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The purpose of this study was to examine associations between ankle dorsiflexion (ankle-DF) displacement and knee and hip kinematics and kinetics during a jump-landing task in females following anterior cruciate ligament reconstruction (ACLR). Females (n = 23) with a history of unilateral ACLR (≥ 6-months post-ACLR) underwent a three-dimensional lower extremity biomechanical evaluation. Pearson Product Moment ( r ) correlations assessed associations between ankle-DF displacement and knee and hip kinematic and kinetic variables. On the involved-limb, individuals with lesser ankle-DF displacement demonstrated greater knee abduction displacement during the loading phase ( r  = -0.645, p  = 0.001). On the uninvolved-limb, individuals with greater ankle-DF displacement demonstrated greater hip flexion displacement ( r  = 0.599, p = 0.003) and knee flexion displacement ( r =  -0.545, p  = 0.007). There were no other significant associations between ankle-DF displacement and ankle, knee, or hip biomechanical variables on either limb ( p  > 0.05). Our findings demonstrate that reduced ankle-DF motion appears to share a different relationship between the involved- and uninvolved-limbs in females post-ACLR.

A greater knee valgus angle is a risk factor for lower extremity injuries. Visually observed medial knee displacement is used as a proxy for knee valgus motion during movement assessments in an attempt to identify individuals at heightened risk for injury. The validity of medial knee displacement as an indicator of valgus motion has yet to be determined during a single-leg squat. This study compared three-dimensional knee and hip angles between participants who displayed medial knee displacement (MKD group) during a single-leg squat and those who did not (control group). Participants completed five single-leg squats. An electromagnetic motion tracking system was used to quantify peak knee and hip joint angles during the descent phase of each squat. MANOVA identified a difference between the MKD and control group kinematics. ANOVA post hoc testing revealed greater knee valgus angle in the MKD (12.86 ± 5.76) compared with the control (6.08 ± 5.23) group. There were no other differences between groups. Medial knee displacement is indicative of knee valgus motion; however, it is not indicative of greater knee or hip rotation, or hip adduction. These data indicate that clinicians can accurately identify individuals with greater knee valgus angle through visually observed medial knee displacement.

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Context: Decreased sagittal-plane motion at the knee during dynamic tasks has been reported to increase impact forces during landing, potentially leading to knee injuries such as anterior cruciate ligament rupture., Objective: To describe the relationship between lower extremity muscle activity and knee-flexion angle during a jump-landing task., Design: Cross-sectional study., Setting: Research laboratory., Patients or Other Participants: Thirty recreationally active volunteers (15 men, 15 women: age = 21.63 ± 2.01 years, height = 173.95 ± 11.88 cm, mass = 72.57 ± 14.25 kg)., Intervention(s): Knee-flexion angle and lower extremity muscle activity were collected during 10 trials of a jump-landing task., Main Outcome Measure(s): Simple correlation analyses were performed to determine the relationship between each knee-flexion variable (initial contact, peak, and displacement) and electromyographic amplitude of the gluteus maximus (GMAX), quadriceps (VMO and VL), hamstrings, gastrocnemius, and quadriceps : hamstring (Q : H) ratio. Separate forward stepwise multiple regressions were conducted to determine which combination of muscle activity variables predicted each knee-flexion variable., Results: During preactivation, VMO and GMAX activity and the Q : H ratio were negatively correlated with knee-flexion angle at initial contact (VMO: r = 0.382, P = .045; GMAX: r = 0.385, P = .043; Q : H ratio: r = 0.442, P = .018). The VMO, VL, and GMAX deceleration values were negatively correlated with peak knee-flexion angle (VMO: r = 0.687, P = .001; VL: r = 0.467, P = .011; GMAX: r = 0.386, P = .043). The VMO and VL deceleration values were negatively correlated with knee-flexion displacement (VMO: r = 0.631, P = .001; VL: r = 0.453, P = .014). The Q : H ratio and GM activity predicted 34.7% of the variance in knee-flexion angle at initial contact (P = .006). The VMO activity predicted 47.1% of the variance in peak knee-flexion angle (P = .001). The VMO and VL activity predicted 49.5% of the variance in knee-flexion displacement (P = .001)., Conclusions: Greater quadriceps and GMAX activation and less hamstrings and gastrocnemius activation were correlated with smaller knee-flexion angles. This landing strategy may predispose an individual to increased impact forces due to the negative influence on knee-flexion position.

