Latest research in football - week 4 - 2014

#1 Validity of the Yo-Yo Intermittent Recovery Test Level 1 for Direct Measurement or Indirect Estimation of Maximal Oxygen Uptake Among Female Soccer Players
Authors: Martínez-Lagunas V, Hartmann U.
Reference: Int J Sports Physiol Perform. 2014 Jan 15. [Epub ahead of print]
Summary: To evaluate the validity of the Yo-Yo Intermittent Recovery Test Level 1 (YYIR1) for the direct assessment and the indirect estimation of maximal oxygen consumption (VO2max) among female soccer players compared to a maximal laboratory treadmill test (LTT). Eighteen female soccer players (21.5 ± 3.4 y, 165.6 ± 7.5 cm, 63.3 ± 7.4 kg; mean ± SD) completed a LTT and a YYIR1 in random order (one week apart). Players' VO2max was directly measured via portable spirometry during both tests and indirectly estimated from a published non-gender-specific formula (YYIR1-F1). The measured VO2max values in LTT and YYIR1 were 55.0 ± 5.3 and 49.9 ± 4.9 mL·kg-1·min-1, while the estimated VO2max values from YYIR1-F1 corresponded to 45.2 ± 3.4 mL·kg-1·min-1. Large positive correlations between the VO2max values from YYIR1 and LTT (r = .83, P < .001, .64 to .92; 90% confidence interval) and YYIR1-F1 and LTT (r = .67, P = .002, .37 to .84) were found. However, the YYIR1 significantly underestimated players' VO2max by 9.4% compared to LTT (P < .001) with B-A 95% LA ranging from -20.0 to 1.4%. A significant underestimation from the YYIR1-F1 (P < .001) was also identified (17.8% with B-A 95% LA ranging from -31.8 to -3.8%). The YYIR1 and YYIR1-F1 are not accurate methods for the direct assessment or indirect estimation of VO2max among female soccer players. The YYIR1-F1 lacks gender-specificity, which might have been the reason of its larger error.


#2 Effects of Creatine Monohydrate Supplementation on Simulated Soccer Performance
Authors: Williams J, Abt G, Kilding AE.
Reference: Int J Sports Physiol Perform. 2014 Jan 15. [Epub ahead of print]
Summary: To determine the effects of acute short-term creatine (Cr) supplementation on physical performance during a 90 minute soccer-specific performance test. A double-blind, placebo-controlled experimental design was adopted during which 16 male amateur soccer players were required to consume 20 g of Cr per day, for seven days or a placebo. A ball-sport endurance and speed test (BEAST) comprising measures of aerobic (circuit time), speed (12 and 20m sprint) and explosive power (vertical jump) abilities performed over 90 min was performed pre- and post-supplementation. Performance measures during the BEAST deteriorated during the second half relative to the first for both Cr (1.2 to 2.3%) and placebo (1.0 to 2.2%) groups, indicating a fatigue effect associated with the BEAST. However, no significant differences existed between groups suggesting that Cr had no performance enhancing effect or ability to offset fatigue. When effects sizes were considered, some measures (12m sprint: -0.53 ± 0.69; 20m sprint: -0.39 ± 0.59 showed a negative tendency, indicating chances of harm were greater than chances of benefit. Acute short-term Cr supplementation has no beneficial effect on physical measures obtained during a 90 minute soccer simulation test, thus questioning its potential as an effective ergogenic aid for soccer players.


