Latest research in football - week 2 - 2015

#1 Neuromuscular and athletic performance following core strength training in elite youth soccer: Role of instability
Reference: Scand J Med Sci Sports. 2015 Jan 6. doi: 10.1111/sms.12403. [Epub ahead of print]
Authors: Prieske O, Muehlbauer T, Borde R, Gube M, Bruhn S, Behm DG, Granacher U.
Summary: Cross-sectional studies revealed that inclusion of unstable elements in core-strengthening exercises produced increases in trunk muscle activity and thus potential extra stimuli to induce more pronounced performance enhancements in youth athletes. Thus, the purpose of the study was to investigate changes in neuromuscular and athletic performance following core strength training performed on unstable (CSTU) compared with stable surfaces (CSTS) in youth soccer players. Thirty-nine male elite soccer players (age: 17 ± 1 years) were assigned to two groups performing a progressive core strength-training program for 9 weeks (2-3 times/week) in addition to regular in-season soccer training. CSTS group conducted core exercises on stable (i.e., floor, bench) and CSTU group on unstable (e.g., Thera-Band® Stability Trainer, Togu© Swiss ball) surfaces. Measurements included tests for assessing trunk muscle strength/activation, countermovement jump height, sprint time, agility time, and kicking performance. Statistical analysis revealed significant main effects of test (pre vs post) for trunk extensor strength (5%, P < 0.05, d = 0.86), 10-20-m sprint time (3%, P < 0.05, d = 2.56), and kicking performance (1%, P < 0.01, d = 1.28). No significant Group × test interactions were observed for any variable. In conclusion, trunk muscle strength, sprint, and kicking performance improved following CSTU and CSTS when conducted in combination with regular soccer training.


#2 ACL injury risk in elite female youth soccer: Changes in neuromuscular control of the knee following soccer-specific fatigue
Reference: Scand J Med Sci Sports. 2014 Dec 30. doi: 10.1111/sms.12355. [Epub ahead of print]
Authors: De Ste Croix MB, Priestley AM, Lloyd RS, Oliver JL
Summary: Fatigue is known to influence dynamic knee joint stability from a neuromuscular perspective, and electromechanical delay (EMD) plays an important role as the feedback activation mechanism that stabilizes the joint. The aim of this study was to investigate the influence of soccer-specific fatigue on EMD in U13-, U15-, and U17-year-old female soccer players. Thirty-six youth soccer players performed eccentric actions of the hamstrings in a prone position at 60, 120, and 180°/s before and after a soccer-specific fatigue trial. Surface electromyography was used to determine EMD from the semitendinosus, biceps femoris and gastrocnemius. A time × age × muscle × velocity repeated measures analysis of variance was used to explore the influence of fatigue on EMD. A significant main effect for time (P = 0.001) indicated that EMD was significantly longer post- compared with pre-fatigue (58.4% increase). A significant time × group interaction effect (P = 0.046) indicated EMD was significantly longer in the U13 age group compared with the U15 (P = 0.011) and U17 (P = 0.021) groups and greater post-fatigue. Soccer-specific fatigue compromised neuromuscular feedback mechanisms and the age-related effects may represent a more compliant muscle-tendon system in younger compared with older girls, increasing risk of injury.


