Effect of elbow joint angle on the magnitude of muscle damage to the elbow flexors.
Level 2 - randomized trial
Within-subject controlled experimental trial (contralateral limb design)
PubMed 11194107 · doi:10.1097/00005768-200101000-00005
What was done
Ten male students completed an experimental trial comparing two maximal eccentric exercise regimens with the same range of motion (80 degrees) but different starting joint angles using a contralateral arm design. One arm completed 24 maximal eccentric actions of the elbow flexors at 50 to 130 degrees (short length condition, S) and the contralateral arm at 100 to 180 degrees (long length condition, L). Maximal isometric force, range of motion, muscle soreness, plasma creatine kinase activity, upper arm circumference, and B-mode ultrasound were tracked pre-exercise and for 5 days post-exercise. Magnetic resonance imaging (MRI) transverse scans of the upper arm were collected 4 days post-exercise.
What was found
All measured markers changed significantly post-exercise in both conditions (P < 0.01), with significantly greater changes occurring in the L condition compared with the S condition (P < 0.01). MRI and ultrasound demonstrated damage confined only to the brachialis in the S condition, whereas both the brachialis and biceps brachii were damaged in the L condition. The abstract did not report absolute numerical values or effect sizes.
Why it matters
The findings demonstrate that muscle length during eccentric exercise strongly modulates the magnitude of muscle damage and determines which synergistic muscle heads are injured.
Limits
The study evaluated a very small sample (n = 10) consisting solely of male students. The abstract does not specify whether arm assignment was randomized or counterbalanced for limb dominance, and quantitative outcome measurements and confidence intervals are omitted.
Cited by
- supports Exercises that load muscles in a stretched position or emphasize the eccentric phase create more muscle damage than exercises loaded in shortened positions.
- supports Hip thrusts and glute bridges create less muscle damage than squat or hinge movements because they train the glutes in a shortened position.