What Do Single-Fiber Studies Tell Us about Exercise Training?

What Do Single-Fiber Studies Tell Us about Exercise Training?

BASIC SCIENCES

Medicine & Science in Sports & Exercise. 39(7):1051-1060, July 2007.
MALISOUX, LAURENT; FRANCAUX, MARC; THEISEN, DANIEL
Abstract:
Many exercise programs designed by trainers have the specific aim to
enhance strength, endurance, or power of certain muscle groups to
improve athletic performance. Muscle training is also an important
component of rehabilitation to limit atrophy associated with
immobilization, aging, or disease. To optimize exercise
interventions, a good understanding of the response to various
training programs and the identification of the mechanisms that
influence muscle function are required. Changes in the performance of
muscle contraction are associated, among other things, with muscle
fiber-type expression and functional properties of the contractile
apparatus.

Chemically skinned, single fibers is the only model that allows study
of the mechanical properties of human muscle fibers as a function of
the expression of myosin heavy-chain isoforms. Recently, this model
has been used to explore the functional adaptations after different
types of solicitations. The current results of the literature
indicate that cross-sectional area and force of a specific fiber type
are enhanced after resistance training, whereas maximal unloaded
shortening velocity is increased by endurance training. Plyometric
training improves both fiber force and shortening velocity. Fiber
peak power is increased after resistance or plyometric training, and
on a long-term basis it is decreased after endurance training.
Studies on elderly individuals indicate that this population may
react differently with respect to some single-fiber adaptations after
training. Generally, training regimens tend to decrease the
proportion of type IIx fibers. The available data in the literature
make it possible to formulate recommendations applicable to sport
science and rehabilitation.