title: Motor unit discharge rate in dynamic movements of the aging soleus.
abstract: Aging is related to a variety of changes at the muscular level. It seems that the age-related changes in motor unit activation are muscle- and intensity dependent. The purpose of this study was to examine the motor unit discharge rate (MUDR) in both isometric and dynamic contractions of the aging soleus muscle. Eight elderly males participated in the study. The subjects performed isometric and dynamic plantar flexions while seated in an ankle dynamometer. The force levels studied were 10, 20, 40, 60, 80 and 100% of the isometric (ISO) maximal voluntary contractions (MVC) in ISO and 10, 20 and 40% in concentric (CON) and eccentric (ECC) contractions. Soleus intramuscular EMG was recorded with bipolar fine-wire electrodes and decomposed to individual trains of motor unit discharges. In ISO the MUDR increased with each force level from 40 to 100% MVC. In dynamic contractions the descriptive analysis showed a higher MUDR in CON compared to ISO or ECC. The difficulties of recording single motor units in dynamic contractions, especially in the elderly is discussed.
authors.affiliation: Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Jouni
authors.initials: J
authors.lastname: Kallio
authors.affiliation: Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark Odense, Denmark.
authors.forename: Karen
authors.initials: K
authors.lastname: Søgaard
authors.affiliation: Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Avela
authors.affiliation: Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Paavo V
authors.initials: PV
authors.lastname: Komi
authors.affiliation: LIKES, Foundation for Sport and Health Sciences Jyväskylä, Finland.
authors.forename: Harri
authors.initials: H
authors.lastname: Selänne
authors.affiliation: Vuokatti Snowpolis, Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä Jyväskylä, Finland.
authors.forename: Vesa
authors.initials: V
authors.lastname: Linnamo
keywords: aging; dynamic contraction; intramuscular electromyography; motor unit; soleus