Premium
Firing rate of the lower motoneuron and contractile properties of its muscle fibers after upper motoneuron lesion in man
Author(s) -
Frontera Walter R.,
Grimby Lennart,
Larsson Lars
Publication year - 1997
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/(sici)1097-4598(199708)20:8<938::aid-mus2>3.0.co;2-7
Subject(s) - myosin , motor unit , lesion , homogeneous , anatomy , fast twitch muscle , chemistry , fibre type , gene isoform , biology , medicine , skeletal muscle , pathology , biochemistry , physics , gene , thermodynamics
We studied motor unit (MU) firing rate and contractile properties and myosin isoform composition of single muscle fibers after upper motoneuron lesion. Single MUs and surface electromyogram (EMG) were recorded during voluntary contractions and locomotion in the paretic (P) and nonparetic (NP) tibialis anterior (TA) of 15 hemiparetics. P TA low‐threshold MUs fired within the lower end of their normal range. High‐threshold MUs fired below their normal range or were not recruited. Surface EMG was abnormally low and high in the P TA and NP TA, respectively. On muscle cross sections stained with histochemical methods, type I fibers represented 99.4%, 74.3%, and 66.6% of NP, P, and control TA, respectively. P TA fibers expressing type I myosin heavy chain (MyHC) were smaller, weaker, and slower. In conclusion, low MU firing rate and activity in the P TA was associated with slower type I MyHC fibers, while increased activity in NP TA resulted in homogeneous expression of type I MyHC. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 938–947, 1997