Objective: To study the morphometric characteristics of the human muscle spindle in normal muscle and to investigate the influence of aging.
Study design: The following variables were studied in 72 spindles: area and diameter of the spindle; thickness of the capsule; number, area and diameter of fibers; and number and area of nuclei.
Results: In deltoid and extensor digitorum brevis muscles, a reduction in the diameter of the spindle as a function of age was found, while no statistically significant change in the variables as a function of age was observed in the quadriceps femoris and biceps muscles. In the deltoid, a reduction in the number of fibers and an increase in their diameter were also observed.
Conclusion: These findings could prove useful in the study of the spindle in relation to disease.