Collagen & Vitamin C Timing

Why Tendons Are Slow to Adapt

Tendons are composed primarily of type I collagen — densely packed, highly organised fibres arranged to transmit the enormous forces generated by muscle contraction. Unlike muscle tissue, which can hypertrophy meaningfully over weeks of training, tendons adapt slowly. Collagen turnover is tightly regulated and the structural changes that make a tendon stiffer, stronger, and more resilient take months, not weeks.

After Achilles rupture, the healing tendon must produce new collagen to repair the damaged tissue. But the quality of that collagen — how well organised it is, how closely it approximates the structure of the original — depends heavily on two things: appropriate mechanical loading through rehabilitation exercise, and the availability of the raw materials and cofactors needed to synthesise it.

This is where the timing of collagen and vitamin C becomes relevant. Mechanical loading (your physio exercises) stimulates tenocytes to produce collagen. But if the building blocks are not circulating in the bloodstream at the moment that synthesis signal is triggered, the opportunity is partly wasted. The goal of the pre-exercise strategy is to ensure those materials arrive in the bloodstream at precisely the time the tendon is being stimulated to use them.

The Landmark Study: Shaw et al., 2017

The foundational research behind this strategy comes from a 2017 study published in the American Journal of Clinical Nutrition by Greg Shaw, Ann Lee-Barthel, and Keith Baar — researchers at the Australian Institute of Sport and the University of California, Davis. It is one of the most directly applicable nutritional studies for anyone in Achilles tendon recovery.

Shaw and colleagues recruited eight healthy male subjects in a randomised, double-blinded, crossover study. Each subject consumed either 5 g of vitamin C-enriched gelatin, 15 g of vitamin C-enriched gelatin, or a placebo control. One hour after consuming the supplement, they performed six minutes of rope-skipping — a brief, targeted loading stimulus for the lower leg. Blood was taken before supplementation and at intervals afterward to measure markers of collagen synthesis, specifically PINP (N-terminal propeptide of type I procollagen), which is a validated marker of collagen production.

The result was striking: the 15 g gelatin group showed more than a twofold increase in collagen synthesis markers compared to placebo. The 5 g group showed a smaller but meaningful increase. Crucially, this effect was not simply from the exercise — the exercise alone (placebo condition) produced a modest synthesis response. The gelatin plus vitamin C, timed one hour before the exercise, doubled it.

The researchers also treated engineered ligament tissue with the blood serum collected from each condition. The ligaments treated with serum from the 15 g gelatin condition showed greater stiffness and collagen content than those treated with placebo serum — suggesting the effect was not just a marker change, but a genuine functional improvement in connective tissue.

Why Vitamin C Is Not Optional

The role of vitamin C in this protocol is not cosmetic or general. It is mechanistically essential. Vitamin C (ascorbic acid) is a required cofactor for the enzyme prolyl hydroxylase — the enzyme that hydroxylates proline residues in pro-collagen chains. This hydroxylation step is not optional: without it, pro-collagen cannot form its characteristic triple-helix structure, cannot be correctly folded, and cannot be secreted from the cell. Collagen that is not hydroxylated is degraded rather than used.

In practice, this means that providing the amino acids of collagen (glycine, proline, hydroxyproline) without adequate vitamin C results in reduced collagen output regardless of the amino acid supply. The two must be present together for the synthesis pathway to function optimally.

Keith Baar's lab discovered this experimentally in a way worth noting. In one experiment, a vitamin C powder that had been stored in front of a sunlit window in California had degraded without the team realising it. When they ran the collagen synthesis protocol with this degraded vitamin C, they saw no increase in collagen synthesis at all. Only when they switched to a fresh vitamin C source (in their case, a concentrated fruit juice providing around 50 mg of vitamin C) did the effect reappear. The lesson: vitamin C must be fresh and of confirmed potency — not degraded, old capsules sitting in a hot cupboard.

The Timing Window: Why 30–60 Minutes Before Exercise

The timing of supplementation is the most practically important aspect of this strategy, and it differs slightly depending on the form of collagen used.

After ingesting hydrolysed collagen peptides, serum hydroxyproline (a collagen-specific amino acid) levels begin rising within 15–30 minutes and reach their peak at approximately 30–60 minutes post-ingestion. They return toward baseline within 7–12 hours. This pharmacokinetic profile — peak amino acid availability at 30–60 minutes — is the basis for the recommendation to take hydrolysed collagen 30 minutes before exercise.

