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J Appl Physiol (August 23, 2002). doi:10.1152/japplphysiol.00604.2002
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Articles in PresS, published online ahead of print August 23, 2002
J Appl Physiol, 10.1152/jap.00604.2002
Submitted on July 8, 2002
Accepted on August 21, 2002

Repeated contractions alter the geometry of human skeletal muscle

Constantinos C Maganaris1*, Vasilios Baltzopoulos1, and Anthony J Sargeant1

1 Centre for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager, Cheshire, United Kingdom

* To whom correspondence should be addressed. E-mail: c.n.maganris{at}mmu.ac.uk.

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. Using 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 deg (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 5th contraction. Electrogoniometry showed that the ankle rotated by ~6.5 deg during contraction, but no differences (P>0.05) were obtained between contractions. The present results show that repeated contractions induce tendon creep, which affects substantially the geometry of the in-series contracting muscles, thus altering their potential for force and joint moment generation.




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