Background: Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively., Methods: Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests., Findings: Anterior tibial translation was correlated with hamstring stiffness (r=-0.538; P=0.002), but not with hamstring strength (r=-0.088; P=0.644). Hamstring stiffness and strength were not correlated (r=0.054; P=0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t(28)=2.186; P<0.037; ES=0.36), but hamstring strength did not differ between these groups (t(28)=1.057; P<0.300; ES=0.17)., Interpretation: Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings' ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Background: Repetitive eccentric loading results in muscle damage and subsequent changes in muscle stiffness and edema accumulation, which manifest as reduced joint range of motion and increased muscle cross-sectional area. The purpose of the study was to evaluate changes in shoulder range of motion and the infraspinatus cross-sectional area with repetitive eccentric contraction., Methods: Twenty physically active participants performed 9 sets of 25 repetitions of eccentric external rotator contractions. The ultrasonographic measurement of the infraspinatus cross-sectional area, and shoulder internal/external rotation and horizontal adduction range of motion were measured before, immediately after, and 24h after the intervention., Findings: Infraspinatus cross-sectional area significantly increased from baseline immediately after exercise (P<0.001), and remained elevated from baseline at the 24-hour follow up (P<0.001). Internal rotation and horizontal adduction range of motion did not change significantly between baseline and post-exercise (P>0.05), but were significantly decreased at the 24-hour follow up from the baseline (internal rotation: P<0.001, horizontal adduction: P<0.001) and the immediate post-exercise (internal rotation: P=1.012, horizontal adduction: P=0.016)., Interpretation: These changes observed after the eccentric contractions may have implications for injury development in pitchers, because 1) the infraspinatus endures repetitive eccentric loading with pitching and 2) decreased internal rotation and horizontal adduction range of motion have been linked to upper extremity injuries. However, since the muscle response after eccentric loading varies by the task and previous exposure to similar stress, future study needs to investigate the time course of recovery of the muscle cross-sectional area and range of motion after pitching in competitive pitchers., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Context: A smaller amount of ankle-dorsiflexion displacement during landing is associated with less knee-flexion displacement and greater ground reaction forces, and greater ground reaction forces are associated with greater knee-valgus displacement. Additionally, restricted dorsiflexion range of motion (ROM) is associated with greater knee-valgus displacement during landing and squatting tasks. Because large ground reaction forces and valgus displacement and limited knee-flexion displacement during landing are anterior cruciate ligament (ACL) injury risk factors, dorsiflexion ROM restrictions may be associated with a greater risk of ACL injury. However, it is unclear whether clinical measures of dorsiflexion ROM are associated with landing biomechanics., Objective: To evaluate relationships between dorsiflexion ROM and landing biomechanics., Design: Descriptive laboratory study., Setting: Research laboratory., Patients or Other Participants: Thirty-five healthy, physically active volunteers., Intervention(s): Passive dorsiflexion ROM was assessed under extended-knee and flexed-knee conditions. Landing biomechanics were assessed via an optical motion-capture system interfaced with a force plate., Main Outcome Measure(s): Dorsiflexion ROM was measured in degrees using goniometry. Knee-flexion and knee-valgus displacements and vertical and posterior ground reaction forces were calculated during the landing task. Simple correlations were used to evaluate relationships between dorsiflexion ROM and each biomechanical variable., Results: Significant correlations were noted between extended-knee dorsiflexion ROM and knee-flexion displacement (r  =  0.464, P  =  .029) and vertical (r  =  -0.411, P  =  .014) and posterior (r  =  -0.412, P  =  .014) ground reaction forces. All correlations for flexed-knee dorsiflexion ROM and knee-valgus displacement were nonsignificant., Conclusions: Greater dorsiflexion ROM was associated with greater knee-flexion displacement and smaller ground reaction forces during landing, thus inducing a landing posture consistent with reduced ACL injury risk and limiting the forces the lower extremity must absorb. These findings suggest that clinical techniques to increase plantar-flexor extensibility and dorsiflexion ROM may be important additions to ACL injury-prevention programs.

Context: Preventing noncontact ACL injuries has been a major focus of athletic trainers and researchers. One factor that may influence female noncontact ACL injury is the fluctuating concentrations of hormones in the body., Objective: To determine whether muscle properties change across the menstrual cycle., Design: Repeated measures. Testing was performed within 3 d after the onset of menses and ovulation. Repeated-measures ANOVAs were used to determine changes in variables across the menstrual cycle, and Pearson correlations were used to determine relationships between variables., Participants: 8 women with normal menstrual cycles., Main Outcome Measures: Active hamstring stiffness and hamstring extensibility., Results: Hamstring extensibility (P = .003) increased at the ovulation testing session but hamstring muscle stiffness (P = .66) did not., Conclusions: The results indicate that hamstring muscle stiffness did not change across the menstrual cycle and hamstring extensibility increased at ovulation, when estrogen concentration increases.

