Kinematics and electromyography of landing preparation in vertical stop-jump: risks for noncontact anterior cruciate ligament injury

BACKGROUND: Biomechanical analysis of stop-jump tasks has demonstrated gender differences during landing and a potential increase in risk of noncontact anterior cruciate ligament injury for female athletes. Analysis of landing preparation could advance our understanding of neuromuscular control in movement patterns and be applied to the development of prevention strategies for noncontact anterior cruciate ligament injury. HYPOTHESIS: There are differences in the lower extremity joint angles and electromyography of male and female recreational athletes during the landing preparation of a stop-jump task. STUDY DESIGN: Controlled laboratory study. METHODS: Three-dimensional videographic and electromyographic data were collected for 36 recreational athletes (17 men and 19 women) performing vertical stop-jump tasks. Knee and hip angular motion patterns were determined during the flight phase before landing. RESULTS: Knee and hip motion patterns and quadriceps and hamstring activation patterns exhibited significant gender differences. Female subjects generally exhibited decreased knee flexion (P = .001), hip flexion (P = .001), hip abduction (P = .001), and hip external rotation (P = .03); increased knee internal rotation (P = .001); and increased quadriceps activation (P = .001) compared with male subjects. Female subjects also exhibited increased hamstring activation before landing but a trend of decreased hamstring activation after landing compared with male subjects (P = .001). CONCLUSION: Lower extremity motion patterns during landing of the stop-jump task are preprogrammed before landing. Female subjects prepared for landing with decreased hip and knee flexion at landing, increased quadriceps activation, and decreased hamstring activation, which may result in increased anterior cruciate ligament loading during the landing of the stop-jump task and the risk for noncontact ACL injury.     

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.     

Jump landing strategies in male and female college athletes and the implications of such strategies for anterior cruciate ligament injury

BACKGROUND: Female athletes are more likely than male athletes to injure the anterior cruciate ligament. Causes of this increased injury incidence in female athletes remain unclear, despite numerous investigations. HYPOTHESIS: Female athletes will exhibit lower hamstring muscle activation and smaller knee flexion angles than male athletes during jump landings, especially when the knee muscles are fatigued. STUDY DESIGN: Controlled laboratory study. METHODS: Eight female and six male varsity college basketball athletes with no history of knee ligament injury performed jump landings on the dominant leg from a maximum height jump and from 25.4 cm and 50.8 cm high platforms under nonfatigued and fatigued conditions. Knee joint angle and surface electromyographic signals from the quadriceps, hamstring, and gastrocnemius muscles were recorded. RESULTS: Women landed with greater knee flexion angles and greater knee flexion accelerations than men. Knee muscle activation patterns were generally similar in men and women. CONCLUSION: As compared with male college basketball players, female college basketball players did not exhibit altered knee muscle coordination characteristics that would predispose them to anterior cruciate ligament injury when landing from jumps. This conclusion is made within the parameters of this study and based on the observation that hamstring muscle activation was similar for both groups. The greater knee flexion we observed in the female subjects would be expected to decrease their risk of injury. CLINICAL RELEVANCE: Factors other than those evaluated in this study need to be considered when attempting to determine the reasons underlying the increased incidence of anterior cruciate ligament injuries consistently observed in elite female athletes.     

Non-contact ACL injuries in female athletes: an International Olympic Committee current concepts statement

The incidence of anterior cruciate ligament (ACL) injury remains high in young athletes. Because female athletes have a much higher incidence of ACL injuries in sports such as basketball and team handball than male athletes, the IOC Medical Commission invited a multidisciplinary group of ACL expert clinicians and scientists to (1) review current evidence including data from the new Scandinavian ACL registries; (2) critically evaluate high-quality studies of injury mechanics; (3) consider the key elements of successful prevention programmes; (4) summarise clinical management including surgery and conservative management; and (5) identify areas for further research. Risk factors for female athletes suffering ACL injury include: (1) being in the preovulatory phase of the menstrual cycle compared with the postovulatory phase; (2) having decreased intercondylar notch width on plain radiography; and (3) developing increased knee abduction moment (a valgus intersegmental torque) during impact on landing. Well-designed injury prevention programmes reduce the risk of ACL for athletes, particularly women. These programmes attempt to alter dynamic loading of the tibiofemoral joint through neuromuscular and proprioceptive training. They emphasise proper landing and cutting techniques. This includes landing softly on the forefoot and rolling back to the rearfoot, engaging knee and hip flexion and, where possible, landing on two feet. Players are trained to avoid excessive dynamic valgus of the knee and to focus on the "knee over toe position" when cutting.     