Gelatin (the form used in the original Shaw et al. study) follows a slightly different curve. Being a less processed form of collagen, its amino acid absorption is delayed by 30–60 minutes compared to hydrolysed collagen. This is why Shaw et al. used a 60-minute pre-exercise window for gelatin, while Praet et al. (2019) — who used specific hydrolysed collagen peptides — used a 30-minute pre-exercise window.

The practical implication: if using hydrolysed collagen peptides, take them 30 minutes before exercise. If using gelatin, take it 60 minutes before. Taking either too early or too late means amino acid availability peaks before or after the exercise-induced synthesis signal — and the synergy is lost.

Clinical Evidence: Does It Actually Help in Achilles Recovery?

Shaw et al. 2017 established the mechanism in healthy subjects. The next question is whether this translates to clinical improvements in patients with tendon injury.

Praet et al., 2019 — Achilles Tendinopathy

A prospective, double-blinded, placebo-controlled crossover trial published in Nutrients investigated specific collagen peptides (2.5 g, twice daily) combined with calf-strengthening exercises in patients with chronic Achilles tendinopathy. Participants were instructed to take the collagen 30 minutes before each exercise session, based on the pharmacokinetic profile described above. Over six months, the collagen group showed greater and faster improvement in functional outcomes and pain reduction compared to placebo — though the authors noted this was a pilot study with limited statistical power and that larger trials are needed. They concluded that specific collagen peptides may accelerate the clinical benefits of a structured calf-strengthening and return-to-running programme.

Jerger et al., 2022 & 2023 — Tendon Structural Changes

Two related studies by Jerger and colleagues investigated whether collagen peptide supplementation combined with resistance training produced structural changes in tendons — not just symptom changes. They found that collagen supplementation augmented both patellar and Achilles tendon hypertrophy alongside increases in tendon stiffness. Stiffer tendons transmit force more effectively from muscle to bone — a directly relevant outcome for Achilles recovery patients trying to restore push-off power.

Lis & Baar, 2019 — Comparing Collagen Forms

Lis and Baar compared different vitamin C-enriched collagen derivatives (gelatin vs. hydrolysed collagen peptides) in terms of their effect on collagen synthesis markers. Both forms produced meaningful increases in collagen synthesis. Hydrolysed collagen at lower doses (5–10 g) appeared to produce synthesis responses comparable to larger doses of gelatin, likely due to greater bioavailability. This work supports using hydrolysed collagen peptides as a practical, lower-dose alternative to gelatin.

Hydrolysed Collagen vs Gelatin: Which to Use

Both forms work on the same principle — they are both sources of collagen-derived amino acids. The practical differences:

Hydrolysed collagen peptides (also called collagen hydrolysate or specific collagen peptides) are enzymatically broken into smaller fragments that are absorbed faster and more completely. They dissolve easily in any liquid, hot or cold, and have a neutral taste. Effective at lower doses (5–10 g). Widely available as powder supplements. This is the form used in the Praet 2019 Achilles clinical trial and the Jerger tendon structural studies.

Gelatin is partially hydrolysed collagen — less processed, dissolves in hot liquid and gels as it cools. Absorption is slightly slower, meaning the pre-exercise window should be 60 minutes rather than 30. Functionally equivalent in terms of amino acid delivery but less convenient. Used in the original Shaw 2017 study at 15 g — a larger dose partly compensating for lower bioavailability. Available as food-grade gelatin sheets or powder.

For daily use during rehabilitation, hydrolysed collagen peptides are the more practical choice. They require a smaller dose, dissolve in any drink, and can be timed more conveniently at 30 minutes before exercise.

Vitamin C: How Much and What Form

The Shaw 2017 study used approximately 50 mg of vitamin C alongside the gelatin — a modest dose. This is below the standard daily supplement dose (500–1000 mg is common in supplements) but above the dietary reference intake. The Baar lab have since noted that vitamin C quality and freshness matter more than quantity — degraded vitamin C (from heat, light, or age) is ineffective regardless of the listed dose on the label.

