groups participated in 10-weeks of a complementary training program based on differential learning approach to improve physical literacy and players' tactical behavior. Variables studied encompassed: motor (vertical jump, speed and repeated change-of direction), technical (pass, dribble and shot), creative (fluency, attempts, versatility) and positioning-related variables (stretch index, spatial exploration index and regularity of the lateral and longitudinal movements). Results revealed that U15E improved both the jump and repeated change-of-direction performance, while the U17E have only improved the jump performance. The U15E showed improvements in all technical variables (small to large effects), and in the fluency and versatility (moderate effects), while the U17 have only improved the successful shots (large effects). From a positional perspective, there was a moderate increase in the stretch index, and decreased longitudinal and lateral regularity (small to moderate effects) in the U15E compared to the U15C. In turn, the U17E revealed a moderate increase of the spatial exploration index and a small decrease in the stretch index. Overall, the results suggest that the complementary training program was effective for the development of the overall performance of the U15E attackers, while more time and/or variability may be needed for older age groups. Nevertheless, the overall higher values found in experimental groups, may suggest that this type of complementary training program improves performance.


#7 The Adductor Strengthening Programme prevents groin problems among male football players: a cluster-randomised controlled trial
Reference: Br J Sports Med. 2018 Jun 10. pii: bjsports-2017-098937. doi: 10.1136/bjsports-2017-098937. [Epub ahead of print]
Authors: Haroy J, Clarsen B, Wiger EG, Oyen MG, Serner A, Thorborg K, Holmich P, Andersen TE, Bahr R
Summary: Groin injuries represent a considerable problem in male football. Previous groin-specific prevention programmes have not shown a significant reduction in groin injury rates. An exercise programme using the Copenhagen Adduction exercise increases hip adduction strength, a key risk factor for groin injuries. However, its preventive effect is yet to be tested. The aim of the study was to evaluate the effect of a single-exercise approach, based on the Copenhagen Adduction exercise, on the prevalence of groin problems in male football players. 35 semiprofessional Norwegian football teams were cluster-randomised into an intervention group (18 teams, 339 players) and a control group (17 teams, 313 players). The intervention group performed an Adductor Strengthening Programme using one exercise, with three progression levels, three times per week during the preseason (6-8 weeks), and once per week during the competitive season (28 weeks). The control group were instructed to train as normal. The prevalence of groin problems was measured weekly in both groups during the competitive season using the Oslo Sports Trauma Research Center Overuse Injury Questionnaire. The average prevalence of groin problems during the season was 13.5% (95% CI 12.3% to 14.7%) in the intervention group and 21.3% (95% CI 20.0% to 22.6%) in the control group. The risk of reporting groin problems was 41% lower in the intervention group (OR 0.59, 95% CI 0.40 to 0.86, p=0.008). The simple Adductor Strengthening Programme substantially reduced the self-reported prevalence and risk of groin problems in male football players.


#8 Football is medicine: it is time for patients to play!
Reference: Br J Sports Med. 2018 Jun 9. pii: bjsports-2018-099377. doi: 10.1136/bjsports-2018-099377. [Epub ahead of print]
Authors: Krustrup P, Krustrup BR
Download link: http://bjsm.bmj.com/content/bjsports/early/2018/06/09/bjsports-2018-099377.full.pdf


#9 Are There Differences in Elite Youth Soccer Player Work Rate Profiles in Congested vs. Regular Match Schedules?
Reference: J Strength Cond Res. 2018 Jun 21. doi: 10.1519/JSC.0000000000002702. [Epub ahead of print]
Authors: Zanetti V, Carling C, Aoki MS, Bradley PS, Moreira A
Summary: Official international tournaments in which youth soccer players participate can involve very congested schedules. Yet, no information regarding physical and technical match performance during congested vs. regular (noncongested) cycles is available. In this study, accelerations, decelerations, mean metabolic power (MP), and technical performance (offensive and defensive variables) were compared across very congested match (VCM; 10 international matches played over 3 successive days, including 2 days with 2 consecutive matches separated by a 4- to 5-hour interval) and 10 regular (noncongested match [NCM]) match periods in elite male Under 15 (U15, n = 11) and Under 17 (U17, n = 13) soccer players. Players wore a 15-Hz Global Positioning System unit with a 100-Hz triaxial accelerometer. The session rating of perceived exertion (RPE) were assessed 30 minutes after match. Results showed a higher number of accelerations per minute observed in VCM vs. NCM (U15; 2.27 ± 0.35 vs. 2.12 ± 0.23; effect size [ES] = 0.49; U17; 2.27 ± 0.41 vs. 2.01 ± 0.31; ES = 0.69). Decelerations per minute were higher during VCM (U15; 1.99 ± 0.27 vs. 1.84 ± 0.25; ES = 0.55; and U17; 1.98 ± 0.35 vs. 1.80 ± 0.27; ES = 0.56). Mean MP was higher in the VCM (U15; 0.42 ± 0.06 vs. 0.37 ± 0.02; ES = 1.08; U17; 0.46 ± 0.03 vs. 0.30 ± 0.03; ES = 1.94). Technical actions per minute were higher in the VCM for U17 (ES = 1.60 and 1.37, for offensive and defensive performance, respectively) but lower (during VCM) for U15 (ES = 3.59 and 0.28, for offensive and defensive performance). U15 reported a higher session RPE in the VCM (7.9 ± 0.5 AUs vs. 6.9 ± 0.5 AUs). The findings suggest that running activity in these youth players was unaffected overall in tournaments with congested schedules, and that the intensity of match-play was actually greater than in regular match schedules.


