Summary

Your COL5A1 result determines tendon and ligament stiffness through type V collagen's role as a fibril diameter regulator — the "stiff" variants increase Achilles tendon and ACL injury risk by producing tendons that store energy well but have a narrower safety margin before failure, while the "flexible" variants create more compliant tendons with greater range of motion.

Genotype spectrum

TT (Flexible tendons)

Your tendons are naturally more flexible and resilient. Greater range of motion and lower tendon injury risk mean you can pursue dynamic sports with confidence.

TC/CT (Intermediate)

Balanced tendon properties. Standard range of motion with adequate injury protection.

CC (Stiff tendons)

Stiff tendons are excellent energy stores. For running, jumping, and bouncing movements, stiff tendons return stored elastic energy more efficiently.

CC (Flexible)

Flexible, resilient tendons.

CT (Intermediate)

Balanced.

TT (Stiff)

Efficient energy storage.

Practical takeaway

For Stiff Phenotype (rs12722 CC and/or rs7181866 TT)

Warm-up is non-negotiable:
• 15-20 minutes before any high-intensity exercise
• Start with 5 min low-intensity movement (walking, light cycling)
• Progress to dynamic stretching: leg swings, hip circles, ankle circles, walking lunges
• Sport-specific movement patterns at 50% → 70% → 90% intensity
• Never go from standing still to maximal effort

Eccentric training protocol — your tendon insurance:
• Eccentric calf raises (Alfredson protocol): 3x15 on a step, controlled 3-second lowering, daily if tolerated. This is the gold standard for Achilles tendon prehab.
• Nordic hamstring curls: 3x5, 2x/week (ACL injury prevention — 51% reduction in hamstring injuries in the meta-analysis by van Dyk et al. 2019)
• Single-leg balance work: builds proprioceptive control that protects against ligament injury

Progressive loading rules:
• Running mileage increase: <10%/week
• Resistance training load increase: <5%/week
• Don't add speed work and mileage in the same training block
• Deload every 3rd-4th week

Mobility maintenance:
• 2-3 dedicated stretching sessions/week, 15-20 minutes
• Focus on calves (gastrocnemius and soleus separately), hamstrings, hip flexors, and shoulders
• Hold stretches 30-60 seconds (static stretching is appropriate post-exercise, not pre-exercise)
• Foam rolling/massage supports tissue quality but doesn't replace stretching

Collagen support:
• 15g hydrolysed collagen + 50mg vitamin C, 30-60 min before exercise
• Supports collagen synthesis during the post-exercise remodelling window
• Not genotype-stratified evidence, but mechanistically targeted: providing building blocks for tissue that genetically produces less type V collagen

What to watch for:
• Morning Achilles stiffness lasting >15 minutes = early warning. Reduce training load.
• Point tenderness on the Achilles (especially 2-6cm above insertion) = early tendinopathy. Seek physiotherapy assessment.
• "Catching" or instability at the knee = ligament concern. Assess before continuing.
For Flexible Phenotype (rs12722 TT and/or rs7181866 CC)
• Your tendons are naturally more resilient. Standard warm-up (10 min) is sufficient.
• If pursuing

Evidence detail

What This Gene Does

COL5A1 encodes the alpha-1 chain of type V collagen, a minor but critical collagen type that acts as a regulator of type I collagen fibril assembly. While type I collagen (COL1A1) provides the bulk structural material of tendons and ligaments, type V collagen sits at the core of each fibril and controls its diameter. Think of type V collagen as the template around which type I collagen fibrils are built — it determines whether you get many thin fibrils (more flexible tissue) or fewer thick fibrils (stiffer tissue).

Two variants in COL5A1 affect this process through different mechanisms:

rs12722 (BstUI site in the 3'UTR): Affects mRNA stability and expression levels of COL5A1. The C allele is associated with stiffer tendons and higher Achilles tendon injury risk.

rs7181866 (intronic variant): Independently associated with tendon properties and injury risk. The T allele is associated with stiffer tendons.

Both variants contribute to an overall stiffness phenotype. Having unfavourable alleles at both loci compounds the effect.

Mechanism

Type V collagen as a fibril diameter controller:

Collagen fibrils in tendons and ligaments are not uniform — they have a range of diameters that determines the tissue's mechanical properties. Type V collagen sits at the core of each fibril during assembly and acts as a nucleation seed. The amount of type V collagen present determines how many fibrils are nucleated:
• More type V collagen (flexible genotype) → more nucleation seeds → more fibrils → smaller diameter fibrils → tissue has more total fibril surface area → more interfibrillar sliding during stretch → greater compliance (flexibility) → wider deformation range before failure
• Less type V collagen (stiff genotype) → fewer nucleation seeds → fewer but thicker fibrils → less interfibrillar sliding → stiffer tissue → less deformation before failure → higher risk of reaching failure threshold during rapid loading

Why stiff tendons get injured:

Tendons function as energy-storing springs. During running, your Achilles tendon stretches as your foot lands and recoils to propel you forward. A stiffer tendon returns more energy per stretch cycle (efficient) but has a narrower range between its elastic limit (reversible stretch) and its failure point (rupture). Think of it as a spring that's tighter: it stores energy well but breaks at a lower elongation.

The injury typically happens during sudden, high-force eccentric loading — landing from a jump, changing direction rapidly, or the push-off phase of sprinting. The tendon is loaded beyond its elastic limit before it can redistribute force, and the stiffer the tendon, the less margin exists.

Why rs12722 CC and rs7181866 TT compound:

These two variants affect COL5A1 expression through independent mechanisms (mRNA stability and transcriptional regulation respectively). Having both unfavourable alleles creates a double reduction in type V collagen, producing the stiffest tendon phenotype with the narrowest safety margin.

COL5A1 Tendon

Summary

Genotype spectrum

Practical takeaway

Evidence detail

Sources (6)