Comparison of eccentric knee extensor muscle actions at two muscle lengths on indices of damage and angle-specific force production in humans.
Level 2 - randomized trial
Randomized contralateral trial in human subjects
PubMed 9663954 · doi:10.1080/02640419808559358
What was done
Seven subjects performed two bouts of 75 maximal voluntary eccentric knee extensor contractions at an angular velocity of 1.57 rad/s. One bout was conducted at a short muscle length (160 to 80 degrees knee range of motion) and the other in the contralateral limb at a long muscle length (120 to 40 degrees range of motion). Maximal voluntary contractile force (MVC) was measured at three knee angles before, 5 minutes after, and at days 3, 5, 7, 10, and 12 post-exercise. Muscle soreness and serum creatine kinase activity were also tracked across the recovery period.
What was found
MVC significantly declined following both exercise bouts (P < 0.01), with a significantly greater reduction observed after the long-length bout (P < 0.05). Muscle soreness was significantly higher following the long-length bout compared to the short-length bout on days 1, 2, 3, 5, and 6 (P < 0.05). Serum creatine kinase activity increased following both bouts (P < 0.01), with no statistically significant difference between muscle lengths. Angle-specific force decrements indicated a transient increase in muscle length only after the long-length bout.
Why it matters
This study demonstrates that the degree of muscle damage and functional impairment from eccentric contractions is strongly dependent on the operating muscle length during contraction, with longer lengths inducing more severe impairment.
Limits
The study evaluated a very small sample size (n = 7) and did not report participant demographics, sex, or training status in the abstract. Absolute numerical values, effect sizes, and confidence intervals were not provided in the abstract.
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.