Tension regulation during lengthening and shortening actions of the human soleus muscle |
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Authors: | G J Pinniger J R Steele A Thorstensson A G Cresswell |
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Institution: | (1) Department of Biomedical Science, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia, AU;(2) Department of Neuroscience, Karolinska Institute, and Stockholm University College of Physical Education and Sports, Box 5626, S-114 86, Stockholm, Sweden e-mail: andrew.cresswell@neuro.ki.se; Fax: +46-8-4022287, SE |
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Abstract: | In the present study we investigated tension regulation in the human soleus (SOL) muscle during controlled lengthening and
shortening actions. Eleven subjects performed plantar flexor efforts on an ankle torque motor through 30° of ankle displacement
(75°–105° internal ankle angle) at lengthening and shortening velocities of 5, 15 and 30° · s−1. To isolate the SOL from the remainder of the triceps surae, the subject's knee was flexed to 60° during all trials. Voluntary
plantar flexor efforts were performed under two test conditions: (1) maximal voluntary activation (MVA) of the SOL, and (2)
constant submaximal voluntary activation (SVA) of the SOL. SVA trials were performed with direct visual feedback of the SOL
electromyogram (EMG) at a level resulting in a torque output of 30% of isometric maximum. Angle-specific (90° ankle angle)
torque and EMG of the SOL, medial gastrocnemius (MG) and tibialis anterior (TA) were recorded. In seven subjects from the
initial group, the test protocol was repeated under submaximal percutaneous electrical activation (SEA) of SOL (to 30% isometric
maximal effort). Lengthening torques were significantly greater than shortening torques in all test conditions. Lengthening
torques in MVA and SVA were independent of velocity and remained at the isometric level, whereas SEA torques were greater
than isometric torques and increased at higher lengthening velocities. Shortening torques were lower than the isometric level
for all conditions. However, whereas SVA and SEA torques decreased at higher velocities of shortening, MVA torques were independent
of velocity. These results indicate velocity- and activation-type-specific tension regulation in the human SOL muscle.
Accepted: 11 October 1999 |
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Keywords: | Electrical stimulation Electromyography Eccentric Plantar flexion Inhibition |
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