Valgus knee motion during landing in high school female and male basketball players

PURPOSE: The purpose of this study was to utilize three-dimensional kinematic (motion) analysis to determine whether gender differences existed in knee valgus kinematics in high school basketball athletes when performing a landing maneuver. The hypothesis of this study was that female athletes would demonstrate greater valgus knee motion (ligament dominance) and greater side-to-side (leg dominance) differences in valgus knee angle at landing. These differences in valgus knee motion may be indicative of decreased dynamic knee joint control in female athletes. METHODS: Eighty-one high school basketball players, 47 female and 34 male, volunteered to participate in this study. Valgus knee motion and varus-valgus angles during a drop vertical jump (DVJ) were calculated for each subject. The DVJ maneuver consisted of dropping off of a box, landing and immediately performing a maximum vertical jump. The first landing phase was used for the analysis. RESULTS: Female athletes landed with greater total valgus knee motion and a greater maximum valgus knee angle than male athletes. Female athletes had significant differences between their dominant and nondominant side in maximum valgus knee angle. CONCLUSION: The absence of dynamic knee joint stability may be responsible for increased rates of knee injury in females but is not normally measured in athletes before participation. No method for accurate and practical screening and identification of athletes at increased risk of ACL injury is currently available to target those individuals that would benefit from neuromuscular training before sports participation. Prevention of female ACL injury from five times to equal the rate of males would allow tens of thousands of young females to avoid the potentially devastating effects of ACL injury on their athletic careers.     

Knee function after anterior cruciate ligament injury in elite collegiate athletes

BACKGROUND: Anterior cruciate ligament injuries are common in athletes, but there are few studies of long-term outcomes. HYPOTHESIS: Long-term knee function of anterior cruciate ligament-injured athletes is inferior to that of their uninjured teammates. STUDY DESIGN: Retrospective cohort study. METHODS: Thirty-three Division I-A athletes who had sustained an anterior cruciate ligament injury during their college career completed a series of questionnaires that assessed knee function and quality of life 2 to 14 years after injury. Their responses were compared with those of a matched cohort of their uninjured teammates. RESULTS: There were no differences in the mean Tegner scores, modified Lysholm scores, or in the scores of the SF-36 between groups. Sixteen anterior cruciate ligament-injured athletes scored A or B in the subjective portion of the International Knee Documentation Committee score and 17 scored C or D, whereas 24 control subjects scored A or B and 9 scored C or D, a statistically significant difference between groups. Five injured and 14 control athletes had participated at a professional or national team level after college. CONCLUSIONS: Quality of life of elite collegiate athletes who sustained an anterior cruciate ligament injury was not significantly different from that of their uninjured teammates, but knee function differed between groups.     

Anterior cruciate ligament injuries in female athletes: Part 2, a meta-analysis of neuromuscular interventions aimed at injury prevention

Female athletes have a 4 to 6 times higher incidence of anterior cruciate ligament injury than do male athletes participating in the same landing and pivoting sports. This greater risk of anterior cruciate ligament injury, coupled with a geometric increase in participation (doubling each decade), has led to a significant rise in anterior cruciate ligament injuries in female athletes. The gender gap in anterior cruciate ligament injury, combined with evidence that the underpinnings of this serious health problem are neuromuscular in nature, leads to the development of neuromuscular interventions designed to prevent injury. A systematic review of the published literature yielded 6 published interventions targeted toward anterior cruciate ligament injury prevention in female athletes. Four of 6 significantly reduced knee injury incidence, and 3 of 6 significantly reduced anterior cruciate ligament injury incidence in female athletes. A meta-analysis of these 6 studies demonstrates a significant effect of neuromuscular training programs on anterior cruciate ligament injury incidence in female athletes (test for overall effect, Z = 4.31, P < .0001). Examination of the similarities and differences between the training regimens gives insight into the development of more effective and efficient interventions. The purpose of this "Current Concepts" review is to highlight the relative effectiveness of these interventions in reducing anterior cruciate ligament injury rates and to evaluate the common training components between the training studies. In addition, the level of rigor of these interventions, the costs and the difficulty of implementation, the compliance with these interventions, and the performance benefits are discussed. This review summarizes conclusions based on evidence from the common components of the various interventions to discuss their potential to reduce anterior cruciate ligament injury risk and assess their potential for combined use in more effective and efficient intervention protocols.     

