Collagen for Tendons: Does the Gelatin-Before-Loading Protocol Work?

Tendon problems are a common reason triathletes miss training. Achilles and patellar tendon pain, in particular, can drag on for months. So it's not surprising that a supplement promising to help tendons, taken with a simple routine before exercise, has become popular with athletes, physiotherapists and coaches.

The protocol is usually described like this: take gelatin or collagen with vitamin C, wait about an hour, then do a short session of tendon loading, such as skipping or calf raises. The idea is that the amino acids reach the tendon just as loading stimulates it to build collagen.

This article looks at where the protocol came from, what later trials have found, and how much evidence actually supports it. The short answer is that the idea is plausible but the evidence is thin, and it shouldn't replace the loading programmes covered in TriForward's "Calf and Achilles Capacity".

Why tendons are slow to adapt

Tendons connect muscle to bone and are made mainly of collagen. They adapt to load, becoming stiffer and sometimes thicker with training, but much more slowly than muscle. Tendons also have a relatively poor blood supply.

That creates two appealing ideas:

• Raising the supply of collagen's building blocks, especially the amino acids glycine, proline and hydroxyproline, which are abundant in gelatin and collagen.
• Timing the supply with loading, so the building blocks are in the blood when the tendon is being stimulated.

Vitamin C is added because it's needed by the enzymes that build collagen. Both ideas are reasonable on paper. The question is whether they produce better tendons or fewer injuries.

The study behind the protocol

The protocol comes mainly from a 2017 study by Greg Shaw, Keith Baar and colleagues, published in the American Journal of Clinical Nutrition.

• Participants: 8 healthy men.
• Design: randomised, double-blind and crossover, so each man took each supplement on different occasions.
• Supplements: 5 g or 15 g of vitamin C-enriched gelatin, or a placebo.
• Exercise: one hour after the drink, 6 minutes of rope skipping. This was repeated three times a day, at least 6 hours apart, for 3 days.

The findings:

• Blood levels of glycine, proline, hydroxyproline and hydroxylysine rose with higher gelatin doses, peaking about an hour after the drink.
• Taking 15 g of gelatin doubled the blood level of PINP, a marker of type I collagen synthesis.
• In a lab experiment, engineered ligaments treated with serum taken after the gelatin drink had more collagen and better mechanical properties than ligaments treated with serum taken before.

The authors concluded that adding gelatin to an intermittent exercise programme might improve collagen synthesis and could help injury prevention and tissue repair.

It's an elegant study, but its limits are important:

• It involved 8 men. No women were included.
• PINP is a whole-body marker. It reflects collagen being made anywhere in the body, including bone and skin, not specifically in the tendon that was loaded.
• The ligaments were grown in a lab, from human cells, not tendons in a living athlete.
• It lasted 3 days. It didn't measure tendon size, stiffness, pain, function or injury.

That doesn't make the study wrong. It means it shows a plausible mechanism, not a proven treatment.

What later trials found

A systematic review of 15 trials

A 2021 systematic review by Khatri and colleagues in Amino Acids included 15 randomised controlled trials of collagen peptides. Twelve involved recreational athletes, two older adults and one untrained premenopausal women.

• Collagen showed the clearest benefit for joint function and joint pain.
• Collagen synthesis rates increased with 15 g a day.
• Collagen didn't significantly affect muscle protein synthesis compared with higher-quality protein sources.

The authors called for larger studies, more women and elite athletes, and more direct measures such as muscle biopsies and MRI.

A 2024 meta-analysis

A 2024 systematic review and meta-analysis by Bischof and colleagues in Sports Medicine looked at collagen peptides taken alongside longer-term training. It included 19 randomised trials with 768 healthy adults (613 men, 155 women), aged about 17 to 65. Most used 15 g a day for around 12 weeks.

For tendons specifically:

• Tendon size (cross-sectional area): 4 studies, 114 participants, a moderate effect (standardised mean difference 0.67). But the certainty was very low, and the effect was no longer significant when one study was removed.
• Tendon mechanical properties, such as stiffness: 4 studies, 111 participants, no significant effect (standardised mean difference 0.05). Certainty was very low.

For muscle soreness after damaging exercise, there was no significant effect at any time point. The authors suggested about 15 g a day for at least 8 weeks may be reasonable, but stressed that the evidence was limited.

Collagen versus whey for connective tissue

A 2023 trial by Aussieker and colleagues in Medicine and Science in Sports and Exercise, from Luc van Loon's group in Maastricht, tested the core idea directly in muscle. It involved 45 recreational athletes (30 men, 15 women) aged around 25.

