Browsing by Author "Suydam, Stephen M."
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Item Ballistic movements: a unique approach to EMG normalizationand its effect on joint moment estimation(University of Delaware, 2011) Suydam, Stephen M.Modeling human movement using a computational based algorithm to predict muscle forces, ligament strains, and joint loads requires several inputs including normalized electromyographic (EMG) signals. Normalizing EMG reduces signal variability caused by electrode placement. EMG inputs scale the model’s output muscle forces and employing normalized values greater than 100% implies muscles are generating supramaximal forces. Signals from maximum voluntary isometric contractions (MVIC) are typically used for normalization, even though ballistic tasks can produce larger EMG singals. Ballistic task EMG signals normalized to MVIC EMG maximums could yield EMG values greater than 100%. Normalizing to maximal values ensures EMG signals remain below 100%. This thesis investigated dynamic signal repeatability and differences between MVIC EMG maximums and maximums from sprinting, jumping, and isokinetic movements to ascertain whether dynamic tasks produce significantly greater signals in search of a task which elicits reliable, maximal EMG. These maximum dynamic signals and the maximum MVIC values were used to normalize the model inputs. The model outputs of the two cases were compared. The results showed a significant increase of peak EMG values between the dynamic and MVIC cases for the lateral gastrocnemius (LG), medial gastrocnemius (MG), soleus (SL), vastus medialis (VM), and vastus lateralis (VL). The peak EMG was significantly greater between the ballistic and MVIC cases for the LG, MG, and SL. Divergences of signal magnitudes were repeated across testing sessions. Intra-session analysis revealed reliability in almost all peak EMG values. The two EMG-driven model outputs established the MVIC normalization procedure as the superior method. The r2 value of the knee moment for the MVIC case was 0.94 while the sprint case was 0.91 and the MVIC case produced a significant decrease in peak knee moment error, with respect to the moment calculated using inverse dynamics. This thesis identified MVIC EMG values as the better choice for normalizing dynamic EMG signals for the EMG-driven model and the results of this work establish a greater confidence in the model’s applicability to highly dynamic activities. This thesis also determined dynamic tasks exist which produce significantly larger, repeatable peak EMG signals than the MVIC tasks.Item The mechanical property changes occurring in the semitendinosus tendon post ACL reconstruction with a hamstring autograft(University of Delaware, 2015) Suydam, Stephen M.The potential strength asymmetries post anterior cruciate ligament (ACL) reconstruction using a bundled semitendinosus (ST) and gracilis tendon autograft can cause asymmetry in functional tasks measuring return previous level of activity. In order to utilize the regrowth of the ST tendon for the purpose of eliminating asymmetry, it is essential to show that the tendon indeed recovers its functional properties and correlate those to bilateral strength differences. Therefore, the aims of this study are as follows: Develop a non-invasive measurement system for determining tendon functional properties, calculate the elastic properties of regrown ST tendons and correlate those properties to bilateral strength compared to the healthy limb. Continuous shear wave elastography (cSWE) was used on gel samples and compared to published standard measure of MR elastography. cSWE matched the published standard with only 8.2% difference. Echogenicity effectiveness was assessed through the use of B-mode ultrasound and isometric contractions on the Achilles tendon. Ultrasound images were taken to track the soleus junction and collect image brightness during isometric contractions. Tendon stress was then correlated to brightness change. Due to minimal correlation between echogenicity and stress (r 2 =0.05), cSWE was used to evaluate the semitendinosus tendon. Sufficient power was reached with 13 subjects, between 6-24 months post-ACL reconstruction, to measure the bilateral difference in shear elastic modulus. To establish the impact of the mechanical property recovery, the same subjects were measured for peak torque during concentric flexion, eccentric flexion, and internal rotation of the leg. Flexion strength was determined at 60o/s and 120o/s and internal rotation strength was determined at 30o/s and 60o/s. The shear elastic modulus was significantly different between the involved and uninvolved legs (p=0.004) and was strongly correlated (r=0.60) to recovery time. The recovery of the tendon's shear modulus was strongly correlated to the difference in internal rotation strength at both 30o/s and 60o/s (r=0.70,0.65). This study is the first to show remaining strength asymmetries previously demonstrated by a semitendinosus resection can be recovered with time. Knowing the tendon recovers its mechanical properties between 6 and 24 months may correlate with the recovery rate within the 2 years following ACL reconstruction.