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.
Subject(s)
Ankle Joint , Ankle , Muscle, Skeletal , Muscles , Range of Motion, ArticularABSTRACT
A study was conducted to examine the effects of exhaustive enduring exercise training on the skeletal muscle of rats. Twenty-six male Wistar rats were divided into 3 groups : an exhaustive training group (EE), a free-eating control group (Co), and a pair weight group in which body weight was matched to EE (PW) . The rats in EE were forced to run on a treadmill with an inclination of 0-3°, 6 days/week for 4 weeks. At first the rats ran at a constant speed for 60 min. Then we gradually added 2 m/min to the basic speed every minute until they were exhausted. The treadmill speed was 20 m/min during the first, 30 m/min during the second, 35 m/min during the third, and 40 m/min during the final week. The muscle wet weight, the quantity of the muscle protein and the isometric tetanic force were measured with the soleus and extensor digitorum longus (EDL) . Food restriction induced significant decreases in EDL weight. Exhaustive enduring exercise training induced noteworthy decreases in soleus weight, but remarkable gains in EDL weight. It also induced significant changes of the quantity of the muscle protein in the two muscles, which corresponded to the changes in muscle weight. The isometric tetanic force of both muscles was not affected by food restriction. The isometric tetanic force showed a significant decreases in EDL in EE comparison Co. The isometric tetanic force of the soleus did not show a significant decreases. However, its degree of decrease corresponded to that of the muscle protein. These findings illustrate that exhaustive endurance exercise training induces degradation of the soleus and hypertrophy of the EDL. However, it also decrease the muscle force which generats the capacity of the two muscles. We think that this phenomenon depends on the skeletal muscle characteristics, such as fiber type, and eccentric or concentric contraction.