Studying professional and recreational female footballers: A bibliometric exercise

OBJECTIVES

Research directed at soccer has seen dramatic growth in the last decade. While published research on soccer has shown exponential growth, the proportion of articles addressing females is lagging behind research addressing males. The purpose of this paper is to explore how the literature on soccer, female soccer, and professional female soccer has changed over time.

METHODS

The Web of Science (WoS) was queried for all "articles" about soccer and association football from 1970 to 2019. This set of records was then queried to collect subsets of papers about females, professional/elite, and female professional/elite. Each of these data subsets was then queried for a number of characteristics and topics. The results were submitted to bibliometric analysis.

RESULTS

WoS returned 16,822 "articles" about soccer from 1970 to 2019, 3242 of which addressed females. A total of 5924 "articles" about professional players was found, of which 919 had a female focus. Articles about anterior cruciate ligament injuries and concussion were the topics with the highest proportion of papers involving females. Articles directed at selective areas of training and performance were relatively infrequent. Prominent journals, authors, affiliations, and influential papers are presented.

CONCLUSIONS

A bibliometric analysis of the published research presents a high-level overview of trends in soccer research. Overall, studies about women accounted for around 20% of all soccer research and about 15% of studies on professional players. There were a number of topics where studies on females account for less than 10%-15% of the research on all professionals, and opens opportunities for future study.

Evolution of soccer as a research topic

Soccer has not only the largest number of worldwide participants, it is also the most studied sport, with nearly 14,000 citations listed on Pubmed and nearly 60% more articles than the next most studied sport. Research about soccer was limited until the late 1970s when exponential growth began; approximately 98% of all soccer-related research publications have occurred since 1980. This vast repository of soccer research shows trends in various major (e.g., 'sex' or 'age group' or 'performance' or 'injury') and specialty (e.g., agility, deceleration, elbow-head impact injuries, behavior) topics. Examining trends of the various topics provides insights into which subjects have come in and out of favor as well as what topics or demographics have been neglected and worthy of inquiry. A further examination can be used by students to learn the most productive researchers, which programs have a strong history of inquiry, and what journals have demonstrated a commitment to publishing research on soccer.

Rotator Cuff Matrix Augmentation and Interposition: A Systematic Review and Meta-analysis

BACKGROUND

Surgical management of rotator cuff tears is controversial and complex, ranging from nonoperative management to reverse shoulder arthroplasty.

PURPOSE

To systematically review and evaluate the outcomes of graft augmentation or interposition versus rotator cuff repair (RCR) alone and evaluate via meta-analysis whether the use of a graft leads to superior outcomes versus RCR alone.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

An electronic literature search (Medline, Embase, CINAHL) was conducted. Studies with a minimum follow-up of 1 year and minimum sample size of 10 that provided clinical results of RCR or rotator cuff reconstruction using any type of augmentation tissue or matrix were included. Methodological quality was evaluated by assessment of the risk of bias in the included studies. Studies comparing outcomes of RCR with graft augmentation or interposition versus repair alone (control group) were subjected to meta-analysis.

RESULTS

The authors identified 774 articles and included 36 in the systematic review; 5 of the 36 studies underwent meta-analysis. Except for one outcome measure in a single study, all surgical interventions (RCR alone, RCR with augmentation, and RCR with interposition) improved clinical scores and outcome measures. Because of variability in study outcomes, no graft option was found to be superior. Compared with RCR alone, graft augmentation or interposition provided significantly lower retear rates ( P = .05) and higher American Shoulder and Elbow Surgeons (ASES) scores ( P = .005), but improvements in UCLA (University of California, Los Angeles) scores ( P = .29) and pain scores ( P = .1) did not reach statistical significance.

CONCLUSION

In the meta-analysis, graft augmentation or interposition appeared to provide a lower retear rate and improved ASES scores when compared with RCR alone. Future prospective, randomized, controlled, and appropriately powered trials are needed for more definitive recommendations.

Relative Age Effect: Beyond the Youth Phenomenon

Introduction. The relative age effect (RAE) refers to performance advantage of youth born in the first quarter of the birth year when auditioning for select, age-restricted sports. This advantage conferred to the older athlete is a result of being more physically and emotionally mature, therefore, assumed to be a more advanced player. We hypothesize an RAE exists in Olympic athletes, and this extends across selected categories of athletes (by gender), such as team versus individual sports, winter versus summer athletes, and sports using a ball versus those not using a ball. Methods. We extended the exploration of an RAE beyond specific sports by examining the birth quarter of more than 44 000 Olympic athlete's birthdates, born between 1964-1996. The data were summarized by birth quarter (January 1 to March 31, etc) and presented as percentages and 95% confidence intervals. Results. The fractions of births in the first versus the fourth quarter were significantly different ( P < .001) from each other for the summer and winter Olympians, ball and nonball sports, and team as well as individual sports. Conclusions. The general presence of an RAE in Olympic athletes exists regardless of global classification.

Muscle changes in aging: understanding sarcopenia

Muscle physiology in the aging athlete is complex. Sarcopenia, the age-related decrease in lean muscle mass, can alter activity level and affect quality of life. This review addresses the microscopic and macroscopic changes in muscle with age, recognizes contributing factors including nutrition and changes in hormone levels, and identifies potential pharmacologic agents in clinical trial that may aid in the battle of this complex, costly, and disabling problem.

LEVEL OF EVIDENCE

Level 5.

"Real world" treatment of metastatic renal cell carcinoma in a joint community-academic cohort: progression-free survival over three lines of therapy

BACKGROUND

New targeted therapeutics approved for metastatic renal cell carcinoma (mRCC) offer multiple options in each line of therapy; however, there are few prospective data beyond the first-line settings, and overall comparative effectiveness data are limited. In the targeted therapy era, progression-free survival (PFS) has been the most common regulatory end point for demonstrating the benefit of new therapies.