A review of electromyographic activation levels, timing differences, and increased anterior cruciate ligament injury incidence in female athletes

Deficits in dynamic neuromuscular control of the knee may contribute to the higher incidence of anterior cruciate ligament (ACL) injury in female athletes. There is evidence that neuromuscular training alters muscle firing patterns, as it decreases landing forces, improves balance, and reduces ACL injury incidence in female athletes. The purpose of this review is to summarise the evidence for altered muscular activation and timing relative to ACL injury risk in female athletes.     

Gender differences in the kinematics of unanticipated cutting in young athletes

PURPOSE: Anterior cruciate ligament (ACL) injuries occur at a greater rate in adolescent females compared with males who participate in the same pivoting and jumping sports. The purpose of this study was to compare knee and ankle joint angles between males and females during an unanticipated cutting maneuver. The hypotheses were that female athletes would display increased knee abduction, increased ankle eversion and decreased knee flexion during the unanticipated cutting maneuver compared with males. METHODS: Fifty-four male and 72 adolescent female middle and high school basketball players volunteered to participate in this study. Knee and ankle kinematics were calculated using three-dimensional motion analysis during a jump-stop unanticipated cut (JSUC) maneuver. RESULTS: Females exhibited greater knee abduction (valgus) angles compared with males. Gender differences were also found in maximum ankle eversion and maximum inversion during stance phase. No differences were found in knee flexion angles at initial contact or maximum. CONCLUSION: Gender differences in knee and ankle kinematics in the frontal plane during cutting may help explain the gender differences in ACL injury rates. Implementation of dynamic neuromuscular training in young athletes with a focus on frontal plane motion may help prevent ACL injuries and their long-term debilitating effects.     

Maturation leads to gender differences in landing force and vertical jump performance: a longitudinal study

BACKGROUND: Female athletes have increased risk of anterior cruciate ligament rupture after the onset of puberty. HYPOTHESES: Male athletes would demonstrate a longitudinal increase in vertical jump height compared with female athletes. There would be longitudinal gender differences in ground-reaction forces and loading rates. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: Sixteen female and 17 male adolescent athletes were evaluated for 2 consecutive years. Subjects were included if they were classified as pubertal during the first year of testing and postpubertal during the second year. As subjects performed a drop vertical jump, ground-reaction force, and vertical jump height were measured. Data analysis consisted of a mixed design analysis of variance with post hoc analysis (paired t tests). RESULTS: The male athletes demonstrated increased vertical jump height with maturation (P < .001); female athletes did not. Boys significantly reduced their landing ground-reaction force (P = .005), whereas girls did not. Takeoff force decreased in girls (P = .003) but not in boys. Both boys and girls had decreased loading rates with maturation (P < .001); however, girls had higher loading rates than did boys at both stages of maturation (P = .037). CONCLUSION: Male athletes demonstrated a neuromuscular spurt as evidenced by increased vertical jump height and increased ability to attenuate landing force. The absence of similar adaptations in female athletes may be related to the increased risk of anterior cruciate ligament injury.     

