Latest research in football - week 11 - 2017

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 Monitoring Elite Soccer Players External Loads Using Real-Time Data
Reference: Int J Sports Physiol Perform. 2017 Mar 2:1-10. doi: 10.1123/ijspp.2016-0516. [Epub ahead of print]
Authors: Barrett S
Summary: The principle aim of the study was to assess the validity of measuring locomotor activities and PlayerLoad using Real-Time (RT) data collection during soccer training. Twenty-nine (n=29) English soccer players participated. Each player wore the same MEMS device (S5, Optimeye, CatapultSports, Melbourne, Australia) during twenty-one training sessions (n= 331 data sets) in the 2015/2016 and 2016/2017 season. A Real-Time receiver (TRX, Catapultsports, Melbourne, Australia) was used to collect the locomotor activities and PlayerLoad data in RT and compared with the post-event downloaded (PED) data. PlayerLoad and locomotor activities (total distance covered, TDC; total high speed running distance covered, >5.5m/s, HSR; total sprinting distance covered, >7m/s, SP; maximum velocity, VEL) were analysed. Correlations were near perfect for all variables analysed (r=0.98-1.00), with a varied level of noise between RT and PED also (0.3-9.7% CV). Locomotor activities and PlayerLoad can be used both RT and PED concurrently to quantify a players physical output during a training session. Caution should be taken with higher velocity based locomotor activities during RT compared to PED.

#2 Long Sprint Abilities in Soccer: Ball vs Running Drills
Reference: Int J Sports Physiol Perform. 2017 Mar 2:1-22. doi: 10.1123/ijspp.2016-0565. [Epub ahead of print]
Authors: Castagna C, Francini L, Póvoas SC, D'Ottavio S
Summary: The purpose of the study was to examine the acute effects of generic (Running Drills, RD) and specific (Small-Sided Games, SSG) Long Sprint Ability (LSA) drills on internal and external load of male soccer-players. Fourteen academy-level soccer-players (mean±SD; age 17.6±0.61 years, height 1.81±0.63 m, body-mass 69.53±4.65 kg) performed four 30s LSA bouts for maintenance (work:rest, 1:2) and production (1:5) with RD and SSG drills. Players' external-load was tracked with GPS technology (20Hz) and heart-rate (HR), blood-lactate concentrations (BLc) and rate of perceived exertion (RPE) were used to characterize players' internal-load. Individual peak BLc was assessed with a 30s all-out test on a non-motorized treadmill (NMT). Compared to SSGs the RDs had a greater effect on external-load and BLc (large and small, respectively). During SSGs players covered more distance with high-intensity decelerations (moderate-to-small). Muscular-RPE was higher (small-to-large) in RD than in SSG. The production mode exerted a moderate effect on BLc while the maintenance condition elicited higher cardiovascular effects (small-to-large). The results of this study showed the superiority of generic over specific drills in inducing LSA related physiological responses. In this regard production RD showed the higher post-exercise BLc. Interestingly, individual peak blood-lactate responses were found after the NMT 30s all-out test, suggesting this drill as a valid option to RD bouts. The practical physiological diversity among the generic and specific LSA drills here considered, enable fitness trainers to modulate prescription of RD and SSG drills for LSA according to training schedule.

#3 Changes in body composition and bone of female collegiate soccer players through the competitive season and off-season

Reference: J Musculoskelet Neuronal Interact. 2017 Mar 1;17(1):386-398.
Authors: Minett MM, Binkley TB, Weidauer LA, Specker BL
Summary: The purpose of the study was to assess body composition and bone changes pre- to post-season (pre-post) and post- to off-season (post-off) in female soccer athletes (SC).
Outcomes were assessed using DXA and pQCT in 23 SC and 17 controls at three times throughout season. SC, non-starters in particular, lost lean mass pre-post (-0.9±0.2 kg, p<0.01; not different from controls, p=0.2) and gained fat mass post-off (1.4±0.3 kg, p<0.01; differed from controls, p=0.01). Baseline femoral neck and hip aBMD were higher in SC than controls (both,p<0.04), but increased in controls more than SC in pre-post and decreased post-off. SC cortical bone mineral content (BMC), cortical area and periosteal circumference increased pre-post (all, p<0.01; differed from controls, p<0.05) and trabecular vBMD decreased post-off (-3.0±1.3 mg/cm3; p=0.02; not different from controls, p=0.4). Both SC and controls increased cortical BMC, cortical area, and thickness post-off (all, p<0.01). Soccer players lost lean mass over the competitive season that was not recovered during off-season. Bone size increased pre- to post-season. Female soccer athletes experience body composition and bone geometry changes that differ depending on the time of season and on athlete's playing status. Evaluations of athletes at key times across the training season are necessary to understand changes that occur.