PATIENTS AND METHODS

Drawing on a joint community-academic retrospective mRCC registry, we analyzed all patients who had undergone at least 1 line of systemic therapy (N = 325) for PFS. Patients were grouped according to treatment choice (sorafenib, sunitinib, temsirolimus, everolimus, and "other") for up to 3 lines of therapy. PFS by treatment choice and line of therapy was evaluated using Kaplan-Meier and Cox regression analyses.

RESULTS

PFS was longest in patients treated with sunitinib in the first and second lines of therapy. First-line PFS for sorafenib, sunitinib, temsirolimus, everolimus, and "other" was 6.9, 8.9, 4.2, not analyzed (too few patients), and 10.8 months, respectively. Second-line PFS was 4.6, 7.0, 3.2, 3.8, and 4.1 months, respectively. Third-line PFS was 4.5, 4.6, 9.9, 4.2, and 2.9, months, respectively. The risk of progression in patients treated with temsirolimus was about twice that of patients treated with sunitinib in the first and second lines of therapy.

CONCLUSION

Patients treated with sunitinib had the longest PFS in the first and second lines of therapy. PFS from practice-based data appear consistent with trial-based expectations; however, practice variation was still evident.

Prevention of football injuries

Purpose

Every sport has a unique profile of injury and risk of injury. In recent years, there have been numerous attempts at conducting injury prevention trials for specific injuries or for injuries within specific sports to provide evidence useful to the sports medicine and sport community. Football has been a focus of a number of randomized injury prevention trials.

Methods

MEDLINE was searched with the first order keywords of “injury prevention” and “sport”. This list was restricted to “clinical trial” or “randomized controlled trial” which had been conducted on children and adults whose goal was preventing common football injuries. Our objective was to find studies with an exercise-based training program, thus projects that used mechanical interventions were excluded.

Results

A structured, generalized warm-up has been shown to be effective at preventing common injuries in football, reducing injuries by about one-third.

Conclusion

The huge participation numbers in the worldwide family of football would suggest that any reduction in injury should have a public health impact. Professionals in sports medicine need to promote injury prevention programs that have been shown to be effective.

Management of the Retired Athlete with Osteoarthritis of the Knee

PURPOSE

Osteoarthritis of the knee is a complex interaction of biological, mechanical, and biochemical factors that are further complicated by injury, which accelerates pathological processes within the joint. As a result, athletes, particularly those with a history of knee injury, have an earlier onset and higher prevalence of osteoarthritis that would be expected based on their age. This can present a clinical dilemma to the physician managing the patient who, despite the presence of radiologically confirmed disease, has few symptoms and wishes to maintain an active lifestyle.

METHODS

We reviewed meta-analyses and systematic reviews of randomized controlled trials about clinical management of knee osteoarthritis with special interest on effect sizes.

RESULTS

Numerous management options have undergone the rigor of clinical trials and subsequently have been summarized in meta-analyses and systematic reviews, the results of which offer evidence regarding varying degrees of effect. Based on the available evidence, most summaries and clinical practice guidelines suggest a regimen of patient education, self-management, weight control, and exercise supported by individualized pain management strategies. Other noninvasive or less invasive strategies are available that have varying degrees of effect.

CONCLUSIONS

Although the evidence supporting many of the clinical management options might be considered modest, those effects are sufficient to permit an active lifestyle and have, given the prevalence of the disease, a public health impact.

Effective injury prevention in soccer

Sports participation is accompanied by risk of injury, and each specific sport has its own unique injury profile. One of the goals of a sports medicine professional is injury prevention, and the past decade has seen numerous reports on the outcomes of injury-prevention studies. Health care professionals have been particularly vigilant in attempting to reduce common injuries in soccer, beginning with work in the early 1980s to the rigorous randomized trials of today. The use of a structured, generalized warm-up program has been shown to be effective in preventing common soccer injuries, reducing overall injury rates by approximately 30%. Given the number of individuals who play soccer worldwide, any injury reductions will likely have an impact on public health. It is an important goal of the sports medicine community to inform physicians and other sports medicine professionals about the effectiveness of prevention programs to increase use and compliance.

The F-MARC study on Ramadan and football: research design, population, and environmental conditions

Ramadan is a month of penance during which Muslims take food or drink only after sunset and before the sun rises. This fast can present a considerable challenge to the Muslim athlete. Sports performance in those who observe Ramadan and those who do not has not been formally compared. Four Tunisian junior football squads participated in the study, and it was the individual's choice whether they observed the Ramadan fast. In this study, 64 players fasted while 36 players did not. Players completed daily questionnaires on perception of training difficulty before and during Ramadan. Anthropometric data were recorded 3 weeks before Ramadan, during the second and fourth weeks of Ramadan, and into the third week after Ramadan. Performance tests (sprint, leg power, agility, aerobic endurance, football-specific skills) were also measured on these test days. Nutritional intake was recorded by recall three times during each phase of the study. Haematological and biochemical analyses were performed on a 7-ml blood sample taken from each participant on each of the test days. Sweat samples were collected during a training session in the third week of Ramadan, when heart rate was also measured. The data analyses are presented and discussed elsewhere in this issue.

Movement patterns in elite Brazilian youth soccer

AIM

The aim of this study was to determine standards for the total distance covered (DC) and motion pattern characteristics of young Brazilian soccer players during competitive matches.

