Applying the Socio-Ecological Model to barriers to implementation of ACL injury prevention programs: A systematic review

Background: Preventing anterior cruciate ligament (ACL) injuries is important to avoid long-term adverse health consequences. Identifying barriers to implementation of these prevention programs is crucial to reducing the incidence of these injuries. Our purpose was to identify barriers of implementation for ACL injury prevention programs and suggest mechanisms for reducing the barriers through application of a SocioEcological Model (SEM). Methods: Studies investigating ACL prevention program effectiveness were searched in Medline via PubMed and the Cochrane Library, and a subsequent review of the references of the identified articles, yielded 15 articles total. Inclusion criteria encompassed prospective controlled trials, published in English, with ACL injuries as the primary outcome. Studies were independently appraised by 2 reviewers for methodological quality using the PEDro scale. Barriers to implementation were identified when reported in at least 2 separate studies. A SEM was used to suggest ways to reduce the identified barriers. Results: Five barriers were identified: motivation, time requirements, skill requirements for program facilitators, compliance, and cost. The SEM suggested ways to minimize the barriers at all levels of the model from the individual through policy levels. Conclusion: Identification of barriers to program implementation and suggesting how to reduce them through the SEM is a critical first step toward enabling ACL prevention programs to be more effective and ultimately reducing the incidence of these injurie

Effects of augmented local abdominal activation patterns on lower extremity biomechanics during landing in males and females

"This research assessed changes in lower extremity biomechanics as a result of augmented local abdominal contractions during double leg landings. The study design followed a two-day (control and intervention days) within subject model in which two conditions on each day were compared, (control-control and control-experimental) with between sex comparisons. Fifty subjects (25 males and 25 females) were activity matched and represented a sample of healthy and recreationally active individuals. A repeated measures ANOVA comparing control and experimental conditions on the intervention day revealed that all subjects significantly increased local abdominal activation during 150ms prior to landing. However, a 2 (sex) x 3 (muscle) x 2 (phase of landing) repeated measures ANOVA demonstrated that only males maintained this contraction during the 150ms time interval after landing. A repeated measures ANOVA evaluating changes in leg spring stiffness (LSS) as a result of the augmented local abdominal contraction showed a sex by condition interaction demonstrating that only males experienced significant increases in LSS from control to experimental condition while females demonstrated no significant changes. No significant differences by condition were noted when assessing changes in ankle, knee, and hip energetics. The evaluation of lower extremity total joint displacements across condition demonstrated that males increased LSS through decreases in hip range of motion while females showed no significant changes in hip range of motion but increased knee and ankle motion. From these results we concluded that augmented local abdominal activation during a double leg landing task increased LSS by decreasing hip range of motion in males. "--Abstract from author supplied metadata

Kinematic analysis of functional lower extremity perturbations

Background. 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. Methods. 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. Findings. External perturbations resulted in significant internal rotation (IR) of the tibia on the femur (mean 7.3 (SD 3.9°)) and IR of the femur on the pelvis (mean 6.8 (SD 5.4°)) (P < 0.05). Internal perturbations resulted in significant external rotation (ER) of the tibia on the femur (mean 6.8 (5.9°)) and ER of the femur on the pelvis (mean 10.7 (SD 96.1°)) (P < 0.05). Additionally the external perturbation results in a significantly greater knee valgus (mean 3.6 (SD 2.2°)) position while the internal perturbation results in a significantly greater knee varus position (mean 2.3 (SD 3.5°)) (P < 0.05). External perturbation hip and knee total joint displace-ments revealed moderate to strong reliability (Intraclass Correlation Coefficient2,k = 0.67–0.94) while internal perturbations revealed slightly higher Intraclass Correlation Coefficients2,k(0.80–0.96). Interpretation. 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

Low levels of anterior tibial loading enhance knee extensor reflex response characteristics

We examined whether neuromuscular reflexes were altered with anterior loads applied to the tibiofemoral joint. A ligament testing device was modified by attaching a reflex hammer to a steel mounted frame to illicit a patellar tendon tap, while anterior directed loads displaced the tibia on the femur. Five trials were acquired while anterior-directed loads (20, 50, 100 N; counterbalanced) were applied to the posterior tibia between 20 N pre (20 NPre) and post (20 NPost baseline conditions on two different days. Surface electromyography (sEMG) recorded mean quadriceps (Q) and hamstring (H) reflex time (RTime = ms) and reflex amplitude (RAmp = %MVIC). A load cell on the anterior tibia measured the timing (KETime = ms) and amplitude (KEAmp = N) of the knee extension force, and was used to calculate electromechanical delay (EMD = ms) and peak knee extension moment (KEMom = Nm/kg). Data from 19 recreationally active subjects revealed good to excellent response consistency between test days and between baseline conditions for RTime, RAmp, KETime and KEAmp. With anterior tibial loading, RTime was faster at 50 N vs. 20 NPost, and RAmp was greater at 20 NPre vs. 20 NPost (Q and H) and at 50 N vs. 100 N (Q only). KEMom was greater at 20 NPre and 50 N vs. 20 NPost, and EMD was shorter at 50 N vs. 20 N, 20 NPre and 20 NPost. These results suggest that knee extensor reflex responses are enhanced with low (50 N) but not moderate (100 N) anterior loading of the knee

