***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Objectives —To undertake a prospect i ve epidemiological study of the injuries sustained in English professional football over two competitive seasons . Methods —Player injuries were annotated by club medical staff at 91 professional football clubs . A specific injury audit question naire was used together with a weekly form that documented each club 's current injury status . Results —A total of 6030 injuries were reported over the two seasons with an average of 1.3 injuries per player per season . The mean ( SD ) number of days absent for each injury was 24.2 ( 40.2 ) , with 78 % of the injuries leading to a minimum of one competitive match being missed . The injury incidence varied throughout the season , with training injuries peaking during July ( p<0.05 ) and match injuries peaking during August ( p<0.05 ) . Competition injuries represented 63 % of those reported , significantly ( p<0.01 ) more of these injuries occurring towards the end of both halves . Strains ( 37 % ) and sprains ( 19 % ) were the major injury types , the lower extremity being the site of 87 % of the injuries reported . Most injury mechanisms were classified as being non-contact ( 58 % ) . Re-injuries accounted for 7 % of all injuries , 66 % of these being classified as either a strain or a sprain . The severity of re-injuries was greater than the initial injury ( p<0.01 ) . Conclusions —Professional football players are exposed to a high risk of injury and there is a need to investigate ways of reducing this risk . Areas that warrant attention include the training programmes implemented by clubs during various stages of the season , the factors contributing to the pattern of injuries during matches with respect to time , and the rehabilitation protocol s employed by clubs Background The injury risk in football is high , but little is known about causes of injury . Purpose To identify risk factors for football injuries using a multivariate model . Study Design Prospect i ve cohort study . Methods Participants were 306 male football players from the two highest divisions in Icel and . Before the 1999 football season started , the following factors were examined : height , weight , body composition , flexibility , leg extension power , jump height , peak O2 uptake , joint stability , and history of previous injury . Injuries and player exposure were recorded throughout the competitive season . Results Older players were at higher risk of injury in general ( odds ratio [ OR ] = 1.1 per year , P = 0.05 ) . For hamstring strains , the significant risk factors were age ( OR = 1.4 [ 1 year ] , P < 0.001 ) and previous hamstring strains ( OR = 11.6 , P < 0.001 ) . For groin strains , the predictor risk factors were previous groin strains ( OR = 7.3 , P = 0.001 ) and decreased range of motion in hip abduction ( OR = 0.9 [ 1 ° ] , P = 0.05 ) . Previous injury was also identified as a risk factor for knee ( OR = 4.6 ) and ankle sprains ( OR = 5.3 ) . Conclusions Age and previous injury were identified as the main risk factors for injury among elite football players from Icel and Objective To study the injury characteristics in professional football and to follow the variation of injury incidence during a match , during a season and over consecutive seasons . Design Prospect i ve cohort study where teams were followed for seven consecutive seasons . Team medical staff recorded individual player exposure and time-loss injuries from 2001 to 2008 . Setting European professional men 's football . Participants The first team squads of 23 teams selected by the Union of European Football Associations as belonging to the 50 best European teams . Main outcome measurement Injury incidence . Results 4483 injuries occurred during 566 000 h of exposure , giving an injury incidence of 8.0 injuries/1000 h. The injury incidence during matches was higher than in training ( 27.5 vs 4.1 , p<0.0001 ) . A player sustained on average 2.0 injuries per season , and a team with typically 25 players can thus expect about 50 injuries each season . The single most common injury subtype was thigh strain , representing 17 % of all injuries . Re-injuries constituted 12 % of all injuries , and they caused longer absences than non re-injuries ( 24 vs 18 days , p<0.0001 ) . The incidence of match injuries showed an increasing injury tendency over time in both the first and second halves ( p<0.0001 ) . Traumatic injuries and hamstring strains were more frequent during the competitive season , while overuse injuries were common during the preseason . Training and match injury incidences were stable over the period with no significant differences between seasons . Conclusions The training and match injury incidences were stable over seven seasons . The risk of injury increased with time in each half of matches Objectives : To undertake a detailed epidemiological study of training injuries sustained by professional rugby union players in order to define their incidence , nature , severity , and causes . Methods : A two season prospect i ve design was used to study training injuries associated with 502 rugby union players at 11 English Premiership clubs . Team clinicians reported all training injuries on a weekly basis and provided details of the location , diagnosis , severity , and mechanism of each injury . Training exposures for individual players were recorded on a weekly basis . Loss of time from training and match play was used as the definition of an injury . Results : The overall incidence of injury was 2.0 per 1000 player-hours , and each injury result ed on average in 24 days lost time . Recurrences , which accounted for 19 % of injuries , were more severe ( 35 days ) than new injuries ( 21 days ) . Twenty two per cent of all training occurred during the preseason but 34 % of all injuries were sustained in this period . Hamstring , calf , hip flexor/quadriceps , and adductor muscle injuries were the most common for backs , whereas hamstring , lateral ankle ligament , and lumbar disc/nerve root injuries predominated for forwards . Lumbar disc/nerve root , shoulder dislocation/instability , and hamstring muscle injuries for forwards and hamstring muscle and anterior cruciate ligament injuries for backs caused the greatest number of days absence . Running was the predominant cause of injury for both forwards and backs , although the overall incidence and severity of injuries sustained during skills training were significantly greater than those sustained during conditioning training . Conclusions : On average , a club will have 5 % of their players unavailable for selection as a consequence of training injuries Background : Hamstring injuries are common in sprinters . Identifying preseason risk factors is essential to target injury-prone athletes and develop injury preventive measures . Objective : To investigate the incidence of hamstring muscle injury in sprinters over an athletic season and to explore the preseason predictor of this injury . Design : Prospect i ve cohort study . Participants : 44 sprinters from the Hong Kong Sports Institute , the Hong Kong Amateur Athletic Association and intercollegiate athletic teams were recruited . Methods : Preseason assessment of hamstring flexibility , concentric and eccentric isokinetic peak torque and peak torque angle were obtained at the beginning of an athletic season . The athletes were followed over 12 months and were asked to report all injuries result ing from training and competition . Results : Eight athletes sustained hamstring injuries over the season . The injury rate was 0.87 per 1000 h of exposure . The incidence of injuries was higher at the beginning of the season , with 58.3 % injuries occurring in the first 100 h of exposure . Cox regression analysis revealed that athletes with a decrease in the hamstring : quadriceps peak torque ratio of less than 0.60 at an angular velocity of 180 ° /s have a 17-fold increased risk of hamstring injury . Conclusion : Performing preseason hamstring : quadriceps peak torque ratio assessment s may be useful to identify sprinters susceptible to hamstring injury Objective —To prospect ively establish risk factors for hamstring muscle strain injury using magnetic resonance imaging ( MRI ) to define the diagnosis of posterior thigh injury . Method —In a prospect i ve cohort study using two elite Australian Rules football clubs , the anthropometric characteristics and past clinical history of 114 athletes were recorded . Players were followed throughout the subsequent season , with posterior thigh injuries being documented . Hamstring intramuscular hyperintensity on T2 weighted MRI was required to meet our criteria for a definite hamstring injury . Statistical associations were sought between anthropometric and previous clinical characteristics and hamstring muscle injury . Results —MRI in 32 players showed either hamstring injury ( n = 26 ) or normal scans ( n = 6 ) . An association existed between a hamstring injury and each of the following : increasing age , being aboriginal , past history of an injury to the posterior thigh or knee or osteitis pubis ( all p<0.05 ) . These factors were still significant when players with a past history of posterior thigh injury ( n = 26 ) were excluded . Previous back injury was associated with a posterior thigh injury that looked normal on MRI scan , but not with an MRI detected hamstring injury . Conclusions —Hamstring injuries are common in Australian football , and previous posterior thigh injury is a significant risk factor . Other factors , such as increasing age , being of aboriginal descent , or having a past history of knee injury or osteitis pubis , increase the risk of hamstring strain independently of previous posterior thigh injury . However , as the numbers in this study are small , further research is needed before definitive statements can be made Background Hamstring muscle strain injuries ( HMSI ) are the greatest injury problem in kicking sports such as Australian Rules Football . Reduced hamstring muscle strength is commonly perceived to be a risk factor for hamstring injury ; however , evidence is inconclusive . Testing hamstring strength with the hip and knee at functional angles and assessing endurance parameters may be more relevant for examining the risk of hamstring injury . Objective The primary aim of this prospect i ve study was to examine if reduced hamstring muscle strength assessed with the single leg hamstring  bridge ( SLHB ) was a risk factor for hamstring injury . Methods Hamstring muscle strength of 482 amateur and semielite players from 16 football clubs , mean age 20.7 ( range 16–34 years ) , was tested during the  2011 preseason .  