Aging alters configuration of fast- and slow-twitch fibers associated with muscle fiber denervation.

Title: Effects of ageing on enzyme-histochemical, morphometrical and contractile properties of the soleus muscle in the rat.

Journal: Journal of the neurological sciences (1989) vol. 93: 105-124

Link: https://doi.org/10.1016/0022-510X(89)90165-2

Comments:

Sarcopenia is age-related loss of muscle mass (in skeletal muscle) and motor function and is a slow process caused by multiple factors such as inactivity, anorexia, inflammation, aging, endocrine, and neurodegeneration. Muscles consist of two types of muscle fibers, slow-twitch and fast-twitch fibers. This paper aimed to investigate whether enzyme-histochemical, morphometrical and physiological properties in the slow-switch soleus muscle of rats are related to ageing.

The cross-sections of muscle fiber were stained for myofibrillar ATPase. The fibers were classified into slow- and fast-twitch fibers according to the pH sensitivity of the myofibrillar ATPase. The total number of muscle fibers got smaller with ageing. While the number of slow-twitch fibers was reduced in old animals, the number of fast-twitch fiber showed a clear age-associated reduction. Fibers of all types increased in size in young adult animals. With advancing age, fast-twitch fibers especially decreased in size.

The tetanus force per muscle weight decreased with age. The contraction time was not significantly altered until after 20 months old. The half-relaxation time tended to increase gradually with age. Thus, the force-generating capacity of residual contractile material was not significantly affected by age and the age-associated decrease in the number of fast-twitch muscle fibers was not an important contributing factor to the decreased speed of contraction.