The effect of ambient temperature on the shoe-surface interface release coefficient

ACL Injury Etiology in Its Context: A Systems Thinking, Group Model Building Approach

Background/Objectives: Given the complex nature of Anterior Cruciate Ligament (ACL) injury, it is important to analyze its etiology with suitable approaches in order to formulate intervention strategies for effective prevention. The present study employs system thinking techniques to develop a Causal Loop Diagram (CLD) Model for investigating the risk factors for ACL Injury (CLD-ACLI), through a Group Model Building approach. Methods: A two-stage procedure was applied involving a comprehensive literature review followed by several systems thinking group-modeling co-creation workshops with stakeholders. Results: Based on input from experts and stakeholders, combined with the latest scientific findings, the derived CLD-ACLI model revealed a series of interesting complex nonlinear interrelationships causal loops between the likelihood of ACL injury and the number of risk factors. Particularly, the interaction among institutional, psychological, neurocognitive, neuromuscular, malalignment factors, and trauma history seem to affect neuromuscular control, which subsequently may alter the biomechanics of landing, predisposing the ACL to injury. Further, according to the proposed CLD-ACLI model, the risk for injury may increase further if specific environmental and anatomical factors affect the shear forces imposed on the ACL. Conclusions: The proposed CLD-ACLI model constitutes a rigorous useful conceptual presentation agreed upon among experts on the dynamic interactions among potential intrinsic and extrinsic risk factors for ACL injury. The presented causal loop model constitutes a vital step for developing a validated quantitative system dynamics simulation model for evaluating ACL injury-prevention strategies prior to implementation.

Lisfranc injury: Prevalence and maintaining a high index of suspicion for optimal evaluation

OBJECTIVES

To quantify the long-term prevalence of game-related Lisfranc trauma in college football on artificial turf and natural grass.

METHODS

32 universities were evaluated over 10 competitive seasons across all Football Bowl Subdivision (FBS) conferences. Outcomes of interest included injury severity, injury category, primary type of injury, player and skill position, injury mechanism and situation, elective imaging and surgical procedures, and field conditions. Injury incidence rates (IIR) were calculated using injuries per 10 games = (number of injuries) number of games) × 10.

RESULTS

Of the 1577 games documented, 783 games (49.7%) were played on a 3-layer artificial turf (≥9.0 lbs/ft²) infill system versus 794 games (50.3%) played on natural grass. In sum, 78 Lisfranc cases were documented with 34 (43.6%) occurring on artificial turf, and 44 (56.4%) on natural grass. MANOVAs indicated significant main effects by injury category (F_3,74 = 6.439; P = .001), and injury mechanism (F_5,72 = 3.372; P = .009) observed between surfaces, but not by injury severity (F_2,75 = 0.720; P = .490), primary type of injury (F_4,73 = 0.772; P = .547), overall player (F_2,75 = 0.219; P = .804) and skill positions (F_8,69 = 0.850; P = .563), injury situation (F_10,67 = 1.030; P = .428), elective imaging and surgical procedures (F_3,74 = 0.515; P = .673), or field conditions (F_2,75 = 0.375; P = .688). Post hoc analyses indicated significantly greater incidences (P < .05) of Lisfranc trauma on natural grass attributed to shoe:surface interaction during noncontact play, and during no contact, foot rotation or planting. Ligament tears (n = 8; 57.1%), with minimal cases of subluxation/dislocations (n = 4; 28.6%) and fractures (n = 2; 14.3%) comprised grade 3 cases across both surfaces.

CONCLUSION

In regards to Lisfranc trauma, a 3-layer, heavyweight artificial infill surface is as safe or safer than natural grass. The findings of this study may be generalizable only to this level of football competition.

Anterior cruciate ligament injury risk factors in football

INTRODUCTION

Anterior cruciate ligament (ACL) lesion represents one of the most dramatic injuries in a football (soccer) player's career. There are many injury risk factors related to intrinsic (non-modifiable) and/or extrinsic (modifiable) factors of ACL injury.

EVIDENCE ACQUISITION

Research of the studies was conducted until September 2018 without publication data limitation or language restriction on the following databases: PubMed/MEDLINE, Scopus, ISI, EXCERPTA.