#3 Physiological Responses of General vs. Specific Aerobic Endurance Exercises in Soccer
Authors: Zouhal H1, Lemoal E1, Wong del P2, Benounis O3, Castagna C4, Duluc C1, Owen AL5, Drust B6.
Reference: Asian J Sports Med. 2013 Sep;4(3):213-20. Epub 2013 May 6.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880666/pdf/ASJSM-4-213.pdf
Summary: The study aimed to compare the physiological and perceptual responses of two high intensity intermittent aerobic exercises (HIIE), i.e. the 15s/15s exercise and an exercise on the Hoff track (HTE).
In this within-subject repeated measures study, seven high-level soccer players (Age: 24.1± 4.5yr; Height: 175± 0.04cm; Body mass: 67.9± 9.0kg;% Body fat: 14.2± 2.4%) performed the two exercises with same total duration (25 minutes) in a randomized order: 1) a 15s/15s protocol at 120% of maximal aerobic speed (MAS), and 2) HTE. Heart rate (HR) and oxygen uptake (VO2) were measured continuously throughout both exercises. The rating of perceived exertion (RPE) was measured 15 min after the end of each exercise. Blood lactate concentration ([La]) was measured at rest before each exercise, between and at the end of each set. The mean VO2 during HTE was significantly higher than 15s/15s exercise (39.3±2.3 vs. 36.8±1.9 mL/min/kg, P<0.05. The total O2 consumed was significantly higher (P<0.05) during HTE (66.8±7.6 L) than during the 15s/15s (62.3±8.6 L). Blood lactate [La] after the first set of HTE was significantly higher than the 15s/15s (12.5±2.0 vs. 10.6±2.0 mmol/L, P<0.05). However, RPE provided by players suggested that the 15s/15s was more intense than the HTE (13±1.8 vs. 11.7±1.4, P<0.05). Our results demonstrate that VO2 and [La] were higher during HTE than during the 15s/15s when matched with duration. However, HTE was perceived less intense than 15s/15s. Thus, the use of HTE appears as an effective alternative for fitness coaches to develop aerobic endurance in soccer players.


#4 Incidence, nature, and pattern of injuries to referees in a premier football (soccer) league: a prospective study
Authors: Kordi R1, Chitsaz A2, Rostami M1, Mostafavi R3, Ghadimi M3.
Reference: Sports Health. 2013 Sep;5(5):438-41. doi: 10.1177/1941738113481428.
Summary: Despite the crucial role of referees in a soccer match, few researchers have targeted the injury profile of referees in their studies. Understanding the incidence, nature, and pattern of injuries could provide important information for educational and preventative efforts at the international level.
The incidence rate and patterns of acute injuries to official referees of the Iranian Premier Football League during the 2009-2010 season are similar to those reported among referees in short-term international competitions such as FIFA World Cup. Demographic data for 74 referees, including 30 main referees and 44 assistant referees, were collected at the beginning of the season. To record injuries and refereeing time, weekly contact was made by a physician. In total, 102 injuries were reported by referees during the football season. The incidence rates of injuries among referees during training and matches were 4.6 and 19.6 injuries per 1000 hours, respectively. Muscular and tendon injuries were found to be the most common type of injury, and the most common site of injury was the lower leg followed by the hip and groin. The results of this study are consistent with similar prospective studies evaluating injuries to referees over the course of a short-term tournament. These findings provide a base for suggesting possible preventive recommendations in future studies.


#5 Progression of Mechanical Properties during On-field Sprint Running after Returning to Sports from a Hamstring Muscle Injury in Soccer Players
Authors: Mendiguchia J1, Samozino P2, Martinez-Ruiz E3, Brughelli M4, Schmikli S5, Morin JB6, Mendez-Villanueva A7.
Reference: Int J Sports Med. 2014 Jan 14. [Epub ahead of print]
Summary: The objectives of this study were to examine the consequences of an acute hamstring injury on performance and mechanical properties of sprint-running at the time of returning to sports and after the subsequent ~2 months of regular soccer training after return. 28 semi-professional male soccer players, 14 with a recent history of unilateral hamstring injury and 14 without prior injury, participated in the study. All players performed two 50-m maximal sprints when cleared to return to play (Test 1), and 11 injured players performed the same sprint test about 2 months after returning to play (Test 2). Sprint performance (i. e., speed) was measured via a radar gun and used to derive linear horizontal force-velocity relationships from which the following variables obtained: theoretical maximal velocity (V 0 ), horizontal force (F H0 ) and horizontal power (Pmax). Upon returning to sports the injured players were moderately slower compared to the uninjured players. F H0 and Pmax were also substantially lower in the injured players. At Test 2, the injured players showed a very likely increase in F H0 and Pmax concomitant with improvements in early acceleration performance. Practitioners should consider assessing and training horizontal force production during sprint running after acute hamstring injuries in soccer players before they return to sports.


