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1 Centre for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager ST7 2HL, United Kingdom; and 2 Institute for Fundamental and Clinical Human Movement Sciences, Vrije University, 10B1 BT Amsterdam, The Netherlands
The aim of this study was to
investigate the effect of repeated contractions on the geometry of
human skeletal muscle. Six men performed two sets (sets A
and B) of 10 repeated isometric plantarflexion contractions
at 80% of the moment generated during plantarflexion maximal voluntary
contraction (MVC), with a rest interval of 15 min between sets. By use
of ultrasound, the geometry of the medial gastrocnemius (MG) muscle was
measured in the contractions of set A and the displacement
of the MG tendon origin in the myotendinous junction was measured in
the contractions of set B. In the transition from the 1st to
the 10th contractions, the fascicular length at 80% of MVC decreased
from 34 ± 4 (means ± SD) to 30 ± 3 mm
(P < 0.001), the pennation angle increased from
35 ± 3 to 42 ± 3° (P < 0.001), the
myotendinous junction displacement increased from 5 ± 3 to
10 ± 3 mm (P < 0.001), and the average
fascicular curvature remained constant (P > 0.05) at
~4.3 m
1. No changes (P > 0.05) were
found in fascicular length, pennation angle, and myotendinous junction
displacement after the fifth contraction. Electrogoniometry showed that
the ankle rotated by ~6.5° during contraction, but no differences
(P > 0.05) were obtained between contractions. The
present results show that repeated contractions induce tendon creep,
which substantially affects the geometry of the in-series contracting
muscles, thus altering their potential for force and joint moment generation.
ultrasound; in vivo; fascicular length; pennation angle; curvature
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