Collagen, tendons and connective tissue: training the structure
Collagen is the rope-like protein that gives tendons, ligaments and skin their tensile strength. The most interesting evidence is narrow but real: taking about 15 g of collagen peptides or gelatin with vitamin C roughly an hour before loading can roughly double a blood marker of collagen synthesis, and in small trials this nudges tendon and ligament tissue in a useful direction. It is not a muscle-building protein, the joint and skin claims are weaker and partly industry-funded, and the loading itself, not the powder, does most of the work.
Key facts
- In a 2017 crossover trial, 15 g of vitamin C-enriched gelatin taken 1 hour before exercise doubled blood PINP, a marker of collagen synthesis, versus placebo; 5 g did nothing.1
- Vitamin C is a required cofactor for the enzymes that hydroxylate proline and lysine; without it collagen cannot form a stable triple helix (the extreme case is scurvy).2
- For building muscle, collagen is a poor choice: it lacks tryptophan and is low in leucine, and whey beat leucine-matched collagen for muscle growth over 10 weeks.5
- A 2025 systematic review found tendon structural gains (cross-sectional area, stiffness) only when collagen was paired with resistance training, with no effect on strength.4
- Tendon collagen turns over far more slowly than muscle, which is why connective tissue adapts over months, not weeks.3
What collagen actually is
Collagen is the most abundant protein in the body and the main structural fibre in tendon, ligament, bone, cartilage and skin. Its building blocks are unusual: it is extremely rich in glycine, proline and hydroxyproline, the amino acids that let three protein strands wind into the tight triple helix that gives connective tissue its strength. Two of those residues, hydroxyproline and hydroxylysine, do not exist in the diet in useful amounts; the body makes them by chemically modifying proline and lysine after the chain is built, and that step depends on vitamin C as a cofactor.2 This is the mechanistic heart of the whole topic: supply the raw materials and the vitamin C, at the moment the tissue is being asked to build, and you may give it more to work with.
Collagen peptides (also sold as hydrolysed collagen) are collagen broken into short fragments so they dissolve and absorb easily. Gelatin is partially broken-down collagen that gels when cool. Both deliver the same characteristic amino acids; peptides are simply more convenient to drink. For how protein and amino acids drive tissue building more broadly, our piece on protein intake and leucine timing covers the muscle side.
The Shaw and Baar evidence: peptides plus vitamin C, timed before loading
The headline studies come from Greg Shaw, Keith Baar and colleagues. In a 2017 randomised, double-blind crossover trial in the American Journal of Clinical Nutrition, eight healthy men took placebo, 5 g or 15 g of vitamin C-enriched gelatin, then did a short bout of rope-skipping an hour later to load their connective tissue.1 The 15 g dose roughly doubled the rise in PINP, a blood marker of new collagen formation, while 5 g was no better than placebo. In the same study, blood taken after the supplement was dripped onto engineered human ligaments in the lab, and that serum increased their collagen content and mechanical strength.1
The logic of the timing is the key insight. Circulating glycine, proline and hydroxyproline peak about an hour after you drink the peptides, and brief loading drives blood flow and a synthesis signal in the tendon. Take the drink so the amino acids arrive just as the tissue is primed. A follow-up dose-finding study by Lis and Baar was messier: high variability in the PINP assay meant the doses did not separate cleanly, a useful reminder that the marker is noisy and the effect is not bulletproof.6
Evidence strength, plainly. Short-term rise in a collagen-synthesis blood marker: reasonably solid but from small, mostly male, mechanistic studies. Real-world tendon structure and stiffness with training: moderate and promising. Fewer injuries or faster return from tendinopathy: not yet proven, larger trials such as JUMPFOOD are ongoing.7
How mechanical loading drives tendon adaptation
The supplement is the supporting actor; loading is the lead. When a tendon is repeatedly stressed, the resident cells (tenocytes) sense the strain and switch on collagen production. Synthesis dips briefly straight after a hard bout, then climbs and stays elevated for one to three days.3 Over months this raises tendon cross-sectional area and stiffness, so the tissue transmits force better and tolerates more. Crucially, tendon collagen turns over much more slowly than muscle protein, which is why tendons strengthen on a timescale of months while muscles visibly respond in weeks, and why a sudden jump in training load outpaces the tendon and invites tendinopathy.3
This explains the central honest caveat: in every positive supplement trial the participants were also training. A 2025 systematic review concluded that collagen at 15 to 30 g per day improved tendon structural measures only alongside resistance exercise, and found no benefit to muscle strength.4 No powder substitutes for progressive, patient loading such as heavy slow resistance work.
