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The purpose of this study was to determine the influence of frontal and transverse plane rotations of the femur and tibia on peak maximum principal stress in the patellar tendon. Using finite element modeling, patellar tendon stress profiles of eight healthy individuals were obtained during a simulated squatting task (45° of knee flexion). The femur and tibia of each model were rotated 10° (in 2° increments) along their respective axes beyond that of the natural degree of rotation. This process was repeated for the transverse plane (internal and external rotation) and frontal plane (adduction and abduction). Quasi-static loading simulations were performed to quantify peak maximum principal stress in patellar tendon. Internal and external rotations of the femur and tibia that exceeded 4° beyond that of the natural rotation resulted in progressively greater patellar tendon stress (p

Excessive hip adduction and internal rotation are common movement impairments associated with patellofemoral pain (PFP). As such, strengthening of the hip abductors and external rotators commonly is recommended. Because tensor fascia latae (TFL) is a hip internal rotator in addition to being an abductor, it is important to select exercises that target the superior gluteus maximus (SUP-GMAX) and gluteus medius (GMED) while minimizing activation of the TFL. To identify hip-targeted exercises resulting in greater activation of the SUP-GMAX and GMED relative to the TFL in persons with PFP. Twelve individuals with PFP participated. Electromyographic (EMG) signals were obtained from the GMED, SUP-GMAX, and TFL using fine-wire electrodes while participants performed 11 hip-targeted exercises. Normalized EMG of GMED and SUP-GMAX was compared to that of the TFL for each exercise using repeated measures ANOVAs and descriptive statistics. Of the 11 hip exercises evaluated, only the clam exercise with elastic resistance resulted in significantly greater activity of both gluteal muscles (SUP-GMAX = 24.2 ± 14.4%MVIC, p =.05; GMED = 37.2 ± 19.7%MVIC, p =.008) relative to the TFL (12.5 ± 11.7%MVIC). Five exercises exhibited significantly lower activation of SUP-GMAX relative to TFL: 1) unilateral bridge: SUP-GMAX = 17.7 ± 9.8%MVIC, TFL = 34.0 ± 17.7%MVIC, p =.01; 2) bilateral bridge: SUP-GMAX = 10.0 ± 6.9%MVIC, TFL = 14.0 ± 7.5%MVIC, p =.04; 3) abduction: SUP-GMAX = 14.2 ± 11.1%MVIC, TFL = 33.0 ± 11.9%MVIC, p =.001; 4) hip hike: SUP-GMAX = 14.8 ± 12.8%MVIC, TFL = 46.8 ± 33.7%MVIC, p =.008; and 5) step-up: SUP-GMAX = 15.0 ± 5.4%MVIC, TFL = 31.7 ± 19.9 %MVIC, p =.02). No differences in gluteal activation relative to TFL were found for the remaining 6 exercises (all p >.05). The clam with elastic resistance exercise was effective at activating the SUP-GMAX and GMED greater than TFL. No other exercises achieved a similar level of muscular recruitment. When attempting to strengthen the gluteal muscles in persons with PFP, care should be taken in assuming that common hip-targeted exercises result in the desired recruitment patterns. [ABSTRACT FROM AUTHOR]

The article informs about the biomechanical aspects of squat exercises, highlighting modifiable parameters like trunk position and tibia inclination and their implications for joint loading and muscle demands. Topics include the influence of trunk inclination on hip and knee flexion moments, the impact of tibia inclination on knee flexion moments, and recommendations for optimizing squat technique for different clinical conditions.

Strengthening of the hip abductors has been advocated for persons with patellofemoral pain (PFP). It is not clear if these individuals activate the hip abductor muscles appropriately to achieve the desired therapeutic effects. To compare activation of the hip abductor muscles between persons with and without PFP during the performance of hip abductor exercises. Thirty-two individuals participated (12 with PFP and 20 without PFP). The average age (± standard deviation) was 29.7 ± 5.9 years for the PFP group and 28.1 ± 6.9 for the control group. Electromyographic (EMG) signals from the gluteus medius (GMED), superior gluteus maximus (SUP-GMAX), and tensor fascia lata (TFL) were obtained using fine-wire electrodes while participants performed 11 different exercises. Normalized EMG activity of each muscle was compared between groups across all exercises. When averaged across all exercises, persons with PFP exhibited significantly greater EMG activity of TFL (mean = 25.3% MVIC; 95% CI = 19.2, 31.3) compared to those without PFP (mean = 17.6% MVIC; 95% CI = 12.8, 22.4) and significantly lower EMG activity of SUP-GMAX (mean = 16.4% MVIC; 95% CI = 11.0, 22.0) compared to those without PFP (mean = 25.4% MVIC; 95% CI = 21.0, 29.8). Persons with PFP exhibited lower EMG activity of GMED, but only for 3 out of the 11 exercises evaluated (hip abduction, hip hike, step-up). Compared to persons without PFP, those with PFP exhibited activation differences during the performance of exercises used to target the hip abductors. Our results highlight the need for activation training prior to the initiation of strengthening exercises to achieve desired therapeutic effects. [ABSTRACT FROM AUTHOR]

