Renate List

Kinematics of the Trunk and the Lower Extremities During Restricted and Unrestricted Squats

Abstract List, R, Gülay, T, Stoop, M, and Lorenzetti, S. Kinematics of the trunk and the lower extremities during restricted and unrestricted squats. J Strength Cond Res 27(6): 1529–1538, 2013—Squatting is a common strength training exercise used for rehabilitation, fitness training, and in preparation for competition. Knowledge about the loading and the motion of the back during the squat exercise is crucial to avoid overuse or injury. The aim of this study was the measurement and comparison of the kinematics of the lower leg, trunk, and spine during unrestricted and restricted (knees are not allowed beyond toes) squats. A total of 30 subjects performed unrestricted and restricted barbell squats with an extra load of 0, 25, and 50% bodyweight. Motion was tracked using a 12-camera Vicon system. A newly developed marker set with 24 trunk and 7 pelvic markers allowed us to measure 3D segmental kinematics between the pelvic and the lumbar regions, between the lumbar and the thoracic segments, and the sagittal curvatures of the lumbar and the thoracic spine. In an unrestricted squat, the angle of the knee is larger and the range of motion (ROM) between the lumbar and the thoracic segments is significantly smaller compared with a restricted squat (p < 0.05). The studied subjects showed significantly increased ROM for thoracic curvature during restricted squats. The unrestricted execution of a squat leads to a larger ROM in the knee and smaller changes in the curvature of the thoracic spine and the range of smaller segmental motions within the trunk. This execution in turn leads to lower stresses in the back. To strengthen the muscles of the leg, the unrestricted squat may be the best option for most people. Thus, practitioners should not be overly strict in coaching against anterior knee displacement during performance of the squat.

Soft Tissue Artefacts of the Human Back: Comparison of the Sagittal Curvature of the Spine Measured Using Skin Markers and an Open Upright MRI

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R2, of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats.

Abstract Lorenzetti, S, Gülay, T, Stoop, M, List, R, Gerber, H, Schellenberg, F, and Stüssi, E. Comparison of the angles and corresponding moments in the knee and hip during restricted and unrestricted squats. J Strength Cond Res 26(10): 2829–2836, 2012—The aim of this study was to compare the angles and corresponding moments in the knee and hip during squats. Twenty subjects performed restricted and unrestricted squats with barbell loads that were 0, ¼, and ½ their body weight. The experimental setup consisted of a motion capture system and 2 force plates. The moments were calculated using inverse dynamics. During the unrestricted squats, the maximum moments in the knee were significantly higher, and those in the hip were significantly lower than during restricted squats. At the lowest position, the maximum knee flexion angles were approximately 86° for the restricted and approximately 106° for the unrestricted techniques, whereas the maximum hip flexion angle was between 95° and 100°. The higher moments in the hip during restricted squats suggest a higher load of the lower back. Athletes who aim to strengthen their quadriceps should consider unrestricted squats because of the larger knee load and smaller back load.

Joint Angles of the Ankle, Knee, and Hip and Loading Conditions During Split Squats

The aim of this study was to quantify how step length and the front tibia angle influence joint angles and loading conditions during the split squat exercise. Eleven subjects performed split squats with an additional load of 25% body weight applied using a barbell. Each subjects movements were recorded using a motion capture system, and the ground reaction force was measured under each foot. The joint angles and loading conditions were calculated using a cluster-based kinematic approach and inverse dynamics modeling respectively. Increases in the tibia angle resulted in a smaller range of motion (ROM) of the front knee and a larger ROM of the rear knee and hip. The external flexion moment in the front knee/hip and the external extension moment in the rear hip decreased as the tibia angle increased. The flexion moment in the rear knee increased as the tibia angle increased. The load distribution between the legs changed < 25% when split squat execution was varied. Our results describing the changes in joint angles and the resulting differences in the moments of the knee and hip will allow coaches and therapists to adapt the split squat exercise to the individual motion and load demands of athletes.