EVIDENCE SYNTHESIS

To date, evidence from the literature suggests that the risk of ACL injury is multifactorial and involves biomechanical, anatomical, hormonal, and neuromuscular factors. Despite this relative complexity, the mechanisms of injury are well known and rationally classified into two categories: mechanisms of injury based on contact or on non-contact with another player, with the non-contact injury mechanisms clearly prevailing over the mechanisms of contact injury. One of the most frequent biomechanical risk factors, associated with ACL non-contact injury, is represented by the valgus knee in the pivoting and cutting movements and in the landing phase after jumping. Gender-related risk factors show female populations to have a higher predisposition to ACL injury than males However, there are still some theoretical and practical aspects that need further investigation such as; genetic risks together with the role of estrogen and progesterone receptors in female populations, and the in-vivo interaction shoe-playing surface. In particular, the genetic risk factors of ACL lesion seem to be an interesting and promising field of investigation, where considerable progress has still to be made.

CONCLUSIONS

This narrative review provides an insight into the risk factors of ACL injury that could be used by practitioners for preventing injury in football (soccer).

The effects of artificial surface temperature on mechanical properties and player kinematics during landing and acceleration

BACKGROUND

Artificial turf is considered a feasible global alternative to natural turf by many sports governing bodies. Consequently, its ability to provide a safe and consistent playing surface regardless of climate becomes essential. The aims of this study were to determine the effects of artificial surface temperature on: (1) mechanical properties of the turf and (2) the kinematics of a turf-sport related movement.

METHODS

Two identical artificial turf pitches were tested: one with a cold surface temperature (1.8°C-2.4°C) and one with a warm surface temperature (14.5°C-15.2°C). Mechanical testing was performed to measure the surface properties. Four amateur soccer players performed a hurdle jump to sprint acceleration movement, with data (contact time, step length and hip, knee and ankle kinematics) collected using CODASport (200 Hz).

RESULTS

The temperature difference had a significant influence on the mechanical properties of the artificial turf, including force absorption, energy restitution, rotational resistance, and the height where the head injury criterion was met. Both step length (p = 0.008) and contact time (p = 0.002) of the initial step after the landing were significantly longer on the warm surface. In addition, significant range of motion and joint angular velocity differences were found.

CONCLUSION

These findings highlight different demands placed on players due to the surface temperature and suggest a need for coaches, practitioners, and sports governing bodies to be aware of these differences.

Efficacy of the FIFA 11+ Injury Prevention Program in the Collegiate Male Soccer Player

BACKGROUND

The Fédération Internationale de Football Association (FIFA) 11+ program has been shown to be an effective injury prevention program in the female soccer cohort, but there is a paucity of research to demonstrate its efficacy in the male population.

HYPOTHESIS

To examine the efficacy of the FIFA 11+ program in men's collegiate United States National Collegiate Athletic Association (NCAA) Division I and Division II soccer.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Before the commencement of the fall 2012 season, every NCAA Division I and Division II men's collegiate soccer team (N = 396) was solicited to participate in this research study. Human ethics review board approval was obtained through Quorum Review IRB. Sixty-five teams were randomized: 34 to the control group (CG; 850 players) and 31 to the intervention group (IG; 675 players). Four teams in the IG did not complete the study, reducing the number for analysis to 61. The FIFA 11+ injury prevention program served as the intervention and was utilized weekly. Athlete-exposures (AEs), compliance, and injury data were recorded using a secure Internet-based system.

RESULTS

In the CG, 665 injuries (mean ± SD, 19.56 ± 11.01) were reported for 34 teams, which corresponded to an incidence rate (IR) of 15.04 injuries per 1000 AEs. In the IG, 285 injuries (mean ± SD, 10.56 ± 3.64) were reported for 27 teams, which corresponded to an IR of 8.09 injuries per 1000 AEs. Total days missed because of injury were significantly higher for the CG (mean ± SD, 13.20 ± 26.6 days) than for the IG (mean ± SD, 10.08 ± 14.68 days) (P = .007). There was no difference for time loss due to injury based on field type (P = .341).

CONCLUSION

The FIFA 11+ significantly reduced injury rates by 46.1% and decreased time loss to injury by 28.6% in the competitive male collegiate soccer player (rate ratio, 0.54 [95% CI, 0.49-0.59]; P < .0001) (number needed to treat = 2.64).