#6 Color of soccer goalkeepers' uniforms influences the outcome of penalty kicks
Authors: Greenlees IA1, Eynon M2, Thelwell RC3.
Reference: Percept Mot Skills. 2013 Aug;117(1):1043-52.
Summary: This study examined the proposition that competing against red-clad opponents hinders the performance of soccer (football) athletes. 40 experienced players took 10 penalty kicks against a goalkeeper wearing a black jersey and, 1 week later, took 10 penalty kicks against a goalkeeper wearing either a red, green, blue, or yellow jersey. Prior to each set of kicks, participants reported their expectancy of success. Players facing red-clad goalkeepers scored on fewer penalty kicks than those facing either blue- or green-clad goalkeepers, but no differences in expectancy of success emerged. The findings indicate that athletes wearing red may have an advantage over their opponents.


#7 Evaluation of the Match Performances of Substitution Players in Elite Soccer
Authors: Bradley PS, Lago-Peñas C, Rey E.
Reference: Int J Sports Physiol Perform. 2014 Jan 10. [Epub ahead of print]
Summary: To evaluate match performances of substitute players using different research designs. English Premier League matches were analysed using a multiple-camera system. Two research designs were adopted: (1) An independent measures analysis comparing the match performance characteristics of players completing the entire match (n=810) versus substitutes (n=286) and the players they replaced (n=286) and (2) A repeated measures analysis comparing the same players completing full matches versus those in which they were introduced as a substitute (n=94). Most substitutions (P<0.05) occurred at half time and between the 60-85 min versus all first half periods and the remaining second half periods (Effect Size [ES]: 0.85-1.21). These substitutions become more (P<0.01) offensive in relation to the positions introduced as the half progressed (ES: 0.93-1.37). Independent measures analysis indicated that high-intensity running was greater (P<0.01) in substitutes compared to players who either completed the entire match or were replaced (ES: 0.28-0.67) but no differences were evident for pass completion rates (ES: 0.01-0.02). Repeated measures analysis highlighted that players covered more (P<0.01) high-intensity running when they were introduced as a substitute compared to the equivalent period of the second but not the first half period (ES: 0.21-0.47). Both research designs indicated that attackers covered more (P<0.05) high-intensity running than peers or their own performances when completing the entire match (ES: 0.45-0.71). Substitutes cover greater high-intensity running distance, this was particularly evident in attackers but pass completion rates did not differ for any position. This information could be beneficial to coaches regarding optimising the match running performances of their players but much more work needs to be undertaken to investigate the overall impact of substitutes (physical, technical indicators and contribution to key moments of matches).


#8 Changes in blood gas transport of altitude native soccer players near sea-level and sea-level native soccer players at altitude (ISA3600)
Authors: Wachsmuth N, Kley M, Spielvogel H, Aughey RJ, Gore CJ, Bourdon PC, Hammond K, Sargent C, Roach GD, Sanchez RS, Claros JC, Schmidt WF, Garvican-Lewis LA.
Reference: Br J Sports Med. 2013 Dec;47 Suppl 1:i93-9. doi: 10.1136/bjsports-2013-092761.
Summary: The optimal strategy for soccer teams playing at altitude is not known, that is, 'fly-in, fly-out' versus short-term acclimatisation. Here, we document changes in blood gas and vascular volumes of sea-level (Australian, n=20) and altitude (Bolivian, n=19) native soccer players at 3600 m. Haemoglobin-oxygen saturation (Hb-sO₂), arterial oxygen content (CaO₂), haemoglobin mass (Hbmass), blood volume (BV) and blood gas concentrations were measured before descent (Bolivians only), together with aerobic fitness (via Yo-YoIR1), near sea-level, after ascent and during 13 days at 3600 m. At baseline, haemoglobin concentration [Hb] and Hbmass were higher in Bolivians (mean ± SD; 18.2 ± 1.0 g/dL, 12.8 ± 0.8 g/kg) than Australians (15.0 ± 0.9 g/dL, 11.6 ± 0.7 g/kg; both p ≤ 0.001). Near sea-level, [Hb] of Bolivians decreased to 16.6 ± 0.9 g/dL, but normalised upon return to 3600 m; Hbmass was constant regardless of altitude. In Australians, [Hb] increased after 12 days at 3600 m to 17.3 ± 1.0 g/dL; Hbmass increased by 3.0 ± 2.7% (p ≤ 0.01). BV decreased in both teams at altitude by ∼400 mL. Arterial partial pressure for oxygen (PaO₂), Hb-sO₂ and CaO₂ of both teams decreased within 2 h of arrival at 3600 m (p ≤ 0.001) but increased over the following days, with CaO₂ overcompensated in Australians (+1.7 ± 1.2 mL/100 mL; p ≤ 0.001). Yo-YoIR1 was lower on the 3rd versus 10th day at altitude and was significantly related to CaO₂. The marked drop in PaO₂ and CaO₂ observed after ascent does not support the 'fly-in, fly-out' approach for soccer teams to play immediately after arrival at altitude. Although short-term acclimatisation was sufficient for Australians to stabilise their CaO₂ (mostly due to loss of plasma volume), 12 days appears insufficient to reach chronic levels of adaption.