Sex differences in lower extremity biomechanics during single leg landings

Background. 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. Methods. Recreationally active males (N = 14) and females (N = 14), completed five single leg landings from a 0.3 m height onto a force platform while three-dimensional kinematics and kinetics were simultaneously collected. Findings. Compared to males, females exhibited (1) less total hip and knee flexion displacements (40% and 64% of males, respectively, P < 0.05) and less time to peak hip and knee flexion (48% and 78% of males, respectively, P < 0.05), (2) 9% greater peak vertical ground reaction forces (P < 0.05), (3) less total lower body energy absorption (76% of males, P < 0.05), and (4) 11% greater relative energy absorption at the ankle (P < 0.05)

Energy absorption as a predictor of leg impedance in highly trained females

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

Sex specific abdominal activation strategies during landing

Control of the trunk segment in landing has been implicated as a contributing factor to the higher incidence of anterior cruciate ligament injuries in females than in males. Investigating the sex-specific abdominal activation strategies during landing lends insight into mechanisms contributing to control of the trunk segment. To examine the abdominal activation strategies used by males and females during a landing task. Mixed-model (between-subjects and within-subjects) design. Laboratory. Healthy, recreationally active males (n = 20, age = 23 ± 4.8 years, height = 1.8 ± 0.1 m, mass = 79.6 ± 9.9 kg, body mass index = 24.8 ± 2.7 kg/ m^sup 2^) and females (n = 22, age = 20.8 ± 4.8 years, height = 1.7 ± 0.1 m, mass = 64.1 ± 9.2 kg, body mass index = 22.9 ± 2.6 kg/m^sup 2^). Subjects performed 5 double-leg landings from a box height of 60 cm. Male and female activation amplitudes for the rectus abdominis (RA), external oblique (EO), and transversus abdominis and lower fibers of the internal oblique (TrA-IO) muscles during preactivation (150-millisecond interval just before landing) and after impact (150-millisecond interval immediately after ground contact). Males had greater TrA-IO activation than females (P < .05). Males preferentially activated the TrA-IO muscles relative to the RA and EO, whereas females demonstrated no significant muscle differences. Males and females also differed by phase, with males having more TrA-IO activation than females during the preactivation landing phase (P < .05) but not during the postimpact phase. The TrA-IO was the only muscle to significantly differ by landing phase, decreasing from preactivation to postimpact (P < .05). Males used different abdominal muscle activation strategies than females in landing. The efficacy of these muscle activation strategies to control the trunk should be assessed through trunk kinematic and kinetic measures in future studies

The Effect of Nordic Hamstring Strength Training on Muscle Architecture, Stiffness, and Strength

Purpose: Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. Methods: Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. Results: The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm3, p\u3c0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm2, p=0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. Conclusions: The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is therefore warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk

The Interaction of Trunk-Load and Trunk-Position Adaptations on Knee Anterior Shear and Hamstrings Muscle Forces During Landing

Context: Because anterior cruciate ligament (ACL) injuries can occur during deceleration maneuvers, biomechanics research has been focused on the lower extremity kinetic chain. Trunk mass and changes in trunk position affect lower extremity joint torques and work during gait and landing, but how the trunk affects knee joint and muscle forces is not well understood. Objective: To evaluate the effects of added trunk load and adaptations to trunk position on knee anterior shear and knee muscle forces in landing. Design: Crossover study. Setting: Controlled laboratory environment. Patients or Other Participants: Twenty-one participants (10 men: age = 20.3 ± 1.15 years, height = 1.82 ± 0.04 m, mass = 78.2 ± 7.3 kg; 11 women: age = 20.0 ± 1.10 years, height = 1.72 ± 0.06 m, mass = 62.3 ± 6.4 kg). Intervention(s): Participants performed 2 sets of 8 double-leg landings under 2 conditions: no load and trunk load (10% body mass). Participants were categorized into one of 2 groups based on the kinematic trunk adaptation to the load: trunk flexor or trunk extensor. Main Outcome Measure(s): We estimated peak and average knee anterior shear, quadriceps, hamstrings, and gastrocnemius forces with a biomechanical model. Results: We found condition-by-group interactions showing that adding a trunk load increased peak (17%) and average (35%) knee anterior shear forces in the trunk-extensor group but did not increase them in the trunk-flexor group (peak: F1,19 = 10.56, P = .004; average: F1,19 = 9.56, P = .006). We also found a main effect for condition for quadriceps and gastrocnemius forces. When trunk load was added, peak (6%; F1,19 = 5.52, P = .030) and average (8%; F1,19 = 8.83, P = .008) quadriceps forces increased and average (4%; F1,19 = 4.94, P = .039) gastrocnemius forces increased, regardless of group. We found a condition-by-group interaction for peak (F1,19 = 5.16, P = .035) and average (F1,19 = 12.35, P = .002) hamstrings forces. When trunk load was added, average hamstrings forces decreased by 16% in the trunk-extensor group but increased by 13% in the trunk-flexor group. Conclusions: Added trunk loads increased knee anterior shear and knee muscle forces, depending on trunk adaptation strategy. The trunk-extensor adaptation to the load resulted in a quadriceps-dominant strategy that increased knee anterior shear forces. Trunk-flexor adaptations may serve as a protective strategy against the added load. These findings should be interpreted with caution, as only the face validity of the biomechanical model was assessed.Originally published in Journal of Athletic Training Vol. 45, No. 1 2010