Myofibril and sarcoplasmic reticulum changes with exercise and growth

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Abstract
The intent of this study was to observe the effects of different treadmill running programs upon selected biochemical properties of soleus muscle from young rats. Young 10 day litter-mates were assigned to endurance (E), sprint (S) and control (C) groups. Each was partitioned into either 21 or 51 day exercising groups and 10 day controls. For C the myofibril ATPase activity at 21 and 51 days were lower than 10 day activity (p≤0.05). In the 51 day E group ATPase activity (0.378±0.009 Μmol Pi·mg−1·min−1) was greater than at 10 and 21 days (0.307±0.006 and 0.323±0.008 Μmol Pi·mg−1·min−1) (p≤0.05). No change occurred in the S group from 10 to 21 and 51 days (p≥0.05). Both the 21 and 51 day S (0.318±0.011 and 0.399±0.010 Μmol Pi·mg−1·min−1) and E (0.323±0.008 and 0.378±0.009 Μmol Pi·mg−1·min−1) groups had higher activity compared to the C group (0.193±0.029 and 0.172±0.031 Μmol Pi·mg−1·min−1) (p≤0.05). Maturation (10–51 day) resulted in a lowered sarcoplasmic reticulum (SR) yield and Ca2+ binding (p≤0.05) while Ca2+ uptake ability did not change (p≥0.05). SR yield, Ca2+ binding and uptake were not altered with S training (p≥0.05). The E training resulted in greater Ca2+ uptake at 51 days compared to C and S (p≤0.05), with no change in Ca2+ binding (p≥0.05). The data suggest that E training alters the normal development pattern of young rat soleus muscle.