Submitted on August 23, 2005
Accepted on November 24, 2005
Stretch-shortening cycle exercises: an effective training paradigm to enhance power output of human single muscle fibers
Laurent Malisoux1, Marc Francaux1, Henri Nielens1, and Daniel Theisen1*
1 Departement of Physical Education and Rehabilitation, Catholic University of Louvain, Louvain-la-Neuve, Belgium
* To whom correspondence should be addressed. E-mail: daniel.theisen{at}edph.ucl.ac.be.
Functional performance of lower limb muscles and contractile properties of chemically skinned single muscle fibers were evaluated before and after 8 weeks of maximal effort stretch-shortening cycle (SSC) exercise training. Muscle biopsies were obtained from the vastus lateralis of 8 men before and after the training period. Fibers were evaluated regarding their mechanical properties and subsequently classified according to their myosin heavy chain content (SDS-PAGE). After training, maximal leg extensor muscle force and vertical jump performance were improved 12% (P<0.01) and 13% (P<0.001), respectively. Single fiber cross sectional area (CSA) increased 23% in type I (P<0.01), 22% in type IIa (P<0.001), and 30% in type IIa/IIx fibers (P<0.001). Peak force (P0) increased 19% in type I (P<0.01), 15% in type IIa (P<0.001), and 16% in type IIa/IIx fibers (P<0.001). When P0 was normalized with CSA no changes were found for any fiber type. Maximal shortening velocity was increased 18, 29 and 22% in type I, IIa and hybrid IIa/IIx fibers, respectively (P<0.001). Peak power was enhanced in all fiber types, and normalized peak power improved 9% in type IIa fibers (P<0.05). Fiber tension upon passive stretch increased in IIa/IIx fibers only (P<0.05). In conclusion, short-term SSC exercise training enhanced single fiber contraction performance via force and contraction velocity in type I, IIa and IIa/IIx fibers. These results suggest that SSC exercises are an effective training approach to improve fiber force, contraction velocity and therefore power.