Sport-dependent variations in arm position during single-limb landing influence knee loading: implications for anterior cruciate ligament injury

BACKGROUND: Increased valgus loading at the knee has been previously identified as a possible risk factor for noncontact anterior cruciate ligament injuries, which are common in sports. Arm position variation may affect risk of injury by altering valgus knee loading. HYPOTHESIS: Sport-dependent variations in arm position increase valgus loading of the knee during run-to-cut maneuvers. STUDY DESIGN: Controlled laboratory study. METHODS: Eleven subjects performed a sidestep cutting maneuver, first with no arm constraints and then with 3 sports-related arm positions in random order (holding a lacrosse stick, holding a football on the plant side, and holding a football on the cut side). The analysis focused on the knee valgus moment relative to the arm positions during the landing phase of the activity. RESULTS: Arm position significantly influenced the valgus moment with an increase in the lacrosse trials and in the plant-side football trials but not in the cut-side football trials (alpha = .05). CONCLUSIONS: Constraining the plant-side arm results in increased valgus loading at the knee during run-to-cut maneuvers, which suggests the possibility of greater risk of anterior cruciate ligament injury during these conditions. CLINICAL RELEVANCE: These results suggest that training methods that consider arm position as a risk factor could help reduce the risk of anterior cruciate ligament noncontact injury.     

Two-dimensional knee valgus displacement as a predictor of patellofemoral pain in adolescent females

Patellofemoral pain (PFP) is a prevalent lower limb musculo-skeletal injury in adolescent females. Female athletes with PFP display increased frontal plane knee joint motion in comparison to control subjects. The current investigation aimed to determine prospectively whether two-dimensional knee valgus displacement during landing could predict the risk of developing PFP. Seventy-six injury-free adolescent female athletes (age = 12.9 ±0.35 years) participated. At baseline participants performed three drop vertical jump trials from a 31-cm box. A standard video camera was used to record frontal plane knee joint kinematics. Over the 24-month follow-up, eight participants developed PFP, as diagnosed by a Chartered Physiotherapist. Knee valgus displacement was significantly increased in those who developed PFP compared to those who did not (mean difference = 7.79°; P = 0.002; partial eta squared = 0.07). Knee valgus displacement ≥10.6° predicted PFP with a sensitivity of 0.75 and specificity of 0.85. The associated positive likelihood ratio was 5. These results have clinical utility suggesting that two-dimensional analysis could be implemented to screen for increased risk of PFP in adolescent female athletes.     

The drop-jump screening test: difference in lower limb control by gender and effect of neuromuscular training in female athletes

BACKGROUND: A valgus lower limb alignment has been noted during noncontact anterior cruciate ligament injuries. A video drop-jump test can indicate an athlete's ability to control lower limb axial alignment in the coronal plane. HYPOTHESES: Female athletes have decreased knee separation distances on landing and acceleration; male athletes have a neutrally aligned lower limb position. A neuromuscular training program will significantly increase knee separation distance in female athletes. STUDY DESIGN: Cohort study; Level of evidence, 2. METHODS: The authors tested 325 female and 130 male athletes aged 11 to 19 years. The distance between the hips, knees, and ankles was measured during a drop-jump test. The separation distance between the knees and ankles was normalized by the hip separation distance. A neuromuscular training program (Sportsmetrics) was completed by 62 female athletes, and their jump-landing characteristics were reexamined. RESULTS: A marked decrease in knee separation distance was found on takeoff in 80% of female athletes and in 72% of male athletes. There was no difference between male and female athletes in the normalized knee and ankle separation distance during the landing and takeoff phases. The knee separation distance on landing was 23 +/- 9 cm in the female athletes and 22 +/- 8 cm in the male athletes. The normalized knee separation distance was 51% +/- 19% in the female athletes and 51% +/- 15% in the male athletes. After training, statistically significant increases were found in the female athletes in the knee separation distance on landing (29 +/- 8 cm, P < .0001) and in the normalized knee separation distance (68% +/- 18%, P < .0001). The trained female athletes had significantly greater knee separation distance and normalized knee separation distance than did the males (P < .0001). CONCLUSIONS: The majority of untrained female and male athletes demonstrated a valgus alignment appearance on the video test. After neuromuscular training, female athletes had improved knee separation distances and a more neutral lower limb alignment on landing and takeoff.     

