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Background: Given the relatively high risk of contralateral anterior cruciate ligament (ACL) injury in patients with ACL reconstruction (ACLR), there is a need to understand intrinsic risk factors that may contribute to contralateral injury. Hypothesis: The ACLR group would have smaller ACL volume and a narrower femoral notch width than healthy individuals after accounting for relevant anthropometrics. Study Design: Cross-sectional study. Level of Evidence: Level 3. Methods: Magnetic resonance imaging data of the left knee were obtained from uninjured (N = 11) and unilateral ACL-reconstructed (N = 10) active, female, collegiate-level recreational athletes. ACL volume was obtained from T2-weighted images. Femoral notch width and notch width index were measured from T1-weighted images. Independent-samples t tests examined differences in all measures between healthy and ACLR participants. Results: The ACLR group had a smaller notch width index (0.22 ± 0.02 vs 0.25 ± 0.01; P = 0.004; effect size, 1.41) and ACL volume (25.6 ± 4.0 vs 32.6 ± 8.2 mm3/(kg·m)−1; P = 0.025; effect size, 1.08) after normalizing by body size. Conclusion: Only after normalizing for relevant anthropometrics, the contralateral ACLR limb had smaller ACL size and narrower relative femoral notch size than healthy individuals. These findings suggest that risk factor studies of ACL size and femoral notch size should account for relevant body size when determining their association with contralateral ACL injury. Clinical Relevance: The present study shows that the method of the identified intrinsic risk factors for contralateral ACL injury could be used in future clinical screening settings.

Context Females have consistently higher anterior cruciate ligament (ACL) injury rates than males. The reasons for this disparity are not fully understood. Whereas ACL morphometric characteristics are associated with injury risk and females have a smaller absolute ACL size, comprehensive sex comparisons that adequately account for sex differences in body mass index (BMI) have been limited. Objective To investigate sex differences among in vivo ACL morphometric measures before and after controlling for femoral notch width and BMI. Design Cross-sectional study. Setting Laboratory. Patients or Other Participants Twenty recreationally active men (age = 23.2 ± 2.9 years, height = 180.4 ± 6.7 cm, mass = 84.0 ± 10.9 kg) and 20 recreationally active women (age = 21.3 ± 2.3 years, height = 166.9 ± 7.7 cm, mass = 61.9 ± 7.2 kg) participated. Main Outcome Measure(s) Structural magnetic resonance imaging sequences were performed on the left knee. Anterior cruciate ligament volume, width, and cross-sectional area measures were obtained from T2-weighted images and normalized to femoral notch width and BMI. Femoral notch width was measured from T1-weighted images. We used independent-samples t tests to examine sex differences in absolute and normalized measures. Results Men had greater absolute ACL volume (1712.2 ± 356.3 versus 1200.1 ± 337.8 mm3; t38 = −4.67, P < .001) and ACL width (8.5 ± 2.3 versus 7.0 ± 1.2 mm; t38 = −2.53, P = .02) than women. The ACL volume remained greater in men than in women after controlling for femoral notch width (89.31 ± 15.63 versus 72.42 ± 16.82 mm3/mm; t38 = −3.29, P = .002) and BMI (67.13 ± 15.40 versus 54.69 ± 16.39 mm3/kg/m2; t38 = −2.47, P = .02). Conclusions Whereas men had greater ACL volume and width than women, only ACL volume remained different when we accounted for femoral notch width and BMI. This suggests that ACL volume may be an appropriate measure of ACL anatomy in investigations of ACL morphometry and ACL injury risk that include sex comparisons.

Background: High anterior knee laxity (AKL) has been prospectively identified as a risk factor for anterior cruciate ligament (ACL) injuries. Given that ACL morphometry and structural composition have the potential to influence ligamentous strength, understanding how these factors are associated with greater AKL is warranted. Hypothesis: Smaller ACL volumes combined with longer T2* relaxation times would collectively predict greater AKL. Study Design: Cross-sectional study; Level of evidence, 3. Methods: College-aged active male (n = 20) and female (n = 30) participants underwent magnetic resonance imaging (MRI) and AKL testing. T2-weighted MRI scans were used to assess ACL volumes, and T2* relaxation times were used to assess ACL structural composition. AKL was measured via a commercial knee arthrometer. Forward stepwise linear regression with sex and weight (first step; suppressor variables) as well as ACL volume and T2* relaxation time (second step; independent variables) was used to predict AKL (dependent variable). Results: After initially adjusting for sex and weight ( R 2 = 0.19; P = .006), smaller ACL volumes combined with longer T2* relaxation times collectively predicted greater AKL ( R 2 = 0.52; P < .001; R 2 Δ = 0.32; P Δ < .001). A smaller ACL volume was the primary predictor of greater AKL ( R 2 Δ = 0.28; P < .001), with a longer T2* relaxation time trending toward a significant contribution to greater AKL ( R 2 Δ = 0.04; P = .062). After adjusting for ACL volume and T2* relaxation time, sex (partial r = 0.05; P = .735) and weight (partial r = 0.05; P = .725) were no longer significant predictors. Conclusion: AKL was largely predicted by ACL volume and to a lesser extent by T2* relaxation time (and not a person’s sex and weight). These findings enhance our understanding of how AKL may be associated with a structurally weaker ACL. The current study presents initial evidence that AKL is a cost-effective and clinically accessible measure that shows us something about the structural composition of the ACL. As AKL has been consistently shown to be a risk factor for ACL injuries, work should be done to continue to investigate what AKL may tell a clinician about the structure and composition of the ACL.

Context: Multiple factors have been suggested to increase the risk of faulty dynamic alignments that predict noncontact anterior cruciate ligament injury. Few researchers have examined this relationship using an integrated, multifactorial approach.Objective: To describe the relationship among static lower extremity alignment (LEA), hip muscle activation, and hip and knee motion during a single-leg squat.Design: Descriptive laboratory study.Setting: Research laboratory.Patients or Other Participants: Thirty men (age = 23.9 ± 3.6 years, height = 178.5 ± 9.9 cm, mass = 82.0 ± 14.1 kg) and 30 women (age = 22.2 ± 2.6 years, height = 162.4 ± 6.3 cm, mass = 60.3 ± 8.1 kg).Main Outcome Measure(s): Pelvic angle, femoral anteversion, quadriceps angle, tibiofemoral angle, and genu recurvatum were measured to the nearest degree; navicular drop was measured to the nearest millimeter. The average root mean square amplitude of the gluteus medius and maximus muscles was assessed during the single-leg squat and normalized to the peak root mean square value during maximal contractions for each muscle. Kinematic data of hip and knee were also assessed during the single-leg squat. Structural equation modeling was used to describe the relationships among static LEA, hip muscle activation, and joint kinematics, while also accounting for an individual's sex and hip strength.Results: Smaller pelvic angle and greater femoral anteversion, tibiofemoral angle, and navicular drop predicted greater hip internal-rotation excursion and knee external-rotation excursion. Decreased gluteus maximus activation predicted greater hip internal-rotation excursion but decreased knee valgus excursion. No LEA characteristic predicted gluteus medius or gluteus maximus muscle activation during the single-leg squat.Conclusions: Static LEA, characterized by a more internally rotated hip and valgus knee alignment and less gluteus maximus activation, was related to commonly observed components of functional valgus collapse during the single-leg squat. This exploratory analysis suggests that LEA does not influence hip muscle activation in controlling joint motion during a single-leg squat.