#9 Comparison of dynamic balance in collegiate field hockey and football players using star excursion balance test
Authors: Bhat R, Moiz JA.
Reference: Asian J Sports Med. 2013 Sep;4(3):221-9. Epub 2013 May 5.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880667/pdf/ASJSM-4-221.pdf
Summary: The preliminary study aimed to compare dynamic balance between collegiate athletes competing or training in football and hockey using star excursion balance test. A total thirty university level players, football (n = 15) and field hockey (n = 15) were participated in the study. Dynamic balance was assessed by using star excursion balance test. The testing grid consists of 8 lines each 120 cm in length extending from a common point at 45° increments. The subjects were instructed to maintain a stable single leg stance with the test leg with shoes off and to reach for maximal distance with the other leg in each of the 8 directions. A pencil was used to point and read the distance to which each subject's foot reached. The normalized leg reach distances in each direction were summed for both limbs and the total sum of the mean of summed normalized distances of both limbs were calculated. There was no significant difference in all the directions of star excursion balance test scores in both the groups. Additionally, composite reach distances of both groups also found non-significant (P=0.5). However, the posterior (P=0.05) and lateral (P=0.03) normalized reach distances were significantly more in field hockey players.

#10 Training profiles and motivation of male and female youth soccer players

Authors: Rumpf, M.C., Schneider, A.S., Schneider, C., and Mayer, H.M.

Reference: International Journal of Sports Science & Coaching 9: 207-216, 2014.

Summary: The objective of this study was to investigate training profiles and motivation of male and female youth soccer players in different age groups and levels of play. A total of 1075 youth soccer players (U15-U19) from the Bavarian Football Association (BFV) in Germany completed a survey which investigated the total hours of training per week, and hours of training spent in endurance, sprint, technical/tactical, strength and other training and warm-up and cool-down procedures. Significant differences (p<0.05) between male high- and low-level players were seen in the amount of hours in sprint, technical/tactical and strength training. These differences were also found on motivation of the players. The total amount of training increased significantly with age in female players, but the only difference between high- and low-level players was in the amount of endurance training in the U19-group and game-related motivation in the U17-group. This study provides guidelines for training load and content in youth soccer players by gender, age and skill levels.


#11 Comparative study of aerobic performance between football and judo groups in prepubertal boys
Authors: Triki M1, Rebai H1, Shamssain M2, Masmoudi K3, Fellmann N4, Zouari H1, Zouari N3, Tabka Z1.
Reference: Asian J Sports Med. 2013 Sep;4(3):165-74. Epub 2013 Apr 20.
Download link: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3880659/pdf/ASJSM-4-165.pdf
Summary: The aim of this study was to compare the impact of the practice of football and judo on lung function and aerobic performance of prepubertal boys. A total of ninety six prepubertal boys were studied. They assessed a measure of body composition using the skin folds method. They performed lung plethysmography at rest, followed by an incremental exercise test. There was no significant difference in baseline spirometry between all groups (P>0.05). The maximal oxygen uptake [VO2max] and the VO2 at the ventilatory threshold [VT] were similar between all groups (P>0.05). The maximal minute ventilation [VEmax] of judokas was significantly higher than footballers (P<0.01) and similar at the [VT]. The Heart rate [HR] at [VT] of footballers and judokas was similar and significantly higher than control group (P<0.01). VO2max was significantly related to LM and negatively associated with FM. At the [VT] there was a significant relationship between P[VT] and LM and mainly with VE to VO2 [VT], P[VT] and HR[VT] in all groups. Training in football and judo does not affect lung volumes and capacities, VO2max and VO2 at the [VT].