METHODS

Seventy-five young soccer players from 5 of the most successful soccer clubs of Sao Paulo's Soccer Federation were divided in 3 categories: under-15 years (U15), under-17 years (U17) and under-20 years (U20) with 25 soccer players in each age group. In the U15 each half lasts for 30 min, in the U17 40 min and in the U20 45 min. The individual measurements were made during games following accepted video-recording methodology. The players were grouped by position: fullbacks, wingers (WG), defensive midfielders, offensive midfielders (OMF) and strikers (STK). The following indices were determined: total distance, and distance jogging, walking, and sprinting. Age and position differences were determined by ANOVA.

RESULTS

The intensity of the U15 (118 m/min) was significantly greater (P<0.05) than U17 (108 m/min) and U20 (109 m/min). WG and midfielders show greater DC than the other players in all other positions. STK and OMF show increased sprinting in U15 and U17 groups, respectively, and WG in U20s. The U15 group showed the greatest mean intensity when the time of each group was corrected to meters per minute.

CONCLUSION

The results show differences in running volume and intensity between the age groups during match play. The data suggest that earlier development, physical training and tactical organization in the young soccer player leads to a high level of energy during competition.

Head injuries in the female football player: incidence, mechanisms, risk factors and management

Although all injuries in sports are a concern for participants, head injuries are particularly troublesome because of the potential for long-term cognitive deficits. To prevent any specific injury, it is important to understand the basic frequency and incidence of injury and then the mechanism of injury. Once these are established, prevention programmes can be tested to see if the rate of injury changes. A primary problem with head injuries is recognising that the injury has occurred. Many athletes are not aware of the seriousness of concussive injury, thus this type of injury is probably under-reported. Once the diagnosis of a concussion is made, the next difficult decision is when to return a player to the game. These two management issues dominate the continuing development of understanding of concussive head injury. This paper explores the known gender differences between head injuries and highlights the areas that need to be considered in future research.

Issues in training the female player

On the surface, the women's game appears to be similar to the men's game. On closer examination, there are subtle differences in the nature of how each gender plays the game, which are evident in the disparity between skills, tactics and fitness. The technical weaknesses of women include the first touch, dribbling, long passing and goal keeping. These skill limitations have dictated specific tactical approaches towards both attack and defence. Specific biological limitations inherent in the female player affect the pace and total work output in the women's game. Although it is unrealistic to expect the women's game to approach the work output of the men's game, specific training of skills and fitness will influence the tactical approach to the game.

Age and gender effects on lower extremity kinematics of youth soccer players in a stop-jump task

BACKGROUND

Gender differences in lower extremity motion patterns were previously identified as a possible risk factor for non-contact anterior cruciate ligament injuries in sports.

HYPOTHESIS

Gender differences in lower extremity kinematics in the stop-jump task are functions of age for youth soccer players between 11 and 16 years of age.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Three-dimensional videographic data were collected for 30 male and 30 female adolescent soccer players between 11 and 16 years of age performing a stop-jump task. The age effects on hip and knee joint angular motions were compared between genders using multiple regression analyses with dummy variables.

RESULTS

Gender and age have significant interaction effects on standing height (P = .00), body mass (P = .00), knee flexion angle at initial foot contact with the ground (P = .00), maximum knee flexion angle (P = .00), knee valgus-varus angle (P = .00), knee valgus-varus motion (P = .00), and hip flexion angle at initial foot contact with the ground (P = .00).

CONCLUSION

Youth female recreational soccer players have decreased knee and hip flexion angles at initial ground contact and decreased knee and hip flexion motions during the landing of the stop-jump task compared to those of their male counterparts. These gender differences in knee and hip flexion motion patterns of youth recreational soccer players occur after 12 years of age and increase with age before 16 years.

CLINICAL RELEVANCE

The results of this study provide significant information for research on the prevention of noncontact anterior cruciate ligament injuries.

Injury history as a risk factor for incident injury in youth soccer

OBJECTIVES

To determine if athletes with a self reported history of previous injury have a higher incident injury rate than athletes without a self reported injury history.

METHODS

A prospective cohort study of Classic League soccer players playing at the level under 12 through under 18. Injury history forms were mailed to all registering Classic League soccer players in the North Carolina Youth Soccer Association during 1997-2000 (n = 7000); 1483 (19%) returned the baseline questionnaire and were followed up for injuries.

RESULTS

There were 5139 player-seasons of follow up and an estimated 171 957 athlete-exposures. More than half self reported an injury history (59.7%). Overall, the unadjusted incidence rate was 4.6 (95% confidence interval (CI) 4.3 to 4.9) incident injuries per 1000 athlete-exposures. Multivariate generalised Poisson regression modelling indicated that players with one previous injury had a twofold greater risk of incident injury (IRR = 2.6; 95% CI 2.0 to 3.3), and those with two or more previous injuries had a threefold greater risk of incident injury (IRR = 3.0; 95% CI 2.3 to 3.8) compared with athletes with no previous injuries.

CONCLUSIONS

Injury history was associated with an increased injury rate. This suggests that, even in these youth soccer players, those with an injury history may be at higher risk.

Effectiveness of a neuromuscular and proprioceptive training program in preventing anterior cruciate ligament injuries in female athletes: 2-year follow-up

BACKGROUND

Among female athletes it has not been established whether a neuromuscular and proprioceptive sports-specific training program will consistently reduce the incidence of anterior cruciate ligament injuries.

PURPOSE

To determine whether a neuromuscular and proprioceptive performance program was effective in decreasing the incidence of anterior cruciate ligament injury within a select population of competitive female youth soccer players.

STUDY DESIGN

Cohort study; Level of evidence, 2.

METHODS

In 2000, 1041 female subjects from 52 teams received a sports-specific training intervention in a prospective non-randomized trial. The control group consisted of the remaining 1905 female soccer players from 95 teams participating in the same league who were age and skill matched. In the 2001 season, 844 female athletes from 45 teams were enrolled in the study, with 1913 female athletes (from 112 teams) serving as the age- and skill-matched controls. All subjects were female soccer players between the ages of 14 and 18 and participated in either their traditional warm-up or a sports-specific training intervention before athletic activity over a 2-year period. The intervention consisted of education, stretching, strengthening, plyometrics, and sports-specific agility drills designed to replace the traditional warm-up.