Changes in anterior knee laxity (AKL), genu recurvatum (GR) and general joint laxity (GJL) were quantified across days of the early follicular and early luteal phases of the menstrual cycle in 66 females, and the similarity in their pattern of cyclic variations examined. Laxity was measured on each of the first 6 days of menses (M1–M6) and the first 8 days following ovulation (L1–L8) over two cycles. The largest mean differences were observed between L5 and L8 for AKL (0.32mm), and between L5 and M1 for GR (0.56°) and GJL (0.26)(P

ABOUT 80,000 to 250,000 anterior cruciate ligament (ACL) injuries of the knee occur annually, with many of these injuries affecting individuals between the ages of 15-25 years. 1 The majority of ACL injuries are noncontact in nature, 2,3 with landing and plant-and- cut maneuvers being the most common activities associated with it. 4 Females participating in sports that involve jump landing and plant-and-cut type activities have a risk level that is 3-8 times greater than that for males during similar activities. 3,4 Anatomical, hormonal, neuromuscular, and biomechanical differences have been suggested to be the major factors that explain this injury bias. 1,5,6

We examined the capabilities of the Vermont Knee Laxity Device (VKLD) in measuring varus (VR)-valgus (VL) and internal (INT)-external (EXT) rotational laxities by quantifying measurement consistency and absolute measurement error (N = 10). Based on the expected measurement error, we then examined side-to-side differences (N = 20). For all measures, the knee was flexed 20 degrees , the thigh securely fixed, and counterweights applied to the thigh and shank to create an initial zero shear and compressive load across the tibiofemoral joint. A 10-Nm torque was applied to the knee for VL and VR during non-weight-bearing, and a 5-Nm torque was applied for INT and EXT during non-weight-bearing and weight-bearing conditions. Position sensors measured angular displacements (deg). Except for INT during weight bearing, measurement consistency was good to excellent (range, 0.68-0.96), with absolute measurement errors generally less than 2 degrees for VR-VL and 3-4 degrees for INT-EXT. Although side-to-side differences were observed, they did not exceed absolute measurement errors. The VKLD yields reliable measures of VR-VL and INT-EXT laxities, with sufficient measurement precision to yield clinically relevant differences.

Females have an increased incident rate of anterior cruciate ligament tears compared to males. Biomechanical strategies to decelerate the body in the vertical direction have been implicated as a contributing cause. This study determined if females would exhibit single leg landing strategies characterized by decreased amounts of hip, knee, and ankle flexion resulting in greater vertical ground reaction forces and altered energy absorption patterns when compared to males.Recreationally active males (N=14) and females (N=14), completed five single leg landings from a 0.3m height onto a force platform while three-dimensional kinematics and kinetics were simultaneously collected.Compared to males, females exhibited (1) less total hip and knee flexion displacements (40% and 64% of males, respectively, P0.05) and less time to peak hip and knee flexion (48% and 78% of males, respectively, P0.05), (2) 9% greater peak vertical ground reaction forces (P0.05), (3) less total lower body energy absorption (76% of males, P0.05), and (4) 11% greater relative energy absorption at the ankle (P0.05).Females in this study appear to adopt a single leg landing style using less hip and knee flexion, absorbing less total lower body energy with more relative energy at the ankle resulting in a landing style that can be described as stiff. This may potentially cause increased demands on non-contractile components of the lower extremity. Preventative training programs designed to prevent knee injury may benefit from the biomechanical description of sex-specific landing methods demonstrated by females in this study by focusing on the promotion of more reliance on using the contractile components to absorb impact energy during landings.

Although leg spring stiffness represents active muscular recruitment of the lower extremity during dynamic tasks such as hopping and running, the joint-specific characteristics comprising the damping portion of this measure, leg impedance, are uncertain. The purpose of this investigation was to assess the relationship between leg impedance and energy absorption at the ankle, knee, and hip during early (impact) and late (stabilization) phases of landing. Twenty highly trained female dancers (age = 20.3 ± 1.4 years, height = 163.7 ± 6.0 cm, mass = 62.1 ± 8.1 kg) were instrumented for biomechanical analysis. Subjects performed three sets of double-leg landings from under preferred, stiff, and soft landing conditions. A stepwise linear regression analysis revealed that ankle and knee energy absorption at impact, and knee and hip energy absorption during the stabilization phases of landing explained 75.5% of the variance in leg impedance. The primary predictor of leg impedance was knee energy absorption during the stabilization phase, independently accounting for 55% of the variance. Future validation studies applying this regression model to other groups of individuals are warranted.

We examined the relationship between anterior knee laxity (AKL), evaluated while the knee was nonweight bearing, and anterior translation of the tibia relative to the femur (ATT), evaluated when the knee transitioned from nonweight-bearing to weight-bearing conditions in response to an applied compressive load at the foot. Twenty subjects with normal knees (10 M, 10 F; 25.2 +/- 4.1 years, 169.8 +/- 11.5 cm, 71.6 +/- 16.9 kg) underwent measurements of AKL and ATT of the right knee on 2 days. AKL was measured at 133N with the KT-2000. ATT was measured with the Vermont Knee Laxity Device and electromagnetic position sensors attached to the patella and the anteromedial aspect of the proximal tibia. Three trials for each measure were averaged and analyzed. Measurement consistency was high for both AKL (ICC = 0.97; SEM = 0.44 mm) and ATT (ICC = 0.88; SEM = 0.84 mm). Linear regression revealed that AKL predicted 35.5% of the variance in ATT (p = 0.006), with a prediction equation of Y(ATT) = 3.20 + 0.543(X(AKL)). Our findings suggest that increased AKL is associated with increased ATT as the knee transitions from nonweight-bearing to weight-bearing conditions. The potential for increased knee joint laxity to disrupt normal knee biomechanics during activities such as landing from a jump, or the foot strike phase of gait deserves further study.

