Engineering to enhance human mobility, play, and exploration
Our skeletal muscles have amazing structure. They provide elegant and efficient actuation to move and explore our worlds. But how do we understand how muscles produce movement?
Dr. Steele presents at the inaugural research symposium for the University of Washington Center for Translational Muscle Research. Her presentation shares examples for how we can use musculoskeletal simulation as a tool to connect muscle biology, dynamics, and mobility.
Journal article in Journal of Electromyography and Kinesiology:
In collaboration with Rehabilitation Medicine here at the University of Washington, we evaluated muscle use of 20 unimpaired participants during three upper-extremity functional tests. An interactive supplement can be found HERE.
Background: Performance-based tests, such as the Jebsen Taylor Hand Function Test or Chedoke Arm and Hand Activity Inventory, are commonly used to assess functional performance after neurologic injury. However, the muscle activity required to execute these tasks is not well understood, even for unimpaired individuals. The purpose of this study was to evaluate unimpaired muscle recruitment and coordination of the dominant and non-dominant limbs during common clinical tests.
Methods: Electromyography (EMG) recordings from eight arm muscles were monitored bilaterally for twenty unimpaired participants while completing these tests. Average signal magnitudes, activation times, and cocontraction levels were calculated from the filtered EMG data, normalized by maximum voluntary isometric contractions (MVICs).
Results: Overall, performance of these functional tests required low levels of muscle activity, with average EMG magnitudes less than 6.5% MVIC for all tests and muscles, except the extensor digitorum, which had higher activations across all tasks (11.7 ± 2.7% MVIC, dominant arm). When averaged across participants, cocontraction was between 25 and 62% for all tests and muscle pairs.
Conclusion: Tasks evaluated by speed of completion, rather than functional quality of movement demonstrated higher levels of muscle recruitment. These results provide baseline measurements that can be used to evaluate muscle-specific deficits after neurologic injury and track recovery using common clinical tests.
Journal article in Clinical Biomechanics:
Kat Steele partnered with Sabrina Lee from Northwestern University and the Rehabilitation Institute of Chicago to investigate shearwave ultrasound elastography as a new tool to quantify changes in muscle properties in cerebral palsy.
Abstract: Individuals with cerebral palsy tend to have altered muscle architecture and composition, but little is known about the muscle material properties, specifically stiffness. Shear wave ultrasound elastography allows shear wave speed, which is related to stiffness, to be measured in vivo in individual muscles. Our aim was to evaluate the material properties, specifically stiffness, as measured by shear wave speed of the medial gastrocnemius and tibialis anterior muscles in children with hemiplegic cerebral palsy across a range of ankle torques and positions, and fascicle strains. Shear wave speed was measured bilaterally in the medial gastrocnemius and tibialis anterior over a range of ankle positions and torques using shear wave ultrasound elastography in eight individuals with hemiplegic cerebral palsy. B-mode ultrasound was used to measure muscle thickness and fascicle strain. Shear waves traveled faster in the medial gastrocnemius and tibialis anterior of the more-affected limb by 14% (P = 0.024) and 20% (P = 0.03), respectively, when the ankle was at 90°. Shear wave speed in the medial gastrocnemius increased as the ankle moved from plantarflexion to dorsiflexion (less affected: r2 = 0.82, P < 0.001; more-affected: r2 = 0.69, P < 0.001) and as ankle torque increased (less affected: r2 = 0.56,P < 0.001; more-affected: r2 = 0.45, P < 0.001). In addition, shear wave speed was strongly correlated with fascicle strain (less affected: r2 = 0.63, P < 0.001; more-affected: r2 = 0.53, P < 0.001). The higher shear wave speed in the more-affected limb of individuals with cerebral palsy indicates greater muscle stiffness, and demonstrates the clinical potential of shear wave elastography as a non-invasive tool for investigating mechanisms of altered muscle properties and informing diagnosis and treatment.