Practical recommendations: 50–100 mg of fresh vitamin C taken with the collagen supplement is sufficient. This can come from a dedicated vitamin C supplement, or from a natural source — a small glass of orange juice (approximately 60–70 mg per 150 ml) is a convenient option. Avoid relying on old vitamin C capsules that have been sitting in heat or light. If using powdered vitamin C, keep it sealed and cool.

A higher dose of vitamin C (500–1000 mg) is not harmful but there is no evidence it augments the collagen synthesis effect further beyond the amounts used in the research. More vitamin C does not mean more collagen production at these doses.

The Practical Protocol

What This Strategy Does Not Do

It is worth being direct about the limitations, because the enthusiasm around collagen supplementation in fitness circles sometimes outruns the evidence.

It does not replace progressive loading. The exercise stimulus is not optional — collagen plus vitamin C without the subsequent loading exercise produces no meaningful collagen synthesis response. The supplement amplifies the response to exercise; it does not substitute for it.

It does not replace total protein intake. Collagen is an incomplete protein — it is low in essential amino acids including leucine, which drives muscle protein synthesis. Taking collagen instead of adequate total protein intake would be counterproductive. It is an addition to a good overall diet, not a replacement for it.

It does not accelerate healing beyond what the biology allows. Tendon collagen remodelling is slow. This strategy improves the quality and quantity of collagen synthesis per loading bout, but it does not compress the months-long timeline that tendon healing requires.

The evidence is not definitive. The mechanistic case is strong, the early clinical data is supportive, but large randomised controlled trials — particularly in Achilles rupture patients specifically — are still limited. This is a low-risk intervention worth adopting, but it should be held with appropriate scientific humility.

1. 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. PubMed 27852613 — Foundational RCT (n=8); 15 g vitamin C-enriched gelatin 1 hour before exercise more than doubled collagen synthesis markers (PINP) vs placebo; dose-dependent effect; engineered ligament stiffness increased in serum from gelatin condition.
2. Praet SFE, Purdam CR, Welvaert M 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. PMC6356409 — Pilot double-blinded placebo-controlled crossover trial; 2.5 g specific collagen peptides twice daily, 30 min before calf exercises; accelerated functional recovery and pain reduction vs placebo; based on pharmacokinetic profile of hydrolysed collagen (peak serum availability at 30–60 min).
3. Lis DM, Baar K. Effects of different vitamin C-enriched collagen derivatives on collagen synthesis. International Journal of Sport Nutrition and Exercise Metabolism. 2019;29(5):526–531. — Compared gelatin vs hydrolysed collagen peptides on collagen synthesis markers; both effective; hydrolysed form produced comparable effect at lower dose due to greater bioavailability.
4. Jerger S et al. Effects of specific collagen peptide supplementation combined with resistance training on Achilles tendon properties. Scandinavian Journal of Medicine & Science in Sports. 2022;32(5):1131–1141. — Collagen supplementation combined with resistance training augmented Achilles tendon hypertrophy; structural changes in tendon tissue confirmed.
5. Jerger S et al. Specific collagen peptides increase adaptations of patellar tendon morphology following 14-weeks of high-load resistance training: a randomized controlled trial. European Journal of Sport Science. 2023;23(11):2329–2339. — RCT showing collagen supplementation augmented patellar tendon structural adaptations alongside resistance training; concomitant increases in tendon stiffness.
6. Iwai K et al. Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates. Journal of Agricultural and Food Chemistry. 2005;53(16):6531–6536. — Established pharmacokinetic profile of hydrolysed collagen: serum hydroxyproline rises within 15–30 min, peaks at 30–60 min post-ingestion; basis for 30-min pre-exercise timing recommendation.
7. Baar K. Stress relaxation and targeted nutrition to treat patellar tendinopathy. Journal of Orthopaedic & Sports Physical Therapy. 2019;49(9):668–675. — Baar's synthesis of the collagen + vitamin C + loading intervention framework; discusses prolyl hydroxylase cofactor role of vitamin C; provides rationale for pre-exercise timing protocol.
8. Chiofalo B 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. Journal of Nutrition. 2023. ScienceDirect — Dose-response study confirming that 30 g hydrolysed collagen produced greater post-exercise collagen synthesis response than 15 g or placebo; supports higher-dose protocols for maximising effect.