#3 Analysis of body mass components in national club football players in republic of Macedonia
Reference: Med Arch. 2014 Jun;68(3):191-4. doi: 10.5455/medarh.2014.68.191-194. Epub 2014 May 31.
Authors: Nikolic S, Todorovska L, Maleska V, Dejanova B, Efremova L, Zivkovic V, Pluncevic-Gligoroska J
Summary: This study aims to analyze body composition in adult male football players and its changes during adulthood. Adult male football players (n=942, mean age 24.11 ±4.69y), all members of national competitive clubs from Macedonia were included in the study. The absolute and the relative body components were calculated: lean body mass (LBMkg), muscle mass (MMkg; MM%), bone mass (BMkg; BM%) and fat components (FMkg; FM%), using the anthropometric protocol by Matiegka. Mean values of anthropometric measures for all included participants were as follows: height=178.39±6.11cm; weight=77.02±7.57; LBM=65.65±6.38; MM%=53.23±2.78; BM%=17.05±1.27; FM%=14.58±1.48. Descriptive statistics for these parameters was made for age specific groups. The results obtained could be used as reference values for adult football players in Republic of Macedonia. In the examined age span (18-35 years) a slight increase of absolute values of all three body components has been registered with advancing age. The most significant increase in the absolute values was registered for the muscle component, followed by the fat and bone components, respectively. Regarding the relative values (%), the muscle and the fat components showed an equally slight positive correlation with the age increase of 1 year, whilst the bone component decreased with advancing age.


#4 The relationship between the frequency of football practice during skeletal growth and the presence of a cam deformity in adult elite football players
Reference: Br J Sports Med. 2015 Jan 7. pii: bjsports-2014-094130. doi: 10.1136/bjsports-2014-094130. [Epub ahead of print]
Authors: Tak I, Weir A, Langhout R, Waarsing JH, Stubbe J, Kerkhoffs G, Agricola R
Summary: Cam deformity (CD) is likely a bony adaptation in response to high-impact sports practice during skeletal growth. We ascertained whether a dose-response relationship exists between the frequency of football practice during skeletal growth and the presence of a CD in adulthood, and if the age at which a football player starts playing football is associated with the presence of a CD in adulthood. Prevalence of a CD (α angle>60°) and a pathological CD (α angle>78°) was studied using standardised anteroposterior (AP) and frog-leg lateral (FLL) radiographs that were obtained during seasonal screening. The age of starting to play football with a low frequency (LF; ≤3 times/week) and high frequency (HF; ≥4 times/week) was retrospectively assessed. The differences in prevalence of a CD per hip, in either view, between groups were calculated by logistic regression with generalised estimating equations. 63 players (mean(±SD) age 23.1(±4.2) years) participated, yielding 126 hips for analysis. The prevalence of a CD in the FLL was 40% (n=82) in players who started playing HF football from the age of 12 years or above, and 64% (n=44) in those playing HF football before the age of 12 years (p=0.042). This was also true for a pathological CD (12% vs 30%, p=0.038). The AP views revealed no difference. Our results indicate a probable dose-response relationship between the frequency of football practice during skeletal growth and the development of a CD, which should be confirmed in future prospective studies.


#5 Effects of hamstring-emphasized neuromuscular training on strength and sprinting mechanics in football players
Reference: Scand J Med Sci Sports. 2014 Dec 30. doi: 10.1111/sms.12388. [Epub ahead of print]
Authors: Mendiguchia J, Martinez-Ruiz E, Morin JB, Samozino P, Edouard P, Alcaraz PE, Esparza-Ros F, Mendez-Villanueva A
Summary: The objective of this study was to examine the effects of a neuromuscular training program combining eccentric hamstring muscle strength, plyometrics, and free/resisted sprinting exercises on knee extensor/flexor muscle strength, sprinting performance, and horizontal mechanical properties of sprint running in football (soccer) players. Sixty footballers were randomly assigned to an experimental group (EG) or a control group (CG). Twenty-seven players completed the EG and 24 players the CG. Both groups performed regular football training while the EG performed also a neuromuscular training during a 7-week period. The EG showed a small increases in concentric quadriceps strength (ES = 0.38/0.58), a moderate to large increase in concentric (ES = 0.70/0.74) and eccentric (ES = 0.66/0.87) hamstring strength, and a small improvement in 5-m sprint performance (ES = 0.32). By contrast, the CG presented lower magnitude changes in quadriceps (ES = 0.04/0.29) and hamstring (ES = 0.27/0.34) concentric muscle strength and no changes in hamstring eccentric muscle strength (ES = -0.02/0.11). Thus, in contrast to the CG (ES = -0.27/0.14), the EG showed an almost certain increase in the hamstring/quadriceps strength functional ratio (ES = 0.32/0.75). Moreover, the CG showed small magnitude impairments in sprinting performance (ES = -0.35/-0.11). Horizontal mechanical properties of sprint running remained typically unchanged in both groups. These results indicate that a neuromuscular training program can induce positive hamstring strength and maintain sprinting performance, which might help in preventing hamstring strains in football players.


