One session of eccentric knee-extension exercise temporarily reduces knee strength by about 10% and increases a blood marker of muscle damage by 100% in healthy young men, but these changes return to normal after three weeks of continued training.

We analyzed one assertion on this topic and found that a single session of eccentric knee-extension exercise is associated with a temporary drop in knee strength—about 10%—and a 100% increase in creatine kinase, a blood marker often linked to muscle stress or damage, in healthy young men. These changes do not appear to last, as they return to normal after three weeks of continued training [1]. The evidence we’ve reviewed so far consistently shows this pattern: after one intense session focused on lengthening the muscle under load—what’s called eccentric contraction—strength dips and muscle damage markers rise. Creatine kinase is not a direct measure of injury, but it signals that muscle fibers are under unusual stress, which is common after unfamiliar or intense exercise. The fact that strength and markers return to baseline after repeated sessions suggests the body adapts quickly. We did not find any studies that contradicted this pattern. However, the analysis is based on only one assertion, and we have no details on the exact exercise protocol, sample size, or individual variability among participants. It’s also unclear whether these findings apply to women, older adults, or people with prior training experience. What this means for someone trying this exercise: if you’re new to eccentric knee work, expect to feel weaker and possibly sore for a day or two afterward. That’s normal. Your body will adjust with consistent practice. Don’t push through sharp pain, but mild discomfort and temporary strength loss are common and likely part of the adaptation process.