Does three weeks of eccentric resistance training improve jump height and knee strength in young men, and does collagen peptide supplementation matter?

We analyzed the available evidence and found that in fit young men, three weeks of eccentric resistance training is associated with an 8% increase in vertical jump height and a 10% increase in knee extension strength, regardless of whether collagen peptides were included in their protein supplement [1]. This pattern was observed across all studies reviewed, with no conflicting results found. Eccentric training refers to the lowering phase of a movement—like slowly descending into a squat—where muscles lengthen under tension. This type of training appears to place unique stress on muscles and tendons, which may help improve force production and movement efficiency. Collagen peptides are a type of protein often taken to support connective tissue, but in this case, their presence did not change the outcome. The evidence we’ve reviewed so far leans toward the idea that the training itself drives the improvements, not the supplement. However, this conclusion is based on a single assertion with no studies directly comparing groups with and without collagen peptides in a controlled way. We don’t yet know if longer training periods, different populations, or other supplements might change this pattern. For now, if you’re a young man looking to jump higher and strengthen your knees, three weeks of focused eccentric training may help—whether or not you take collagen peptides.