Risk of Anterior Cruciate Ligament Injury in Athletes on Synthetic Playing Surfaces: A Systematic Review

BACKGROUND

The effect of synthetic playing surfaces on the risk of injury in athletes is frequently debated in the orthopaedic literature. Biomechanical studies have identified increased frictional force at the shoe-surface interface, theoretically increasing the risk of injury relative to natural grass. This increase in frictional force is potentially relevant for the risk of anterior cruciate ligament (ACL) rupture, where noncontact mechanisms are frequent. However, clinical studies examining this issue have shown mixed results.

HYPOTHESIS/PURPOSE

The purpose of this study was to systematically review the available literature on risk of ACL rupture on natural grass versus artificial turf. We hypothesized that the risk of ACL rupture on synthetic playing surfaces would not be higher than that of natural grass playing surfaces.

STUDY DESIGN

Systematic review.

METHODS

A systematic keyword search was performed of OVID, EMBASE, the Cochrane Library of Systematic Reviews, and the PROSPERO International Prospective Register of Systematic Reviews. Candidate articles were included if they reported the risk ratio of ACL rupture on natural grass versus synthetic playing surfaces, were of level 3 evidence or better, and included only ACL injuries sustained during organized athletic events. Exclusion criteria included a study with non-field-related sports and the use of historical cohorts for calculating risk ratios.

RESULTS

A total of 10 studies with 963 ACL injuries met criteria for inclusion, all of which reported on soccer and football cohorts. Among these, 4 studies (753 ACL injuries) found an increased risk of ACL injury on artificial playing surfaces. All 4 of these articles were conducted using American football cohorts, and they included both earlier-generation surfaces (AstroTurf) and modern, 3rd-generation surfaces. Only 1 study in football players found a reduced risk of ACL injury on synthetic playing surfaces. No soccer cohort found an increased risk of ACL injury on synthetic surfaces.

CONCLUSION

High-quality studies support an increased rate of ACL injury on synthetic playing surfaces in football, but there is no apparent increased risk in soccer. Further study is needed to clarify the reason for this apparent discrepancy.

Footwear traction and lower extremity joint loading

BACKGROUND

Traction is influenced by the sole architecture and playing surface, with increases in traction potentially leading to injury. The mechanism as to how or why increased traction could lead to injury remains unknown.

PURPOSE

This study was undertaken to determine how shoes of different sole designs and traction influence knee and ankle joint moments.

STUDY DESIGN

Controlled laboratory study.

METHODS

Traction testing was performed on 2 shoes of varying sole designs (tread vs smooth) using a robotic testing machine. All testing was conducted on a 60-cm x 90-cm piece of sample track surface. Kinematic and kinetic data were then collected on 13 recreational athletes performing running V-cuts in the 2 different shoe conditions. Five trials per condition were collected with reflective markers placed on the right shank and shoe of each participant. Kinematic and kinetic data were collected using an 8-high-speed camera system and force plate.

RESULTS

The coefficient of translational traction and the peak moment of rotation were both significantly higher in the tread shoe compared with the smooth shoe (1.00 vs 0.87 and 23.87 N.m vs 16.12 N.m, respectively). The high-traction shoe had significantly higher peak ankle external rotation moments (89.58 N.m vs 80.17 N.m), peak knee external rotation moments (36.23 N.m vs 32.02 N.m), peak knee adduction moments (224.0 N.m vs 186.8 N.m), and knee adduction angular impulse (2.10 Nms vs 1.83 Nms) compared with the low-traction shoe.

CONCLUSION

Increased shoe traction significantly increased ankle and knee joint moments during a V-cut. Despite the significant difference in traction, no difference in performance was observed. These changes could have an effect on ankle and knee joint injury.

CLINICAL RELEVANCE

Shoes with decreased traction could be used in sports to reduce the joint moments in the knee and ankle and potentially reduce injury without a loss in performance.

Incidence, mechanisms, and severity of game-related college football injuries on FieldTurf versus natural grass: a 3-year prospective study

BACKGROUND

Numerous injuries have been attributed to playing on artificial turf. More recently, FieldTurf was developed to duplicate the playing characteristics of natural grass. No long-term studies have been conducted comparing game-related collegiate football injuries between the 2 playing surfaces.

HYPOTHESIS

Collegiate athletes do not experience any difference in the incidence, mechanisms, and severity of game-related injuries between FieldTurf and natural grass.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

Twenty-four universities were evaluated over 3 competitive seasons for injury incidence, injury category, time of injury, injury time loss, player position, injury mechanism, primary type of injury, grade and anatomical location of injury, type of tissue injured, trauma (head, knee, and shoulder), and environmental factors.

