Acute muscle damage responses in elbow flexors following eccentric quasi-isometric exercise

This study aimed to compare acute muscle damage responses of the elbow flexors following eccentric quasi-isometric (EQI) and eccentric (ECC) exercise. Thirty healthy young men were randomly assigned to EQI or ECC (n = 15/group). Participants performed five sets of dumbbell elbow flexion to volitional failure. Maximal voluntary isometric contraction (MVC), elbow joint range of motion (ROM), upper arm circumference (CIR), pressure pain threshold (PPT), plasma creatine kinase (CK), and myoglobin (Mb) were measured before, immediately after, and 1, 2, 3, and 7 days post-exercise. Time under tension (TUT) was recorded. TUT was approximately 3.5-fold longer in EQI than ECC. ECC induced greater reductions in MVC (- 30% vs. -15%) and ROM (- 27% vs. -13%), and larger increases in CIR (+ 5% vs. +2%). Peak CK (11,601 ± 9,483 vs. 135.2 ± 33.1 IU/L) and Mb (406.7 ± 271.8 vs. 17.7 ± 6.2 ng/mL) were markedly higher following ECC. Distal PPT was 13-19% lower in ECC. Most variables returned to baseline by day 7 in EQI. Despite longer TUT, EQI induced substantially less acute muscle damage and faster recovery than ECC when both were performed to volitional failure at the same relative external load.