Why this is not whey, and the honest read on joints and skin
Collagen is widely mis-sold as a muscle protein. It is an incomplete protein: it contains no tryptophan and little leucine, the amino acid that switches on muscle protein synthesis. When researchers gave untrained adults leucine-matched collagen or whey across a 10-week resistance programme, the whey group gained more muscle thickness.5 If your goal is muscle, use whey or another complete protein and treat collagen as a connective-tissue tool only.
For joints, a 2023 meta-analysis of randomised trials in knee osteoarthritis found a moderate reduction in pain with collagen peptides, but rated the underlying trials as high risk of bias.8 For skin, meta-analyses report improvements in hydration and elasticity, yet a 2025 review made the uncomfortable observation that the benefit largely disappeared in studies not funded by supplement manufacturers.9 Both areas are plausible and possibly real, but the evidence is softer and more conflicted than the marketing implies.
| Claim | What the evidence shows | Strength |
|---|---|---|
| Collagen synthesis marker (acute) | 15 g + vitamin C before loading roughly doubled PINP1 | Reasonably solid (small studies) |
| Tendon structure with training | Greater cross-sectional area and stiffness at 15 to 30 g/day4 | Moderate |
| Injury prevention / tendinopathy | Mechanistically plausible; large RCTs ongoing7 | Not yet proven |
| Muscle growth | Inferior to whey; lacks leucine and tryptophan5 | Evidence against |
| Joint pain (knee OA) | Moderate pain benefit, but biased trials8 | Mixed |
| Skin elasticity / hydration | Benefit shrinks in non-industry-funded studies9 | Weak / conflicted |
Dosing: dull, specific, and timed
If you want to apply the connective-tissue findings, the protocol from the research is straightforward. Take around 15 g of collagen peptides or gelatin with a source of vitamin C (the trials used roughly 50 mg, easily met by a small glass of orange juice or a vitamin C tablet), 30 to 60 minutes before the loading session that targets the tendon you care about.1 Doses below about 15 g have not worked in these trials, and there is no good evidence that going far higher helps; one acute study saw a larger marker response at 30 g, but that is a single endpoint, not proof of better tissue.10 Collagen is generally well tolerated, with occasional mild digestive upset. You can sanity-check it against the rest of your routine with our stack builder.
Worth knowing. Collagen supplements are not licensed medicines and are not regulated for tendinopathy; using them to treat an injury is an off-label, self-directed choice. They do not replace a graded rehabilitation programme. People who are pregnant or breastfeeding, or who have a kidney condition that limits protein, should take advice first, and anyone with a fish, bovine or porcine allergy should check the source.
What to ask your GP or physiotherapist
- Is my tendon problem one that needs a structured loading programme rather than rest?
- Would heavy slow resistance or eccentric work be appropriate for my specific tendon?
- Is there any reason a 15 g daily protein-type supplement would be unwise for me?
- Should we rule out an inflammatory or other cause before assuming it is simple tendinopathy?
References
- Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. Am J Clin Nutr. PMID 27852613, 2017.
- Levine M, Violet PC. Breaking down, starting up: can a vitamin C-enriched gelatin supplement before exercise increase collagen synthesis? (editorial) Am J Clin Nutr. PMID 28003207, 2017.
- Kjaer M, Langberg H, Heinemeier K, et al. From mechanical loading to collagen synthesis, structural changes and function in human tendon. Scand J Med Sci Sports. PMID 19706001, 2009.
- Collagen supplementation on tendon-related structural and performance outcomes: a systematic review. J Funct Morphol Kinesiol. MDPI (JFMK 2026;11:130).
- Oikawa SY, et al. Whey protein supplementation is superior to leucine-matched collagen peptides to increase muscle thickness during a 10-week resistance training program in untrained young adults. Int J Sport Nutr Exerc Metab. PMID 35042187, 2022.
- Lis DM, Baar K. Effects of different vitamin C-enriched collagen derivatives on collagen synthesis. Int J Sport Nutr Exerc Metab. PMID 30859848, 2019.
- Jonkers AAM, et al. The JUMPFOOD study: additional effect of hydrolyzed collagen and vitamin C to exercise treatment for patellar tendinopathy in athletes (protocol for a double-blind RCT). Trials. PMID 38017500, 2023.
- Luo C, et al. Analgesic efficacy of collagen peptide in knee osteoarthritis: a meta-analysis of randomized controlled trials. J Orthop Surg Res. PMC10505327, 2023.
- Effects of collagen supplements on skin aging: a systematic review and meta-analysis of randomized controlled trials. Am J Med. AJM 2025.
- Aussieker T, et al. The collagen synthesis response to an acute bout of resistance exercise is greater when ingesting 30 g hydrolyzed collagen compared with 15 g and 0 g in resistance-trained young men. J Nutr. PMC11282471, 2024.
This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.