#4 The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise
Reference: Eur J Appl Physiol. 2017 Feb 28. doi: 10.1007/s00421-017-3561-9. [Epub ahead of print]
Authors: Goodall S, Thomas K, Harper LD, Hunter R, Parker P, Stevenson E, West D, Russell M, Howatson G
Download link:*~hmac=5dd338e5036a46152a7d9f94e33901a365f57c98ec7ccb3aa84adee932e5d4e7
Summary: This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions. Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response. At HT, FT, and ET, reductions in maximal voluntary force (MVC; -11, -20 and -27%, respectively, P ≤ 0.01), potentiated twitch force (-15, -23 and -23%, respectively, P < 0.05), voluntary activation (FT, -15 and ET, -18%, P ≤ 0.01), and voluntary activation measured with TMS (-11, -15 and -17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6-11%; ICC2,1 0.83-0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5-18%; ICC2,1 0.63-0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3-6%; ICC2,1 0.90-0.98). Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanisms.

#5 Soccer and head injuries: What is the risk?
Reference: Neurology. 2017 Feb 28;88(9):e74-e77. doi: 10.1212/WNL.0000000000003669.
Authors: Allen B, Karceski S.
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#6 Lack of eye discipline during headers in high school girls soccer: A possible mechanism for increased concussion rates
Reference: Med Hypotheses. 2017 Mar;100:10-14. doi: 10.1016/j.mehy.2016.12.016. Epub 2017 Jan 5.
Authors: Clark JF, Elgendy-Peerman HT, Divine JG, Mangine RE, Hasselfeld KA, Khoury JC, Colosimo AJ
Summary: The sport of soccer is the fastest growing and most popular sport worldwide. With this growth and popularity, attention needs to be given to this athletic population. Sports related concussions is a topic that has gained attention both in the media and by governmental organizations, with growing initiatives in diagnosis, prevention and treatment. The act of soccer heading is thought to contribute to increased concussion incidence. Current evidence reveals that within the high school soccer athletic population, female athletes incur a higher concussion rate than males. This is often attributed to many things including differing cervical spinal musculature, skull thickness, etc., but a definitive reason has not yet been found. Other behaviors, such as field awareness and eye discipline™ on the field of play, may also be contributing factors that result in females incurring a greater concussion rate than males. For the purposes of this paper we define eye discipline™ as the ability to keep the eyes engaged in sporting activity with high risk potential. We present our hypothesis that high school female soccer players are more likely to have their eyes closed when in position for heading the ball as compared to high school male soccer players and this lack of visual awareness may increase the risk of concussion. Should these differences be substantiated between males and females, it may initiate and promote discussion of the need for vision training in the high school athletic setting. As a tool for injury prevention, vision training may improve specific visual parameters improving athletes' abilities to process the field of play and prepare for or avoid injury causing situations. Through ocular motor and visual conditioning, an athlete may become more eye disciplined™, and more likely to have their eyes open during heading of the ball, and more likely to avoid concussions.

#7 Youth Football Injuries: A Prospective Cohort
Reference: Orthop J Sports Med. 2017 Feb 10;5(2):2325967116686784. doi: 10.1177/2325967116686784. eCollection 2017.
Authors: Peterson AR, Kruse AJ, Meester SM, Olson TS, Riedle BN, Slayman TG, Domeyer TJ, Cavanaugh JE, Smoot MK
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Summary: There are approximately 2.8 million youth football players between the ages of 7 and 14 years in the United States. Rates of injury in this population are poorly described. Recent studies have reported injury rates between 2.3% and 30.4% per season and between 8.5 and 43 per 1000 exposures. Youth flag football has a lower injury rate than youth tackle football. The concussion rates in flag football are lower than in tackle football. Three large youth (grades 2-7) football leagues with a total of 3794 players were enrolled. Research personnel partnered with the leagues to provide electronic attendance and injury reporting systems. Researchers had access to deidentified player data and injury information. Injury rates for both the tackle and flag leagues were calculated and compared using Poisson regression with a log link. The probability an injury was severe and an injury resulted in a concussion were modeled using logistic regression. For these 2 responses, best subset model selection was performed, and the model with the minimum Akaike information criterion value was chosen as best. Kaplan-Meier curves were examined to compare time loss due to injury for various subgroups of the population. Finally, time loss was modeled using Cox proportional hazards regression models. A total of 46,416 exposures and 128 injuries were reported. The mean age at injury was 10.64 years. The hazard ratio for tackle football (compared with flag football) was 0.45 (95% CI, 0.25-0.80; P = .0065). The rate of severe injuries per exposure for tackle football was 1.1 (95% CI, 0.33-3.4; P = .93) times that of the flag league. The rate for concussions in tackle football per exposure was 0.51 (95% CI, 0.16-1.7; P = .27) times that of the flag league. Injury is more likely to occur in youth flag football than in youth tackle football. Severe injuries and concussions were not significantly different between leagues. Concussion was more likely to occur during games than during practice. Players in the sixth or seventh grade were more likely to suffer a concussion than were younger players.

