Contralateral versus ipsilateral protective effect against muscle damage of the elbow flexors and knee extensors induced by maximal eccentric exercise.
Level 2 - randomized trial
Randomized controlled trial in healthy humans
PubMed 37642310 · doi:10.1111/sms.14482
What was done
Fifty-two healthy sedentary young men (aged 20–28 years) were randomized into four groups of 13: ipsilateral elbow flexors (IL-EF), ipsilateral knee flexors (IL-KF), contralateral elbow flexors (CL-EF), and contralateral knee flexors (CL-KF). Participants completed maximal eccentric contractions (30 for EF, 60 for KF) across two exercise bouts separated by a 2-week interval. Muscle damage markers (maximal voluntary contraction torque, muscle soreness, plasma creatine kinase activity) and proprioception measures were assessed before and up to 5 days post-exercise.
What was found
Changes in all muscle damage variables were significantly greater (p < 0.05) after the first bout than after the second bout for all groups, and changes were greater (p < 0.05) for EF than KF. Following the second bout, changes were significantly larger (p < 0.05) in the CL condition than in the IL condition for both muscle groups. The average protective effect was 33% for CL-EF and 32% for CL-KF, compared to 67% for IL-EF and 61% for IL-KF (p < 0.05 between IL-EF and IL-KF), indicating that the contralateral protective effect was approximately 50% of the ipsilateral effect in both limbs.
Why it matters
This study demonstrates that cross-education provides a consistent level of protection against muscle damage across both upper and lower extremities, confirming a substantial central neural contribution to the repeated bout effect.
Limits
The study was conducted exclusively in young, sedentary men with a small sample size (n = 13 per group), limiting generalizability to females, older populations, and trained individuals. Central neural mechanisms were inferred rather than directly measured using neuroimaging or electrophysiological methods. Additionally, the title references knee extensors whereas the abstract text specifies knee flexors.
Cited by
- supports The repeated bout effect causes the body to adapt and experience progressively less muscle soreness when repeating the same exercise over time.