Objective: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10°, 20°, and 30°. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles. Design: A repeated-measures design. Setting: Motion analysis laboratory. Participants: Twenty (10 female; 10 male) healthy, recreationally active volunteers. Interventions: A rotary perturbation in single leg stance. Outcome Measurements: Response times of the medial and lateral quadriceps, hamstrings, and gastrocnemius. Results: There was a trend toward faster response times for all muscles closer toward extension. A consistent neuromuscular recruitment pattern for both males and females was evident for each knee angle tested. Females, however, contracted their quadriceps faster than males at all knee flexion angles. Conclusions: Small changes in knee angle near extension do not alter muscle response times and hence neuromuscular recruitment patterns in males and females. Regardless of knee flexion angle, following a perturbation in single leg stance, females contract their quadriceps faster than males. Clinical Relevance: Earlier contraction of the quadriceps in females may increase anterior tibial translation and hence anterior cruciate ligament strain, thereby heightening injury risk.

Rehabilitation professionals facilitate healthy movement and mobility in individuals seeking to engage in physically active lifestyles. The disparate rate of injury to the anterior cruciate ligament of the knee in physically active females in comparison to males serves as an excellent example of the challenges faced by rehabilitation professionals. The surgical reconstruction of the ligament and post-surgical rehabilitation has received a great deal of attention, but far less emphasis has been placed on the etiology and prevention of this disabling injury. This article addresses the impact of increased physical activity among females on ACL injury incidence, what is known and unknown about injury risk, and the importance of identifying strategies for prevention of injury to the ACL. One example of a research program that is exploring the potential risk factors for ACL injury in the physically active female is discus

Sudden changes in direction on a single weight-bearing-limb are commonly associated with injury to the lower extremity. The purposes of this study were to assess the between day reliability of hip, knee, and ankle kinematic displacements achieved with internal and external femur-on-weight-bearing-tibia rotation perturbations and to determine the effect of these perturbations on three dimensional hip, knee and ankle kinematics.Twenty recreationally active, healthy college students with no history of significant orthopedic injury (10 male, 10 female) were subjected to a forward and either internal or external rotary perturbation of the trunk and thigh on the weight-bearing-tibia while three dimensional kinematics were simultaneously collected. The protocol was repeated 24-48 h later to assess reliability.External perturbations resulted in significant internal rotation (IR) of the tibia on the femur (mean 7.3 (SD 3.9 degrees)) and IR of the femur on the pelvis (mean 6.8 (SD 5.4 degrees)) (P0.05). Internal perturbations resulted in significant external rotation (ER) of the tibia on the femur (mean 6.8 (5.9 degrees)) and ER of the femur on the pelvis (mean 10.7 (SD 96.1 degrees)) (P0.05). Additionally the external perturbation results in a significantly greater knee valgus (mean 3.6 (SD 2.2 degrees)) position while the internal perturbation results in a significantly greater knee varus position (mean 2.3 (SD 3.5 degrees)) (P0.05). External perturbation hip and knee total joint displacements revealed moderate to strong reliability (Intraclass Correlation Coefficient(2,k)=0.67-0.94) while internal perturbations revealed slightly higher Intraclass Correlation Coefficients(2,k)(0.80-0.96).The lower extremity perturbation device provides a consistent external and internal perturbation of the femur on the weight-bearing-tibia. The observed transverse and frontal plane kinematics are similar to motions observed during cross-over and side-stepping tasks.

A case of tarsal tunnel syndrome in a male collegiate lacrosse player is presented. The subject reported symptoms consistent with tarsal tunnel syndrome following two incidents of medial ankle sprain in one lacrosse season. Conservative treatment was successful following the first ankle sprain but failed to relieve pain and paresthesia in his heel and medial arch following the second injury. Laboratory tests provided an inconclusive diagnosis, and the subject underwent a retinacular release 5 months after the second ankle sprain. Following a 13-week rehabilitation program, the subject returned to full participation in his sport.

The purpose of this study was to determine how isokinetic eccentric and concentric peak torque/body weight ratios and time to peak torque values relate to drop vertical jump heights in 30 healthy subjects (12 men and 18 women, age = 22.7±2.2 yr, ht =169.6±8.0 cm, wt =67.2f11.9 kg). Drop vertical jumps were performed from a box 50 cm high. Subjects were tested isokinetically on each leg for the motions of knee extension and ankle plantar flexion. Eccentric and concentric peak torque (PT)/body weight ratios along with time (s) to eccentric and concentric peak torque were extracted from the Kin Com II computer. A stepwise multiple regression analysis was conducted to determine the relationship between the eight predictor variables and drop vertical jump height. Knee extension concentric PT/body weight ratio was the most significant predictor of drop vertical jump height, accounting for 23% of-the variance. This finding suggests that the stretch-shortening cycle can be simulated using isokinetic strength measurements and that drop vertical jump height can be attributed in part to concentric knee extension strength.

Aging is associated with decreases in strength and muscle mass. In addition, the ability to maintain balance decreases with age. Few studies have examined the relationship between isokinetic muscle performance and balance performance. It was the purpose of this study to determine if there is a relationship between muscle and balance performance, and to discover how this relationship is affected by age. Fifty-five healthy females were recruited from two different age groups, 28 females who were 18-30 years of age {mean age = 22.9 years ( ± 3.4), height = 163.5 cm (±6.5), weight = 64.8 kg (± 15.7)) and 26 females who were > 60 years of age {mean age = 68.1 years (+ 4.8), height = 159.7 cm (± 10.0), weight = 68.0 kg (± 11.4)1. Concentric and eccentric isokinetic muscle performance for the hip, knee, and ankle was measured using the KinCom isokinetic dynamometer. Balance performance was measured using the sharpened Romberg and one-legged stance tests. Younger subjects performed significantly better than older subjects on all muscle and balance performance variables (P = 0.05 to P = 0.0001), except the sharpened Romberg test with the eyes open. The older group exhibited significant relationships between balance and muscle performance measures (r — 0.10 to r — 0.57). In the older group, hip muscle performance was shown to correlate significantly better with balance performance than knee or ankle muscle performance. Also noted was a significantly greater relationship between muscle performance and balance performance with the eyes closed in the older group, as compared to the younger group. This is the first study known to thoroughly examine the relationship between muscle and balance performance. The presence of significant relationships warrants further examination. It is recommended that this relationship be examined in a broad spectrum of young, old, healthy and disabled populations.