Given that increased use of the knee extensors relative to the hip extensors may contribute to various knee injuries, there is a need for a practical method to characterize movement behavior indicative of how individuals utilize the hip and knee extensors during dynamic tasks. The purpose of the current study was to determine whether the difference between sagittal plane trunk and tibia orientations obtained from 2D video (2D trunk-tibia) could be used to predict the average hip/knee extensor moment ratio during athletic movements. Thirty-nine healthy athletes (15 males and 24 females) performed 6 tasks (step down, drop jump, lateral shuffle, deceleration, triple hop, and side-step-cut). Lower-extremity kinetics (3D) and sagittal plane video (2D) were collected simultaneously. Linear regression analysis was performed to determine if the 2D trunk-tibia angle at peak knee flexion predicted the average hip/knee extensor moment ratio during the deceleration phase of each task. For each task, an increase in the 2D trunk-tibia angle predicted an increase in the average hip/knee extensor moment ratio when adjusted for body mass (all P < .013, R² = .17-.77). The 2D trunk-tibia angle represents a practical method to characterize movement behavior that is indicative of how individuals utilize the hip and knee extensors during dynamic tasks. [ABSTRACT FROM AUTHOR]

Peak knee valgus has been shown to predict anterior cruciate ligament injury. The purpose of the current study was to compare peak rate of torque development (RTD) to peak isometric torque as a predictor of peak knee valgus during landing. Twenty-three healthy females participated. Hip abductor muscle performance was quantified using 2 types of isometric contractions: sustained and rapid. Peak isometric torque was calculated from the sustained isometric contraction. Peak RTD was calculated from the rapid isometric contraction (0-50 and 0-200 ms after force initiation). Kinematic data were collected during the deceleration phase of a double-leg drop jump task. Linear regression was used to assess the ability of hip abductor muscle performance variables to predict peak knee valgus. Increased peak RTD during the 0 to 50 milliseconds window after force initiation was found to significantly predict lower peak knee valgus (P = .011, R² = .32). In contrast, neither peak RTD from 0 to 200 milliseconds after force initiation window (P = .45, R² = .03) nor peak isometric torque (P = .49, R² = .03) predicted peak knee valgus. The inability of the hip abductors to rapidly generate muscular force may be more indicative of "at-risk" movement behavior in females than measures of maximum strength. [ABSTRACT FROM AUTHOR]

Context: A limitation of previous studies on squatting mechanics is that the influence of trunk and shank inclination on the knee-extensor moment (KEM) has been studied in isolation. Objective: The purpose of the current study was to determine the influence of segment orientation on the KEM during freestanding barbell squatting. Design: Repeated-measures cross sectional. Setting: University research laboratory. Participants: Sixteen healthy individuals (8 males and 8 females). Intervention: Each participant performed 8 squat conditions in which shank and trunk inclinations were manipulated. Main Outcome Measures: 3D kinematic and kinetic data were collected at 250 and 1500 Hz, respectively. Regression analysis was conducted to identify the individual relationships between the KEM and the trunk and shank inclination at 60° and 90° of knee flexion. To identify the best predictor(s) of the KEM, stepwise regression was implemented. Results: Increased shank inclination increased the KEM (P <.001, R2 =.21–.25). Conversely, increased trunk inclination decreased the KEM (P <.001, R2 =.49–.50). For the stepwise regression, trunk inclination entered first and explained the greatest variance in the KEM (all P <.001, R2 =.49–.50). Shank inclination entered second (all P <.010, R2 =.53–.54) and explained an additional 3% to 5% of the variance. Conclusions: Our results confirm that inclination of the trunk and shank have an opposing relationship with the KEM. Increased forward shank posture increases the KEM, while increased forward trunk posture decreases the KEM. However, when viewed in combination, the trunk was the superior predictor of the KEM, highlighting the fact that increased quadriceps demand created by a forward shank can be offset by trunk inclination. [ABSTRACT FROM AUTHOR]