The response of adult and developing rat plantaris muscle to overload

Abstract

The effect of overload on the rat plantaris muscle was studied in animals of different ages. Overload was induced by removal of gastrocnemius and soleus muscles. As expected, when the operation was carried out in adults, the plantaris muscle became heavier and stronger. These changes occured within 30 days after the operation. In animals in which the operation was carried out 1-12 days after birth and the muscle examined 6-20 weeks later, different results were obtained. In the group operated at 1-9 days of age, the muscles developed a lower maximal twitch and tetanic tension than the contralateral plantaris muscle. There was no difference in the time to peak or muscle weight between the overloaded and the contralateral muscles. Similar changes were observed in animals where the overload was induced at 11 or 12 days of age except for the weight which was significantly higher than that of the control plantaris muscles. The number of slow fibers increased in animals where overload was induced 11-12 days postnatally or in adults, but not when muscles were overloaded at 9 days of age. The possible reasons for the different response of adult and neonatal muscles to overload are discussed.

Force regulation and electrical properties of motor units in overloaded muscle

“…The finding of higher TetF values in this study for all MU types of overloaded MG was in accordance with earlier observations . Olha et al .…”

“…The results summarized in Table indicate that notable overload effects were induced in the MG muscle, as the majority of basic MU properties were modified in accordance with previous observations . Effects of the 3‐month compensatory overload affected all MU types, but the most noticeable were in relation to FR units.…”

Adaptation of mouse skeletal muscle to a novel functional overload test: changes in myosin heavy chains and SERCA and physiological consequences

“…Although this con®rms the results found in previous studies using other methods of overload (Ianuzzo et al 1976;Baldwin et al 1982;Timson et al 1985;Frischknecht and Vrbova 1991;Frischknecht et al 1995;Yamaguchi et al 1996), the reported increase in muscle mass observed in these studies was larger than that observed in the present work. This may be due to the difference in application of the overload: in the present work, the load was applied to the whole hindlimb and all muscles were kept intact; thus a large portion of the overload was carried by other muscles, and in particular by gastrocnemius muscle.…”