Biomechanics

Effects of Adiposity on Walking Muscle Function in Children: Implications for Bio-Feedback and Assistive Devices

Altered gait biomechanics associated with pediatric obesity may increase the risk of musculoskeletal injury/pathology during physical activity and/or diminish a child’s ability to engage in sufficient physical activity. The biomechanical mechanisms responsible for the altered gait in obese children are not well understood, particularly as they relate to increases in adipose tissue. The purpose of this study was to investigate the role of adiposity (i.e. body fat percentage, BF%) on lower extremity kinematics, muscle force requirements and their individual contributions to the acceleration of the center of mass (COM) during walking. We scaled a musculoskeletal model to the anthropometrics of each participant (n=14, 8-12 years old, BF%: 16-41%) and generated dynamic simulations of walking to predict muscle forces and their contributions to the acceleration of the COM. Muscle force output was normalized to muscle mass. BF% was correlated with average knee flexion angle during stance (r=−0.54) and pelvic obliquity range of motion (r=0.78), as well as with relative vasti (r=−0.60), gluteus medius (r=0.65) and soleus (r=0.59) force production. Contributions to COM acceleration from the vasti were negatively correlated to BF% (vertical: r=−0.75, posterior: r=−0.68, respectively), but there was no correlation between BF% and COM accelerations produced by the gluteus medius. The functional demands and relative force requirements of the hip abductors during walking in pediatric obesity may contribute to altered gait kinematics. Our results provide insight into the muscle force requirements during walking in pediatric obesity that may be used to improve the quality/quantity of locomotor activity in this population.
Listed In: Biomechanical Engineering, Biomechanics, Gait


The Influence of Trunk Posture on Hip and Knee Moments during Over-ground Running

A high incidence of lower extremity injuries has been reported in runners, with half of the injuries occurring at the knee joint. Sagittal plane trunk posture was shown to influence hip and knee kinetics during landing. This suggests trunk posture may be a risk factor of running injuries. The purpose of this study was aimed to examine the influence of sagittal plane trunk posture on hip and knee kinetics during running. Forty runners were recruited. Three-dimensional kinematics (250Hz, Qualisys) and ground reaction force data (1500Hz, AMTI) were collected while subjects ran with a self-selected trunk posture (speed: 3.4m/s). Mean trunk flexion angle and peak hip and knee extensor moments during the stance phase were calculated. Subjects were dichotomized into High-Flex and Low-Flex groups based on trunk flexion angles. On average, the two groups demonstrate 7.4°difference in trunk flexion. Independent t-tests showed that the Low-Flex group demonstrated significantly higher knee extensor moments and lower hip extensor moments compared to the High-Flex group. Pearson correlations showed that trunk flexion angle was positively correlated with peak hip extensor moment (r=0.44) and inversely correlated with peak knee extensor moment (r=-0.51). The results suggested a small difference in trunk flexion angle has significant influences on hip and knee kinetics. Individuals who run with a more upright trunk posture may be predisposed to a higher risk of patellar tendinopathy and patellofemoral pain. Incorporating a forward lean trunk may be utilized as an intervention strategy to reduce knee loading and risk of knee injuries in runners.


Listed In: Biomechanics, Physical Therapy, Sports Science


Impacts of Stifle Joint Remodeling on Vertical Ground Reaction Forces Following MCL Transection and Medial Meniscectomy

Functional demands placed on the human knee’s anterior cruciate ligament (ACL) vary with activity but remain impossible to measure directly in-vivo. Our lab is characterizing these demands in the sheep model by recording in vivo knee kinematics and ACL transducer voltages during activities of daily living (ADLs), reproducing these motions using the instrumented limb, and measuring the 3D forces in the ligament. However, up to 13% of patients sustaining ACL injuries will also sustain dual medial meniscus (MM) injuries and up to 10% will sustain dual medial collateral ligament (MCL) injuries. These structures are frequently left unrepaired, which may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. Although these structures have been shown to alter ACL loading in cadaveric studies, the extent to which they impact ACL functionality during in vivo ADLs remains unknown. Moreover, changes in ACL functionality over time due to joint healing and remodeling have yet to be investigated. In this study, we aimed to track stifle joint remodeling in response to surgically imposed MCL transections and medial meniscectomies through monitoring vertical ground reaction forces (VGRFs) for three ADLs over 12 weeks. Results of this study may then be used in conjunction with future robotic studies as a tool to estimate in vivo load requirements for ACL reconstructions in patients with dual injuries.