• After one resistance session, participants took 30 g of whey, 30 g of collagen or a placebo.
• Collagen raised blood glycine and proline more than whey.
• Neither collagen nor whey increased muscle connective protein synthesis over 5 hours compared with placebo.
• Only whey increased myofibrillar (muscle) protein synthesis.

This measured the connective tissue in muscle, not tendon, and over a few hours. But it's a direct test of whether extra collagen building blocks speed up connective tissue synthesis after exercise, and it didn't find that they did.

Achilles tendinopathy

A 2019 pilot trial by Praet and colleagues in Nutrients tested collagen in 20 adults (13 men, 7 women) with chronic mid-portion Achilles tendinopathy, with an average age of 44.

• Design: double-blind, placebo-controlled crossover. Everyone did a daily calf-strengthening programme and a return-to-running plan for 6 months.
• Supplement: 2.5 g of specific collagen peptides twice a day, 30 minutes before exercise, or a placebo, for 3 months each.
• Findings: in the first 3 months, symptoms and function (VISA-A score) improved by 12.6 points with collagen versus 5.3 with placebo. After 6 months, both groups had improved similarly.

The authors described the study as underpowered and needing confirmation. It was funded by the manufacturer of the product tested. Inference: collagen may have sped up improvement, but loading was the common factor in everyone who got better.

Female footballers

A 2023 trial by Lee and colleagues in Frontiers in Physiology involved 17 female soccer players aged around 17 in a professional club's under-21 squad.

• After each training session, for 10 weeks, players took 30 g of collagen (8 players) or a placebo (9 players). Both groups also took 500 mg of vitamin C.
• Patellar tendon stiffness increased by 18.0% with collagen versus 5.1% with placebo.
• Tendon size, muscle thickness and strength didn't change in either group.

It's one of the few trials in women, but it was small, involved young footballers, and measured tendon properties rather than injury.

Gelatin, collagen peptides and food

The trials above don't all use the same product, which makes them harder to compare:

• Gelatin is cooked collagen. It's what sets jelly, and it's what the Shaw study used.
• Hydrolysed collagen or collagen peptides are collagen broken into smaller fragments, so they dissolve easily. Most of the later trials used these, at 15 g or 30 g.
• Specific collagen peptides are branded products made to a particular fragment profile. The Achilles trial used one of these at a much smaller dose, 2.5 g twice a day.

All of them are rich in glycine, proline and hydroxyproline, and all are low in leucine and some other essential amino acids, which is why the whey comparison above matters. Inference: there's no strong evidence that one form is better for tendons than another, and claims that a specific branded peptide "targets" tendons haven't been tested against cheaper products.

Why the protocol spread so quickly

The gelatin protocol has a lot going for it as an idea. It came from a respected lab, it has a clear mechanism, it's cheap and it's easy to do. It also fits neatly with tendon loading, which athletes and physiotherapists already use. Those features help an idea spread, but they aren't evidence that it works.

It's also worth separating two claims that often get blurred:

• "Gelatin raises a collagen marker in the blood." Supported by one small trial.
• "Gelatin before loading heals or protects tendons." Not yet tested in a trial that measured tendon injuries.

Men, women and age

Most collagen research involves men. The Shaw study included only men, and the 2024 meta-analysis had about four men for every woman. The female footballers' trial is one of the few to study women, and its participants were around 17. Older athletes are also underrepresented, although tendon problems are common in masters triathletes. Inference: it's reasonable to think the mechanism applies to everyone, but the size of any benefit in women or older triathletes is unknown.

Putting the evidence together

Graded honestly, the evidence for collagen and tendons looks like this:

• Mechanism: plausible. Gelatin raises the blood amino acids needed for collagen, and one small trial found a rise in a whole-body collagen marker.
• Tendon structure: mixed. Two small trials found greater stiffness or faster recovery, but a meta-analysis found no overall effect on tendon mechanical properties.
• Injury prevention: not tested. No trial here measured tendon injuries.
• Timing: not tested against other timings. The "one hour before loading" timing comes from the Shaw study's design, not from a comparison of different timings.

TriForward rates the evidence as limited. It's a small, mostly male, often industry-funded body of research with very few tendon-specific outcomes.