Orthotic devices have been shown to successfully modify selected aspects of lower extremity mechanics and enhance foot stability during the support phase of running. It was hypothesized that orthotic intervention would relieve excessive strain on the ankle ligaments and reduce postural sway, especially in subjects with acute ankle sprains. The primary purpose of this study was to determine if orthotics would reduce postural sway in injured and uninjured subjects. Thirteen subjects with acute inversion ankle sprains and 12 uninjured subjects were assessed for postural sway on the Balance System under two treatment conditions (orthotic and nonorthotic) and four platform movements. A three-factor repeated measures analysis of variance revealed a significant group x treatment interaction, suggesting that postural sway with orthotic intervention improved significantly more in injured subjects than in uninjured subjects. A significant platform movement x treatment interaction, furthermore, revealed that postural sway for the four movement conditions was dependent upon treatment (orthotic vs. no orthotic). Tukey post hoc analysis revealed that orthotic intervention significantly reduced postural sway when the platform moved in the medial/lateral plane and inversion/eversion plane. This research suggests that custom-fit orthotics may restrict undesirable motion at the foot and ankle and enhance joint mechanoreceptors to detect perturbations and provide structural support for detecting and controlling postural sway in ankle-injured subjects.

The purpose of this study was to investigate the effects of induced anesthesia of the lateral ankle joint on proprioception as assessed in weight-bearing and non-weight-bearing conditions. Sixteen subjects were assessed under normal conditions and following an 8-cc injection of lidocaine into the anterior talofibular ligament of the ankle being tested. Center of balance and postural sway measurements were analyzed, revealing a significant lateral adjustment of center of balance during the stable tests compared to a medial adjustment during the dynamic tests under the anesthetized condition. ANOVA of postural sway scores revealed no main effect for condition (anesthesia vs. no anesthesia), but sway scores were higher during the two dynamic conditions as compared to the stable condition. ANOVA of joint position error scores revealed no main effect for condition. Findings suggest that inhibition of the joint receptor afferent fibers adversely affected joint proprioception as assessed while subjects were weight bearing but not while they were non-weight bearing.

The purpose of this study was to estimate intertester reliability of active and passive ankle joint position sense measurements in uninjured subjects. Subjects were 10 males and 10 females. Active and passive ankle joint position sense was assessed by two testers. Each subject was positioned supine on a modified examination table with his or her ankle placed in 25° of plantar flexion. Joint position sense (IPS) measurements, on two separate occasions, were recorded in degrees of error from four predetermined test positions. Test order was counterbalanced according to mode (active/passive) and test position. Two trials were performed for each sequence and the average of the two was recorded for analysis. The results revealed that both the active and passive JPS protocols yielded poor to moderate intertester reliability. It was concluded that further research is needed to develop reliable protocols for testing joint position sense of the ankle joint.

This study evaluated the effectiveness of ibuprofen in treating delayed onset muscle soreness (DOMS) of the elbow flexors when taken prior to and following exercise. Twenty subjects received either 2,400 mg/day ibuprofen or a placebo four times per day. Subjects performed intense eccentric exercise of the elbow flexors to elicit DOMS. Concentric and eccentric peak torque production against an isokinetic resistance of 0.52 radls, range of motion at the elbow, and subjective soreness of the elbow flexors were measured. ANOVA indicated no significant group-by-time interaction for concentric peak torque, eccentric peak torque, or pain. A significant interaction was revealed for range of motion. There was a significant difference within each group's ROM but no interaction between groups. It was concluded that the use of 2,400 mg/day ibuprofen prior to and following intense eccentric exercise was no more effective than a placebo in treating DOMS of the elbow flexors.

This study examined the test-retest reliability of a prototype device used to measure ankle inversion and eversion isokinetic average torque values. The purpose of this paper was to illustrate a situation where common isokinetic measures were reliable but not valid. Concentric and eccentric average torque was assessed at 90 deg/s on the Kin Com II dynamometer using 14 healthy subjects in two sessions; a manufactured prototype ankle inversion/eversion attachment device was used. Reliability was assessed by performing separate intraclass correlations (ICC 2,1) on the results. The data indicated that the average torque calculated from the clockwise direction was consistently higher than those values from the counterclockwise direction, regardless of ankle movement or side measured. The validity of this prototype device to accurately measure average torque for these two ankle motions is questionable. This finding demonstrates a situation where the measures appear to be reliable while the validity of the device used to obtain the measures is suspect.

Agility running activities are commonly used in the latter stages of rehabilitation for anterior cruciate ligament (ACL) reconstruction. However, the effects of agility running on anterior knee laxity in these patients have not been examined. The purpose of this study was to examine changes in anterior knee laxity before and after 30 minutes of agility running exercise. Subjects (N = 9) were female athletes (mean age = 20.1 +/- 1.5 years; height = 171.7 +/- 10.4 cm; weight = 65.7 +/- 8.6 kg) with unilateral ACL reconstruction (central 1/3 patella tendon graft, postoperation range = 9-52 months, mean = 24.2 months). Measurements were made at 20 degrees and 90 degrees of knee flexion bilaterally with KT-1000 arthrometry (MEDmetric, San Diego, CA) and recorded in millimeters of displacement. Data were analyzed with an analysis of variance (ANOVA) with repeated measures (p0.05). Results showed no statistical differences between the ACL-reconstructed knee and the normal knee at 20 degrees and 90 degrees knee flexion. The authors conclude that the central 1/3 patella tendon graft performs comparable to the normal knee when stressed with agility running exercise; therefore, agility exercise is an appropriate, safe, short-term activity.

