Abstract
Age-related impairments in motor performance are caused by a deterioration in mechanical
and neuromuscular functions, which have been investigated from the macro-level of
muscle-tendon unit to the micro-level of the single muscle fiber. When compared to
the healthy young skeletal muscle, aged skeletal muscle is: (1) weaker, slower and
less powerful during the performance of voluntary contractions; (2) less steady during
the performance of isometric contractions, particularly at low levels of force; and
(3) less susceptible to fatigue during the performance of sustained isometric contractions,
but more susceptible to fatigue during the performance of high-velocity dynamic contractions.
These impairments have been discussed to be mainly the result of: a) loss of muscle
mass and selective atrophy of type II muscle fibers; b) altered tendon mechanical
properties (decreased tendon stiffness); c) reduced number and altered function of
motor units; d) slower muscle fiber shortening velocity; e) increased oscillation
in common synaptic input to motor neurons; and f) altered properties and activity
of sarcoplasmic reticulum. In this second part of a two-part review we have detailed
the age-related impairments in motor performance with a reference to the most important
mechanical and neuromuscular contributing factors.
Key words
aging - muscle strength - muscle power - force steadiness
