Collagen for Tendons: Can It Protect Runners?

How does collagen supplementation actually work?

Tendons are built largely from type I collagen, and the working theory is that supplying collagen-derived amino acids around a loading stimulus supports the tissue's synthesis of new collagen. The foundational work here is Shaw et al. (2017), a randomised crossover trial in eight healthy men. Consuming 15 g of vitamin C-enriched gelatin one hour before a short bout of intermittent exercise roughly doubled blood levels of PINP, a marker of collagen synthesis, compared with placebo. Serum from the supplemented men also increased the collagen content and mechanical strength of engineered ligaments grown in the laboratory.

Two details matter for runners. First, timing: the amino acids are taken about an hour before loading so they are available when the tendon is stimulated. Second, vitamin C acts as a cofactor for collagen formation. The mechanism is plausible, but Khatri et al. (2021) caution that the exact pathways remain unclear and call for biopsy and imaging confirmation rather than blood markers alone.

Can collagen strengthen tendons in healthy runners?

The most direct evidence comes from two randomised, placebo-controlled trials by the same group. Jerger et al. (2022) had 40 healthy young men complete 14 weeks of high-load resistance training. Those taking 5 g/day of specific collagen peptides increased Achilles tendon cross-sectional area by 11.0%, against 4.7% in the placebo group. Jerger et al. (2023) repeated the design in 50 moderately active men and found a greater increase in patellar tendon cross-sectional area with collagen than placebo.

The important nuance is what did not differ. In both trials, muscle strength and tendon stiffness rose equally in the collagen and placebo groups, so the collagen effect showed up in tissue size rather than in how strong or stiff the tendon became. In the 2022 Achilles study, muscle thickness also increased significantly more with collagen (+7.3%) than placebo (+2.7%). A bigger tendon may distribute load over more tissue, which is a reasonable proxy for resilience, but these studies measured morphology rather than injury rates. The benefit also depended entirely on the concurrent heavy loading.

Does collagen help with existing tendon injuries?

For runners already dealing with Achilles pain, the signal is more clinically relevant. Praet et al. (2019) studied 20 patients with chronic mid-portion Achilles tendinopathy who all followed a calf-strengthening programme. Adding 2 x 2.5 g (5 g/day) of specific collagen peptides accelerated recovery: VISA-A scores, a validated measure of Achilles symptoms and function, rose by 12.6 points after three months on collagen versus only 5.3 points on placebo.

The interpretation is that collagen sped the response to loading rehabilitation, potentially shortening the road back to running. A supporting, though much weaker, thread comes from Baar (2019), a single case report of a professional basketball player whose chronic patellar tendinopathy resolved on MRI over roughly 18 months using gelatin plus vitamin C and heavy isometric loading. A case study is hypothesis-generating only. Both point in the same direction, but neither replaces the calf-loading programme that did the structural work.

What is the right dose and timing?

The literature uses two broadly different doses depending on the target. For tendon-specific outcomes, the trials by Jerger et al. (2022, 2023) used 5 g/day of specific collagen peptides, and Praet et al. (2019) used 2 x 2.5 g (5 g/day) for Achilles tendinopathy. For collagen synthesis and joint outcomes, Khatri et al. (2021) describe a common protocol of around 15 g taken roughly 60 minutes before exercise, mirroring the 15 g used by Shaw et al. (2017).

Bischof et al. (2024) note in their meta-analysis that dosing appears to be endpoint-dependent, with higher doses near 15 g used for muscle and body-composition outcomes and lower doses adequate for tendon morphology. Vitamin C is included in the pre-exercise protocols as a synthesis cofactor. The practical reading for a runner: a modest 5 to 15 g dose taken about an hour before a loading session is consistent with the trials, though the optimal dose has not been precisely established.

Where is the evidence weak or mixed?

This is where balance matters. Kirmse et al. (2024) pooled 13 studies with 450 participants and found no significant effect of collagen peptides on strength-related performance; 48 of 55 performance measures showed no change. They acknowledge collagen can increase Achilles and patellar tendon size but explicitly warn against overstating functional or performance benefits. In other words, a bigger tendon on imaging has not translated into measurable running or strength gains.