Background: Anterior cruciate ligament (ACL) injuries often occur during landing, with female athletes at higher injury risk than male athletes. Interestingly, female dancers have lower ACL injury rates than do female athletes in general. Hypothesis: Female dancers will have earlier and greater lower extremity muscle activity and higher sagittal knee joint and leg stiffness than will female basketball players. Study Design: Cross-sectional group comparison. Methods: Fifty-five healthy female athletes (35 dancers, 20 basketball players) performed 5 double-leg drop jumps from a 45-cm box. Surface electromyography (onsets and amplitudes; prelanding and postlanding) was recorded from the lateral gastrocnemius, medial and lateral hamstrings, lateral quadriceps muscles with a 3-dimensional electromagnetic tracking system, and forceplates recording biomechanics (leg spring stiffness and knee joint stiffness). Results: Compared with basketball players, dancers had greater leg spring stiffness ( P = 0.047) but similar knee joint stiffness ( P = 0.44). Although no significant differences were observed in overall muscle onset times ( P = 0.22) or activation amplitudes (prelanding, P = 0.60; postlanding, P = 0.78), small to moderate effect sizes (ESs) suggest trends in dancers toward earlier (ES = 0.53) and higher medial hamstrings activation pre- (ES = 0.55) and post- (ES = 0.41) landing and lower lateral quadriceps (ES = 0.30) and higher gastrocnemius (ES = 0.33) postlanding muscle activation. Conclusions: In dancers, the higher leg spring stiffness and trends toward higher hamstrings prelanding and postlanding, as well as lower quadriceps and higher gastrocnemius activation postlanding with similar knee joint stiffness, indicate lower extremity neuromechanical differences across other joints. Clinical Relevance: Female dancers may have lower extremity neuromechanics that are different from those of basketball players during drop jumps. If dancers use ACL-protective strategies during activity, then their training routines should be further investigated to improve ACL injury prevention programs.

The purpose of this study was to assess anterior translation of the tibia using the Tibial Fixator Device (a mechanical leg stabilizer that controls tibial alignment) with the leg in three positions: neutral (N), internal rotation of 15° (IR), and external rotation of 15° (ER). Displacement was measured using a modified KT-1000 arthrometer. Eleven subjects with anterior cruciate ligament lesions were examined bilaterally in the three positions at 45, 67, and 89 newtons of anterior force. Three-factor repeated-measures ANOVA revealed a significant position effect regardless of force (p < .001). This effect was significant in the injured and noninjured legs. Displacement was greatest in ER and least in IR. These data indicate that the position of the tibia, maintained with an external leg restraint, has a significant effect on anterior displacement of the knee. Control of tibiofemoral alignment and modifications to the KT-1000 provide new potentials for instrumented arthrometry.

Medial elbow injuries of athletes, such as baseball pitchers and javelin throwers, can prove to be debilitating and may have a negative effect on performance. The most significant injury to the elbow occurs is an ulnar collateral ligament (UCL) sprain or rupture, which compromises the medial stability of the elbow joint. It has been found that the anterior oblique portion of the UCL is the primary stabiliser of the elbow, and that trauma to this complex may significantly hinder normal elbow function. An accurate diagnosis will dictate the degree of injury to the elbow as well as determine the most appropriate means of treatment.

The purpose of this study was to determine whether external compression would cause a decrease in the isokinetic muscular endurance of the quadriceps and hamstring muscle groups. Subjects were tested on the Cybex II dynamometer (Cybex, Ronkonkoma, NY) under two conditions: with external compression applied to the thigh and without external compression applied to the thigh. External compression was applied with a lower extremity blood pressure cuff inflated to a predetermined clinically standardized pressure. The subjects performed an isokinetic endurance test consisting of 30 maximal repetitions at 180 deg/sec under both conditions. A paired t test showed no statistical differences (p > 0.05) between the mean total work, work over the first five repetitions, and work over the last five repetitions between the two conditions for the quadriceps and the hamstring muscle groups. Results indicated that external compression applied to the thigh at 30 mm Hg caused no significant decrease in the isokinetic muscular endurance of the quadriceps or hamstrings. Further research is indicated to determine whether external compression could influence other aspects of muscular performance.

Nineteen patients with the clinical diagnosis of anterior cruciate ligament injury were examined by KT-1000 ar thrometry before arthroscopy in an effort to differentiate partial from complete tears. To this end, the KT-1000 arthrometer was equipped with a strain gauge and pro cessor that permitted the required force to increase the anterior displacement by 1-mm increments, to be read on a light-emitting diode. The measured force has been plotted against anterior displacement expressed in non linear increments along the x-axis to allow for the vis coelastic nature of the ligament. The results show that stress-strain diagrams of partially torn and completely torn ligaments are similar to those obtained by graded stress radiography. Using arthroscopy as the standard of measurement, partial tears can be differentiated from complete tears with a sensitivity of 80% and a specificity of 100%. The figures for complete tears versus partial tears are 100% and 80%, respectively. Graded arthrom etry with x-y recording of the force-displacement rela tionship that allows for the viscoelastic qualities of liga ment further extends the capabilities of instrumented arthrometry.

This study examined the effect of the Swede-O ankle brace on talar tilt in subjects with unstable ankle joints. Six college-age females with talar tilts greater than 9.5° at 15 decaNewtons (daN) of force on a Telos stress test device participated in the study. Each subject was X-rayed at five levels of force (0,6,9, 12, and 15 daN), first with a bare ankle then wearing a Swede-O ankle brace. A two-factor (Brace × Force) analysis of variance revealed a main effect for force, but no main effect for brace and no Brace × Force interaction. For the unbraced ankles, mean displacements were 8.2, 10.4, 11.9, and 13.1° at the four levels of force, respectively. After application of the brace, the talar tilts were 5.7, 8.5, 11.1, and 12.8°, respectively. These findings suggest that the Swede-O ankle brace was not effective in reducing talar tilt in subjects with unstable ankles. Any efficacy of the brace may be due to other factors, such as proprioceptive feedback during inversion.

to better understand how sex differences in anterior knee laxity (AKL) affect knee joint biomechanics, we examined the consequence of greater absolute baseline (males and females) and cyclic increases in AKL during the menstrual cycle (females) on anterior tibial translation (ATT) as the knee transitioned from non-weight-bearing to weight-bearing conditions, while also controlling for genu recurvatum (GR).males and females (71 females and 48 males, aged 18-30 yr) were measured for AKL and GR and underwent measurement of ATT. Women were tested on the days of their cycle when AKL was at its minimum (T1) and maximum (T2); males were matched in time to a female with similar AKL. Linear regressions examined relationships between absolute baseline (AKLT1, GRT1) and cyclic changes (Δ = T2 - T1; AKLΔ, GRΔ) (females only) in knee laxity with ATT as measured at T1 and T2 and Δ (T2 - T1) (females only).AKL and GR increased in females, but not in males, from T1 to T2. Greater AKLT1 and GRT1 predicted greater ATTT1 and ATTT2 in males (R = 21.0, P0.007). The combination of greater AKLT1, AKLΔ, and less GRΔ predicted greater ATTT1 and ATTT2 in females (R = 12.5-13.1, P0.05), with AKLΔ being a stronger predictor (coefficient, P value) of ATTT2 (0.864, P = 0.027) compared with ATTT1 (0.333, P = 0.370). AKLΔ was the sole predictor of ATTΔ (R = 0.104 and 0.740, P = 0.042).greater absolute baseline and cyclic increases in AKL were consistently associated with greater ATT produced by transition of the knee from non-weight-bearing to weight-bearing. Because the anterior cruciate ligament is the primary restraint to ATT, these findings provide insight into the possible mechanisms by which greater AKL may be associated with at-risk knee biomechanics during the weight acceptance phase of dynamic tasks.