Players were then monitored throughout the 2011 playing season for HMSI . Results A total of 28 hamstring injuries , 16 right and 12 left , were recorded . Players who sustained a right HMSI during the season had a significantly lower mean right SLHB score ( p=0.029 ) , were older ( p=0.002 ) and were more likely to have sustained a past right hamstring injury ( p=0.02 ) or right knee injury ( p=0.035 ) . For left-sided hamstring injury , the injured group was more likely to be left leg dominant ( p=0.001 ) , older athletes ( p=0.002 ) and there was a trend towards a history of left hamstring injury ( p=0.07 ) . Conclusions This study demonstrated a significant deficit in preseason SLHB scores on the right leg of players that subsequently sustained a right-sided hamstring injury . Age , previous knee injury and a history of hamstring injury were other risk factors supported in this study . Low hamstring strength appears to be a risk factor for hamstring injury ; however , due to the confounding variables and low injury rate in this study , further studies are required Background Warm-up and stretching are suggested to increase hamstring flexibility and reduce the risk of injury . This study examined the short-term effects of warm-up , static stretching and dynamic stretching on hamstring flexibility in individuals with previous hamstring injury and uninjured controls . Methods A r and omised crossover study design , over 2 separate days . Hamstring flexibility was assessed using passive knee extension range of motion ( PKE ROM ) .  18 previously injured individuals and 18 uninjured controls participated . On both days , four measurements of PKE ROM were recorded : ( 1 ) at baseline ; ( 2 ) after warm-up ; ( 3 ) after stretch ( static or dynamic ) and ( 4 ) after a 15-minute rest . Participants carried out both static and dynamic stretches , but on different days . Data were analysed using Anova . Results Across both groups , there was a significant main effect for time ( p < 0.001 ) . PKE ROM significantly increased with warm-up ( p < 0.001 ) . From warm-up , PKE ROM further increased with static stretching ( p = 0.04 ) but significantly decreased after dynamic stretching ( p = 0.013 ) . The increased flexibility after warm-up and static stretching reduced significantly ( p < 0.001 ) after 15 minutes of rest , but remained significantly greater than at baseline ( p < 0.001 ) . Between groups , there was no main effect for group ( p = 0.462 ) , with no difference in mean PKE ROM values at any individual stage of the protocol ( p > 0.05 ) . Using ANCOVA to adjust for the non-significant ( p = 0.141 ) baseline difference between groups , the previously injured group demonstrated a greater response to warm-up and static stretching , however this was not statistically significant ( p = 0.05 ) . Conclusion Warm-up significantly increased hamstring flexibility .  Static stretching also increased hamstring flexibility , whereas dynamic did not , in agreement with previous findings on uninjured controls . The effect of warm-up and static stretching on flexibility was greater in those with reduced flexibility post-injury , but this did not reach statistical significance . Further prospect i ve research is required to vali date the hypothesis that increased flexibility improves outcomes .Trial Registration Background : Previous injury is often proposed to be a risk factor for football injury , but most studies rely on players reporting their own medical history and are thus potentially subject to recall bias . Little is known about the natural variation in injury pattern between seasons . Objectives : To study whether prospect ively recorded injuries during one season are associated with injuries sustained during the following 
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The conventional hamstring to quadricep strength ratios were also reduced well after return to play ( 60:60 ° /s , d=-0.32 ; 240:240 ° /s , d=-0.43 ) and functional ( 30:240 ° /s , d=-0.88 ) , but these effects were inconsistent across measurement methods .
After hamstring strain , acute isometric and passive straight leg raise deficits resolve within 20 - 50 days .
Deficits in eccentric and concentric strength and strength ratios persist after return to play , but this effect was inconsistent across measurement methods .