- A sample of fibers from deep (close to the bone) and superficial (away from the bone) regions of the plantaris (PLT) and medial (MG) and lateral (LG) gastrocnemius muscles of a neonatal, a 17-day-old and an adult giraffe were typed qualitatively as dark or light based on alkaline preincubation myosin ATPase staining properties and then sized.
- Each muscle at all ages showed a higher percentage and a larger cross-sectional area (CSA) of light ATPase fibers in the deep than the superficial region. This relationship was qualitatively, although not quantitatively, similar to that reported in hindlimb muscles of other mammals.
- At all ages, the PLT, the deepest muscle in the synergistic group, had the highest relative total CSA of light ATPase fibers among the muscles sampled.
- At birth, the PLT had an unusually high percentage of light ATPase fibers in comparison to that found in the same muscle of other mammals. With age, the total CSA of light ATPase fibers increased dramatically in the PLT and decreased slightly in the MG and LG.
- These data suggest that the PLT, especially the deep portion, may functionally replace the soleus muscle which is absent in the giraffe. In addition, the fiber type results demonstrate that the changes in the fiber type composition of individual muscles observed at different postnatal ages in the giraffe are relatively similar to that reported in smaller mammals, suggesting the existence of similar regulatory mechanisms.
