Effect of elbow joint angle on the magnitude of muscle damage to the elbowflexors

Purpose: It has been shown that eccentric actions at a long muscle length r esult in a larger decrease in force and more muscle tenderness compared wit h those at a short muscle length. To further investigate the effect of elbo w joint angle on the development of muscle damage, this study compared two maximal eccentric exercise regimens in which the starting position of the a ction was different, but the range of movement was the same. Methods: One a rm of 10 male students performed 24 maximal eccentric actions of the elbow flexors at the elbow joint angle from 0.87 to 2.27 rad (50-130 degrees: S c ondition) and the other arm at the elbow joint angle from 1.74 to 3.14 rad (100-180 degrees: L condition). Maximal isometric force, range of motion, m uscle soreness, plasma creatine kinase activity, upper arm circumference an d B-mode ultrasound pictures of the elbow flexors (US) were measured before and for 5 d postexercise in both conditions. Magnetic resonance imaging (M RI) of the transverse scans of the upper arm was taken at 4 d after exercis e. Results: All measures changed significantly (P < 0.01) after exercise fo r bath conditions; however, significantly (P < 0.01) larger changes in the measures were found in the L condition compared with the S condition. MRI a nd US displayed that only the brachialis was damaged for the S condition bu t the biceps brachii was also damaged for the L condition. Conclusion: The greater development of muscle damage in the L condition compared with the S condition is likely to be associated with the elbow flexors muscles affect ed by the exercise.