The Muscle Damage And Adaptation Of The Repeated Bout Eccentric Exercise And The Mechanism

Eccentric exercise is already an important part of athlete training and fitness exercise,one bout unaccustomed eccentric exercise often induces serious muscle damage,but after the repeated bout eccentric exercise1 or 2 weeks later,the muscle damage will decrease obviously,this phenomenon is known as "the repeated bout effect" or "protective effect".And researches also show us that the protective effect will decrease 4-6 weeks after the first bout eccentric exercise,but there are no researches show us whether this protective effect will decrease within 4weeks,or whether continuous eccentric training will keep and increase this protective effect.In my research SD rats were randomly divided into groups running downhill(-16°,16m/min) and college students did maximal voluntary eccentric is kinetic exercise with their elbow flexors as the first bout eccentric exercises,and 2/4/8/16days(students also 32days) later,the same exercise was done separately as the repeated bout exercise.And groups of rats also did the repeated bout eccentric exercise after 3 weeks continuous training.The muscle samples were taken and check under microscopy and electro-microscopy,Desmin was checked with imunohistochemistry technique,maximal isometric titanic force,CK and LDH in blood,MDA and SOD in muscle were assessed for rats,before and after exercises to show muscle damage,maximal isometric torque,muscle soreness, circumference of the arm,range of motion of the elbow were assessed before and after exercise to show muscle damage,maximal eccentric torque, optimal angle of the elbow,total work during exercise were also assessed for college students.And we found that:1) The first bout eccentric exercise induced serious muscle damage,and there were still muscle damage before the repeated bout exercise 2 and 4 days later,the muscle damage didn't increase but decrease after the repeated bout exercise. 2) There were no obvious muscle damage before the repeated bout exercise 8/16 and 32 days later,there were no or only modest muscle damage after the repeated bout exercise,show us that there were good protective effect during repeated bout exercise 8/16 and 32 days later.3) The protective effect of eccentric exercise diminished as the time between the two bout exercises increased,and the indexes showed different changes during the diminishing of the protective effect.4) There were no obvious muscle damage,muscle soreness,nor swelling of muscle,no decrease of range of motion of elbow after the repeated bout exercise 8 days later,show better protective effect;but after the repeated bout exercise 16 and especially 32 days later,there were some muscle soreness,swelling of muscle and decrease of range of motion of the elbow.5) There were obvious muscle damage after repeated bout eccentric exercise 4 days and 8 days after 3 weeks continuous training,show us continuous eccentric training kept and increased this protective effect.6) This protective effect were the results of adaptations with many mechanisms,including:the adaptation of nerves system to shift to recruitment of more slow twitch motor units;the adaptation of cytoskeleton and strength of the structure of muscle fiber;the adaptation and change of redox environment,become stronger against oxidative stress;the regeneration and increase of sarcomeres in series.