RESULTS

During the 2000 season, there was an 88% decrease in anterior cruciate ligament injury in the enrolled subjects compared to the control group. In year 2, during the 2001 season, there was a 74% reduction in anterior cruciate ligament tears in the intervention group compared to the age- and skill-matched controls.

CONCLUSION

Using a neuromuscular training program may have a direct benefit in decreasing the number of anterior cruciate ligament injuries in female soccer players.

Effect of fatigue on knee kinetics and kinematics in stop-jump tasks

BACKGROUND

Altered motor control strategies in landing and jumping maneuvers are a potential mechanism of noncontact anterior cruciate ligament injury. There are biomechanical differences between male and female athletes in the landing phase of stop-jump tasks. Fatigue is a risk factor in musculoskeletal injuries.

HYPOTHESIS

Lower extremity muscle fatigue alters the knee kinetics and kinematics during the landing phase of 3 stop-jump tasks and increases an athlete's risk of anterior cruciate ligament injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

Three-dimensional videography and force plate data were collected for 20 recreational athletes (10 male and 10 female athletes) performing 3 stop-jump tasks before and after completing a fatigue exercise. Knee joint angles and resultant forces and moments were calculated.

RESULTS

Both male and female subjects had significantly increased peak proximal tibial anterior shear forces (P = .01), increased valgus moments (P = .03), and decreased knee flexion angles (P = .03) during landings of all 3 stop-jump tasks when fatigued. Fatigue did not significantly affect the peak knee extension moment for male or female athletes.

CONCLUSION

Fatigued recreational athletes demonstrate altered motor control strategies, which may increase anterior tibial shear force, strain on the anterior cruciate ligament, and risk of injury for both female and male subjects. CLINIC RELEVANCE: Fatigued athletes may have an increased risk of noncontact anterior cruciate ligament injury.

Immediate effects of a knee brace with a constraint to knee extension on knee kinematics and ground reaction forces in a stop-jump task

BACKGROUND

A small knee flexion angle in landing tasks was identified as a possible risk factor for noncontact anterior cruciate ligament injuries that are common in sports.

HYPOTHESIS

A specially designed knee brace with a constraint to knee extension would significantly increase the knee flexion angle at the landing of athletic tasks preceded with horizontal movement components, such as stop-jump tasks.

STUDY DESIGN

Repeated measure design for brace effects.

METHODS

Three-dimensional videographic and force plate data were collected for 10 male and 10 female recreational athletes performing a stop-jump task with and without the specially designed brace. Knee flexion angle at landing, maximum knee flexion angle, and peak ground reaction forces during the stance phase of the stop-jump task were determined for each subject with and without the knee brace.

RESULTS

The knee brace decreased the knee flexion angle at the landing by 5 degrees for both genders but did not significantly affect the peak ground reaction forces during the landing.

CONCLUSIONS

The specially designed knee brace may be a useful device in the prevention and rehabilitation of noncontact anterior cruciate ligament injuries in sports.

Theoretical study of the effect of ball properties on impact force in soccer heading

PURPOSE

The objective of this study was to theoretically model, based on the Hertz contact theory, the impact force and contact time, as well as the linear and angular head accelerations during heading in children using two neck stiffness conditions (infinite and negligible stiffness).

METHODS

The following mathematical model inputs were obtained: elastic modulus and mass of size three, four, and five balls at inflation pressures of 10, 12, and 14 psi, head modulus, head mass, head length, head and trunk moment of inertia, and the precontact ball velocity. The model outputs consisted of linear and angular head acceleration, impact force, contact time between the ball and head, and head impact criteria (HIC) all at the point of impact. Head mass and length were obtained as a percentage of body weight and height, respectively, based on age.

RESULTS

With an increase in head mass, there is a decrease in the linear and angular head acceleration. With an increase in ball size, for the same head mass, there is an increase in the contact time between the head and the ball. Changing ball inflation pressure has little effect on the impact characteristics. Infinite neck stiffness decreased linear and angular head acceleration and HIC.

CONCLUSION

Head mass and ball size have an effect on linear and angular head acceleration and contact time, respectively, whereas ball inflation pressure has a minimal effect on the impact characteristics. These results indicate that children should be restricted to using the appropriate ball for their age. Smaller head size within an age group is an underemphasized though important identifier of a player's injury risk.

Clinical perspectives regarding eccentric muscle injury

Muscle strain injuries occur to predictable muscles at consistent locations during expected sporting maneuvers when a muscle is stretched and then activated, particularly during high intensity bursts of activity. More than 30% of the injuries seen in the clinician's office are injuries to skeletal muscle. The typical location of the injury is just proximal to the distal muscle tendon junction regardless of strain rate or architecture of the muscle. After the injury, the muscle is weaker, continues to weaken, then recovers during the next week. An inflammatory response is seen in the following 1 to 2 days. By the seventh day, fibrous tissue replaces the inflammatory reaction and a scar forms. When a muscle is stretched, its tension still is reduced making the healing muscle more susceptible to a repeat injury. Viscoelastic properties of muscle also can help explain how muscle can be protected against strain injury. A 1 degree C increase in muscle temperature (warm-up) increases the muscle length to failure and a fatigued muscle is more susceptible to strain injury. It probably is impossible to prevent muscle strain injury; however, preventive measures can make muscle more resistant to these stretch-induced injuries.

