Collagen peptides nudge strength, but only just

Collagen peptides have become one of the most heavily marketed supplements in sports nutrition, promoted for connective tissue health, injury prevention and performance. The trial record has been genuinely mixed, with benefits appearing in some studies and not others, which leaves buyers guessing. The interesting question is not whether collagen does something detectable in a lab, but whether adding it to weeks of ordinary training changes strength, tissue structure, recovery or body composition in healthy people. Nobody had previously pulled all the long-term trials together across those outcomes at once. That is the gap this review set out to close.

The authors followed PRISMA with PERSiST guidelines and searched PubMed, Scopus, CINAHL and SPORTDiscus in December 2023. Eligible trials randomised healthy adults over 17 years of age, of normal to overweight body size, to daily collagen peptides for at least eight weeks alongside exercise. One three-week trial was admitted for maximal strength only, and recovery studies using a one-week supplementation period without exercise were also allowed. Nineteen trials with 768 participants qualified. Study quality was scored on the PEDro scale, and change scores were combined using a random-effects model covering strength, tendon and muscle structure, functional recovery and body composition.

The largest pooled effects were for tendon morphology (SMD 0.67) and fat-free mass (SMD 0.48), both statistically significant. Muscle architecture improved more modestly (SMD 0.39), and recovery of reactive strength 48 hours after exercise-induced muscle damage also favoured collagen (SMD 0.43). Maximal strength was the smallest effect in the set at SMD 0.19, though it still reached significance. Certainty was uneven: moderate for body composition, low for most other outcomes and very low for tendon morphology and mechanical properties. The authors singled out tendon mechanical properties and short-term intake without exercise as the areas where the evidence is thinnest.

This is the first comprehensive pooling of long-term collagen peptide trials combined with regular training in healthy adults, so it consolidates a literature that had been read selectively in both directions. It supports the more modest version of the collagen story: consistent small effects on tissue and body composition rather than dramatic strength gains. It does not settle the mechanism, and the very low certainty around tendon mechanical properties means the most-cited claim in collagen marketing remains the least well supported. Open questions include how the effects arise, whether tendon stiffness genuinely changes, and what short bursts of supplementation do without any training attached.

This is a reason to think collagen peptides act as a small adjunct to training rather than a driver of results. The training itself remains the variable doing the heavy lifting, and the pooled strength effect here was the smallest of everything measured. If connective tissue or recovery is your interest, the review offers grounds for cautious optimism, with the honest note that confidence in the tendon numbers is very low. Anyone weighing the cost can reasonably read this as a marginal-gains supplement, not a transformative one.