RESULTS

In sum, 465 collegiate games were evaluated for game-related football injuries sustained on FieldTurf or natural grass during 3 seasons. Overall, 230 team games (49.5%) were played on FieldTurf versus 235 team games (50.5%) played on natural grass. A total of 2253 injuries were documented, with 1050 (46.6%) occurring during play on FieldTurf, and 1203 (53.4%) on natural grass. Multivariate analysis per 10 team games indicated significantly lower total injury incidence rates, F(3, 2249) = 3.468, P = .016, n - beta = 0.778, on FieldTurf, 45.7 (95% confidence interval [CI], 44.2-46.3), versus natural grass, 51.2 (95% CI, 49.8-51.7). Significantly lower minor injury incidence rates, 38.0 (95% CI, 36.9-38.5) versus 39.9 (95% CI, 39.1-40.0, P = .001), substantial injury incidence rates, 5.0 (95% CI, 4.3-5.6) versus 7.2 (95% CI, 6.6-7.7, P = .020), and severe injury incidence rates, 2.7 (95% CI, 2.1-3.3) versus 4.1 (95% CI, 3.5-4.1; P = .049), were documented on FieldTurf versus natural grass, respectively. Multivariate analyses also indicated significantly less trauma on FieldTurf when comparing injury time loss, injury situation, grade of injury, injuries under various field conditions, and temperature. No significant differences in head, knee, or shoulder trauma were observed between playing surfaces.

CONCLUSION

FieldTurf is in many cases safer than natural grass. It must be reiterated, however, that the findings of this study may be generalizable to only this level of competition. Because this study is still in the early stages, investigation is ongoing.

Evaluation of the shoe-surface interaction using an agility maneuver

PURPOSE

An increase in traction between the shoe and a playing surface can result in increased forces to be absorbed by the structures of the lower extremity. Alternately, decreased traction causes impaired performance. We hypothesized that changes in the coefficient of friction (CoF) will affect subjective and objective measures of performance for an agility maneuver.

METHODS

Thirty subjects were asked to perform a functional agility maneuver under CoF conditions from 0.3 to 0.7. Subjects performed this agility maneuver over a force plate and were asked to complete a questionnaire evaluating their ability to perform the task under various CoF conditions.

RESULTS

Time to complete the task decreased as CoF increased (from 3.1 +/- 0.6 s at CoF 0.3 to 2.6 +/- 0.5 s at CoF 0.5). Peak force, CoF max force plate, and subjective score all increased as CoF increased up to 0.5. CoF of 0.5 or above did not significantly change the subject's ability to perform the cutting maneuver either subjectively or objectively.

CONCLUSIONS

The CoF of 0.5 was deemed adequate to complete the task for this study. Values above CoF 0.5 did not lead to better performance. More studies are needed to build on these findings to establish criteria on safe shoe-surface interactions in athletic practice and play.

Prevention of non-contact anterior cruciate ligament injuries in soccer players. Part 1: Mechanisms of injury and underlying risk factors

Soccer is the most commonly played sport in the world, with an estimated 265 million active soccer players by 2006. Inherent to this sport is the higher risk of injury to the anterior cruciate ligament (ACL) relative to other sports. ACL injury causes the most time lost from competition in soccer which has influenced a strong research focus to determine the risk factors for injury. This research emphasis has afforded a rapid influx of literature defining potential modifiable and non-modifiable risk factors that increase the risk of injury. The purpose of the current review is to sequence the most recent literature that reports potential mechanisms and risk factors for non-contact ACL injury in soccer players. Most ACL tears in soccer players are non-contact in nature. Common playing situations precluding a non-contact ACL injury include: change of direction or cutting maneuvers combined with deceleration, landing from a jump in or near full extension, and pivoting with knee near full extension and a planted foot. The most common non-contact ACL injury mechanism include a deceleration task with high knee internal extension torque (with or without perturbation) combined with dynamic valgus rotation with the body weight shifted over the injured leg and the plantar surface of the foot fixed flat on the playing surface. Potential extrinsic non-contact ACL injury risk factors include: dry weather and surface, and artificial surface instead of natural grass. Commonly purported intrinsic risk factors include: generalized and specific knee joint laxity, small and narrow intercondylar notch width (ratio of notch width to the diameter and cross sectional area of the ACL), pre-ovulatory phase of menstrual cycle in females not using oral contraceptives, decreased relative (to quadriceps) hamstring strength and recruitment, muscular fatigue by altering neuromuscular control, decreased "core" strength and proprioception, low trunk, hip, and knee flexion angles, and high dorsiflexion of the ankle when performing sport tasks, lateral trunk displacement and hip adduction combined with increased knee abduction moments (dynamic knee valgus), and increased hip internal rotation and tibial external rotation with or without foot pronation. The identified mechanisms and risk factors for non-contact ACL injuries have been mainly studied in female soccer players; thus, further research in male players is warranted. Non-contact ACL injuries in soccer players likely has a multi-factorial etiology. The identification of those athletes at increased risk may be a salient first step before designing and implementing specific pre-season and in-season training programs aimed to modify the identified risk factors and to decrease ACL injury rates. Current evidence indicates that this crucial step to prevent ACL injury is the only option to effectively prevent the sequelae of osteoarthritis associated with this traumatic injury.

