Biomedical subjects

Catherine A Stevermer

Publications and source records attributed to Catherine A Stevermer.

3 recordsLinked to original sources

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.

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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↗