[Inhibitory effect of running exercise on age-induced muscle atrophy]

The effects of a 10-week running exercise on the histochemical and morphological properties of muscle fibers in the soleus (SOL) and tibialis anterior (TA) muscles and also in spinal motoneurons were investigated in 4 groups of female rats. Animals of the control groups were 20, 90 and 100 weeks old. Animals of the experimental group were 100 weeks old, and were exercised on a running wheel for 10 weeks. Muscle fibers examined were classified as slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG) or fast-twitch glycolytic (FG) according to their contractile and metabolic profiles. Spinal motoneurons innervating the SOL and TA were identified by retrograde neuronal labelling of fluorescent dye, nuclear yellow. Oxidative enzyme activities of motoneurons in the neuron pool were examined by microspectrophotometry. When compared to 20 week old rats, a decrease in the number of FOG in the SOL and of FG in the TA was observed in 90 and 100 week old rats. Findings of atrophy were observed in SO and FOG of the SOL and in FOG and FG of the TA in 90 to 100 week old rats. Practically no changes were observed with aging in the number and oxidative capacity of motoneurons in the SOL neuron pool. However, a decrease with aging was observed in the number and oxidative capacity of motoneurons in the TA neuron pool. From these results it is indicated that exercise inhibits the age-induced atrophy of SO fibers in the SOL.