If you want to try it

The following is inference from the trials above, not a tested recommendation:

1. Prioritise loading. Heavy, slow calf raises and progressive tendon loading have better evidence than any supplement. TriForward's "Calf and Achilles Capacity" covers this.
2. Use the doses the trials used if you try it. Most trials used 15 g a day, and the Shaw study used 15 g of gelatin with vitamin C about an hour before a short loading session.
3. Give it time. The longer-term trials ran for 10 weeks to 3 months.
4. Don't expect to feel a difference. Even in positive trials, effects were modest and measured with ultrasound or questionnaires.
5. Check total protein. Collagen lacks some essential amino acids, so don't use it to replace higher-quality protein. TriForward's "Protein for the Lifting Triathlete" covers protein needs.

Supplement safety

Collagen and gelatin are generally regarded as low-risk foods. But a few points matter:

• Allergies: products come from cow, pig or fish sources. Check the source if you have a fish or other food allergy.
• Kidney disease: these are protein supplements, so talk to your doctor if you've been advised to limit protein.
• Contamination: the 2018 International Olympic Committee consensus statement on dietary supplements, led by Ronald Maughan, warns that inadvertent intake of banned substances is a known risk of some supplements. It notes that third-party testing schemes can help athletes find products at low risk, though no product can be guaranteed safe. Batch-tested products are the safer choice, especially if you could be drug-tested.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 46-year-old triathlete has had stiff, painful Achilles tendons for two months as he builds his run volume for an autumn marathon-distance race. A training partner recommends gelatin before skipping.

Based on the evidence above, he might:

• See a physiotherapist first to confirm it's tendinopathy and get a structured loading programme.
• Adjust his running load while the tendon settles.
• Consider collagen as an optional add-on, knowing that the evidence is limited and that the loading programme is doing most of the work.
• Choose a batch-tested product and check it doesn't clash with any allergies.

Common mistakes

• Treating collagen as a treatment. It's an unproven add-on, not a replacement for loading.
• Skipping the loading. In the Shaw protocol, the exercise was the stimulus. The supplement was added to it.
• Assuming a blood marker means stronger tendons. PINP rose in 8 men, but tendons weren't measured.
• Assuming the evidence applies equally to women. Only a minority of participants were women.
• Buying untested products, which may be mislabelled or contaminated.

What we don't know

• Whether collagen reduces tendon injuries in triathletes or any other athletes.
• Whether timing matters, since no trial here compared taking it before loading with taking it at another time.
• Effects in women and older athletes, who are underrepresented.
• Whether collagen adds anything when total protein intake is already good.
• Long-term effects, since most trials lasted three months or less.

References

• Shaw G, Lee-Barthel A, Ross MLR, Wang B, Baar K. Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. American Journal of Clinical Nutrition, 2017;105(1):136–143. doi:10.3945/ajcn.116.138594
• Khatri M, Naughton RJ, Clifford T, Harper LD, Corr L. The effects of collagen peptide supplementation on body composition, collagen synthesis, and recovery from joint injury and exercise: a systematic review. Amino Acids, 2021;53(10):1493–1506. doi:10.1007/s00726-021-03072-x
• Bischof K, Moitzi AM, Stafilidis S, König D. Impact of collagen peptide supplementation in combination with long-term physical training on strength, musculotendinous remodeling, functional recovery, and body composition in healthy adults: a systematic review with meta-analysis. Sports Medicine, 2024;54(11):2865–2888. doi:10.1007/s40279-024-02079-0
• Aussieker T, Hilkens L, Holwerda AM, Fuchs CJ, Houben LHP, Senden JM, et al. Collagen protein ingestion during recovery from exercise does not increase muscle connective protein synthesis rates. Medicine and Science in Sports and Exercise, 2023;55(10):1792–1802. doi:10.1249/MSS.0000000000003214
• Praet SFE, Purdam CR, Welvaert M, Vlahovich N, Lovell G, Burke LM, et al. Oral supplementation of specific collagen peptides combined with calf-strengthening exercises enhances function and reduces pain in Achilles tendinopathy patients. Nutrients, 2019;11(1):76. doi:10.3390/nu11010076
• Lee J, Bridge JE, Clark DR, Stewart CE, Erskine RM. Collagen supplementation augments changes in patellar tendon properties in female soccer players. Frontiers in Physiology, 2023;14:1089971. doi:10.3389/fphys.2023.1089971
• Maughan RJ, Burke LM, Dvorak J, Larson-Meyer DE, Peeling P, Phillips SM, et al. IOC consensus statement: dietary supplements and the high-performance athlete. British Journal of Sports Medicine, 2018;52(7):439–455. doi:10.1136/bjsports-2018-099027