#6 Effect of vertical, horizontal and combined plyometric training on explosive, balance and endurance performance of young soccer players
Reference: J Strength Cond Res. 2014 Dec 31. [Epub ahead of print]
Authors: Ramírez-Campillo R, Gallardo F, Henriquez-Olguín C, Meylan C, Martínez C, Álvarez C, Caniuqueo A, Cadore EL, Izquierdo M.
Summary: Our aim was to compare the effects of 6-weeks of vertical, horizontal, or combined vertical and horizontal plyometric training on muscle explosive, endurance and balance performance. Forty young soccer players between 10 to 14 y of age were randomly divided into: control (CG; n = 10), vertical plyometric group (VG; n = 10), horizontal plyometric group (HG; n = 10) and combined vertical and horizontal plyometric group (VHG; n = 10). Players performance in the vertical (VCMJ) and horizontal (HCMJ) countermovement jump with arms, 5 multiple bounds test (MB5), 20 cm drop jump reactive strength index (RSI20), maximal kicking velocity (MKV), sprint, change of direction speed (CODS), Yo-Yo intermittent recovery level 1 test (Yo-Yo IR1) and balance was measured. No significant or meaningful changes in the CG, apart from small change in the Yo-Yo IR1, were observed while all training programs resulted in meaningful changes in explosive, endurance and balance performance. However, only VHG showed a statistically significant (p<0.05) increase in all performance test and most meaningful training effect difference with the CG across tests. Although no significant differences in performance changes were observed between experimental groups, the VHG program was more effective compared to VG (i.e. jumps, MKV, sprint, CODS and balance performance) and HG (i.e. sprint, CODS and balance performance) to small effect. The study demonstrated that vertical, horizontal and combined vertical and horizontal jumps induced meaningful improvement in explosive actions, balance and intermittent endurance capacity. However, combining vertical and horizontal drills seems more advantageous to induce greater performance improvements.


#7 Effect of progressive volume-based overload during plyometric training on explosive and endurance performance in young soccer players
Reference: J Strength Cond Res. 2014 Dec 31. [Epub ahead of print]
Authors: Ramírez-Campillo R, Henríquez-Olguín C, Burgos C, Andrade D, Zapata D, Martínez C, Álvarez C, Baez EI, Castro-Sepúlveda M, Peñailillo L, Izquierdo M.
Summary: The purpose of the study was to compare the effects of progressive volume-based overload to constant volume-based overload on muscle explosive and endurance performance adaptations during a bi-weekly short-term (i.e. six weeks) plyometric training intervention in young soccer players. Three groups of young soccer players (age 13.0 ± 2.3 y) were divided into: control (CG; n = 8), plyometric training with (PPT; n = 8) and without (NPPT; n = 8) a progressive increase in volume (i.e. 16 jumps per leg/week, with an initial volume of 80 jumps per leg each session). Bilateral and unilateral horizontal and vertical countermovement jump with arms (CMJA), 20 cm drop jump reactive strength index (RSI20), maximal kicking velocity (MKV), 10-m sprint, change of direction speed (CODS) and Yo-Yo intermittent recovery level 1 test (Yo-Yo IR1) were measured. Although both experimental groups significantly increased CMJA, RSI20, CODS and endurance performance, only PPT showed a significant improvement in MKV and 10-m sprint time. In addition, only PPT showed a significantly higher performance improvement in jumping, MKV and Yo-Yo IR1 compared to CG. Also, PPT showed higher meaningful improvement compared to NPPT in all (except one) jump performance measures. Furthermore, although PPT involved a higher total volume compared to NPPT, training efficiency (i.e. percentage change in performance/total jump volume) was similar between groups. Our results show that PPT and NPPT ensured significant improvement in muscle explosive and endurance performance measures. However, a progressive increase in plyometric training volume seems more advantageous to induce soccer-specific performance improvements.


