Biomedical subjects

Jason C Gillette

Publications and source records attributed to Jason C Gillette.

7 recordsLinked to original sources

PubMed2006

Lower extremity mechanics of iliotibial band syndrome during an exhaustive run.

Injury patterns in distance running may be related to kinematic adjustments induced by fatigue. The goal was to measure changes in lower extremity mechanics during an exhaustive run in individuals with and without a history of iliotibial band syndrome (ITBS). Sixteen recreational runners ran to voluntary exhaustion on a treadmill at a self-selected pace. Eight runners had a history of ITBS. Twenty-three reflective marker positions were recorded by an eight-camera 120 Hz motion capture system. Joint angles during stance phase were exported to a musculoskeletal model (SIMM) with the iliotibial band (ITB) modeled as a passive structure to estimate strain in the ITB. For ITBS runners, at the end of the run: (1) knee flexion at heel-strike was higher than control (20.6 degrees versus 15.3 degrees, p=0.01); (2) the number of knees with predicted ITB impingment upon the lateral femoral epicondyle increased from 6 to 11. Strain in the ITB was higher in the ITBS runners throughout all of stance. Maximum foot adduction in the ITBS runners was higher versus control at the start of the run (p=0.003). Maximum foot inversion (p=0.03) and maximum knee internal rotation velocity (p=0.02) were higher versus control at the end of the run. In conclusion, ITB mechanics appear to be related to changes in knee flexion at heel-strike and internal rotation of the leg. These observations may suggest kinematic discriminators for clinical assessment.

Adult↗

PubMed2006

Optimization of foot placement for individuals with total knee replacements during sit-to-stand transfers.

Sit-to-stand transfers are a fundamental activity of daily living, but it remains unknown how to systematically recommend a foot placement that matches an individual's physical capabilities. The first goal of this study was to measure biomechanical changes in sit-to-stand movements as a function of foot placement. The second goal was to develop a model that would optimize foot placement for ease of sit-to-stand and would determine challenging foot placements for strengthening. A female older adult who had undergone bilateral total knee replacement participated in the study. Video and force platform data were collected for sit-to-stand movements from foot-back, foot-neutral, right-staggered, and left-staggered placements. The optimal foot placement was determined by minimizing the highest strength percentage for any single joint torque. Strength-challenging foot placements were found by maximizing the highest strength percentages for targeted joint torques. The right-staggered placement was optimal and had a limiting factor of left hip extension torque (strength percentage 74.7%). Maximum left hip extension torque (76.7 Nm) was similar to the maximum right hip extension torque (79.5 Nm) for this foot placement. The strength-challenging foot placement with the highest strength percentage was for left ankle plantar flexion torque (89.4%) and occurred while using the left-staggered placement. The optimal right-staggered foot placement for this older adult balanced the hip extension torques between the stronger, painful right side and the weaker, less painful left side. This model-based technique has the potential to allow clinicians to select foot placements that may enhance the functional independence of older adults with osteoarthritis.

Aged↗

PubMed2005

Support torques during simulated sit-to-stand movements.

Sit-to-stand movements are a fundamental daily activity and a prerequisite to upright posture. Previous simulations of spinal cord injured individuals using functional neuromuscular stimulation (FNS) suggested a forward foot placement would reduce hand-support forces. However, this recommendation has proved to be difficult for able-bodied individuals standing hands-free and for individuals with spinal cord injuries standing with a walker. This inverse model is a step towards the goal of using forward simulations to determine efficient sit-to-stand strategies. Initial seated postures varied from 80-110 degrees of knee flexion and 90-120 degrees of hip flexion. Realistic progressions of lower extremity joint angles including development of linear momentum were created using sigmoid functions. These kinematic values were used to estimate the required resultant joint torques to complete sit-to-stand. Joint torque values that act to raise the body were combined to indicate sit-to-stand difficulty from different seated postures. A representative foot-forward placement (knee 80 degrees, hip 90 degrees) resulted in a maximum combined torque of 544 Nm. In contrast, a representative foot-back placement (knee 110 degrees, hip 120 degrees) resulted in a maximum combined torque of 661 Nm. An intermediate seated posture (knee 97 degrees, hip 90 degrees) produced the lowest maximum combined torque of 401 Nm (2 Nm ankle plantarflexion, 201 Nm knee extension, 198 Nm hip extension). Foot-forward placement required substantial ankle dorsiflexion torques. The most efficient strategy appeared to be combining a foot back placement with momentum generation using hip flexion. By generalizing the sit-to-stand model beyond FNS-driven movements, further insight may be gained into other populations (i.e., elderly).

Computer Simulation↗

PubMed2004

NMES-assisted standing model from varied seated postures.

