Tendon injuries account for 30-50% of all running-related injuries, with the Achilles tendon and patellar tendon being the most frequent casualties. The fundamental problem is a mismatch in adaptation rates: skeletal muscle responds to training stimulus within 2-3 weeks, while tendons require 8-12 weeks to remodel and strengthen. This gap means your cardiovascular fitness and muscular strength can outpace your tendon capacity, especially during rapid mileage increases.
Understanding tendon biology is the first step toward prevention. Tendons are composed primarily of type I collagen fibres arranged in parallel bundles, embedded in a matrix of proteoglycans and water. Unlike muscle, tendons have relatively poor blood supply — the Achilles tendon's mid-portion is particularly avascular, which is why that region is most prone to degeneration. Training stimulates collagen synthesis, but only if the loading dose, recovery period, and nutritional environment are optimised.
The Heavy Slow Resistance (HSR) Protocol
Heavy slow resistance training is the gold standard for tendon strengthening. A landmark 2015 study by Beyer et al. in the American Journal of Sports Medicine showed that HSR produced tendon structural improvements equal to traditional eccentric training but with significantly higher patient satisfaction and better compliance.
The HSR protocol for the Achilles tendon uses bilateral heel raises performed slowly:
- 3-second concentric (raise), 3-second eccentric (lower)
- Start with 4 sets of 12 reps at moderate load
- Progress to 4 sets of 6 reps at heavy load over 12 weeks
- Perform 3 times per week on non-consecutive days
- Use a loaded backpack or Smith machine to add resistance progressively
For the patellar tendon, the equivalent exercise is the single-leg leg press or Spanish squat (leaning back against a wall with a resistance band behind the knees), using the same 3-second tempo and progressive loading scheme.
Isometric Loading for Pain Management
If you are currently experiencing tendon pain (a score below 70 on the VISA-A or VISA-P questionnaire), isometric holds are the starting point. Research by Rio et al. (2015) demonstrated that isometric contractions held for 45 seconds at 70% of maximum voluntary contraction reduced patellar tendon pain by an average of 6.8 points on a 10-point scale — immediately and for at least 45 minutes post-exercise.
Protocol: 5 x 45-second isometric holds at 70% maximum effort, with 2-minute rest between sets. For the Achilles, perform a bilateral heel raise and hold at the top. For the patellar tendon, use a wall sit at 60 degrees of knee flexion. Perform twice daily. This is a bridge strategy — use it to manage pain while you build toward the HSR protocol.
The Alfredson Eccentric Protocol
The Alfredson protocol remains the most-studied intervention for midportion Achilles tendinopathy. It involves 180 eccentric heel drops per day (3 sets of 15 on each leg, performed twice daily — once with a straight knee, once with a bent knee). The exercise is performed off a step, lowering below the level of the step to achieve full eccentric range.
Key detail: the protocol is designed to be performed into mild discomfort (up to 5/10 on a pain scale). Pain-free exercise is not the goal during the initial 4-6 weeks. Expect improvements at 6-12 weeks. Compliance is the main challenge — the 12-week completion rate in clinical trials ranges from 55-72%. Adding load via a weighted backpack once bodyweight becomes pain-free is essential for continued tendon adaptation.
Collagen and Vitamin C Supplementation
A 2017 study by Shaw et al. in the American Journal of Clinical Nutrition demonstrated that consuming 15g of hydrolysed collagen peptides with 50mg of vitamin C 30-60 minutes before exercise doubled the rate of collagen synthesis in engineered ligaments. The vitamin C serves as a cofactor for prolyl hydroxylase — the enzyme required for proper collagen cross-linking.
Practical protocol:
- 15g hydrolysed collagen peptides dissolved in 200ml water
- 50mg vitamin C (equivalent to one orange or a supplement)
- Consume 30-60 minutes before a 6-minute bout of targeted loading (e.g., heel raises or jump rope)
- The 6-minute exercise window is critical — it signals the tendon cells to synthesise new collagen at the peak of amino acid availability
Sleep, Recovery, and Tendon Remodelling
Collagen synthesis peaks during deep sleep — growth hormone, released primarily during Stage 3 NREM sleep, is a key driver of tendon remodelling. Athletes sleeping fewer than 7 hours per night show 68% lower rates of collagen synthesis compared to those sleeping 8+ hours, according to data from the Australian Institute of Sport.
Additional recovery considerations: avoid NSAIDs (ibuprofen, naproxen) during tendon rehabilitation — they reduce inflammation but also impair collagen synthesis by up to 50%. Paracetamol is a safer analgesic choice when pain management is needed. For a deeper dive into Achilles-specific rehabilitation and return-to-running timelines, see our comprehensive Achilles tendinopathy guide for runners. If you are building back training volume after a tendon injury, use the Race Day Nutrition Planner to ensure your nutrition supports the increased collagen demands of recovery.