#8 Effects of Northbound Long-haul International Air Travel on Sleep Quantity and Subjective Jet-Lag and Wellness in Professional Australian Soccer Players
Reference: Int J Sports Physiol Perform. 2015 Jan 8. [Epub ahead of print]
Authors: Fowler P, Duffield R, Howle K, Waterson A, Vaile J.
Summary: The present study examined the effects of 10 h northbound air travel across one time-zone on sleep quantity, together with subjective jet-lag and wellness ratings in sixteen male professional Australian football (soccer) players. Player wellness was obtained throughout the week prior to (home training week) and the week of (away travel week) travel from Australia to Japan for a pre-season tour. Sleep quantity and subjective jet-lag were measured two days prior to (Pre 1 and 2), the day of and for five days following travel (Post 1-5). Sleep duration was significantly reduced during the night prior to travel (Pre 1; 4.9 (4.2-5.6) h) and night of competition (Post 2; 4.2 (3.7-4.7) h) compared to every other night (P<0.01, d>0.90). Moreover, compared to the day prior to travel, subjective jet-lag was significantly greater for the five days following travel (P<0.05, d>0.90), and player wellness was significantly lower one day post-match (Post 3) compared to all other time points (P<0.05, d>0.90). Results from the present study suggest that sleep disruption, as a result of an early travel departure time (08:00) and evening match (19:30), and fatigue induced by competition had a greater effect on wellness ratings than long-haul air travel with a minimal time zone change. Furthermore, subjective jet-lag may have been misinterpreted as fatigue from sleep disruption and competition, especially by the less experienced players. Therefore, northbound air travel across one time-zone from Australia to Asia appears to have negligible effects on player preparedness for subsequent training and competition.


#9 Localized BIA identifies structural and pathophysiological changes in soft tissue after post-traumatic injuries in soccer players
Reference: Conf Proc IEEE Eng Med Biol Soc. 2014 Aug;2014:3743-6. doi: 10.1109/EMBC.2014.6944437.
Authors: Nescolarde L, Yanguas J, Lukaski H, Rodas G, Rosell-Ferrer J.
Summary: Localized bioimpedance (BIA) was measured with a single frequency phase-sensitive analyzer at 50 kHz in three post-traumatic types of injuries on four professional soccer players: (1) myositis ossificans, (2) intramuscular seroma and (3) trochanteric (hip) bursitis. Normal reference value (no injury) was obtained from the contra lateral not injured limb at a mirror-like location of the injury. The relative variations resistance (R) and reactance (Xc) at the time of injury was confronted with the not injured values. Relative variations between acute measurements and post medication ones on intramuscular seroma and bursitis have been computed. In intramuscular seroma and trochanteric bursitis we have obtained a percent of change between injury data and after medical intervention. On myositis ossificans, localized BIA showed a 7-8 % decrease in Xc whereas the percent of change of R was negligible (1 %). These percent of changes are in concordance with histological evidence. In the case of a presence of seroma or the lower thigh and trochanteric bursitis, the soft tissue cavity accumulates fluid. Post-injury localized BIA, relative with respect to non-injured side, confirmed sizeable soft tissue destruction evidenced by 50 % decrease of Xc and 24-31 % decrease of R due to interstitial fluid accumulation. Once the seroma and the blood in the bursitis was removed the localized the immediate post-injury BIA parameters increased as follows: a) intramuscular seroma + 10 % on R and + 74 % of Xc; b) trochanteric bursitis + 20 % of R and +24 % of Xc. Localized BIA other than classifying soft tissue injuries, can be useful to understand the pathophysiology and structural impairments of other kind of injuries and to understand their behavior.