#8 Football nutrition: time for a new consensus?
Reference: Br J Sports Med. 2017 Mar 2. pii: bjsports-2016-097260. doi: 10.1136/bjsports-2016-097260. [Epub ahead of print]
Authors: Collins J, McCall A, Bilsborough J, Maughan R
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#9 Effect of lifelong football training on the expression of muscle molecular markers involved in healthy longevity
Reference: Eur J Appl Physiol. 2017 Mar 1. doi: 10.1007/s00421-017-3562-8. [Epub ahead of print]
Authors: Mancini A, Vitucci D, Labruna G, Imperlini E, Randers MB, Schmidt JF, Hagman M, Andersen TR, Russo R, Orru S, Krustrup P, Salvatore F, Buono P
Summary: We investigated whether lifelong football training affects the expression of healthy longevity-related muscle molecular markers. Biopsies were collected from the vastus lateralis muscle of 10 lifelong football-trained men (68.2 ± 3.0 years) and of 10 active untrained healthy men (66.7 ± 1.3 years). Gene and protein expression was measured by RTqPCR on RNA and by western blotting on protein extracts from muscle biopsies, respectively. The expression of AMPKα1/α2, NAMPT, TFAM and PGC1α, which are markers of oxidative metabolism, and MyHC β isoform expression was higher in the muscle of football-trained men vs untrained men. Also citrate synthase activity was higher in trained than in untrained men (109.3 ± 9.2 vs 75.1 ± 9.2 mU/mg). These findings were associated with a healthier body composition in trained than in untrained men [body weight: 78.2 ± 6.5 vs 91.2 ± 11.2 kg; body mass index BMI: 24.4 ± 1.6 vs 28.8 ± 4.0 kg m-2; fat%: 22.6 ± 8.0 vs 31.4 ± 5.0%)] and with a higher maximal oxygen uptake (VO2max: 34.7 ± 3.8 vs 27.3 ± 4.0 ml/min/kg). Also the expression of proteins involved in DNA repair and in senescence suppression (Erk1/2, Akt and FoxM1) was higher in trained than in untrained men. At BMI- and age-adjusted multiple linear regression analysis, fat percentage was independently associated with Akt protein expression, and VO2max was independently associated with TFAM mRNA and with Erk1/2 protein expression. Lifelong football training increases the expression of key markers involved in muscle oxidative metabolism, and in the DNA repair and senescence suppression pathways, thus providing the molecular basis for healthy longevity.

#10 Increased Training Volume Improves Bone Density and Cortical Area in Adolescent Football Players
Reference: Int J Sports Med. 2017 Mar 1. doi: 10.1055/s-0042-124510. [Epub ahead of print]
Authors: Varley I, Hughes DC, Greeves JP, Fraser WD, Sale C
Summary: Habitual football participation has been shown to be osteogenic, although the specific volume of football participation required to cause bone adaptations are not well established. The aim of the present study is to investigate tibial bone adaptations in response to 12 weeks of increased training volume in elite adolescents who are already accustomed to irregular impact training. 99 male adolescent elite footballers participated (age 16±0 y; height 1.76±0.66 m; body mass 70.2±8.3 kg). Tibial scans were performed using peripheral quantitative computed tomography immediately before and 12 weeks after an increase in football training volume. Scans were obtained at 4, 14, 38 and 66% of tibial length. Trabecular density (mg/cm3), cortical density (mg/cm3), cross-sectional area, cortical area (mm2), cortical thickness (mm) and strength strain index (mm3) were assessed. Trabecular (4%) and cortical density (14, 38%), cortical cross-sectional area (14, 38%), total cross-sectional area (66%), cortical thickness (14, 38%) and strength strain index (14, 38%) increased following 12 weeks of augmented volume training (P<0.05). Increased density of trabecular and cortical compartments and cortical thickening were shown following an increased volume of training. These adaptive responses may have been enhanced by the adolescent status of the cohort, supporting the role of early exercise intervention in improving bone strength.

#11 Return to play criteria after hamstring muscle injury in professional football: a Delphi consensus study
Reference: Br J Sports Med. 2017 Feb 28. pii: bjsports-2016-097131. doi: 10.1136/bjsports-2016-097131. [Epub ahead of print]
Authors: Zambaldi M, Beasley I, Rushton A
Summary: Hamstring muscle injury (HMI) is the most common injury in professional football and has a high re-injury rate. Despite this, there are no validated criteria to support return to play (RTP) decisions. The purpose was to use the Delphi method to reach expert consensus on RTP criteria after HMI in professional football. All professional football clubs in England (n=92) were invited to participate in a 3-round Delphi study. Round 1 requested a list of criteria used for RTP decisions after HMI. Responses were independently collated by 2 researchers under univocal definitions of RTP criteria. In round 2 participants rated their agreement for each RTP criterion on a 1-5 Likert Scale. In round 3 participants re-rated the criteria that had reached consensus in round 2. Descriptive statistics and Kendall's coefficient of concordance enabled interpretation of consensus. Participation rate was limited at 21.7% (n=20), while retention rate was high throughout the 3 rounds (90.0%, 85.0%, 90.0%). Round 1 identified 108 entries with varying definitions that were collated into a list of 14 RTP criteria. Rounds 2 and 3 identified 13 and 12 criteria reaching consensus, respectively. Five domains of RTP assessment were identified: functional performance, strength, flexibility, pain and player's confidence. The highest-rated criteria were in the functional performance domain, with particular importance given to sprint ability. This study defined a list of consensually agreed RTP criteria for HMI in professional football. Further work is now required to determine the validity of the identified criteria.

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