After spinal cord injury (SCI), intact lower motor neurons can be electrically activated to produce functional muscular contractions and enhance one's capabilities beyond seated activities. Even with neuromuscular electrical stimulation (NMES), significant amounts of hand-support forces are commonly required to move from a sitting to standing position. The goal of this project was to determine initial seated postures that reduce vertical hand-support forces while keeping anterior/posterior hand-support forces below levels that would cause walker slipping or tipping. A multi-segment biomechanical model was further developed and expanded to test multiple combinations of initial postures. The muscles that were analyzed included the vastus lateralis and semimembranosus. Varying the initial knee and hip angles created alternative seated postures. For vastus lateralis stimulation, the lowest vertical hand-support forces (63-66% of body weight) were predicted at the lower (70-74 degrees) and upper (110 degrees) ranges of initial knee flexion. With combined vastus lateralis and semimembranosus stimulation, the lowest predicted vertical hand-support forces were 2-10% of body weight at initial knee flexion angles between 70-82 degrees. Initial hip flexion angles above 110 degrees were required to prevent walker slipping and tipping in these cases. The development of hip extensor torque with semimembranosus stimulation was critical in reducing the vertical hand-support forces. One implication is that when training with parallel bars for NMES-assisted standing, hand-support forces should be monitored to avoid conditions that would tip a walker. In future models, optimizing the timing sequence for stimulating muscles may produce smoother coordination of joint rotations and further reduce the vertical hand-support forces.

Computer Simulation↗

PubMed2003

Foot placement alters the mechanisms of postural control while standing and reaching.

This study investigated the effects of altering foot placement on the strategies used by able-bodied subjects to perform reaching tasks while standing. The motivation for this study was to consider the results in the context of a person with a spinal cord injury using a functional neuromuscular stimulation (FNS) system to stand while reaching. Three foot placement conditions were compared as subjects reached to the left, right, and center. Centers of pressure (COP), joint angles, and joint moments were calculated as postural parameters using force platform and video marker data. Side-by-side and wide foot placements resulted in similar postural parameters. In contrast, the modified tandem stance (feet spaced at pelvic width with one foot shifted forward) resulted in anterior/posterior COP excursions that were larger in magnitude and more consistent across reach directions when compared to the other foot placement conditions. Furthermore, the movement patterns used during the tandem stance were more consistent and may be more readily achievable with FNS than the movement patterns utilized with the side-by-side and wide stances. These results suggest that the modified tandem stance may enhance the functionality of FNS standing systems and may also be useful in other standing rehabilitation programs.

Adaptation, Physiological↗

PubMed2003

Simulation of functional neuromuscular stimulation assisted sit-to-stand movements.

Functional neuromuscular stimulation (FNS) has the potential to enhance the capability for individuals with a spinal cord injury (SCI) to perform activities of daily living. Individuals with SCI have successfully used FNS to stand, but the transition from sitting to standing is often awkward and may require excessive amounts of arm support. The long-term goal of this research project is to provide stimulation patterns that reduce the demands on an FNS user's arms and provide a smooth, stable sit-to-stand transition. A multi-segment, dynamic model has been developed to simulate different combinations of stimulated muscles and stimulation patterns. The model includes individualized anthropometric parameters, active and passive muscle and joint mechanics, and arm support forces (experimentally measured or an assumed pattern). Stimulated muscle properties were derived using SIMM software (Musculographics, Chicago, IL), and the simulations were run in Matlab (Mathworks, Natick, MA). Initial simulation results have estimated that ramped stimulation of the vastus lateralis and semimembranosus muscles reduces the peak vertical arm support forces from 91% to 42% of body weight as compared to unassisted sit-to-stand. Kinematic results also suggested that the hand support forces remained excessive due to a lack of joint coordination and insufficient ankle joint stiffness. In further simulations, additional muscles will be stimulated to increase joint stiffness and stimulation patterns will be designed to mimic able-bodied sit-to-stand motions. This model will be validated and improved using results of sit-to-stand experiments with FNS users once an optimized set of muscles and stimulation patterns has been determined.

Arm↗

PubMed2002

Center of pressure measures to assess standing performance.

Functional neuromuscular stimulation (FNS) systems have provided individuals with spinal cord injury (SCI) varying levels of standing capability. Our long-term goal is to enhance an FNS user's ability to perform activities of daily living by providing sufficient standing stability. However, control of standing posture with complete SCI is compromised by a lack of sensory feedback from receptors in the feet. The goals of this study were: a) to document a variety of center of pressure (COP) measures during standing, b) to compare able-bodied and FNS standing, and c) to relate various measures to overall quality of standing performance. Two subjects with complete SCI that stand with FNS (one with a surface system and one with an implanted stimulation system) and five able-bodied subjects stood quietly on force platforms. Reduced hand support forces were coincident with anterior/posterior (A/P) mean COPs that were further posterior in the base of support and medial/lateral (M/L) mean COPs that were more centered between the feet. In addition, M/L COP excursions, maximum A/P COP velocities, and maximum M/L COP velocities were all significantly greater for FNS users than for able-bodied standers. Furthermore, maximum A/P COP velocities and mean A/P COP frequencies were significantly greater during FNS standing trails that required increased support from the hands. COP measures such as these may be useful tools to assess standing performance and to determine strategies for adjusting posture that can reduce an FNS user's reliance on upper extremity support while maintaining stable balance.

Activities of Daily Living↗