Individual Muscle Forces during Sit to Stand Transfer

Engineering: 2nd Place (The Ohio State University Edward F. Hayes Graduate Research Forum)Due to weakened muscles or diseased joints, more than 2 million Americans over the age of 64 have difficulty accomplishing a sit-to-stand (STS) transfer independently. Previous studies have examined joint torques and muscle activations during STS by using motion capture or rigid body models. However, individual muscle forces during STS have yet to be investigated, and such knowledge will potentially inform rehabilitation strategies for patients with weakened muscles to improve performance with STS transfer. The first step toward accomplishing this goal was to examine individual muscle forces as well as inter-limb differences in muscle forces during STS transfer in a young, healthy population. Subject-specific simulations were created for each subject’s STS trial with a custom three-dimensional musculoskeletal model. Static optimization was implemented to estimate individual muscle forces. We found that vastus lateralis generated the largest force, reaching its peak value after maximum hip flexion occurred, while the medial gastrocnemius generated the smallest force out of all the muscles examined throughout STS once maximum hip flexion was reached. Inter-limb differences, quantified as a percent difference, showed high variability between subjects as the standard deviation values were over 100% for some of the muscles examined across the phases of STS. Understanding individual muscle forces as well as symmetry of muscle forces between legs during STS transfer in healthy subjects is the first step to analyzing muscle function and weakness in patients with pathologic conditions such as osteoarthritis and may potentially inform rehabilitation strategies that could improve these patients’ functional performance with this task.A one-year embargo was granted for this item

Integrated genomic approaches implicate osteoglycin (Ogn) in the regulation of left ventricular mass

Left ventricular mass (LVM) and cardiac gene expression are complex traits regulated by factors both intrinsic and extrinsic to the heart. To dissect the major determinants of LVM, we combined expression quantitative trait locus1 and quantitative trait transcript (QTT) analyses of the cardiac transcriptome in the rat. Using these methods and in vitro functional assays, we identified osteoglycin (Ogn) as a major candidate regulator of rat LVM, with increased Ogn protein expression associated with elevated LVM. We also applied genome-wide QTT analysis to the human heart and observed that, out of 22,000 transcripts, OGN transcript abundance had the highest correlation with LVM. We further confirmed a role for Ogn in the in vivo regulation of LVM in Ogn knockout mice. Taken together, these data implicate Ogn as a key regulator of LVM in rats, mice and humans, and suggest that Ogn modifies the hypertrophic response to extrinsic factors such as hypertension and aortic stenosi

Exploring the Relationship between Multi-Segment Foot Kinematics and Plantar Pressure Data in Adolescents with Planus and Cavus Foot Deformities: A Pilot Study

The medial longitudinal arch (MLA) plays a significant role in shock absorption and elasticity with respect to the motion of the foot. Pes planus (low MLA) and pes cavus (high MLA) are two deformities of the MLA commonly present in children with neurologic disabilities, which can contribute to abnormal walking patterns and the development of chronic foot pain long-term. It is often assumed that a change in MLA height equates with a change in medial or lateral plantar pressure. However, this relationship has not been sufficiently studied. The aim of this study was to investigate the relationship between MLA height and plantar pressure for specific regions of the foot to test the validity of this assumption. This study was accomplished by conducting a retrospective study using data gathered from the computerized gait analysis laboratory of a local rehabilitation hospital. By using a technique developed to integrate a multi-segment foot (MSF) model and plantar pressure data, the relationship between the severity of foot deformity and plantar pressure was examined; Spearman and Pearson coefficient values were calculated to determine the relationship between selected plantar pressure variables with respect to the mean stance MLA angle (MLAA); the relationship was considered statistically significant if the coefficient value was greater than .50 with a p-value of less than .05. More pes planus feet were found to have significantly higher impulse and contact area values in the plantar pressure of the medial midfoot region and more cavus feet were found to have higher mean pressure and impulse values in the plantar pressure of the lateral forefoot region. By measuring the MLAA from MSF kinematics interfaced with plantar pressure data, the magnitude of planus and cavus appears able to be assessed objectively, providing a useful way for tracking the progression of these common foot deformities over time