Khatri et al. (2021) reached a similar split verdict: collagen most consistently helped joint functionality and pain, while evidence for muscle protein synthesis and body composition was weaker, and mechanisms stayed unclear. Bischof et al. (2024) flag substantial heterogeneity between studies. Crucially, no trial has measured whether collagen reduces the incidence of running injuries such as Achilles tendinopathy or stress-related tendon problems. The morphological changes are real; the leap to injury prevention is an inference, not a demonstrated outcome.

Does collagen work without training?

Consistently across the literature, the answer is no. Every positive tendon finding is tethered to a loading stimulus. Shaw et al. (2017) delivered gelatin before exercise. Jerger et al. (2022, 2023) paired collagen with 14 weeks of high-load resistance training. Praet et al. (2019) combined peptides with a calf-strengthening programme. Baar (2019) added collagen to heavy isometric loading.

Bischof et al. (2024) make the point directly in their meta-analysis: benefits depended on concurrent training. This is the single most important framing for runners. Collagen is not a stand-alone tendon builder; it appears to act as a modest amplifier of the adaptations that loading already drives. For a runner, that means the heavy calf raises, hill work and progressive mileage are the intervention. Collagen, taken before those sessions, is at best a small tailwind. Spending on the supplement while neglecting the loading has no support in any of these trials.

So should runners take collagen for their tendons?

A reasonable, evidence-led position: collagen is low-risk, inexpensive relative to many supplements, and has plausible mechanistic and morphological support, so a runner already doing structured tendon loading could trial 5 to 15 g with vitamin C about an hour before key sessions. The strongest case is for runners rehabilitating Achilles tendinopathy alongside a calf programme, where Praet et al. (2019) showed faster symptom recovery.

Keep expectations calibrated. The tendon-size increases in Jerger et al. (2022, 2023) are real but did not improve strength or stiffness, and Kirmse et al. (2024) found no performance benefit. No trial demonstrates fewer injuries. Collagen will not compensate for training errors, rapid mileage jumps or inadequate strength work, which remain the dominant drivers of running tendon problems. Treat it as an optional adjunct to good loading, not a substitute for it, and judge it accordingly.

Does collagen prevent running injuries?

No study has directly shown that. Trials such as Jerger et al. (2022) show collagen can increase tendon cross-sectional area when paired with loading, and Praet et al. (2019) show faster recovery from Achilles tendinopathy, but none measured whether collagen lowers injury rates in runners. Injury prevention is an inference from tendon morphology, not a demonstrated outcome, so treat the claim cautiously.

How much collagen should a runner take?

The trials cluster around two doses. Tendon-specific studies by Jerger et al. (2022, 2023) used 5 g/day, and Praet et al. (2019) used 2 x 2.5 g (5 g/day) for Achilles tendinopathy. Collagen-synthesis protocols in Shaw et al. (2017) and Khatri et al. (2021) used around 15 g taken about an hour before exercise. A 5 to 15 g pre-session dose is consistent with the evidence.

Why is vitamin C taken with collagen?

Vitamin C is a cofactor in collagen formation. Shaw et al. (2017) used vitamin C-enriched gelatin, and the pre-exercise protocols reviewed by Khatri et al. (2021) include it alongside the collagen or gelatin dose. Taking the two together around an hour before loading reflects the design of the studies that showed increased collagen-synthesis markers, though the vitamin C dose itself has not been separately optimised.

Does collagen improve running performance or strength?

The evidence says no. Kirmse et al. (2024) pooled 13 studies and found no significant effect of collagen peptides on strength-related performance, with 48 of 55 performance measures unchanged. Even in trials where tendon size increased, muscle strength and tendon stiffness rose equally with and without collagen. The measurable effect is on tendon morphology, not on how fast or strong you become.

Does collagen work if I do not do strength training?

Not according to the evidence. Every positive tendon finding is tied to a loading stimulus: resistance training in Jerger et al. (2022, 2023), calf strengthening in Praet et al. (2019), and exercise before dosing in Shaw et al. (2017). Bischof et al. (2024) confirm in their meta-analysis that benefits depended on concurrent training. Collagen appears to amplify loading adaptations rather than create them alone.

Can collagen help an existing Achilles injury?

There is modest support. Praet et al. (2019) found that adding 2 x 2.5 g (5 g/day) of collagen peptides to a calf-strengthening programme raised VISA-A scores by 12.6 points at three months versus 5.3 points on placebo, suggesting faster recovery. Baar (2019) describes a single case of patellar tendinopathy resolving with collagen plus loading. The loading rehab remains the primary treatment; collagen is a possible adjunct.