Hamstring muscle injury is a complex problem for athletes, physicians, physical therapists, and athletic trainers. This injury tends to recur and to limit participation in athletic competition. The etiology of hamstring muscle injury continues to be confusing and incomplete for clinicians and researchers. The purposes of this paper are: 1) to review briefly hamstring muscle group anatomy and function, 2) to review the clinical and animal research literature concerning the role of strength, flexibility, warm-up, and fatigue in hamstring muscle injury, 3) to present an evaluation and rehabilitation scheme for hamstring muscle injury, 4) to describe a theoretical multiple factor hamstring injury model, and 5) to offer recommendations concerning prevention of hamstring muscle injury. During preseason screening and rehabilitation following hamstring muscle injury, clinicians should consider the influence of hamstring strength, flexibility, warm-up, and fatigue on muscle performance. Additional research concerning these factors is recommended. J Orthop Sports Phys Ther 1992;16(1):12-18.

Knee injury rehabilitation often includes the step-up exercise. However, the authors have been unable to locate documentation of the effect of the step-up exercise on lower extremity strength indices. The purpose of this study was to determine the effect of a six-week lateral step-up exercise protocol on quadriceps muscle group strength. Twenty female nonathletes (age = 20 +/- 1.5 yrs, ht = 162.6 +/- 4.9 cm, wt = 64.1 +/- 0.5 kg) were randomly assigned to a control or experimental group. Pretest concentric and eccentric strength measures were obtained at 60 degrees /sec on a Kin-Com isokinetic dynamometer. Thigh girth measurements were obtained 10 and 20 cm superior to the knee joint line. An independent t-test of the difference between pre and post isokinetic strength and girth measurements between the control and experimental groups revealed no significant difference (p.05). In addition, no significant difference was found for the exercised and nonexercised extremity for the experimental group (p.05). These findings suggest that this lateral step-up protocol did not provide sufficient overload to increase isokinetic strength of the quadriceps muscle group or increase thigh girth in healthy subjects. In addition, open chain assessment of muscle strength may not adequately assess strength changes incurred via closed chain exercise. Clinicians should use caution in assuming that step-up exercises provide sufficient overload to increase thigh girth or isokinetic quadriceps peak torque values. J Orthop Sports Phys Ther 1992;15(3):151-155.

David H. Perrin, PhD, ATC* • Evan V. Hellwig, PT, ATC* Laurie L. Tis, MEd, ATC* • Byron S. Shenk, EdDt University of Virginia . ------------------This study examined the effect of gravity correction on concentric and eccentric average force of the right and left side shoulder rotator muscles and on the external/internal rotation reciprocal muscle group ratios. Thirty-three males were tested on a Kinetic Communicator dynamometer at 150 deg/sec from a seated position with the shoulder abducted to 90 deg and positioned along the frontal plane. Gravity correction procedures were followed prior to testing, and both the gravity-uncorrected (GU) and gravity-corrected (GC) values were obtained from the dynamometer's software. Paired t-tests indicated the gravity correction procedure increased every value obtained during external rotation and decreased all values obtained during internal rotation. Also, the concentric and eccentric external/internal rotation reciprocal muscle group ratios were all higher as a result of the gravity correction procedure. These findings were consistent with previous reports on the effect of gravity correction on lower extremity muscle groups. In particular, gravity correction significantly added to the muscle group opposed by gravity (external rotators) and detracted from the muscle group assisted by gravity (internal rotators). Therefore correction for the effects of gravity is recommended during isokinetic assessment of the shoulder internal and external rotator muscle groups.

Background Torsional joint stiffness is thought to play a role in the observed sex bias in noncontact anterior cruciate ligament injury rates. Hypothesis Women will exhibit lower torsional stiffness values of the knee in response to varus/valgus and internal/external rotations than will men. Study Design Controlled laboratory study. Methods Knee kinematics of 20 university students (10 men, 27.3 ± 3.4 years, 177.3 ± 6.8 cm, 81.1 ± 7.0 kg; 10 women, 22.9 ± 1.5 years, 169.0 ± 7.1 cm, 66.1 ±11.4 kg) were measured while 0 to 10 Nm of varus and valgus torques were applied with the subject nonweightbearing and while 0 to 5 N.m of internal and external torques were applied with the subject nonweightbearing and weightbearing with the use of a custom joint testing device. Joint stiffness values were calculated at 1-N.m increments. Results When low magnitudes of torque were applied to the knee, women had significantly lower stiffness values than did men-With the exception of applied external torque with the joint weightbearing and varus torque with the joint nonweightbearing, women demonstrated an increase in joint stiffness as the magnitude of torque increased from lower to higher magnitudes. In contrast, for the men, joint stiffness values remained unchanged as the magnitude of applied torque increased. Conclusion Women exhibited lower knee stiffness in response to low magnitudes of applied torque compared to men and demonstrated an increase of joint stiffness as the magnitude of applied torque increased. Clinical Relevance The decreased stiffness behavior of the knee in response to low torques that was observed for women may have a role in detrimentally affecting knee biomechanics and resulting neuromuscular function, particularly when an individual transitions from nonweightbearing to weightbearing.

Background. Females experience a disproportionate number of anterior cruciate ligament injuries compared to males. Increased estradiol concentration has been suggested to alter ligament properties and strength. Determining whether the knee responds differently to an external load at various hormonal levels may be helpful in further explaining the gender disparity. Methods. Estradiol, progesterone and testosterone were quantified at menses, near ovulation and at the mid-luteal phase. With one knee serving as the control limb and the other as the experimental limb, displacement at 134 N and stiffness between 90 and 134 N were recorded with a knee ligament arthrometer on both knees before and after a loading protocol. The protocol consisted of three, 3-min, posterior to anterior normalized loads directed to the posterior calf with a ligament testing device. Findings. The loading protocol produced a measurable increase in displacement but not stiffness. Neither displacement nor stiffness measures however were affected by day of the menstrual cycle. No consistent relationships between hormonal concentrations and displacement or stiffness were evident. Interpretation. Following a controlled, static external load, displacement and stiffness were not affected differently by day of the menstrual cycle. 2004 Elsevier Ltd. All rights reserved.

