Collagen Peptides and Vitamin C for Tendons: A Pre-Loading Protocol to Take to Your Physio

Collagen for tendon recovery is one of the few supplement ideas with a believable mechanism and a few decent trials behind it. Collagen for muscle growth is not. Mixing the two up is how people end up spending money on a tub that was never going to add a gram of muscle.

This article is a focused add-on to our evidence-based guide to fitness supplements. Here we separate the connective tissue claims that hold up (modestly) from the bodybuilding claims that do not, and walk through a practical protocol you can bring to your physio.

Why tendons are a different problem from muscle

Muscle has a rich blood supply. Tendon does not. A tendon is a dense, slow-turnover rope of collagen with few cells and limited blood flow, which is why a sore Achilles or patellar tendon can drag on for months while a pulled muscle settles in weeks.

Holwerda and van Loon explain in their narrative review that connective tissue proteins are constantly being remodelled, and that eating normal protein raises muscle protein synthesis but does not seem to raise muscle connective tissue protein synthesis. One proposed reason is not enough glycine and/or proline, the two amino acids collagen is full of. Dietary collagen has been proposed as a way to supply them. That is a hypothesis the review lays out, not a settled fact.

So the idea is simple: give the tendon its raw materials at the moment it is being asked to adapt. Whether that actually produces a better tendon is the open question.

What did the Shaw gelatin study actually find?

This is the study behind most “Keith Baar protocol” posts, so it is worth reading carefully. Shaw and colleagues (2017) ran a randomized, double-blind crossover trial in eight healthy men. They drank 5 g or 15 g of vitamin C-enriched gelatin, or a placebo.

Here is what they measured:

• Blood amino acids. Glycine, proline, hydroxyproline and hydroxylysine rose with the dose and peaked about an hour after drinking it.
• Engineered ligaments. Lab-grown ligaments treated for 6 days with serum from after the gelatin showed more collagen content and better mechanics.
• PINP in the blood. Men who took 15 g of gelatin an hour before six minutes of rope skipping had double the amino-terminal propeptide of collagen I (PINP), a marker of collagen I synthesis.

Does collagen help with tendinopathy?

For actual tendon pain, the best-known trial is small. Praet and colleagues (2019) gave 20 people with chronic mid-portion Achilles tendinopathy either specific collagen peptides or placebo alongside a twice-daily calf-strengthening program for 6 months, in a crossover design. On the VISA-A symptom score, the group on collagen first improved by 12.6 points at 3 months versus 5.3 points for placebo first. After crossing over, both groups gained again, with the collagen phase showing larger gains. No adverse events were reported.

The authors concluded collagen may accelerate the benefit of a well-structured calf program. Note the words “may” and “pilot study.” Twenty patients is a hint, not a verdict.

Zoom out and the picture stays cautious. A 2022 systematic review of nutrition and tendinopathy found 19 studies, 14 of them on supplements, and collagen-derived peptides were the most common ingredient. Combining training with supplements seemed to give better clinical and functional outcomes. But the authors flagged the shortage of high-quality studies and said firm dietary recommendations remain out of reach.

What if you are healthy and just want stronger tendons?

Here the research disagrees, which is worth saying plainly.

• Miyamoto et al. (2025): 50 sedentary young men took 10 g of collagen peptides or placebo daily for 16 weeks, without a training program. Calf muscle and Achilles tendon stiffness and rate of torque development rose in the collagen group but not the placebo group, with no change in tendon size or maximal strength. Several authors work for Morinaga, a food company, which is worth knowing when you weigh the result. Study here.
• Balshaw et al. (2023): 39 recreationally active young men lifted three times a week for 15 weeks and took 15 g of collagen peptides or placebo daily. Patellar tendon stiffness rose about 17-21% in both groups, with no difference between them. Study here.

Why might they differ? One used sedentary men with no training at all, the other used lifters training hard enough to remodel tendon on their own. A different tendon (Achilles vs patellar), a different dose and a different supplement formulation could all matter too. The cautious reading: collagen might add something when there is little or no training stimulus, and add little when heavy lifting is already doing the job. Training is the bigger lever either way.

Does collagen build muscle?

No. This is the part the supplement labels quietly skip. We cover it in depth in collagen protein: joint support vs muscle building, so here is the short version.

Collagen is not a complete protein. It is dense in glycine and proline, but low in several essential amino acids, particularly leucine, and it has no tryptophan. Leucine is the amino acid most closely tied to switching on muscle protein synthesis (see our piece on the leucine trigger hypothesis). So a protein with little leucine is a weak candidate for building muscle.