Kinematic instep kicking differences between elite female and male soccer players

The rapid rise in female participation in soccer worldwide has not been followed by a corresponding increase in the number of studies biomechanically that target female kicking patterns to determine if differences exist between males and females. The objectives of this study were to examine kinematic instep kicking differences between elite female and male soccer players in dominant and nondominant limbs. Eight elite soccer players, six females and two males, volunteered as subjects in the study. Subjects took a two-step angled approach of 45-60 degrees to a stationary soccer ball positioned between two force platforms and kicked the ball with the instep portion of the foot as hard as possible into netting which was draped from the ceiling. Ball velocity was the dependent variable. We evaluated six additional variables that have previously been shown to be important predictors of instep kicking ball speed. The males generally kicked the ball faster than the females and displayed greater kinematic variables, including maximum toe velocity, ball contact ball velocity, mean toe velocity, mean toe acceleration, and ankle velocity at ball contact, all of which contributed to faster ball speed. There was one exception. One of the elite females kicked faster than the two elite males and demonstrated higher or similar kinematic patterns when compared with the males. Our conclusions were that females do not instep kick the ball as fast as males, but there are exceptions, as our data demonstrates.

A comparison of knee kinetics between male and female recreational athletes in stop-jump tasks

We compared the knee kinetics of 10 male and 10 female recreational athletes (aged 19 to 25 years) performing forward, vertical, and backward stop-jump tasks. Three-dimensional videography and force plate data were used to record the subjects' performance of the three stop-jump tasks, and an inverse dynamic procedure was used to estimate the knee joint resultant forces and moments. Women exhibited greater proximal anterior shear force than did men during the landing phase. All subjects exhibited greater proximal tibia anterior shear force during the landing phase of the backward stop-jump task than during the other two stop-jump tasks. Women also exhibited greater knee extension and valgus moments than did men during the landing phase of each stop-jump task. Men exhibited greater proximal tibia anterior shear force than did women during the takeoff phase of vertical and backward stop-jump tasks. These results indicate that female recreational athletes may have altered motor control strategies that result in knee positions in which anterior cruciate ligament injuries may occur. The landing phase was more stressful for the anterior cruciate ligament of both women and men than the takeoff phase in all stop-jump tasks. Technical training for female athletes may need to be focused on reducing the peak proximal tibia anterior shear force in stop-jump tasks. Further studies are needed to determine the factors associated with the increased peak proximal tibia anterior shear force in female recreational athletes.

No evidence of impaired neurocognitive performance in collegiate soccer players

A high incidence of cerebral concussion has been reported among soccer players. We studied whether long-term or chronic neuropsychological dysfunction was present in collegiate soccer players. Two hundred forty subjects from a National Collegiate Athletic Association division I institution were stratified into three groups: soccer athletes (91), nonsoccer athletes (96 women's field hockey, women's lacrosse, and baseball players), and controls (53 college students). Subjects completed a concussion history questionnaire and underwent preseason baseline neuropsychological testing before the start of either the freshman or sophomore year. Data were collected on the results of six neuropsychological tests and from a concussion history questionnaire for number of previous concussions, Scholastic Aptitude Test results, and exposure to soccer and heading. Despite an average of 15.3 seasons of soccer exposure and a higher prevalence of previous concussions, the soccer athletes did not demonstrate impaired neurocognitive function or scholastic aptitude when compared with the nonsoccer athletes or the student nonathletes. Additionally, there was no significant relationship between a history of soccer-related concussion and either neurocognitive performance or scholastic aptitude. Neither participation in soccer nor a history of soccer-related concussions was associated with impaired performance of neurocognitive function in high-level United States soccer players.

Heading and head injuries in soccer

In the world of sports, soccer is unique because of the purposeful use of the unprotected head for controlling and advancing the ball. This skill obviously places the player at risk of head injury and the game does carry some risk. Head injury can be a result of contact of the head with another head (or other body parts), ground, goal post, other unknown objects or even the ball. Such impacts can lead to contusions, fractures, eye injuries, concussions or even, in rare cases, death. Coaches, players, parents and physicians are rightly concerned about the risk of head injury in soccer. Current research shows that selected soccer players have some degree of cognitive dysfunction. It is important to determine the reasons behind such deficits. Purposeful heading has been blamed, but a closer look at the studies that focus on heading has revealed methodological concerns that question the validity of blaming purposeful heading of the ball. The player's history and age (did they play when the ball was leather and could absorb significant amounts of water), alcohol intake, drug intake, learning disabilities, concussion definition and control group use/composition are all factors that cloud the ability to blame purposeful heading. What does seem clear is that a player's history of concussive episodes is a more likely explanation for cognitive deficits. While it is likely that the subconcussive impact of purposeful heading is a doubtful factor in the noted deficits, it is unknown whether multiple subconcussive impacts might have some lingering effects. In addition, it is unknown whether the noted deficits have any affect on daily life. Proper instruction in the technique is critical because if the ball contacts an unprepared head (as in accidental head-ball contacts), the potential for serious injury is possible. To further our understanding of the relationship of heading, head injury and cognitive deficits, we need to: learn more about the actual impact of a ball on the head, verify the exposure to heading at all ages and competitive levels, determine stable estimates of concussive injury rates across the soccer spectrum, conduct prospective longitudinal studies on soccer players focusing on exposure, injury and cognition, and determine the minimum safe age to begin instruction on the skill of heading. Only then will we be able to speak with some authority on the issue of heading and head injuries in soccer.

