Muscle activation during single leg squat is affected by position of the nonstance limb

ABSTRACT Context: The single leg squat (SLS) is appropriate for targeting activation, strengthening, and/or neuromuscular retraining of the gluteus maximus, gluteus medius, and quadriceps. However, the effect of different non-stance leg positions on muscle activity has not been fully evaluated. Objective: To compare the muscle activity of selected stance leg hip muscles during the SLS with 3 non-stance leg positions: in front, in the middle, and in back. Design: Controlled laboratory study. Setting: Biomechanics laboratory. Participants: Seventeen healthy adults. Main Outcome Measure(s): Surface EMG data of the gluteus maximus, gluteus medius, lateral hamstrings, medial hamstrings, rectus femoris, and TFL as well as kinetic data of the hip and knee were collected while participants performed the 3 SLS tasks. Mean muscle activation levels during the descent phase and ascent phase for the selected hip muscles were compared for the 3 tasks. Hip and knee kinetics in all 3 planes were also compared for the 3 tasks. Each variable of interest was analyzed using a separate linear regression model with a generalized estimating equations correction. Results: Muscle activation levels of the gluteus maximus, gluteus medius, medial hamstrings, rectus femoris, and TFL on the stance leg during descent, and the medial hamstrings and TFL during ascent were significantly different between SLS tasks. The greatest number of differences occurred between SLS-Front and SLS-Back. During descent, gluteal muscle activity was greater in SLS-Front and SLS-Middle than in SLS-Back. For both phases, TFL activity was greater during SLS-Front than both SLS-Middle and SLS-Back. Kinetic differences at the hip and knee between SLS tasks were also observed. Conclusion: The 3 SLS tasks have different muscle activation and kinetic profiles. Clinician and researchers can vary non-stance leg position during the SLS to manipulate muscle activation levels and tailor the exercise to assist with goals at different stages of rehabilitation.

Knee Kinetics and Kinematics in Patients With Ankle Arthroplasty and Ankle Arthrodesis

Background: Previous literature suggests that patients treated with total ankle arthroplasty (TAA) versus ankle arthrodesis (AA) may have better function and lower risk for adjacent joint arthritis in the foot. Little is known on how these interventions affect proximal joints such as the knee. Questions: We sought to assess whether patients with TAA and AA exhibited altered biomechanics linked to the onset and progression of knee osteoarthritis (KOA). We used the knee adduction moment (KAM), a surrogate measure for the mechanical load experienced at the medial tibiofemoral compartment, because it is linked with the onset and progression of KOA. Methods: At a minimum of 2 years postoperatively, instrumented 3-dimensional walking gait was recorded in 10 TAA and 10 AA patients at self-selected walking speeds. TAA patients had either a Salto Talaris or INBONE prosthesis. Average first and second peak KAMs (Nm/kg), KAM impulse (Nm-s/kg), and range-of-motion (ROM, °) were calculated on both the affected and unaffected limbs for each patient. Results: There were no significant differences in the KAM’s first and second peaks, impulse, or knee ROM in any plane between the unaffected and affected limbs, or between TAA and AA. Conclusion: TAA and AA may not meaningfully affect ipsilateral knee kinetics and KAMs in short-term follow-up. This study highlights the importance of continuing to study these parameters in larger cohorts of patients with longer follow-up to determine how our treatment of end-stage ankle arthritis may affect the incidence or progression of ipsilateral KOA.

Knee Kinetics in Baseball Hitting and Return to Play After ACL Reconstruction

The purpose of this study was to describe the knee kinetics of baseball hitting, develop a tool to predict knee kinetics from easily obtainable measures, and to compare knee kinetics to other exercises along the rehabilitation continuum to determine a timeline for when hitting may resume after ACL reconstruction. Nineteen high school baseball athletes (16.3±0.8 yrs, 180.6±5.7 cm, 78.4±10.8 kg) participated. Participants took ten swings off a tee. Kinetic data were recorded using an electromagnetic tracking system. Data from swings with the top three exit velocities were averaged for analysis. Linear regressions were used to determine if predictors of height, mass, age and exit velocity could predict the following torques: bilateral knee net, extension, internal and external rotation, valgus and varus torque; and anterior force. Backwards regression models revealed independent variables could significantly predict front knee net, internal and external rotation, extension, and varus torque, and anterior force; and back knee net and valgus torque. Based on the kinetics of baseball hitting compared to those of rehabilitation exercises, if the involved knee is the front, we suggest tee hitting may be initiated at 13 weeks after ACL reconstruction. If the involved knee is the back, we suggest tee hitting may initiated at 17 weeks after ACL reconstruction.

Linear Discriminant Analysis Successfully Predicts Knee Injury Outcome From Biomechanical Variables

Background: The most commonly damaged structures of the knee are the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and menisci. Given that these injuries present as either isolated or concomitant, it follows that these events are driven by specific mechanics versus coincidence. This study was designed to investigate the multiplanar mechanisms and determine the important biomechanical and demographic factors that contribute to classification of the injury outcome. Hypothesis: Linear discriminant analysis (LDA) would accurately classify each injury type generated by the mechanical impact simulator based on biomechanical input variables (ie, ligament strain and knee kinetics). Study Design: Controlled laboratory study. Methods: In vivo kinetics and kinematics of 42 healthy, athletic participants were measured to determine stratification of injury risk (ie, low, medium, and high) in 3 degrees of knee forces/moments (knee abduction moment, anterior tibial shear, and internal tibial rotation). These stratified kinetic values were input into a cadaveric impact simulator to assess ligamentous strain and knee kinetics during a simulated landing task. Uniaxial and multiaxial load cells and implanted strain sensors were used to collect mechanical data for analysis. LDA was used to determine the ability to classify injury outcome by demographic and biomechanical input variables. Results: From LDA, a 5-factor model (Entropy R2 = 0.26) demonstrated an area under the receiver operating characteristic curve (AUC) for all 5 injury outcomes (ACL, MCL, ACL+MCL, ACL+MCL+meniscus, ACL+meniscus) of 0.74 or higher, with “good” prediction for 4 of 5 injury classifications. A 10-factor model (Entropy R2 = 0.66) improved the AUC to 0.86 or higher, with “excellent” prediction for 5 injury classifications. The 15-factor model (Entropy R2 = 0.85), produced 94.1% accuracy with the AUC 0.98 or higher for all 5 injury classifications. Conclusion: Use of LDA accurately predicted the outcome of knee injury from kinetic data from cadaveric simulations with the use of a mechanical impact simulator at 25° of knee flexion. Thus, with clinically relevant kinetics, it is possible to determine clinical risk of injury and also the likely presentation of singular or concomitant knee injury. Clinical Relevance: LDA demonstrates that injury outcomes are largely characterized by specific mechanics that can distinguish ACL, MCL, and medial meniscal injury. Furthermore, as the mechanics of injury are better understood, improved interventional prehabilitation can be designed to reduce these injuries.