This study investigated the effects of anterior knee joint laxity on muscle activation patterns prior to and following a lower extremity perturbation. Participants were subjected to a forward and either internal (IR) or external (ER) rotation perturbation of the trunk and thigh on the weight-bearing shank. Pre-activity (%MVIC) before the perturbation, and reflex time (ms) and mean reflex amplitude (%MVIC) following the perturbation were recorded via surface electromyography (sEMG) in the medial and lateral gastrocnemius, hamstring and quadriceps muscles. Twenty-one NCAA DI intercollegiate female athletes with below average anterior knee laxity (3-5 mm) were compared to 21 with above average anterior knee laxity (7-14 mm) as measured by a standard knee arthrometer. Groups differed in reflex timing by muscle (P = 0.013), with females with above average knee laxity (KT((7 mm))) demonstrating a 16 ms greater delay in biceps femoris reflex timing compared to females with below average knee laxity (KT((5 mm))). Groups also differed in muscle activation amplitude by response, muscle and direction of rotation (i.e. a 4-way interaction; P = 0.027). The magnitude of change from pre to post perturbation was significantly less in KT((7 mm)) vs. KT((5 mm)) for the medial (MG) and lateral (LG) gastrocnemius muscles, primarily due to higher levels of muscle preactivity while awaiting the perturbation (MG = 20% vs. 12% MVIC, P = 0.05; LG = 33% vs. 21% MVIC, P = 0.11). Further, KT((7 mm)) demonstrated higher activation levels in the biceps femoris than KT((5 mm)) (47% vs. 27% MVIC; P = 0.025) regardless of response (pre vs. post perturbation) or direction of rotation. These findings suggest females with increased knee laxity may be less sensitive to joint displacement or loading (delayed reflex), and are more reliant on active control of the gastrocnemius and biceps femoris muscles to potentially compensate for reduced passive joint stability.

Cold (cryotherapy) is commonly applied to an athlete immediately before and/or after sports participation. The purpose of this study was to determine the effect of cold water submersion (CWS) on isokinetic strength of the plantar flexor muscle group. Eleven women and five men (mean age 22.1 years, height 170.8 cm, weight 64.5 kg) with no history of ankle joint pathology were tested for peak torque, average power, and total work of the dominant foot at 60 deg/sec with a Cybex II isokinetic dynamometer. Before isokinetic testing subjects were randomly assigned to either CWS or an inactive rest period (RP). Subjects returned 1 week later to receive the opposite treatment and undergo isokinetic testing. The CWS consisted of placing the leg in a 15°C tub of water for 20 minutes. The RP consisted of remaining seated for a 20-minute period. Paired t tests were computed to determine if any differences existed in peak torque, average power, and total work between the CWS and RP conditions. Results indicated concentric isokinetic strength values were lower after CWS for peak torque, average power and total work of the plantar flexor muscle group. These findings indicate that concentric isokinetic torque, power, and work of the plantar flexor muscle group are reduced immediately after CWS. Further research should be undertaken to determine the length of time isokinetic output is reduced before returning to normal responses after CWS is present.

Previous research indicates that both the extent and timing of muscular activation at the knee can be influenced by muscle activity state, joint angle, weight-bearing status and trunk position. However, little research to date has evaluated protective neuromuscular response times and activation patterns to an imposed perturbation with the knee joint in a functional, weight-bearing stance. Hence, we designed a lower extremity perturbation device to produce a sudden, forward and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Surface electromyography (EMG) recorded long latency reflex times of the medial and lateral quadriceps, hamstring and gastrocnemius muscles in 64 intercollegiate lacrosse and soccer players in response to both internal and external rotation perturbation. We found the gastrocnemius fired significantly faster that the hamstring, which in turn fired significantly faster than the quadriceps. There was also a significant difference in activation times of the medial and lateral hamstring not found for the quadriceps or gastrocnemius muscles. Our findings confirmed that reactive neuromuscular responses following this functional perturbation differ markedly from those previously reported using seated, partial weight-bearing and/or uni-planar models under relaxed conditions.

The minimum amount of change which represents clinical improvement following ankle sprains is unknown. This study considers the usefulness of physiological and behavioral measures commonly employed for this purpose in sports rehabilitation settings. Thirteen collegiate athletes of both genders were measured at approximately 3 and 10 days post-grade I or II ankle sprain. Volumetric displacement and sagittal plane ankle range of motion measures were used as impairment indicators. Motor ability scores (activity count) and a perceived athletic ability measure (visual analog scale) were used to indicate functional limitations. Volumetric displacement and both functional limitation measures demonstrated responsiveness to change between two occasions of measurement separated by 1 week. Observed changes in range of motion deficits could not be distinguished from measurement error. The results of this study suggest that behavioral measures of motor activity and perceived athletic ability may be at least as useful as physical measures of organic dysfunction for assessing clinical improvement following acute ankle sprains among athletes.

Exercises to improve joint proprioception and coordination of the functionally unstable ankle are advocated throughout the literature, yet there is little evidence that these exercise have any effect on proprioception and balance. The purpose of this study was to determine the effects of a 6-week coordination and balance training program on proprioception of subjects with functional ankle instability. Forty-five subjects (age = 22.53 +/- 3.95 years, height = 172.04 +/- 10.0 cm, weight = 71.72 +/- 15.7 kg) were randomly placed into a control (Group 1), sham (Group 2), or experimental (Group 3) group. The experimental group trained 3 days per week, 10 minutes each day, performing various balance and proprioception exercises. Postural sway and active and passive joint position sense were assessed. Analysis of variance for postural sway modified equilibrium score for anterior and posterior sway, as well as medial and lateral sway revealed significant four-way interactions. Tukey post hoc analyses revealed that Group 3 performed significantly better (p < .05) than Group 1 and Group 2 on the posttests. There were no significant differences for joint position sense or postural sway index. Results suggest that balance and coordination training can improve some measures of postural sway. It is still unclear if joint position sense can be improved in the functionally unstable ankle.

