Latest research in football - week 33 - 2013

#1 Morphological and motor characteristics of Croatian first league female football players
Authors: Jelaska PM, Katić R, Jelaska I.
Reference: Coll Antropol. 2013 May;37 Suppl 2:69-76.
Summary: The aim of this study was to determine the structure of morphological and motor characteristics of Croatian first league female football players and their impact on the estimated quality of the players. According to the goal of the research, a sample consisted of 70 Croatian first league female football players. Participants were measured in 18 tests for assessing morphological characteristics, a set of 12 basic motor abilities tests and a set of 7 tests for assessing football-specific motor abilities. Exploratory factor analysis strategy was applied separately to all measured tests: morphological, basic motor abilities and football specific motor abilities. Factor analysis of morphological tests has shown existence of 3 significant latent dimensions that explain 64% of the total variability. Factors are defined as transverse dimensionality of the skeleton and voluminosity (35%), subcutaneous fat tissue (16%) and longitudinal dimensionality of the skeleton (13%). In the area of basic motor abilities, four factors were extracted. The first factor is responsible for the integration of agility and explosive power of legs, i.e. a factor of movement regulation (agility/lower body explosiveness) (23%), the second one defines muscle tone regulation (15%), the third one defines the frequency of leg movements (12%), while the fourth one is recognized as responsible for the manifestation of basic strength, particularly of basic core strength (19%). Two factors were isolated in the space of football-specific motor abilities: football-specific efficiency (53%) and situational football coordination (27%). Furthermore, by use of factor analysis on extracted latent dimensions (morphological, basic and football specific motor abilities) two higher order factors (explaining 87% of common variability) were extracted. They were named morphological-motor factor (54%) and football-specific motor abilities factor (33%). It is assumed that two extracted higher-order factors fully describe morphological and motor status of first league female football players. Furthermore, the linear regression results in latent space showed that the identified factors are very good predictors of female football players quality (delta = 0.959). In doing so, both specific motor abilities factors and the first factor of basic motor abilities as a factor of general motor efficiency have the greatest impact on player quality, and these factors have been identified as most important predictors of player quality in Croatian women's first league and elite female football players in general. Obtained results provide deep insight into the structure of relations between the morphological, motor and specific motor variables and also indicate the importance of such definition of specific motor abilities. Consequently, results explicitly indicate the necessity of early, continuous, and systematic development of football-specific motor abilities in female football players of high competitive level but also, adjusted, to the younger age categories.


#2 Monitoring Accelerations With GPS in Football: Time to Slow Down?
Authors: Buchheit M, Al Haddad H, Simpson BM, Palazzi D, Bourdon PC, Di Salvo V, Mendez-Villanueva A.
Reference: Int J Sports Physiol Perform. 2013 Jul 30. [Epub ahead of print]
Summary: The aim of the present study was to 1) examine the magnitude of between-GPS model differences in commonly reported running-based measures in football, 2) examine between-unit variability and 3) assess the effect of software updates on these measures. Fifty identical brand GPS units (15 SPI-proX and 35 SPI-proX2, 15 Hz, GPSports, Canberra, Australia) were attached to a custom-made plastic sled towed by a player performing simulated match running activities. GPS data collected during training sessions over 4 weeks from 4 professional football players (n = 53 files) were also analyzed before and after 2 manufacturer-supplied software updates. There were substantial differences between the different models (e.g., standardized difference for the number of acceleration >4 m.s-2 = 2.1; 90% confidence limits (1.4, 2.7), with 100% chance of a true difference). Between-unit variations ranged from 1% (maximal speed) to 56% (number of deceleration >4 m.s-2). Some GPS units measured 2 to 6 times more acceleration/deceleration occurrences than others. Software updates did not substantially affect the distance covered at different speeds or peak speed reached, but one of the updates led to large and small decreases in the occurrence of accelerations (-1.24;-1.32,-1.15) and decelerations (-0.45; -0.48,-0.41), respectively. Practitioners are advised to apply care when comparing data collected with different models or units, or when updating their software. The metrics of accelerations and decelerations show the most variability in GPS monitoring and must be interpreted cautiously.


#3 Time-Motion and Physiological Profile of Football Training Sessions Performed by Under 15, Under 17 and Under 19 Elite Portuguese Players
Authors: Abade EA, Gonçalves BV, Leite NM, Sampaio JE.
Reference: Int J Sports Physiol Perform. 2013 Aug 6. [Epub ahead of print]
Summary: The aim of this study was to provide the time-motion and physiological profile of regular training sessions (TS) performed during the competitive season by under 15 (U15), under 17 (U17) and under 19 (U19) elite level Portuguese players. 151 elite players of U15 (age 14.0±0.2 n=56), U17 (age 15.8±0.4 n=66) and U19 (age 17.8±0.6 n=29) participated in the study during a 9-week period. Time-motion and body impact data were collected using GPS technology (15Hz) across 38 randomly selected TS that resulted in a total of 612 samples. Also, the heart rate was continuously monitored (1Hz) in the selected TS.  The total distances covered (m) were higher in U17 (4648.3±831.9), followed by U19 (4212.5±935.4) and U15 (3964.5±725.4) players (F=45.84, p<.001). Total body impacts and relative impacts were lower in U15 (total: 490.8±309.5, F=7.3, p<.01), but no differences were identified between U17 (total: 584.0±363.5) and U19 (total: 613.1±329.4). U19 players had less high/very high intensity activity (above 16 Km.h-1) (F=11.8, p<.001) and moderate intensity activity (10.0-15.9 Km.h-1) (F=15.07, p<.001). The heart rate values showed significant effects of zones (F=575.7, p<.001) and interaction with age groups (F=9.7, p<.001) with pairwise differences between all zones (zone 1, <75%; zone 2, 75% - 84.9%; zone 3, 85% - 89.9%; zone 4, ≥ 90%). All players spent most of time below 75% HRmax (U15, ~50%; U17, ~42%; U19, ~50%). Results showed high variability between training sessions, refraining from identifying meaningful trends when measuring performance, although, different demands were identified according to the age groups. The U15 TS were less physiologically demanding, probably caused by increased focus on small-sided games to develop basic tactical principles and technical skills. The focus on game like-situations imposed a higher external and internal workload on U17 and U19 players.


