What stimulates tendon repair?

The stimuli in the cell's own order: strain, the cell's own growth factors, and substrate

What stimulates tendon repair is a question that tendon cell biology answers more precisely than the supplement aisle does, and the honest page answers it by listing the stimuli a tendon cell, a tenocyte, actually responds to in the cell's own order of importance, because the shelf lists them in the order of what it has to sell and the two orders are nearly reversed. The first and master stimulus is mechanical strain. Tenocytes sit between the collagen fibres of a tendon attached to the matrix around them, and when the tendon is loaded the matrix deforms and the cells sense the deformation through those attachments, responding by switching on the genes for collagen and for the enzymes that remodel matrix; measured directly in human tendon after exercise, collagen synthesis rises to a peak around twenty-four hours after a loading bout and stays raised for up to three days, breakdown rises earlier and falls sooner, and the net balance is negative in the hours after a session and positive from around thirty-six to seventy-two hours, which is the repair, laid down in response to the load. Unloading does the reverse: a tendon rested or immobilised lowers its synthesis below baseline, loses matrix quality within weeks and heals, after a tear, into a disorganised scar, which is why progressive loading is the treatment of tendinopathy, why early controlled loading after a rupture repair outperforms immobilisation, and why nothing swallowed stimulates a tendon that is not being loaded. The second stimulus is the growth factors, and the honest page places them second because they are the shelf's favourite and the cell's own. In response to strain, tenocytes and the cells around them release signalling proteins, transforming growth factor beta, insulin-like growth factor one, platelet-derived growth factor and others, which act locally over hours to coordinate the repair, recruiting cells, raising synthesis and directing the matrix turnover; they are the mechanism by which the master stimulus becomes tissue, and they are produced in the tendon at the moment they are needed. Supplying them from outside is the logic of platelet-rich plasma and of the injectable peptides, and the difficulty is that the cell makes exactly what it needs when it is loaded and a syringe cannot time or target that, which is a reason the trials of supplied growth factors disappoint. The third stimulus is not a stimulus so much as a condition: substrate. A stimulated cell builds collagen from glycine, proline and lysine with vitamin C and iron as cofactors for the enzymes that fold the chains, copper for the enzyme that cross-links them and zinc for the enzymes that remodel matrix, all met from an ordinary plate carrying 1.6 to 2.2g of protein per kilogram, and an under-fed or smoking reader has starved the cell the load has stimulated. This is where the collagen pre-loading protocol sits and the only place it sits: 15g of gelatin or hydrolysed collagen with vitamin C about an hour before the loading session, timing the substrate to the stimulus, with a doubled blood marker of collagen synthesis in the Baar trial and one small six-month Achilles outcome trial at 2.5g beside calf strengthening as its evidence, an adjunct to the load that stimulates and never a stimulus itself.

The stimuli sold, in the order of their evidence, and what the list means for a sore tendon

The stimuli sold come fourth in the cell's order and first on the shelf, and the honest page gives each its evidence rather than its price. Platelet-rich plasma, a person's own blood spun to concentrate the platelets and their growth factors and injected into the tendon, has the most plausible logic of the sold stimuli, supplying the second item on the cell's list directly; in randomised trials across Achilles, patellar and elbow tendinopathy the results are inconsistent, with several well-designed trials finding no benefit over a saline injection or over exercise alone and others finding modest gains, so that guidelines place it, where they place it at all, behind a completed loading programme as an option for people who have not responded. Extracorporeal shockwave therapy, pressure waves delivered through the skin to the tendon, shows modest benefit in some chronic tendinopathies, calcific shoulder and plantar heel pain among them, as an adjunct to loading rather than a replacement, with a proposed mechanism of stimulating the cells and disrupting degenerate tissue, and it too sits behind the programme. Corticosteroid injection relieves pain for weeks and worsens outcomes at six and twelve months, which makes it an anti-stimulus for repair however it feels. And the injectable peptides sold online as tendon healers, BPC-157 above all, have rodent data in which healing was faster in transection models, no randomised trial in humans for any indication, no licensed product anywhere, sale outside pharmaceutical quality control, a place on the prohibited list in sport, and unknown human dosing and safety, so they are not a stimulus with evidence but a hypothesis with a syringe, and the honest page does not describe how they are used. What the list means for a reader with a sore tendon is a sequence that follows the cell's order. Load the tendon progressively, from isometric holds for pain through heavy slow resistance every second or third day to the energy storage work the sport demands, because strain is the only stimulus with outcome trials behind it and the one that produces the growth factors on site. Feed the stimulated cell, with protein at target, vitamin C, iron, copper and zinc from food, sleep and no smoking, and time the collagen protocol to the session if wanted. Hold the sold stimuli in reserve: shockwave or PRP are a specialist's conversation after months of a properly completed programme, steroid injection is declined for the long term, and the peptides are left alone. The worked example is the substrate adjunct at habit scale, stated on its true terms: two capsules, 1200mg hydrolysed type 1 marine collagen with 12mg vitamin C at 15% of its reference value plus zinc, 120 for £16.99 at 28p a day, lab tested and UK made, below the 15g protocol dose, carrying vitamin C's collagen formation sentence for cartilage and bones and no tendon claim. What stimulates tendon repair: load, which makes the cell release its own stimuli, with substrate to build from and nothing sold yet shown to add to it.

What to check on the label