Valgus laxity of the ulnar collateral ligament of the elbow in collegiate athletes

In this investigation, we determined the patterns of valgus laxity and acquired valgus laxity of the ulnar collateral ligament in the elbows of collegiate athletes involved in overhead and nonoverhead sports. Acquired valgus laxity of the elbow is defined as the differential amount of stress valgus opening between the dominant and nondominant elbows. Forty-eight asymptomatic male athletes involved in sports that require overhead arm movements (baseball, tennis, and swimming) and 88 asymptomatic male athletes involved in nonoverhead sports (track, lacrosse, fencing, and wrestling) underwent fluoroscan examination of both their elbows with (13 daN) and without (0 N) valgus stress. There were no statistically significant differences in the amount of valgus stress opening or in acquired valgus laxity between the two groups. In fact, 25% (34 of 136) of the athletes showed an acquired valgus laxity of more than 0.5 mm, and 51.5% (70 of 136) had an acquired valgus laxity that was actually negative. There was also no correlation between the number of years played and acquired valgus laxity. Our results show that acquired valgus laxity does not exist in asymptomatic athletes involved in overhead sports, and there is no threshold value of measurement indicative of acquired valgus laxity.

A comparison of knee joint motion patterns between men and women in selected athletic tasks

BACKGROUND

Women have higher non-contact anterior cruciate ligament injury rate than men do in sport activities. Non-contact anterior cruciate ligament injuries frequently occur in sports requiring cutting tasks. Alternated motor control strategies have identified as a potential risk factor for the non-contact anterior cruciate ligament injuries. The purpose of this study was to compare the patterns of knee kinematics and electromyographic activities in running, side-cutting, and cross-cutting between men and women recreational athletes.

METHODS

Three-dimensional kinematic data of the knee and electromyographic data of selected muscles across the knee joint were collected for 11 men and 9 women recreational athletes in running, side-cutting, and cross-cutting. Regression analyses with dummy variables for comparison of knee motion patterns between men and women.

RESULTS

Women tend to have less knee flexion angles, more knee valgus angles, greater quadriceps activation, and lower hamstring activation in comparison to men during the stance phase of each of the three athletic tasks. Literatures suggest these alternated knee motion patterns of women tend to increase the load on the anterior cruciate ligament.

CONCLUSION

Women on average may have certain motor control strategies that may alter their knee motion patterns. Women's altered knee motion patterns may tend to increase the load on the anterior cruciate ligament in the selected athletic tasks, which may contribute to the increased anterior cruciate ligament injury rate among women.

RELEVANCE

Non-contact anterior cruciate ligament injuries frequently occur in sports. Altered motor control strategies and lower extremity motion patterns are likely to play an important role in non-contact anterior cruciate ligament injuries. Non-contact anterior cruciate ligament injuries may be prevented by correcting altered motor control strategies and associated lower extremity motion patterns through certain training programs.

Heading in Soccer: Integral Skill or Grounds for Cognitive Dysfunction?

OBJECTIVE: To critically review the literature concerning the effect of purposeful heading of a soccer ball and head injuries on reported cognitive dysfunction in soccer players. DATA SOURCES: We searched MEDLINE (1965-2001) and SPORTDiscus (1975-2001) for refereed articles in English combining key words for soccer (eg, soccer, football, association football ) with key words for head injuries (eg, concussion, head injury). In addition, literature on cognition and head injuries was obtained. We reviewed reference lists of current literature for pertinent citations that might not have been found in the search procedures. DATA SYNTHESIS: The fact that soccer players (and other athletes) have selected cognitive deficits is not questioned, and the popular press is quick to publicize results of questionable validity. The reasons for such deficits are many. Much of the early data implied that heading was the culprit; however, subsequent research has suggested that other interpretations and factors may be potential explanations for these deficits. The current focus is on concussions, a known factor in cognitive dysfunction and a common head injury in soccer. CONCLUSIONS/RECOMMENDATIONS: It is difficult to blame purposeful heading for the reported cognitive deficits when actual heading exposure and details of the nature of head-ball impact are unknown. Concussions are a common head injury in soccer (mostly from head-head or head-ground impact) and a factor in cognitive deficits and are probably the mechanism of the reported dysfunction.

Shoulder muscle activation during aquatic and dry land exercises in nonimpaired subjects

STUDY DESIGN

Randomized, single blind experimental design using electromyography to measure shoulder muscle activation in nonimpaired subjects.

OBJECTIVES

To compare the muscle activation of rotator cuff and shoulder synergists during rehabilitation exercises performed in water or on dry land.

BACKGROUND

Early motion is critical to restoration of normal shoulder function. Aquatic therapy has been promoted as a method for increasing range of motion while minimizing stress on the shoulder.

METHODS AND MEASURES

The integrated electromyography amplitude of 6 muscles of the shoulder girdle was examined on the nondominant shoulders of 6 subjects (supraspinatus, infraspinatus, and subscapularis, anterior, middle, and posterior deltoids). Each subject performed elevation (0 degree to 90 degrees) in the scapular plane with neutral rotation on land and in water at 3 different speeds of elevation (30 degrees/s, 45 degrees/s, and 90 degrees/s). The mean percentage of the maximal voluntary contraction was determined for each of the 3 test speeds on land and in water. Comparisons between water and dry land were made with a repeated measures analysis of variance.

RESULTS

For all 6 muscles tested, muscle activation during the 30 degrees/s test speed and all muscles tested at the 45 degrees/s test speed was significantly less when performed in water versus when performed on land. For example, electromyography activation of the supraspinatus muscle was 16.68% of a maximal voluntary contraction when elevation at was performed at 30 degrees/s on dry land versus 3.93% when performed in water.

CONCLUSION

These data suggest that shoulder elevation in the water at slower speeds resulted in a significantly lower activation of the rotator cuff and synergistic muscles. This decreased muscle activation during aquatic physical therapy allows for earlier active motion in the postoperative period without compromising patient safety.