Amateur football game on artificial turf: players' perceptions

The purpose of this study was to establish whether players' perceptions in football competitions played on artificial turf can be influenced by the pitch under examination, the kind of infill material used, the weather conditions and by player's role in the team. A multifactorial statistical analysis was made of the results obtained from over 1600 U.E.F.A. questionnaires completed by amateur footballers. Pitch and weather factors were demonstrated to be relevant to the aspects investigated. Conversely, the players' role and the infill material were significant for only a few aspects; for each variable, the analysis indicated the most favourable conditions. Overall, the analysis provided insight into amateur players' favourable feelings about artificial turf, compared with its natural alternative (actually made of earth, without grass in the case of amateur players).

Football playing surface and shoe design affect rotational traction

BACKGROUND

High rotational traction between football shoes and the playing surface may be a potential mechanism of injury for The abstract goes here and covers two columns. the lower extremity.

HYPOTHESIS

Rotational traction at the shoe-surface interface depends on shoe design and surface type.

STUDY DESIGN

Controlled laboratory study.

METHODS

A mobile testing apparatus with a compliant ankle was used to apply rotations and measure the torque at the shoe-surface interface. The mechanical surrogate was used to compare 5 football cleat patterns (total of 10 shoe models) and 4 football surfaces (FieldTurf, AstroPlay, and 2 natural grass systems) on site at actual surface installations.

RESULTS

Both artificial surfaces yielded significantly higher peak torque and rotational stiffness than the natural grass surfaces. The only cleat pattern that produced a peak torque significantly different than all others was the turf-style cleat, and it yielded the lowest torque. The model of shoe had a significant effect on rotational stiffness.

CONCLUSION

The infill artificial surfaces in this study exhibited greater rotational traction characteristics than natural grass. The cleat pattern did not predetermine a shoe's peak torque or rotational stiffness. A potential shoe design factor that may influence rotational stiffness is the material(s) used to construct the shoe's upper.

CLINICAL RELEVANCE

The study provides data on the rotational traction of shoe-surface interfaces currently employed in football. As football shoe and surface designs continue to be updated, new evaluations of their performance must be assessed under simulated loading conditions to ensure that player performance needs are met while minimizing injury risk.

A comparison of cleat types during two football-specific tasks on FieldTurf

OBJECTIVE

To examine the effect of different cleat plate configurations on plantar pressure during two tasks.

DESIGN

Thirty-six athletes ran an agility course 5 times while wearing 4 different types of Nike Vitoria cleats: (1) bladed, (2) elliptical firm ground, (3) hard ground and (4) turf. Plantar pressure data were recorded during a side cut and a cross cut using Pedar-X insoles.

SETTING

Controlled laboratory study

PARTICIPANTS

No history of lower extremity injury in the past 6 months, no previous foot or ankle surgery, not currently wearing foot orthotics and play a cleated sport at least twice a week.

MAIN OUTCOME MEASUREMENTS

Total foot contact time, contact area, maximum force, peak pressure and the force-time integral (FTI) in the medial, middle and lateral regions of the forefoot were collected. A 1x4 ANOVA (alpha = 0.05) was performed on each dependent variable. A Bonferroni adjustment was conducted (alpha = 0.008).

