First, notice the pattern
When does the stiffness start? How long does it last? Is it new, one-sided, swollen or getting worse? Those details can matter more than the supplement label. The cause of stiffness is not something an article can determine.
What has been studied
A 2013 trial enrolled 55 healthy adults who experienced knee discomfort during a stepmill test. The UC-II group showed some improvements in measured knee extension and the time before discomfort after 120 days. A 2008 study examined collagen hydrolysate in athletes with activity-related pain. These were different ingredients, populations and protocols.
The caution that changes the answer
A 2020 study of collagen peptides in active older adults with self-reported knee pain did not find significant between-group differences on its primary pain and function outcomes. The 2025 combined-form trial also did not outperform placebo. A neat headline cannot erase those differences in the evidence.
A practical next step
If symptoms persist or interfere with normal movement, consider a health professional’s advice. If you are comparing supplements, match the study form and dose to the label rather than relying on the word “collagen” alone.