#10 Personality and Risk Taking in Sports: A Focus on Unintentional and Intentional Head Impacts in Amateur Soccer Players
Reference: Clin J Sport Med. 2018 Jun 21. doi: 10.1097/JSM.0000000000000627. [Epub ahead of print]
Authors: Levitch CF, Ifrah C, Kim M, Stewart WF, Lipton RB, Zimmerman ME, Lipton ML
Summary: In soccer, unintentional and intentional (heading) head impacts are associated with concussive symptoms and cognitive dysfunction. We examined whether personality traits were associated with these behaviors in soccer players. Participants completed study visits at the Albert Einstein College of Medicine. A total of 307 adult amateur soccer players, recruited from New York City and the surrounding area, completed 737 HeadCount-2w questionnaires. Personality traits (intellect/imagination, conscientiousness, extraversion, agreeableness, and neuroticism) were assessed with the Mini-International Personality Item Pool questionnaire at the baseline study visit were used as predictor variables. Main outcome variables were an online questionnaire (HeadCount-2w) to ascertain frequency of intentional head impacts and occurrence of unintentional head impacts every 3 to 6 months. Generalized estimating equations repeated-measures regressions determined whether personality predicted unintentional and intentional impacts. Personality traits were not associated with unintentional head impact(s) or frequency of intentional head impacts. These findings have important clinical implications, suggesting that personality is not driving the association between high levels of unintentional and intentional head impacts and worse neuropsychological functioning and concussive symptoms.


#11 Does Man Marking Influence Running Outputs and Intensity During Small-Sided Soccer Games?
Reference: J Strength Cond Res. 2018 Jun 20. doi: 10.1519/JSC.0000000000002668. [Epub ahead of print]
Authors: Aasgaard M, Kilding AE
Summary: Small-sided games (SSGs) are considered an effective training tool for physical development in soccer. Small-sided games can be modified in several ways to manipulate the physical demands to best match the game demands, player characteristics, and session objectives. The aim of this study was to compare the physiological, perceptual, and Global Positioning System (GPS)-derived time-motion characteristics of man marking (MM) vs. non-man marking (NMM) in 2v2, 3v3, and 4v4 SSGs. In an acute crossover design, 8 amateur soccer players (mean age ± SD: 23.6 ± 3.3 years) played 2v2, 3v3, and 4v4 SSGs consisting of 4 × 4-minute bouts, with 2-minute passive recovery. During all SSGs, players wore a heart rate (HR) monitor and GPS unit and reported their rating of perceived exertion (RPE). Average percent HR (%HRave) induced small to moderate effects with MM compared with NMM (%Δ = 1-2.7%; effect size [ES] = 0.22-0.65). Comparisons between MM formats indicated a decrease in %HRave with increased player numbers (%Δ = 1.6-3.5%; ES = 0.39-0.86). Perceptual load increased with MM compared with NMM (%Δ = 6.7-17.6%; ES = 0.66-2.09), whereas increases in player numbers (MM only) reduced RPE output (%Δ = 9.4-24.3%; ES = 1.14-3.61). Time-motion characteristics revealed substantially greater total distance covered in MM irrespective of player number (%Δ = 6.8-14.7%; ES = 1.34-2.82). There were very likely increases in distances covered at striding (13.1-17.8 km·h) (%Δ: 23.4-33.2; ES = 2.42-4.35) and high-intensity running (HIR) (17.9-21 km·h) (%Δ: 47.3-104; ES = 0.91-1.68) for MM compared with NMM irrespective of player number. In conclusion, MM substantially elevated perceptual load and distances from striding to HIR regardless of player number, whereas differences between NMM and MM for internal load remain unclear. Use of MM may allow coaches to condition for particularly demanding phases of the game and prescription of larger SSG formats to increase distance covered at higher velocities.