The data match the theory. In McKendry and colleagues (2024), 31 healthy older men (average age 72) ate a controlled diet at the RDA for protein, then added an extra 50 g/day of whey (n = 10), pea (n = 11) or collagen (n = 10) for about a week. Integrated muscle protein synthesis rose with whey (1.59 vs 1.46 %/day) and pea (1.59 vs 1.46 %/day), but stayed unchanged with collagen.

A systematic review of 15 randomized trials reached a similar conclusion. Collagen synthesis rates rose with 15 g/day, but collagen had no significant effect on muscle protein synthesis compared with isonitrogenous higher-quality proteins. The same review noted some improvements in body composition and strength, but it also said the mechanisms are unclear and the studies were small. So “no hypertrophy effect” is the safe call, with the caveat that most data come from older or recreationally active people, not experienced lifters in a growth phase.

If your goal is muscle, put your money into whey, curd, paneer, eggs, soya or dal plus rice combinations. Our protein calculator shows your daily target, and our guide to whey isolate vs concentrate helps with the powder decision.

The pre-loading protocol, step by step

Nobody has run a trial that proves one perfect schedule. What follows is a practical template based on the Shaw design and the dose ranges used in the studies above. Take it to your physiotherapist rather than treating it as a prescription.

1. Dose. 10-15 g of collagen peptides or gelatin. Shaw reported the doubled PINP response for the 15 g dose, so 5 g is not the dose with that evidence.
2. Add vitamin C. The study gelatin was vitamin C-enriched. A glass of nimbu pani, an amla, an orange or a guava does the job, and it costs almost nothing.
3. Time it. About 45-60 minutes before the session. Blood levels of glycine, proline and hydroxyproline peaked at one hour in Shaw.
4. Load the tendon. This is the step people skip. In Shaw the drink came before six minutes of rope skipping, and in the Praet trial it sat alongside a structured calf program. The collagen is raw material, the loading is the signal.
5. Space it out. In the Shaw protocol, doses were repeated with at least 6 hours between exercise bouts. Do not drink it all day.

Is it worth the money? Collagen peptides and gelatin run from cheap to expensive depending on the brand. Gelatin powder from a grocery shop is the budget route, though the studies used specific products, so we cannot promise they behave identically. Check the label for 10-15 g of actual collagen per serving, and see our piece on decoding proprietary blends so you are not paying for fairy dust.

Where collagen fits in your rehab (and where it does not)

The mistake we see most often is treating collagen as the treatment. It is not. Tendon rehab is built on progressive loading: heavy slow resistance, isometrics, gradually increasing demand, and fixing whatever overloaded the tendon in the first place. If your knee pain starts on squat day, our guide to knee-friendly leg workout modifications is a better first step than a tub of gelatin. Elbow pain from rows and curls? See golfer’s and tennis elbow in lifters.

Collagen’s best realistic role is a low-risk extra on top of that work. If you are weighing it against other joint products, our comparison of glucosamine, MSM and collagen for joints covers the wider picture.

When to see a doctor

Collagen is not a diagnosis tool and not a treatment for an injury you have not had checked. Book an appointment if you notice any of these:

• Tendon pain lasting more than a few weeks despite reducing load
• Visible swelling, heat or a lump along the tendon
• A sudden pop or snap followed by weakness or inability to push off
• Pain at night or at rest, or numbness and tingling
• A recent course of fluoroquinolone antibiotics or steroid injections near the painful tendon

Also check first if you are pregnant, have kidney disease, take regular medication, or have any allergy to bovine, porcine or fish products.

So is collagen worth it?

Here is the honest ledger.

Claim	Evidence	Verdict
Raises a collagen synthesis marker after exercise	One small crossover trial (Shaw, n = 8)	Promising, short-term, marker only
Speeds symptom relief in Achilles tendinopathy	One small crossover pilot (n = 20)	Possible, needs bigger trials
Stiffens tendon in healthy people	One positive trial, one null trial	Mixed
Builds muscle	Older men: no change in muscle protein synthesis	Not supported
Replaces rehab exercise	No evidence	No

Use it if you have a stubborn tendon, you are already doing proper loading work, and the cost does not bother you. Skip it if you are buying it for biceps or quads. Either way, your tendon responds first to the load you give it. If you want to see your protein number first, start with the free protein calculator.