Amy Adkins – Abstract

Early Evidence for a Decrease in Biceps Optimal Fascicle Length Based on In Vivo Muscle Architecture Measures in Individuals with Chronic Hemiparetic Stroke

Adkins AN[1, 4, 5], Garmirian L[1, 2, 4], Nelson CM[1, 2], Dewald JPA[1, 2, 3], and Murray WM[1, 2, 3, 4, 5]
1. Department of Biomedical Engineering, Northwestern University, Evanston, Illinois, USA
2. Department of Physical Therapy and Human Movement Science, Northwestern University, Chicago, Illinois, USA
3. Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, Illinois, USA
4. Shirley Ryan AbilityLab, Chicago, Illinois, USA
5. Edward Hines, Jr. VA Hospital, Hines, Illinois, USA

There are currently no comprehensive in vivo muscle architecture studies that allow for the calculation of optimal fascicle length (OFL) in any impaired population or any upper limb muscle. Here we combined novel imaging methods to determine OFL and physiological cross-sectional area (PCSA) in the biceps brachii. We compared inter-limb differences in 5 participants with moderate to severe chronic hemiparetic stroke (2F/3M, 48-72yrs, Fugl-Meyer 12-33) and one able-bodied participant (M, 61yrs). Sarcomere length, fascicle length, and muscle volume of the biceps were measured in vivo in both arms under passive conditions. PCSA and OFL were calculated from these data using 2.7µm as optimal sarcomere length. To image sarcomeres in vivo, second-harmonic generation (SHG) microendoscopy (Zebra Medical Technology) was implemented on the long head of the biceps. The SHG signal was used to directly measure sarcomere length as a distance between A-bands(1). Separately, extended field-of-view ultrasound images were obtained(2); 3 images were obtained per arm, 4 fascicles were measured per image. In both studies, participants were seated, secured to a chair, with their arms supported in a controlled posture. In a third study, the Dixon method, a fat suppression MRI sequence, was used to acquire volume of biceps contractile material(3). For the able-bodied participant, absolute differences between limbs were <5% for all parameters. Inter-limb differences in fascicle and sarcomere length resulted in an OFL that was substantially shorter in the paretic limb of all stroke participants (30±10%). Inter-limb differences in volume and PCSA were less consistent across participants.

1. Sanchez G (2015) Neuron 88, 1109-1120
2. Nelson CM (2016) Journal of Biomechanics 49, 1948-1952
3. Garmirian L (2017) Proceedings of ASB, Boulder, CO, 2017