The authors of Muscle Imbalances – Fact or Fiction, have correctly identified the complexities of quantifying muscle imbalances as related to predisposition to injury. It seems intuitive that significant muscle imbalance would predispose one to injury during high performance sport or strenuous activities common with laborers in industrial settings. However, scientific evidence in support of this impression requires prospective research paradigms involving pre-injury screening of large numbers of uninjured subjects. One good analogy is the clinical assumption that stretching and muscle extensibility reduces sports injury risk. Thacker et al. [1] conducted a systemic review and meta-analysis of the literature in an attempt to find evidence that stretching prevents or reduces injuries in sports. The authors found that stretching is not significantly associated with a reduction in injury risk, and concluded that the evidence for or against stretching is equivocal. The authors have also correctly pointed out that single-factor-related analysis (e.g., uniplanar strength ratios) of muscle function reflects an insufficient approach to identifying a higher risk of overuse or traumatic injury or re-injury. However, I continue to contend that open chain analysis of single muscle group performance is the best way to identify preor postinjury deficits in torque, power, and work, that can be overlooked with more functional closed chain analysis. For example, Kowalk et al. [2] evaluated bilateral joint angles, moments, powers, and work in uninjured and anterior cruciate ligament (ACL) deficient subjects during stair climbing preand 6 months post-operatively. Post-operative deficits were found for peak moment, power, and work in the injured knee, yet these reductions were compensated by increases in excursion, moment, and power in the contralateral ankle. Ernst et al. [3] conducted a video analysis of ACL reconstructed and matched uninjured subjects during vertical jump, lateral step-up, and hop activities. They found that the ACL-injured side had lower knee extension moments compared to the uninjured side and matched subjects. However, no differences in hip+knee+ankle summated moments were found, and the injured side hip was found to have compensated for the knee moment deficits. These studies provide evidence that while closed chain functional analysis is important, it alone is insufficient in identifying single muscle group deficits that can be masked with proximal or distal joint, or contralateral extremity compensations. I agree with the authors that a detailed analysis of muscle function that includes passive and active characteristics of muscle lengthening (flexibility, stiffness) and sensorimotor function parameters (e.g., stabilometry, proprioceptive aspects, reflex and electromyographic activity) would more comprehensively assess injury risk. However, this comprehensive analysis of muscle function is impractical for screening large num

Nonballistic, active range of motion exercises have been advocated as more effective than static stretching for increasing range of motion, yet no published data exist to support this claim. This study compared the effect of nonballistic, repetitive active knee extension movements performed in a neural slump sitting position with static stretching technique on hamstring flexibility. Forty healthy, adult volunteer subjects with limited right hamstring flexibility (i.e., minimum of 15 degrees loss of active knee extension measured with femur held at 90 degrees of hip flexion) were randomly assigned to one of three groups. Group 1 (static stretch) performed a 30-second stretch twice daily. Group 2 (active stretch) performed 30 repetitions of active knee extension while sitting in a neural slump position twice daily. Group 3 served as a control. Hamstring flexibility was determined by an active knee extension test before and after 6 weeks of stretching. Goniometric measurement of knee joint flexion angle was obtained from videotape recording of the active knee extension test. A 3 (group) x 2 (test) repeated measures analysis of variance and subsequent Tukey post hoc testing revealed no significant difference in knee joint range of motion gains between the static (mean = 8.9 degrees) and active stretch (mean = 10.2 degrees). Both stretch groups' knee joint range of motion improved significantly (p.05) more than the control group. We conclude that 6 weeks of nonballistic, repetitive active knee extensions (30 repetitions, twice daily) performed in a neural slump sitting position improves hamstring flexibility in uninjured subjects, but is no different compared with static stretching (30 seconds, twice daily).

Traditionally, clinicians have utilized various physical characteristics as criteria to assess the functional status of anterior cruciate ligament (ACL)-insufficient athletes without validating the efficacy of such assessments. The primary purposes of this study were to determine the relationship between traditionally used physical characteristics and functional capacity of individuals with an ACL insufficiency and to compare functional results of two groups of ACL-insufficient athletes. Forty-one subjects were tested for strength and power on an isokinetic device, anthropometric characteristics, and function using three functional performance tests (FPT). Results revealed that conventional physical characteristics correlated poorly (r = .01 to r = .42) with the functional tests. Additionally, athletes who were able to return to preinjury levels of activity performed significantly (p0.05) better on the FPT than those who were unable to return to preinjury activities. Based on the results of this study, use of such traditional physical characteristics for predicting function in the ACL-insufficient athlete may be inappropriate, and the functional performance tests designed for this study appear to be the most valuable assessment of the athlete's functional capacity. J Orthop Sports Phys Ther 1992;16(4):174-181.

The purpose of this study was to compare isokinetic strength and flexibility measures between hamstring injured and noninjured athletes. Sixteen university athletes with history of hamstring injury were matched by motor dominance, sport, and position to sixteen university athletes without history of hamstring injury. Each subject was tested for concentric and eccentric quadriceps and hamstring peak torque and reciprocal muscle group ratios on a Kinetic Communicator(R) (KIN-COM) dynamometer at 60 degrees /sec and 180 degrees /sec. Each subject's hamstring flexibility was determined by passively extending the knee while the hip was maintained at 90 degrees of flexion. Analysis of variance indicated that the injured extremity was significantly less flexible than the noninjured extremity within the hamstring injured group, and the hamstring injured group was less flexible than the noninjured group. No significant strength differences existed between the hamstring injured and noninjured group on any isokinetic measure evaluated. The importance of assessing hamstring flexibility is emphasized. J Orthop Sports Phys Ther 1991;13(3):118-125.

beta-Endorphin (BEP) has been implicated in the analgesic response to transcutaneous electrical nerve stimulation (TENS). The anterior pituitary gland is a source of beta-endorphin which shares the prohormone proopiomelanocortin (POMC) with adrenocorticotropin (ACTH). Current theory proposes that the stimulation-induced breakdown of POMC results in ACTH release with a subsequent elevation in blood cortisol levels. The purpose of this study was to determine the potential application and mechanism of TENS as an anti-inflammatory agent. Eight female subjects received low frequency, 300 musec pulse width TENS at four sites associated with relief of upper arm pain once when pain free and again while experiencing delayed onset muscle soreness (DOMS) of the elbow flexor muscle group. Blood samples were withdrawn 15 and 1 minute before and 1, 20, and 40 minutes after treatment. Serum was analyzed for cortisol by radioimmunoassay. TENS treatment failed to elevate serum cortisol concentration, but there was a significant reduction in perception of pain (p < 0.05) and an improvement in range of elbow extension (p < 0.05) when subjects were treated for DOMS. These results suggest that the anterior pituitary is not a source of BEP in TENS-induced analgesia. J Orthop Sports Phys Ther 1989;11(3):100-103.