Coactivation of the rotator cuff is vital to glenohumeral joint stability by centralising the humeral head within the glenoid fossa. Yet in individuals with subacromial impingement, it is hypothesised that rotator cuff coactivation abnormalities are present that could contribute to their shoulder pain. The purpose of this study was to determine if abnormal rotator cuff coactivation and deltoid activation patterns exist in participants with subacromial impingement. Rotator cuff (supraspinatus, infraspinatus, and subscapularis) coactivation and middle deltoid activation was assessed during an elevation task. ANOVA models were used to compare muscle activation patterns in 10 participants with subacromial impingement and 10 control participants. Participants with impingement exhibited decreased rotator cuff coactivation (subscapularis-infraspinatus and supraspinatus-infraspinatus) and increased middle deltoid activation at the initiation of elevation (0-30 degrees of humeral elevation). The participants with impingement also had higher subscapularis-infraspinatus and supraspinatus-infraspinatus coactivation above the level of the shoulder where pain is typically present (90-120 degrees of humeral elevation). The results indicate that individuals with subacromial impingement exhibit rotator cuff muscle coactivation and deltoid activation abnormalities during humeral elevation that might contribute to the encroachment of the subacromial structures associated with subacromial impingement.

Objective: To measure the influence of humeral torsion on interpretation of clinical indicators of posterior shoulder tightness in overhead athletes., Design: Cross-sectional control group comparison., Setting: A university-based sports medicine research laboratory., Participants: Twenty-nine healthy intercollegiate baseball players and 25 college-aged control individuals with no history of participation in overhead athletics were enrolled., Intervention: In all participants, bilateral humeral rotation and humeral horizontal adduction variables were measured with a digital inclinometry. Bilateral humeral torsion was measured with ultrasonography., Main Outcome Measures: Group and limb comparisons were made for clinical indicators of posterior shoulder tightness (humeral rotation and horizontal adduction variables) and humeral torsion variables. The relationship between humeral torsion and clinical indicators of posterior shoulder tightness were established., Results: The dominant limb of the baseball players demonstrated greater humeral torsion, and less internal rotation and total rotation range of motion, compared with control participants and the nondominant limb in both groups. Once corrected for torsion, no group or limb differences in internal rotation were present. Statistically significant relationships existed between the amount of humeral torsion and measures of posterior shoulder tightness., Conclusions: Although limb differences in clinical indicators of posterior tightness exist in healthy overhead athletes, these measures appear to be influenced by humeral torsion rather than soft tissue tightness. Once torsion is accounted for, the limb differences observed clinically were minimal in healthy overhead athletes. When possible, accounting for humeral torsion when interpreting clinical measures of posterior shoulder tightness may aid in treatment decisions.

Background: An erect posture and greater knee valgus during landing have been implicated as anterior cruciate ligament injury risk factors. While previous research suggests coupling of knee and hip kinematics, the influence of trunk positioning on lower extremity kinematics has yet to be determined. We hypothesized that greater trunk flexion during landing would result in greater knee and hip flexion and lesser knee valgus. Identification of a modifiable factor (e.g. trunk flexion) which positively influences kinematics of multiple lower extremity joints would be invaluable for anterior cruciate ligament injury prevention efforts., Methods: Forty healthy individuals completed two drop landing tasks while knee, hip, and trunk kinematics were sampled. The first task constituted the natural/preferred landing strategy (Preferred), while in the second task, subjects actively flexed the trunk upon landing (Flexed)., Findings: Peak trunk flexion angle was 47 degrees greater for Flexed compared to Preferred (P<0.001), and was associated with increases in peak hip flexion angle of 31 degrees (P<0.001) and peak knee flexion angle of 22 degrees (P<0.001)., Interpretation: Active trunk flexion during landing produces concomitant increases in knee and hip flexion angles. A more flexed/less erect posture during landing is associated with a reduced anterior cruciate ligament injury risk. As such, incorporating greater trunk flexion as an integral component of anterior cruciate ligament injury prevention programs may be warranted.

Objective: To differentiate hip and trunk motion during double-leg stance., Design: Trunk and hip angular position variances were measured on different support surfaces with and without vision., Background: Postural control results from motion about the hips and trunk during bilateral stance. While the hip joint has been studied extensively, information concerning relative amounts of hip and trunk motions during postural control is limited., Methods: Trunk flexion/extension, trunk lateral flexion, right and left hip flexion/extension and abduction/adduction angular position variances were assessed in 14 normal subjects using an electromagnetic tracking system during bilateral stance on firm, foam, and multiaxial support surfaces with and without vision., Results: Significantly greater amounts of motion occurred at all joints for the multiaxial-eyes closed condition compared to all other surface-vision conditions. No significant differences were found between any other surface-vision conditions. Within the multiaxial-eyes closed condition, right and left hip flexion/extension and abduction/adduction magnitudes were significantly greater than those of trunk flexion and lateral flexion, and left hip flexion/extension motion was significantly greater than that of the right hip., Conclusions: Postural control mechanisms involve similar amounts of motion at the hips and trunk, except for conditions under which a rigid base of support becomes unstable and vision is eliminated., Relevance: These results suggest that the trunk and hips should be considered separately during kinematic analysis of postural control. This information may be useful in providing a more sensitive assessment of postural control to identify balance-related pathologies associated with stroke, concussion, and somatosensory deficits.