Muscle Forces and Their Contributions to Vertical and Horizontal Acceleration of the Center of Mass During Sit-to-Stand Transfer in Young, Healthy Adults

Sit-to-stand transfer is a common task that is challenging for older adults and others with musculoskeletal impairments. Associated joint torques and muscle activations have been analyzed two-dimensionally, neglecting possible three-dimensional (3D) compensatory movements in those who struggle with sit-to-stand transfer. Furthermore, how muscles accelerate an individual up and off the chair remains unclear; such knowledge could inform rehabilitation strategies. We examined muscle forces, muscleinduced accelerations, and interlimb muscle force differences during sit-to-stand transfer in young, healthy adults. Dynamic simulations were created using a custom 3D musculoskeletal model; static optimization and induced acceleration analysis were used to determine muscle forces and their induced accelerations, respectively. The gluteus maximus generated the largest force (2009.07 ± 277.31 N) and was a main contributor to forward acceleration of the center of mass (COM) (0.62 ± 0.18 m/s(2)), while the quadriceps opposed it. The soleus was a main contributor to upward (2.56 ± 0.74 m/s(2)) and forward acceleration of the COM (0.62 ± 0.33 m/s(2)). Interlimb muscle force differences were observed, demonstrating lower limb symmetry cannot be assumed during this task, even in healthy adults. These findings establish a baseline from which deficits and compensatory strategies in relevant populations (eg, elderly, osteoarthritis) can be identified

Forces Generated by Vastus Lateralis and Vastus Medialis Decrease with Increasing Stair Descent Speed

Stair descent (SD) is a common, difficult task for populations who are elderly or have orthopaedic pathologies. Joint torques of young, healthy populations during SD increase at the hip and ankle with increasing speed but not at the knee, contrasting torque patterns during gait. To better understand the sources of the knee torque pattern, we used dynamic simulations to estimate knee muscle forces and how they modulate center of mass (COM) acceleration across SD speeds (slow, self-selected, and fast) in young, healthy adults. The vastus lateralis and vastus medialis forces decreased from slow to self-selected speeds as the individual lowered to the next step. Since the vasti are primary contributors to vertical support during SD, they produced lower forces at faster speeds due to the lower need for vertical COM support observed at faster speeds. In contrast, the semimembranosus and rectus femoris forces increased across successive speeds, allowing the semimembranosus to increase acceleration downward and forward and the rectus femoris to provide more vertical support and resistance to forward progression as SD speed increased. These results demonstrate the utility of dynamic simulations to extend beyond traditional inverse dynamics analyses to gain further insight into muscle mechanisms during tasks like SD

Relationship between simple gait parameters and patient function before and after total knee arthroplasty

Human gait can change as a function of age and disease. The onset of knee osteoarthritis (OA) is associated with muscle weakness and knee instability, and results in a decreased knee range of motion compared to healthy controls [1]. Advanced cases of OA require a total knee arthroplasty (TKA) in attempt to relieve pain and improve function; however, suboptimal outcomes are very common. Patients often report knee instability and walking abnormalities, such as reduced range of motion in the knee joint and irregular muscle co-activation [2]. The purposes of this study were to determine if there are differences in the footpath ellipse during gait before and after TKA and to determine if characteristics of the footpath ellipse were related to a patient’s function

Post-operative function and muscle modules during gait at 6 and 24 months following total knee arthroplasty

The theory of muscle modules (or synergies) suggests that groups of muscles are activated synergistically via a common neural command [1]. While this idea has provided insight into the control of simple tasks like locomotion [2], the clinical relevance of this theory has only recently begun to be explored. For example, patients with higher function at one year following a cruciate-retaining (CR) total knee arthroplasty (TKA) displayed a higher number of muscle modules (n=4-5) compared to patients with lower function (n=2-3) [3]. This relationship between number of modules and function suggests that if muscle modules are able to change over time, it may be possible to develop module-focused clinical programs to improve patient function. The aim of this study was to determine muscle modules in patients with TKA during gait at 6 & 24 months post-operatively and to compare these modules to patient function. We hypothesized that (i) participants with a higher number of modules would demonstrate higher function and (ii) changes in patient function would be accompanied by changes in the number and characteristics of muscle modules