Changes of Length and Active Force of the Soleus Muscle According to the Position of Ankle Joint in Rabbit

Park, Yong Bum; Sohn, Young Jin; Seong, In Ho; Kim, Sung Tae; Baek, Goo Hyun; Chung, Moon Sang

Abstract

The dynamic performance of a skeletal muscle depends on the length-force and force-velocity relationships. The length-force relationship of muscle was described by Blix for the first time. The contractile elements of muscles produce the active length-force curve. The objective of this study is to determine the length-force relationship of the rabbit's soleus muscle and changes of tetanic force according to the position of ankle joint. The amount of excursion of the soleus muscle for full range of motion of the ankle joint was 25 mm. The ratio of excursion compared to the length of neutral position was 24%. That means that the soleus muscle has large amount of excursion that is responsible for producing active force throughout the whole range of ankle motion. The length at which active force of the muscle is maximal is called optimum length(Lo). The ratio of the optimum length compared to the length of neutral position was 98%. This means that the active force of the soleus muscle was maximal at the position of slight plantarflexion(about 2 degrees of plantarflexion). The value of the tetanic force was 3.1kg/cm2 in average, and the active length-force curve showed asymmetrical shape. The effective range is a length change from minimal point of zero active force to maximal point of zero active force. In this study, the minimal point of zero active force was 11mm shorter and maximal point of zero active force was 13mm longer than optimum length. Therefore, the effective range was 24mm. Active force increased abruptly at which muscle length was 90% of neutral length. At that point, active force was less than 20% of maximal tetanic force.