Neuromuscular and hormonal factors associated with knee injuries in female athletes. Strategies for intervention

Female athletes who participate in jumping and cutting sports are 4 to 6 times more likely to sustain a serious knee injury than male athletes participating in the same sports. More than 30,000 serious knee injuries are projected to occur in female intercollegiate and high school athletics in the US each year. The majority of these injuries occur by non-contact mechanisms, most often during landing from a jump or making a lateral pivot while running. Knee instability, due possibly to decreased neuromuscular strength and coordination or increased ligamentous laxity, may underlie the increased incidence of knee injury in females. Neuromuscular training can significantly increase dynamic knee stability in female athletes. Female sex hormones (i.e. estrogen, progesterone and relaxin) fluctuate radically during the menstrual cycle and are reported to increase ligamentous laxity and decrease neuromuscular performance and, thus, are a possible cause of decreases in both passive and active knee stability in female athletes. Oral contraceptives stabilise hormone levels during the menstrual cycle and may function to either passively or actively stabilise the knee joint. The long term objective of clinicians and researchers should be to determine the factors that make women more susceptible than men to knee ligament injury and to develop treatment modalities to aid in the prevention of these injuries. The immediate objectives of this review are to examine how female and male athletes differ in neuromuscular and ligamentous control of the lower extremity. The review will examine the effects of neuromuscular training on knee stability. The effects of female hormone levels and oral contraceptives on neuromuscular control of the female athletes' knee will also be discussed.     

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.     

Exercise and Sudden Death

Abstract

High school and collegiate female athletes have a significantly increased risk of sustaining a noncontact anterior cruciate ligament injury compared with male athletes participating in the same sport. This review summarizes the current knowledge of the risk factors hypothesized to influence this problem, and the neuromuscular training programs designed to correct certain biomechanical problems noted in female athletes. The risk factors include a genetic predisposition for sustaining a knee ligament injury, environmental factors, anatomical indices, hormonal influences, and neuromuscular factors. The greatest amount of research in this area has studied differences between female and male athletes in movement patterns during athletic tasks; muscle strength, activation, and recruitment patterns; and knee joint stiffness under controlled, preplanned, and reactive conditions in the laboratory. Neuromuscular retraining programs have been developed in an attempt to reduce these differences. The successful programs teach athletes to control the upper body, trunk, and lower body position; lower the center of gravity by increasing hip and knee flexion during activities; and develop muscular strength and techniques to land with decreased ground reaction forces. In addition, athletes are taught to preposition the body and lower extremity prior to initial ground contact to obtain the position of greatest knee joint stability and stiffness. Two published programs have significantly reduced the incidence of noncontact anterior cruciate ligament injuries in female athletes participating in basketball, soccer, and volleyball. Other programs were ineffective, had a poor study design, or had an insufficient number of participants, which precluded a true reduction in the risk of this injury. In order to determine which risk factors for noncontact anterior cruciate ligament ruptures are significant, future investigations should include larger cohorts of athletes in multiple sports, analyze factors from all of the major risk categories, and follow athletes for at least one full athletic season. Future risk assessment studies should incorporate reactive tasks under more realistic sports conditions.     

Limb asymmetries in landing and jumping 2 years following anterior cruciate ligament reconstruction.

OBJECTIVE: Female athletes who are at increased risk for anterior cruciate ligament (ACL) injury demonstrate biomechanical differences between limbs during athletic tasks that may persist following anterior cruciate ligament reconstruction (ACLR). This may limit an athlete's potential for safe return to sports competition. The purpose of this study was to determine if female athletes demonstrate lower limb asymmetries in landing and takeoff force following ACLR and clearance for return to competitive sports participation. We hypothesized that females following ACLR would demonstrate side-to-side differences in landing and jumping kinetics after their return to sport (2+ years) that would not be observed in a group of healthy female controls. DESIGN: Case control study. SETTING: The Sports Medicine Biodynamics Center at Cincinnati Children's Hospital Medical Center. PATIENTS: Fourteen female athletes at a mean of 27 months following ACLR and 18 healthy female athletes participated in the study. ASSESSMENT: All subjects executed a drop vertical jump (DVJ) task onto 2 force plates. Vertical ground reaction force (VGRF) was measured during landing and takeoff and was used to calculate landing phase loading rates. A 2-way analysis of variance was used to determine differences between the involved, uninvolved, and control limbs. RESULTS: Females who had undergone ACLR demonstrated increased VGRF (P = 0.001) and loading rate (P < 0.001) on the uninvolved limb during landing when compared with the involved limb and the control group. During takeoff, the involved limb showed significantly less ability to generate force (P = 0.03) than the uninvolved limb and the control limbs. CONCLUSIONS: Female athletes who have undergone ACLR and returned to sport may continue to demonstrate biomechanical limb asymmetries 2 years or more after reconstruction that can be identified during landing.     

