Myofibril and sarcoplasmic reticulum changes with exercise and growth

Summary

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.