#4 Incidence and risk factors of lower leg fractures in Belgian soccer players
Authors: Vanlommel L, Vanlommel J, Bollars P, Quisquater L, Van Crombrugge K, Corten K, Bellemans J.
Reference: Injury. 2013 Aug 2. pii: S0020-1383(13)00309-4. doi: 10.1016/j.injury.2013.07.002. [Epub ahead of print]
Summary:
Soccer is the world's most popular sport and one that is physically demanding and highly competitive. Consequently, the rate of injuries resulting from this sport is only increasing. It is estimated that 2-20% of all such injuries are fractures, one-third of which are located in the lower extremities. The aim of this epidemiological study was to investigate the incidence of lower-leg fractures (LLFs) in Belgian soccer players and determine the possible risk factors that lead to them. All injuries of players associated with the Royal Belgium Football Association (RBFA) were reported and collected in a nationwide registry. We retrospectively compared the incidence rate of and risk factors for LLFs in Belgian soccer players during two seasons, 1999-2000 and 2009-2010. In total, 1600 fractures (3%) were located in the lower leg. After a decade, the number of LLFs remained unchanged. Ankle fractures were the most common (37%), followed by foot and tibia fractures (33% and 22%, respectively). The least common were fibula fractures, which accounted for just 9%. A higher incidence of every type of LLF was observed in older and amateur-level soccer players, when compared with their younger and professional counterparts. Male players experienced more tibia and foot fractures, whereas the incidences of ankle and fibula fractures were comparable with those in female soccer players. The vast majority of fractures occurred during soccer games. Ankle fractures and foot fractures represented two-thirds of all fractures noted in this analysis. Male gender, recreational level and adult age were important risk factors for LLFs. After 10 years, the incidence of LLFs did not decrease. Given the socioeconomic impact of these injuries, improved prevention techniques are required to reduce their incidence, particularly with regard to the frequently occurring ankle and foot fractures in this population.


#5 Young male soccer players exhibit additional bone mineral acquisition during the peripubertal period: 1-year longitudinal study
Authors: Zouch M, Vico L, Frere D, Tabka Z, Alexandre C.
Reference: Eur J Pediatr. 2013 Aug 7. [Epub ahead of print]
Summary: The aim of this study was to determine whether soccer could have different bone benefits in prepubescent and pubescent boys. We investigated 76 boys aged 10 to 13 years during a 1-year study. All boys were prepubescent at the beginning of the study (T0); pubescent status was determined by a complete 24-h urine hormonal assay of FSH-LH, with LH ≤ 0.31 IU/24 h and FSH ≤ 2.19 IU/24 h corresponding to prepubescent Tanner stage I and with 0.31 < LH < 0.95 IU/24 h and 1.57 < FSH < 3.77 IU/24 h corresponding to pubescent Tanner stage II. At the end of the study (T1), 35 boys remained prepubescent (22 soccer players (F1) and 13 controls (C1)), and 41 boys had entered puberty (26 soccer players (F2) and 15 controls (C2)). Soccer players completed 2 to 5 h of training plus one competition game per week during the school year, and controls only had physical education at school. Bone mineral content (BMC) was measured at T0 and T1 by DPX in the lumbar spine, total hip, and whole body (WB) for a comparison between soccer players and controls. At T0, no BMC difference was found between F1 and C1, but BMC was higher in F2 than C2 in WB and weight-bearing sites. At T1, BMC was higher in WB and weight-bearing sites in both F1 and F2 compared to their respective controls. Between T0 and T1, soccer induced a BMC gain at weight-bearing sites in both F1 and F2 compared to C1 and C2, respectively. The soccer-related bone gain was greater in WB and weight-bearing (the lumbar spine, total hip, and supporting leg) and non-weight-bearing bones (dominant arm and nondominant arm) in boys who became pubescent than in boys who remained prepubescent. In conclusion, 1-year study in young male soccer players demonstrates that the process of bone accretion at the very early phase of puberty is more intensely stimulated by the combination of physical exercise and sexual impregnation than by one of these factors alone.


#6 Comparison of the Short-Term Oxidative Stress Response in National League Basketball and Soccer Adolescent Athletes
Authors: Perrea A, Vlachos IS, Korou LM, Doulamis IP, Exarhopoulou K, Kypraios G, Kalofoutis A, Perrea DN.
Reference: Angiology. 2013 Aug 5. [Epub ahead of print]
Summary: Physical exercise is considered protective against oxidative stress-related disorders. However, there is increasing evidence that strenuous activity may induce increased oxidative stress response. This study investigated the impact of vigorous physical activity on serum oxidative stress markers in 36 soccer and 12 basketball National League adolescent athletes 40 minutes before and 15 minutes after a National League game. Serum total peroxide, fibrinogen, polymorphonuclear (PMN) elastase, and myeloperoxidase levels were determined. No significant differences in any of the measured parameters were observed before the match. Soccer players exhibited significantly lower total peroxide (P < .05) and higher PMN elastase concentrations (P < .05) than that of the basketball athletes after the game. A number of important differences between these 2 sports, such as duration or total aerobic and anaerobic demands, may affect oxidative status. These parameters need to be further examined in order to elucidate the different effects of these 2 sports on postexercise oxidative status.