The Spinal Curvature of Three Different Sitting Positions Analysed in an Open MRI Scanner

Sitting is the most frequently performed posture of everyday life. Biomechanical interactions with office chairs have therefore a long-term effect on our musculoskeletal system and ultimately on our health and wellbeing. This paper highlights the kinematic effect of office chairs on the spinal column and its single segments. Novel chair concepts with multiple degrees of freedom provide enhanced spinal mobility. The angular changes of the spinal column in the sagittal plane in three different sitting positions (forward inclined, reclined, and upright) for six healthy subjects (aged 23 to 45 years) were determined using an open magnetic resonance imaging (MRI) scanner. An MRI-compatible and commercially available office chair was adapted for use in the scanner. The midpoint coordinates of the vertebral bodies, the wedge angles of the intervertebral discs, and the lumbar lordotic angle were analysed. The mean lordotic angles were 16.0 ± 8.5° (mean ± standard deviation) in a forward inclined position, 24.7 ± 8.3° in an upright position, and 28.7 ± 8.1° in a reclined position. All segments from T10-T11 to L5-S1 were involved in movement during positional changes, whereas the range of motion in the lower lumbar segments was increased in comparison to the upper segments.

Three-Dimensional Kinematics of an Unconstrained Ankle Arthroplasty: A Preliminary In Vivo Videofluoroscopic Feasibility Study:

Background: Understanding the functionality of total ankle arthroplasties (TAA) requires thorough knowledge of the kinematics during activities of daily life. Videofluoroscopy enables the in vivo measurement of the 3D kinematics of implant components more accurately than by means of skin marker tracking. The aim of the present preliminary study was to quantify the 3D kinematics of a TAA during the stance phase of level and slope walking using single plane videofluoroscopy. Methods: The experimental set up consisted of a videofluoroscopy system (BV Pulsera, Philips Medical Systems, Switzerland, 25 Hz, 1 ms shutter time) integrated in a walkway, allowing the assessment of free level gait, uphill, downhill and cross-slope walking. 2D/3D registration was performed using the CAD models of the TAA. In a preliminary feasibility study, the presented method was applied on four patients with successful unilateral TAA (Mobility™ Total Ankle, DePuy) with good outcomes. Results: Isolated 3D TAA kinematics was quantified with a rotational and translational error of 0.2 degrees and 0.4 mm in plane and 1.3 degrees and 2.1 mm out of plane. In the feasibility study it was found that only minor limitations occurred in sagittal plane motion. Any restrictions were caused by a limitation in dorsiflexion, whereas plantarflexion was for all gait conditions sufficiently provided. Transverse and frontal plane rotation was marginal, the main rotation occurred around the talar construction axis itself. Conclusion: The presented method enabled accurate estimation of the 3D TAA kinematics in vivo, without being limited by skin movement artifacts and isolated from subtalar motion. Since the available amount of dorsiflexion is the crucial factor to allow unrestrictive gait, walking uphill is an appropriate motion task to challenge and evaluate the performance of the TAA. Clinical Relevance: The presented method has the potential to identify specific kinematic patterns and thereby help clinicians and implant developers to evaluate current designs and future design modifications.

Subject-specific modeling of muscle force and knee contact in total knee arthroplasty

Understanding the mechanical loading environment and resulting joint mechanics for activities of daily living in total knee arthroplasty is essential to continuous improvement in implant design. Although survivorship of these devices is good, a substantial number of patients report dissatisfaction with the outcome of their procedure. Knowledge of in vivo kinematics and joint loading will enable improvement in preclinical assessment and refinement of implant geometry. The purpose of this investigation was to describe the mechanics of total knee arthroplasty during a variety of activities of daily living (gait, walking down stairs, and chair rise/sit). Estimates of muscle forces, tibial contact load, location, and pressure distribution was performed through a combination of mobile fluoroscopy data collection, musculoskeletal modeling, and finite element simulation. For the activities evaluated, joint compressive load was greatest during walking down stairs; however, the highest contact pressure occurred during chair rise/sit. The joint contact moment in the frontal plane was mainly varus for gait and walking down stairs, while it was valgus during chair rise/sit. Excursion of the center of pressure on the tibial component was similar during each activity and between the medial and lateral sides. The main determinants of center of pressure location were internal–external rotation, joint load, and tibial insert conformity.