Deficits in neuromuscular control of the trunk predict knee injury risk: a prospective biomechanical-epidemiologic study

BACKGROUND: Female athletes are at significantly greater risk of anterior cruciate ligament (ACL) injury than male athletes in the same high-risk sports. Decreased trunk (core) neuromuscular control may compromise dynamic knee stability. HYPOTHESES: (1) Increased trunk displacement after sudden force release would be associated with increased knee injury risk; (2) coronal (lateral), not sagittal, plane displacement would be the strongest predictor of knee ligament injury; (3) logistic regression of factors related to core stability would accurately predict knee, ligament, and ACL injury risk; and (4) the predictive value of these models would differ between genders. STUDY DESIGN: Cohort study (prognosis); Level of evidence, 2. METHODS: In this study, 277 collegiate athletes (140 female and 137 male) were prospectively tested for trunk displacement after a sudden force release. Analysis of variance and multivariate logistic regression identified predictors of risk in athletes who sustained knee injury. RESULTS: Twenty-five athletes (11 female and 14 male) sustained knee injuries over a 3-year period. Trunk displacement was greater in athletes with knee, ligament, and ACL injuries than in uninjured athletes (P < .05). Lateral displacement was the strongest predictor of ligament injury (P = .009). A logistic regression model, consisting of trunk displacements, proprioception, and history of low back pain, predicted knee ligament injury with 91% sensitivity and 68% specificity (P = .001). This model predicted knee, ligament, and ACL injury risk in female athletes with 84%, 89%, and 91% accuracy, but only history of low back pain was a significant predictor of knee ligament injury risk in male athletes. CONCLUSIONS: Factors related to core stability predicted risk of athletic knee, ligament, and ACL injuries with high sensitivity and moderate specificity in female, but not male, athletes.     

Neuromuscular performance and knee laxity do not change across the menstrual cycle in female athletes

Female athletes incur anterior cruciate ligament ruptures at a rate at least twice that of male athletes. Hypothesized factors for the increased injury risk in females include biomechanical, neuromuscular, and hormonal differences between genders. A wealth of literature exists examining these potential predispositions individually, but the interactions between these factors have not been examined extensively. Our purpose was to investigate changes in neuromuscular control and laxity at the knee across the menstrual cycle of healthy females. Fourteen female collegiate athletes with normal, documented ovulatory menstrual cycles, confirmed ovulation, and no history of serious knee injury participated. The presence and timing of ovulation was determined during a screening cycle with ovulation detection kits and during an experimental cycle with collection of daily urine samples and subsequent analysis of urinary estrone-3-glucuronide (E3G) and pregnanediol-3-glucoronide (PdG), which correlate with circulating estrogen and progesterone. Each subject had measures of knee neuromuscular performance and laxity once during the mid-follicular, ovulatory, and mid-luteal stages of her menstrual cycle. The test battery included assessments of knee flexion and extension peak torque, passive knee joint position sense, and postural control in single leg stance. Knee joint laxity was measured with an arthrometer. Analyses of variance revealed that E3G and PdG levels were significantly different across the three testing sessions, but there were no significant differences in the measures of strength, joint position sense, postural control, or laxity. No significant correlations were found between changes in E3G or PdG levels and changes in the performance and laxity measures between sessions. These results suggest that neuromuscular control and knee joint laxity do not change substantially across the menstrual cycle of females despite varying estrogen and progesterone levels.