The anterior cruciate ligament enigma. Injury mechanisms and prevention

The reasons for the higher frequency of anterior cruciate ligament injuries in women are largely conjecture. These injuries may result from direct contact or, more frequently, from no direct contact to the knee during activities that most athletes consider routine to their sport. This implies that there are intrinsic factors that lead to anterior cruciate ligament rupture. For the anterior cruciate ligament to tear, there must be excess anterior tibial translation or rotation of the femur on the tibia. In the former case, the tibia can move anteriorly during quadriceps activation that is not counterbalanced by hamstring activation. Patients describe their injury as occurring when landing, stopping, or when planting to change directions. The knee typically was near full extension. Mechanically, the angle of the patellar tendon and tibial shaft increases as the knee approaches full extension. This gives a mechanical advantage to the quadriceps. During cutting maneuvers, athletes tend to cut with a knee near extension (0 degree-20 degrees) when the quadriceps are active and the hamstrings are neither very active nor at a knee flexion angle that offers much of a mechanical advantage. In performing cutting and landing maneuvers, women tend to perform the activities more erect; that is, with their knee and hips closer to extension. One possible factor to help reduce the frequency of anterior cruciate ligament injuries in women may be in proper instruction for performing cutting and landing maneuvers which will lower their center of gravity thereby denying the quadriceps the opportunity to shift the tibia anteriorly.

Electromyographic analysis and energy expenditure of harness supported treadmill walking: implications for knee rehabilitation

Harness supported treadmill ambulation has been recommended for patients as a way of decreasing loads on the healing tissues, conserving energy and reducing pain. We quantified muscle activation levels around the knee and metabolic responses during harness supported treadmill walking. Ten healthy recreational athletes (age 28.9+/-7.8 years) walked on the treadmill (1.34 m/s) for 5 min each at full weight bearing (FWB), 20 and 40% body weight support (BWS). Electromyography (EMG) was monitored for the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, medial hamstrings and the gastrocnemius. Oxygen consumption was collected by open circuit spirometry and the heart rate was collected by a heartwatch. A statistically significant reduction in EMG was found at 40% BWS for the quadriceps. Oxygen consumption decreased by 6% (20% BWS) and by 12% (40% BWS) from FWB (P<0.05). The heart rate was unchanged. BWS ambulation reduces energy cost, but does not significantly alter muscle activation, except for the quadriceps at 40% BWS.

Fluid and electrolyte replacement in soccer

Soccer can be played under a wide range of environmental conditions. Traditionally, fluid replacement is limited during the game, but in reality, there are numerous opportunities for fluid ingestion during a match. Many of the recommendations on fluid replenishment have been directed at continuous exercise, and application of those suggestions can be applied to an intermittent sport like soccer.

The effects of aging and training on skeletal muscle

Aging results in a gradual loss of muscle function, and there are predictable age-related alterations in skeletal muscle function. The typical adult will lose muscle mass with age; the loss varies according to sex and the level of muscle activity. At the cellular level, muscles loose both cross-sectional area and fiber numbers, with type II muscle fibers being the most affected by aging. Some denervation of fibers may occur. The combination of these factors leads to an increased percentage of type 1 fibers in older adults. Metabolically, the glycolytic enzymes seem to be little affected by aging, but the aerobic enzymes appear to decline with age. Aged skeletal muscle produces less force and there is a general "slowing" of the mechanical characteristics of muscle. However, neither reduced muscle demand nor the subsequent loss of function is inevitable with aging. These losses can be minimized or even reversed with training. Endurance training can improve the aerobic capacity of muscle, and resistance training can improve central nervous system recruitment of muscle and increase muscle mass. Therefore, physical activity throughout life is encouraged to prevent much of the age-related impact on skeletal muscle.

Concussion history in elite male and female soccer players

A unique feature of soccer is the purposeful use of the head for controlling, passing, and shooting a soccer ball. Some concern has been expressed in the literature on the cumulative effects of heading on soccer players. Certain neurophysiologic and neuropsychologic changes have been reported in current or retired players, with heading being blamed. A major factor that could influence some of the findings is a player's history of concussive episodes, which are known to influence brain function. These episodes can occur during aspects of the game other than heading. We interviewed all male and female soccer players (N = 137, average age = 20.5 years) who competed at the U.S. Olympic Sports Festival in 1993. The mechanisms of injuries, frequency, and sequelae were determined. There were 74 concussions in 39 male players (grade I = 50) and 28 concussions in 23 female players (grade I = 19). For the men, 48 of the 74 episodes were from collisions with another player. For the women, 20 of 28 were from such collisions. Headaches, being "dazed," and dizziness were the most common symptoms reported. Based on concussion history, the odds are 50% that a man, and 22% that a woman, will sustain a concussion within a 10-year period. The data indicate that concussions from player-to-player contact are a frequent hazard in soccer. Head injuries incurred this way may be more of an influence for published findings of physiologic and psychologic deficiencies than routine heading of the soccer ball.

Concussion incidence in elite college soccer players

A unique aspect of soccer is the use of the head for directing the ball. The potential for resultant head injuries has been the focus of discussions worldwide. Prior work has attributed neuropsychologic deficits to the cumulative effects of heading, without evaluating concussion rates in soccer players. We prospectively studied the seven men's and eight women's varsity soccer teams in the Atlantic Coast Conference during two seasons to document concussion incidence. The 29 concussions diagnosed over the 2 years in 26 athletes, 17 (59%) concussions in men and 12 (41%) in women, resulted from contact with an opponent's head (8, 28%), elbow (4, 14%), knee (1, 3%), or foot (1, 3%); the ball (7, 24%); the ground (3, 10%); concrete sidelines (1, 3%); goalpost (1, 3%); or a combination of objects (3, 10%). Twenty concussions (69%) occurred in games; none resulted from intentional heading of the ball. The basic incidence was 0.96 concussions per team per season. The overall incidence was 0.6 per 1000 athlete-exposures for men, and 0.4 per 1000 athlete-exposures for women. By concussion grade, there were 21 (72%) grade 1, 8 (28%) grade 2, and no grade 3 concussions. These findings suggest that concussions are more common in soccer than anticipated and that acute head injuries may have potential for long-term neuropsychologic changes.