Listed In: Biomechanical Engineering, Biomechanics, Gait, Orthopedic Research


Accelerometry for outdoor effort quantification

Assessing the lower limb properties in-situ is of a major interest for analyzing the athletic performance. From a physical point of view, the lower limb could be modeled as single linear spring which supports the whole body mass. The main mechanical parameter studied when using this spring-mass-model is the leg-spring stiffness (k). In laboratory conditions, the movements are assessed using a force plate (Meth1) which measures the ground reaction force (GRF), and a motion capture system which could estimate the displacement of the centre of mass (CoM). In this way, k is calculated as shown in equation (2).More recent methods allow to calculate k in field conditions by using either foot switches (Meth2) or accelerometry-based instruments (Meth3) which are both wireless devices. The associated calculated methods assume that force-time signal is a sine wave, described by the equation (3) with equation (4) (CT: contact time; FT: flight time). In these cases, the kinematic measurement (CoM) could be calculated either by a mathematical approach (Eq.(5)) (meth2), or by double integrating the acceleration (meth3) in order to calculate k.Thanks to their transportability, the methods 2 and 3 offer not only the possibility to assess the lower limb movements, but also, to objectively follow up the athletic abilities (performance, reactivity, force and power, stiffness) in-situ.


Listed In: Biomechanical Engineering, Biomechanics, Sports Science


Study of biomechanical patterns for identifying biomarkers for knee osteoarthritis

Osteoarthritis (OA) is a chronic joint disease, the most common musculoskeletal complaint worldwide, and is associated with significant health and welfare costs. Previous research indicates that co-activation of muscles may lead to the onset of knee OA. Therefore, investigation of muscle recruitment patterns and neuromuscular efficiency in healthy individuals compared to patients with knee OA in simple closed chain exercises using electromyography (EMG), motion analysis system and force plates may lead to a better understanding of how knee OA develops (6). The present studies chosen were in the frontal plane while performing lateral step up and step down tasks for a 4 inch and 8 inch step height. In the stepping tasks it was discovered that there is a greater magnitude EMG and ground reaction force (GRF) for 8 inch rather than a 4 inch step. Additionally, a higher activation of gluteus medius, gluteus maximus and quadriceps muscles (rectus femoris , vastus lateralis , vastus medius) was revealed in both the stepping tasks.


Listed In: Biomechanics, Orthopedic Research, Physical Therapy


Between Landing Kinetic and Kinematic Differences in a Drop Vertical Jump

ACL ruptures are catastrophic injuries that are debilitating to athletes. Specific kinematic and kinetic variables observed in landing and cutting are associated with increased ACL injury risk. The drop vertical jump (DVJ) test has been established as an ideal task to evaluate neuromuscular control and simulate motions and moments that place athletes at risk for ACL injuries. A DVJ involves an athlete landing from a 31 cm drop followed by a maximal vertical jump and subsequent landing. This study aimed to examine kinetic and kinematic differences between the first and second landing of a DVJ. 239 middle and high school athletes each performed 3 trials of a DVJ task for a 10 camera motion analysis system while landing on AMTI force platforms. Kinematic variables demonstrated a decrease in peak hip and knee flexion, hip adduction, and knee abduction angles from the first to second landing. Kinetic variables demonstrated smaller peak knee flexion, knee abduction, and hip flexion moments in the second landing. Overall, the second landing exhibited mechanics characteristic of a higher intensity athletic task or lower neuromuscular control. The second landing may serve as a better screening tool for sagittal plane risk factors, while the first landing may prove optimal for the assessment of frontal plane control and injury risk.


Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Sports Science


Considerations when using a residual analysis to determine the optimum cutoff frequency for kinetic waveforms

Despite its use in biomechanics research, there exists no standardized method for implementing a residual analysis to define the optimum cutoff frequency (OCF) of low-pass digital filters. Given the potential for this processing to have an impact on results, an objective routine is necessary for consistent data treatment between investigations and laboratories. Therefore, the goal of this study was to formalize an objective routine to implement a residual analysis, and examine whether it could be applied to kinetic signals. METHODS - Part I: The following parameters were hypothesized to effect the OCF determined through residual analysis: (i) linearity criterion magnitude, (ii) frequency axis resolution and (iii) range of cutoff frequencies included in the analysis. Part II: Two existing datasets were used to evaluate the objective routine that was developed. For each study, four dependent measures were calculated from ground reaction force data, including: (i) peak force, (ii) time to peak force, (iii) rate of force development and (iv) impulse. To examine the influence of using a digital Butterworth filter with OCF, each measure was compared to both the raw signal and a commonly applied cutoff frequency of 20 Hz. RESULTS - The objective routine developed was found to be most sensitive to the range of frequencies included in the analysis. In Part II, both the F-20 and OCF filtering conditions had minimal impact on all force-time dependent measures, except for rate of force development. IMPLICATIONS - Residual analysis may not be appropriate for selecting an OCF when filtering kinetic signals.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Orthopedic Research, Sports Science