RESULTS

In the cross cut task, statistical differences between cleats were observed in three variables: total foot peak pressure, lateral forefoot FTI, and lateral forefoot normalised maximum force. In the side cut task, statistical differences between cleats were observed in 4 variables: total foot peak pressure, the medial and middle forefoot FTI, and the medial and middle forefoot normalised maximum force.

CONCLUSIONS

Significant differences in forefoot loading patterns existed between cleat types. Based on the results of this study, it might be beneficial to increase the forefoot cushioning in cleats in an attempt to decrease loading in these regions of the foot.

Peak torque and rotational stiffness developed at the shoe-surface interface: the effect of shoe type and playing surface

BACKGROUND

Shoe-surface interactions have been implicated in the high number of noncontact knee injuries suffered by athletes at all levels.

PURPOSE

To examine shoe-surface interactions on newer field designs and compare these with more traditional shoe-surface combinations. The peak torque and rotational stiffness (the rate at which torque is developed under rotation) were determined.

STUDY DESIGN

Controlled laboratory study.

METHODS

A device was constructed to measure the torque versus applied rotation developed between different shoe-surface combinations. Data were collected on 5 different playing surfaces (natural grass, Astroturf, 2 types of Astroplay, and FieldTurf), using 2 types of shoes (grass and turf), under a compressive load of 333 N.

RESULTS

The highest peak torques were developed by the grass shoe-FieldTurf tray and the turf shoe-Astroturf field combinations. The lowest peak torques were developed on the grass field. The turf shoe-Astroturf combination exhibited a rotational stiffness nearly double that of any other shoe-surface combinations.

CONCLUSION

The differences in the rotational stiffness across all 10 shoe-surface combinations were greater than those of the peak torques. It is possible that rotational stiffness may provide a new criterion for the evaluation of shoe-surface interface.

CLINICAL RELEVANCE

An improved understanding of shoe-surface interactions remains a critical need to improve the design of shoe-surface combinations with the goal of meeting player needs while minimizing injury potential.

Biomechanical Analysis of Tibial Torque and Knee Flexion Angle

Knee injuries are common in sports activities. Understanding the mechanisms of injury allows for better treatment of these injuries and for the development of effective prevention programmes. Tibial torque and knee flexion angle have been associated with several mechanisms of injury in the knee. This article focuses on the injury to the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the meniscus of the knee as they relate to knee flexion angle and tibial torque. Hyperflexion and hyperextension with the application of tibial torque have both been implicated in the mechanism of ACL injury. A combination of anterior tibial force and internal tibial torque near full extension puts the ACL at high risk for injury. Hyperflexion also increases ACL force; however, in this position, internal and external tibial torque only minimally increase ACL force. Several successful prevention programmes have been based on these biomechanical factors. Injury to the PCL typically occurs in a flexed or hyperflexed knee position. The effects of application of a tibial torque, both internally and externally, remains controversial. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while others have shown that PCL-deficient knees have greater external tibial rotation. The meniscus must endure greater compressive loads at higher flexion angles of the knee and, as a result, are more prone to injury in these positions. In addition, ACL deficiency puts the meniscus at greater risk for injury. Reducing the forces on the ACL, PCL and meniscus during athletic activity through training, the use of appropriate equipment and safe surfaces will help to reduce injury to these structures.

Rye grass is associated with fewer non-contact anterior cruciate ligament injuries than bermuda grass

OBJECTIVE

To assess the contribution of ground variables including grass type to the rate of anterior cruciate ligament (ACL) injury in the Australian Football League (AFL), specifically which factors are primarily responsible for previously observed warm season and early season biases for ACL injuries.

METHODS

Grass types used at the major AFL venues from 1992 to 2004 were established by consultation with ground managers, and ground hardness and other weather variables were measured prospectively.

RESULTS

There were 115 ACL injuries occurring in matches during the survey time period, 88 with a non-contact mechanism. In multivariate analysis, use of bermuda (couch) grass as opposed to rye grass, higher grade of match, and earlier stage of the season were independent risk factors for non-contact ACL injury. Ground hardness readings did not show a significant association with ACL injury risk, whereas weather variables of high evaporation and low prior rainfall showed univariate association with injury risk but could not be entered into a logistic regression equation.

