Frank Arthur Witzmann

The Effect of Ageing and Exercise on Skeletal Muscle Function

The contractile and selected biochemical properties of fast- and slow-twitch skeletal muscle were studied at 9, 18, and 28 months of age in sedentary and regularly exercised rats. The isometric twitch duration was prolonged with aging in both the fast- and slow-twitch muscle. This effect was primarily due to a prolonged one-half relaxation time (1/2RT), which developed late in life. Regular exercise tended to further prolong the twitch duration, particularly in the slow-twitch soleus. Surprisingly, twitch and tetanic tension (Po), peak rate of tension development and decline, and the maximal shortening velocity were all unaltered between 9 and 28 months of age. Furthermore, regular exercise (running or swimming) had little or no effect on these properties. The prolonged 1/2RT with aging could not be explained by a decreased rate of Ca2+ sequestration by the sarcoplasmic reticulum, as the rate of Ca2+ uptake measured in muscle homogenates was unaltered in any of the muscles studied between 9 and 28 months. The degree of muscle fatigue (decline in Po) with 30 min of contractile activity in the slow-twitch soleus was not affected by aging. However, lactate reached two-fold higher levels and glycogen fell to considerably lower levels in the muscles of the old rats. This suggests an increased glycolysis and glycogen utilization during contractile activity in aged rats.

A comparison of sarcoplasmic reticulum function in fast and slow skeletal muscle using crude homogenate and isolated vesicles

Abstract Sarcoplasmic reticulum vesicles (FSR) were isolated from relatively homogeneous muscle samples representative of type I, IIA, and IIB fibers and Ca 2+ uptake (V max and total capacity) determined. Crude homogenates of these same fiber populations were also assayed for Ca 2+ uptake and the results compared to the FSR values. Both techniques produced qualitatively similar results and demonstrated distinct fiber type differences in both the rate and extent of Ca 2+ uptake. The results obtained support the contention that the crude homogenate technique accurately reflects the activity of the sarcoplasmic reticulum.

The effect of exercise-training on sarcoplasmic reticulum function in fast and slow skeletal muscle

Abstract The effect of endurance exercise on the capacity of crube homogenates (CH) to sequester Ca 2+ was determined in the slow type I soleus, the fast type IIA deep region of the vastus lateralis (DVL), and the fast type IIB superficial region of the vastus lateralis (SVL). The Ca 2+ uptake capacity was affected by exercise in a fiber type specific manner. The fast-twitch SVL showed a 35% decrease in the maximal rate of Ca 2+ uptake (V max ) and a significantly lower K m while the slow soleus and fast DVL were unaltered. The time course of Ca 2+ uptake, and the peak amount of Ca 2+ sequestered was not altered by exercise in any of the muscles studied. The homogenates from the exercise-trained soleus muscles exhibited an increased ability to retain Ca 2+ and in this capacity became more like fast muscle.