Model-based estimation of active knee stiffness

Knee joint impedance varies substantially during physiological gait. Quantifying this modulation is critical for the design of transfemoral prostheses that aim to mimic physiological limb behavior. Conventional methods for quantifying joint impedance typically involve perturbing the joint in a controlled manner, and describing impedance as the dynamic relationship between applied perturbations and corresponding joint torques. These experimental techniques, however, are difficult to apply during locomotion without impeding natural movements. In this paper, we propose a method to estimate the elastic component of knee joint impedance that depends on muscle activation, often referred to as active knee stiffness. The method estimates stiffness using a musculoskeletal model of the leg and a model for activation-dependent short-range muscle stiffness. Muscle forces are estimated from measurements including limb kinematics, kinetics and muscle electromyograms. For isometric validation, we compare model estimates to measurements involving joint perturbations; measured stiffness is 17% lower than model estimates for extension, and 42% lower for flexion torques. We show that sensitivity of stiffness estimates to common approaches for estimating muscle force is small in isometric conditions. We also make initial estimates of how knee stiffness is modulated during gait, illustrating how this approach may be used to obtain parameters relevant to the design of transfemoral prostheses.

Kinetic and kinematic differences between deadlifts and goodmornings

BackgroundIn order to improve training performance, as well as avoid overloading during prevention and rehabilitation exercises in patients, the aim of this study was to understand the biomechanical differences in the knee, hip and the back between the exercises “Goodmornings” (GMs) and “Deadlifts” (DLs).MethodsThe kinetics and kinematics of 13 subjects, performing GMs and DLs with an additional 25% (GMs), 25% and 50% (DLs) body weight (BW) on the barbell were analysed. Using the kinetic and kinematic data captured using a 3D motion analysis and force plates, an inverse approach with a quasi-static solution was used to calculate the sagittal moments and angles in the knee, hip and the trunk. The maximum moments and joint angles were statistically tested using ANOVA with a Bonferroni adjustment.ResultsThe observed maximal flexion angle of the knee was 5.3 ± 6.7° for GMs and 107.8 ± 22.4° and 103.4 ± 22.6° for DLs with 25% and 50% BW respectively. Of the hip, the maximal flexion angle was 25% smaller during GMs compared to DLs. No difference in kinematics of the trunk between the two exercises was observed. For DLs, the resulting sagittal moment in the knee was an external flexion moment, whereas during GMs an external extension moment was present. Importantly, no larger sagittal knee joint moments were observed when using a heavier weight on the barbell during DLs, but higher sagittal moments were found at the hip and L4/L5. Compared to GMs, DLs produced a lower sagittal moment at the hip using 25% BW while generating the same sagittal moment at L4/L5.ConclusionsThe two exercises exhibited different motion patterns for the lower extremities but not for the trunk. To strengthen the hip while including a large range of motion, DLs using 50% BW should be chosen. Due to their ability to avoid knee flexion or a knee flexion moment, GMs should be preferentially chosen over DLs as ACL rupture prevention exercises. Here, in order to shift the hamstring to quadriceps ratio towards the hamstrings, GMs should be favoured ahead of DLs using 50% BW before DLs using 25% BW.

Comparison of distinctive gait variables using two different biomechanical models for knee joint kinematics in subjects with knee osteoarthritis and healthy controls.

BACKGROUND Gait analysis is an important instrument in clinical research and results should be objective. The purpose of this study was to quantify clinical outcomes of two biomechanical models with different anatomical coordinate systems and angle decomposition strategies for knee joint kinematics. METHODS The study was designed to compare a functional approach and a predictive approach with a single comprehensive marker set. 10 healthy subjects and 12 subjects with knee osteoarthritis were analysed. Distinctive gait variables were averaged across five trials. Agreement between methods was illustrated with the so-called levels of agreement. Differences between models were quantified using a paired t-test or Wilcoxon-Signed Rank test in case of non-normality (Shapiro-Wilk test). Unpaired t-tests/Wilcoxon tests were used to compare gait variables between healthy subjects and subjects with knee osteoarthritis, and to examine whether statistical analysis of this comparison would yield different data interpretations when using different models. FINDINGS Outcome variables differed between the functional and predictive approaches in the sagittal plane (0.1-3.1°), and transverse plane (1.0-3.7°). With respect to the range of motion in the given movement plane, variables in the sagittal plane of the knee were more consistent between methods. The functional approach was more sensitive for detecting differences between groups for sagittal plane kinematics. Statistical analysis for transverse plane kinematics differed substantially between models. INTERPRETATION Sensitivity to detect differences of kinematic data between population groups can vary between biomechanical models. Rotational gait variables are inconsistent between models and should not be used as clinical outcome variables in daily routine.