Function and biomechanics of tendons

Tendon is a highly organized connective tissue joining muscle to bone, capable of resisting high tensile forces while transmitting forces from muscle to bone. The dense, regularly arranged collagenous tissue is made up of fibers, cells of various shapes and ground substance. The mechanical and physiological characteristics of collagen (nearly 85% of the dry weight of tendon) dictate the qualities of tendon. In addition, tendon is flexible so that it can bend at joints, as well as acting as a damping tissue to absorb shock and limit potential damage to muscle (1). Tendon also shows a degree of extensibility. If the strain used to stretch a tendon could be recovered, a beneficial elastic effect would be achieved. Muscles lengthen and shorten in a cyclical manner. During the lengthening period, elastic energy can be stored and used as elastic recoil. For example, the Achilles tendon is stretched late in the stance phase as the triceps surae muscles contract and the ankle dorsiflexes. Prior to plantarflexion, muscle activation ceases and stored energy helps to initiate planter flexion.

Technical considerations for electromyographic research on the shoulder

This study compared 2 methods of indwelling bipolar electrode insertion. One method used a single needle for the insertion of both wire leads, and the second method used 2 needles for the independent insertion of both leads at a specified interdetection distance. Simultaneous electromyography recordings from the 2 different electrode configurations were made during the activation of nonfatigued supraspinatus and infraspinatus muscles from 10 healthy subjects. Subjects performed 6 different isometric contractions at 3 different levels of force (100%, 60%, and 30% effort). In this study, the bipolar electrode configuration using 2 hypodermic needles for placement of the 2 leads produced superior electromyography recordings than did the configuration using a single needle for the wire lead insertion. The separated bipolar electrodes produced a significantly higher amplitude electromyography signal with less intersubject variability and greater partial correlation with force. This study suggests an alternative method of bipolar wire electrode placement that results in improved signal characteristics and decreased variability of signal acquisition. A standardization of wire electromyography examination of the shoulder that improves signal characteristics and acquisition ultimately will lead to more accurate results with greater clinical use and validity.

A 20-yr longitudinal study of Olympic oarsmen

Nine 1972 silver-medalist oarsmen were studied before the Olympic Games and 10 and 20 yr later. Peak power, metabolic responses, and heart rate were recorded during rowing ergometry; blood lactate was measured following exercise. The skinfold equation yielded percent body fat. The average change (multiple analysis of variance) among measurements from 1972 to 1992 was 37.5 +/- 3% (P < 0.01). Average changes between 1972 and 1982 and between 1982 and 1992 were similar, 17 and 18%, respectively (P < 0.01). The most significant change between 1972 and 1992 was decreased peak blood lactate (106%). Decreases in peak power, VE, and VO2 (ml.kg-1.min-1) were all similar, approximately 40%, and were significant. Body fat increased (from 12.3 to 15.6%), and absolute VO2 and relative VO2 (lean body mass) decreased 30% (P < 0.01). Only body weight, heart rate, and O2 pulse showed smaller changes, but these changes were still significant (P < 0.05). Relative peak VO2 decreased from 65.5 to 46.8 ml.kg-1.min-1 from 1972 to 1992 and at a rate of 10%.decade-1. The most significant changes between 1972 and 1982 were increases in percent body fat (from 12.3 to 16.3%) and decreases in VO2 values (P < 0.01). There was less change in body fat between 1982 and 1992, but lactate significantly decreased (P < 0.01), as did peak power and absolute and relative VO2 and VE. Although fitness levels in former elite oarsmen decreased each decade, these declines were somewhat arrested by regular aerobic training. Body fat increased and metabolic capacity decreased rapidly during the first decade, whereas anaerobic capacity decreased more significantly in the second decade. Anaerobic capacity diminished at a significantly greater rate than aerobic capacity, probably as a result of the aging process and emphasis on aerobic training in post-competitive years.

Optimal normalization tests for shoulder muscle activation: an electromyographic study

To accurately compare electromyographic data from different muscles and different subjects, it is necessary to normalize the integrated data obtained from each muscle. The purpose of this study was to identify the manual muscle testing positions that elicit maximal neural activation (integrated electromyography) of three rotator cuff muscles (supraspinatus, infraspinatus, and subscapularis) and five shoulder synergists (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids). The electromyographic activity of these eight muscles was examined in the nondominant shoulders of nine subjects. Indwelling wire electrodes (supraspinatus, infraspinatus, and subscapularis) and surface adhesive electrodes (pectoralis major, latissimus dorsi, and anterior, middle, and posterior deltoids) were placed. Each subject performed a series of 27 isometric contractions, and optimal tests (maximal neural activation) were identified for each muscle. Four tests were identified that resulted in the maximal neural activation of all eight shoulder muscles: 90 degrees of scapular elevation with -45 degrees of humeral rotation for the supraspinatus, anterior deltoid, and middle deltoid: external rotation at 90 degrees of scapular elevation and -45 degrees of humeral rotation for the infraspinatus and posterior deltoid: internal rotation at 90 degrees of scapular elevation and neutral humeral rotation for the subscapularis and latissimus dorsi: and internal rotation at 0 degree of elevation and neutral rotation for the pectoralis major. These results identify four standard testing positions that will provide reference values for normalization of maximal voluntary contraction for the eight muscles of the shoulder examined in this study. Standardization of these test positions offers normalization guidelines that can be used in future dynamic electromyography studies of the shoulder.