Muscle damage induced by maximal eccentric exercise of the elbow flexors after 3-week immobilization

The present study investigated the effects of a 3-week immobilization (IM) on muscle damage induced by maximal eccentric exercise (MaxEC) to test the hypothesis that the IM would make muscles prone to muscle damage. Young healthy sedentary men were pseudo-randomly assigned to IM or control group (n = 12/group). Non-dominant arms of the IM group participants were immobilized at 90° elbow flexion by a cast for 21 days. All participants performed MaxEC consisting of five sets of six elbow flexor contractions by lowering a dumbbell set at 100% of pre-exercise maximal voluntary isometric contraction (MVC) strength of the non-dominant arm. This was performed at 2 days after the cast removal for the IM group. MVC torque, range of motion (ROM), muscle thickness (MT), muscle hardness, position sense (PS), and joint reaction angle (JRA) of the elbow flexors were measured at baseline, post-immobilization, and before, immediately after, and one to 5 days after MaxEC. The IM decreased MVC torque (-17 ± 2%), ROM (-2 ± 1%), MT (-7 ± 3%), and JRA (-12 ± 6%), and increased in muscle hardness (20 ± 6%) and PS (11 ± 2%) (p < 0.05). Changes in MVC (e.g., 2 days: -40 ± 5 vs. -30 ± 9%), ROM (2 days: -11 ± 2 vs. -9 ± 3%), muscle soreness (peak: 63 ± 22 vs. 48 ± 14 mm), plasma CK activity (peak: 7820 ± 4011 vs. 4980 ± 1363 IU/L), PS (maximal change: -23 ± 2 vs. -18 ± 3%), and JRA (maximal change: -37 ± 4 vs. -26 ± 3%) after MaxEC were greater (p < 0.05) for the IM than control group. These results supported the hypothesis and showed that the IM made the muscles more vulnerable to muscle damage induced by eccentric exercise.