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Use of motor units in relation to muscle fiber type and size in man
Author(s) -
Jakobsson Finnbogi,
Borg Kristian,
Edström Lars,
Grimby Lennart
Publication year - 1988
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/mus.880111205
Subject(s) - motor unit , fiber type , muscle fibre , heel , fiber , anatomy , muscle power , medicine , fast twitch muscle , physical medicine and rehabilitation , materials science , skeletal muscle , composite material
The use of the musculus tibialis anterior during walking and the type and size of its muscle fibers were determined in 15 young normal subjects (29 ± 4 years) and in 13 old healthy subjects (70 ± 3 years). In the average step cycle 16 ± 6% of the maximal surface EMG was recorded during the swing phase and 44 ± 15% during 100 msec at the heel strike. Single motor unit recordings showed that low‐ threshold units fired at 10–15 Hz during the swing and at 20–25 Hz during the heel strike peak. Usually, high‐threshold units did not participate in the ordinary step cycle. A significantly higher mean use was found in the old subjects as compared with the young ones presumably due to lower muscle power in relation to body weight. In the young subjects 76 ± 7% of the muscle fibers were type 1 and 22 ± 7% were type 2A. In the old subjects 84 ± 9% were type 1 and 15 ± 8% were type 2A. In the young subjects the mean cross‐sectional area of type 1 fibers was 3950 ± 950 μm 2 and of type 2 fibers was 8070 ± 1850 μm 2 . In the old subjects the corresponding numerals were 4050 ± 890 μm 2 and 5700 ± 1970 μm 2 , respectively. The significance of physiological variations in use for muscle fiber type composition and size is discussed.