Changes in postural muscle dynamics as a function of age

Histologic studies have demonstrated both a decrease in size and loss in nu mber of type II muscle fibers with increasing age. Although these age-relat ed histologic changes are believed to result in decreased strength and func tional capacity age-related changes in muscle force dynamics have not been clearly elucidated. Using vibromyographic (VMG) techniques, we recorded mus cle activity of the soleus in 40 healthy adult volunteers spanning the age range of 20-82 years to test whether changes in postural muscle dynamics, i n the frequency range of 0.1-50 Hz were also associated with age. Although muscle dynamics below 15 Hz do not change with aging, the 30-50 Hz frequenc y components of the VMG were found to change significantly with advancing a ge (r = -.619, p = .0001). This was observed in both sexes independently. T he observed age-related changes in muscle force dynamics demonstrate distin ct physiologic alterations in muscle fiber activity. Further research will be required to fully elucidate the relationship between age-related changes in muscle fiber activity and other age-related conditions such as postural instability and osteoporosis.