The long-term goal of this research is to understand the architecture and behavior of motor units in different human muscles. The motor unit is the basic functional unit of the neuromuscular system. The way muscle fibers are organized into motor units and the way motor unit activity is coordinated are important determinants of a muscle's ability to produce force and movement. The focus of this proposal is to investigate motor-unit organization and coordination in long, parallel-fibered human muscles. The fibers in these muscles are often assumed to span the entire length of the muscle. However, preliminary work supports the idea that some muscles, including brachioradialis, may instead have a complex architecture, consisting of arrays of shorter fibers arranged in series over a scaffolding of longer fibers. Some of the longer fibers receive innervation from more than one motoneuron at widely separated endplate zones. The way in which in-series fibers are organized into motor units, and the way these motor units are coordinated to transfer force effectively to the tendon are not known. The proposed study will investigate these issues through the following specific aims: (1) determining the innervation pattern in brachioradialis; (2) determining how motor units in brachioradialis are organized; (3) elucidating the strategy used to coordinate motor units at different proximodistal levels in brachioradialis; and (4) determining whether polyneuronally innervated fibers exist in other long, parallel-fibered muscles, including brachial biceps, sartorius, gracilis, and latissimus dorsi. A novel electrophysiological approach will be used. Electromyographic signals will be recorded during voluntary contractions using multiple fine-wire and needle electrodes. The signals will be decomposed to identify individual motor-unit action potentials. Motor-unit architectural properties, including endplate locations and fiber lengths, will be estimated by analyzing the action-potential waveforms, Motor-unit control properties, including recruitment and synchronization, and the existence of polyneuronally innervated fibers will be determined by analyzing the motor-unit discharge patterns. The proposed work will contribute knowledge about the structure and function of particular human muscles which will be directly relevant to several clinical applications, including tendon-transfer and reconstructive surgery, functional electrical stimulation, neurological and kinesiological electromyography, and therapeutic exercise. ? ?

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
1R01AR049894-01
Application #
6602368
Study Section
Geriatrics and Rehabilitation Medicine (GRM)
Program Officer
Lymn, Richard W
Project Start
2003-05-15
Project End
2007-04-30
Budget Start
2003-05-15
Budget End
2004-04-30
Support Year
1
Fiscal Year
2003
Total Cost
$176,346
Indirect Cost
Name
Palo Alto Institute for Research & Edu, Inc.
Department
Type
DUNS #
624218814
City
Palo Alto
State
CA
Country
United States
Zip Code
94304
McGill, Kevin C; Lateva, Zoia C (2011) History dependence of human muscle-fiber conduction velocity during voluntary isometric contractions. J Appl Physiol 111:630-41
Lateva, Zoia C; McGill, Kevin C; Johanson, M Elise (2010) The innervation and organization of motor units in a series-fibered human muscle: the brachioradialis. J Appl Physiol 108:1530-41
Lateva, Zoia C; McGill, Kevin C (2007) Electrophysiological evidence of doubly innervated branched muscle fibers in the human brachioradialis muscle. Clin Neurophysiol 118:2612-9
McGill, K C (2004) Surface electromyogram signal modelling. Med Biol Eng Comput 42:446-54