title: Adaptive transformation of rat soleus motor units during growth.
abstract: Soleus motor units of 5 and 34 week-old rats, weighing 150 and 520 g respectively, were examined for contraction time at 36 degrees C, innervation ratio as well as cross-sectional area, ATPase and SDH activity of fibres. The muscle was continuously adjusted to the growth of the animal. Between 5 and 34 weeks the proportion of Type II fibre units with 15-26 msec contraction time decreased from 33% to 10% and Type I fibre units with 27-40 msec contraction time thus increased from 67 to 90%. This was parallelled by approximately the same relative changes in number of Type II and Type I fibres.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D006003:Glycogen / Q000378:metabolism; D008297:Male; D009119:Muscle Contraction; D024510:Muscle Development; D009132:Muscles / Q000201:enzymology; D051381:Rats; D013385:Succinate Dehydrogenase / Q000378:metabolism
chemical_list: D006003:Glycogen; D013385:Succinate Dehydrogenase; D000251:Adenosine Triphosphatases