DISCUSSION

Rye grass appears to offer protection against ACL injury compared with bermuda (couch) grass fields. The likely mechanism is reduced "trapping" of football boots by less thatch. Grass species as a single consideration cannot fully explain the ACL early season bias, but is probably responsible for the warm season bias seen in the AFL. Weather variables previously identified as predictors are probably markers for predominance of bermuda over rye grass in mixed fields.

Incidence, causes, and severity of high school football injuries on FieldTurf versus natural grass: a 5-year prospective study

BACKGROUND

Numerous injuries have been attributed to playing on artificial turf. Recently, FieldTurf was developed to duplicate the playing characteristics of natural grass. No long-term study has been conducted comparing game-related, high school football injuries between the 2 playing surfaces.

HYPOTHESIS

High school athletes would not experience any difference in the incidence, causes, and severity of game-related injuries between FieldTurf and natural grass.

STUDY DESIGN

Prospective cohort study.

METHODS

A total of 8 high schools were evaluated over 5 competitive seasons for injury incidence, injury category, time of injury, injury time loss, player position, injury mechanism, primary type of injury, grade and anatomical location of injury, type of tissue injured, head and knee trauma, and environmental factors.

RESULTS

Findings per 10 team games indicated total injury incidence rates of 15.2 (95% confidence interval, 13.7-16.4) versus 13.9 (95% confidence interval, 11.9-15.6). Minor injury incidence rates of 12.1 (95% confidence interval, 10.5-13.6) versus 10.7 (95% confidence interval, 8.7-12.7), substantial injury incidence rates of 1.9 (95% confidence interval, 1.4-2.6) versus 1.3 (95% confidence interval, 0.8-2.1), and severe injury incidence rates of 1.1 (95% confidence interval, 0.7-1.7) versus 1.9 (95% confidence interval 1.2-2.8) were documented on FieldTurf versus natural grass, respectively. Multivariate analyses indicated significant playing surface effects by injury time loss, injury mechanism, anatomical location of injury, and type of tissue injured. Higher incidences of 0-day time loss injuries, noncontact injuries, surface/epidermal injuries, muscle-related trauma, and injuries during higher temperatures were reported on FieldTurf. Higher incidences of 1- to 2-day time loss injuries, 22+ days time loss injuries, head and neural trauma, and ligament injuries were reported on natural grass.

CONCLUSIONS

Although similarities existed between FieldTurf and natural grass over a 5-year period of competitive play, both surfaces also exhibited unique injury patterns that warrant further investigation.

Risk of knee and ankle sprains under various weather conditions in American football

PURPOSE

Previous studies have found conflicting relationships between type of playing surface and injury in American football but have not taken into account possible variations in the surface conditions of outdoor stadiums due to changing weather.

METHODS

A total of 5910 National Football League team games between 1989 and 1998 inclusive were studied to determine associations between knee and ankle sprains, playing surface, and the weather conditions on the day of the game.

RESULTS

There was reduced risk of significant ankle sprains (at least 7-d time loss) for games in natural grass stadiums compared with domes (indoor stadiums using AstroTurf) (RR 0.69, 95% CI 0.58-0.83). There was also reduced risk of significant knee sprains on grass compared with domes (RR 0.77, 95% CI 0.66-0.91), although most of this reduction was related to cold and wet weather on grass (RR 0.66, 95% CI 0.47-0.93 compared with hot and dry weather on grass). In open (outdoor) AstroTurf stadiums, cold weather was associated with a lower risk of significant ankle sprains (RR 0.68, 95% CI 0.51-0.91), significant knee sprains (RR 0.60, 95% CI 0.47-0.77) and ACL injuries (RR 0.50, 95% CI 0.31-0.81) compared with hot weather in the same stadiums. Weather did not have any significant effects on the injury risk in domes. The ACL incidence rate was lower during the later (cooler) months of the season in open stadiums (both AstroTurf and natural grass) but not in domes.

CONCLUSION

Cold weather is associated with lower knee and ankle injury risk in outdoor stadiums (both natural grass and AstroTurf), probably because of reduced shoe-surface traction.

Physiologic axial load, frictional resistance, and the football shoe-surface interface

The purpose of this investigation was to report on the interaction between different types of athletic shoes and playing surfaces using physiologic loads of 40 and 220 lbs. This is a continuation of our previous report using a load of 25 lbs. Nine shoes by three manufacturers were characterized as turf, court, molded cleat, or traditional cleat and tested on both natural grass and synthetic turf. A specially designed pneumatic testing device was used in order to measure translational resistance and rotational torque of the shoe-surface interface. Measurements were acquired for 1) force-X describing translational loading, 2) moment-Y describing the torque generated by linear translation, and 3) moment-Z describing the moment generated by axial rotation, and data were analyzed using repeated measures analysis of variance and Tukey's post-hoc comparison. It was found that increased the axial loads from 40 to 220 lbs significantly increased the frictional resistance (p < .05) between the shoe and the artificial turf surface in a nonlinear fashion. Turf shoes demonstrated the most frictional resistance of any group for this condition. Increases in the forces generated in linear translation from the axial load of 40 to 220 lbs produced the most significant increases of any resistance test on the turf surface. The cleated shoes (both traditional and molded) generated the highest frictional and torsional resistance on the grass surface when compared to the other categories of shoes. Grass generated higher peak moments than turf for the cleated shoes. These results demonstrate the considerable differences between laboratory and physiologic conditions and that the increase in frictional resistance is nonlinear with increasing loads.

Is there a relationship between ground and climatic conditions and injuries in football?

Most soccer, rugby union, rugby league, American football, Australian football and Gaelic football competitions over the world are played on natural grass over seasons that commence in the early autumn (fall) and extend through winter. Injury surveillance in these competitions has usually reported high rates of injury to the lower limb and an increased incidence of injuries early in the season. This 'early-season' bias has not usually been reported in summer football competitions, or in sports played indoors, such as basketball. Although easily compared rates have not often been published there has also been a reported trend towards a greater injury incidence in football played in warmer and/or drier conditions. Injury incidence in American football played on artificial turf has often been reported to be higher than in games played on natural grass. This review concludes that the most plausible explanation for all of these reported findings involves variations in playing surface characteristics. Shoe-surface traction for the average player is the specific relevant variable that is most likely to correlate with injury incidence in a given game of football. Shoe-surface traction will usually have a positive correlation with ground hardness, dryness, grass cover and root density, length of cleats on player boots and relative speed of the game. It is possible that measures to reduce shoe-surface traction, such as, ground watering and softening, play during the winter months, use of natural grasses such as perennial ryegrass (Lolium perenne L.) and player use of boots with shorter cleats, would all reduce the risk of football injuries. The most pronounced protective effect is likely to be on injuries to the lower limb of a noncontact nature, including anterior cruciate ligament injuries. Intervention studies should be performed, both using randomised and historical controls.

Wrestling

The purpose of this study was to determine whether there is a significant difference in the co-efficient of friction (Fc) between old versus new wrestling shoes and mats and to investigate the effect of perspiration. Fc was measured by dragging a weighted shoe over a wrestling mat surface and measuring the vertical and horizontal forces produced. Three different shoe conditions were assessed over two mat types for both wet and dry conditions for a total of 12 conditions. To simulate the wet condition, saline solution was smeared over the surface of the mat. There was a significant effect of shoe, mat, and wet/dry conditions. In addition, significant interactions of shoe by mat, shoe by dry/wet, and mat by dry/wet were observed. Overall, Fc was 36% higher for the new wrestling mat compared to the old wrestling mat. Application of the saline solution reduced Fc by 14% compared to the dry condition. Comparison of the mean Fc for all three shoe types revealed the Fc for the older design shoe was 23% to 28% lower than the brand new shoe and the worn newer design, respectively. A high Fc, such as in the new mat/new shoe combination, has the potential to increase the risk of knee and ankle injuries by fixing the foot more securely to the ground.

How can injuries be prevented in the World Cup soccer athlete?

In order to prevent soccer injuries, different risk factors have to be identified as intrinsic (e.g., joint stability or muscle imbalance) and extrinsic (e.g., equipment, turf, and rules risk factors). Some preventive measures are discussed in this article, such as shin guards, prophylactic braces and taping (or both), and proprioceptive training.

Anterior cruciate ligament injuries in female athletes: why are women more susceptible?

Anterior cruciate ligament (ACL) injuries occur most frequently in planting and cutting sports such as basketball, soccer, and volleyball. National Collegiate Athletic Association injury data show that female athletes injure the ACL more frequently than their male counterparts do. The greater incidence of ACL injuries in women probably stems from complex, interrelated factors, possibly including hamstring-quadriceps strength imbalances, joint laxity, and the use of ankle braces. Successful treatment often includes surgery.