Why This Matters Clinically

The Achilles tendon transmits forces of 6–10× body weight during running and jumping, making it one of the most highly loaded structures in the body. Its capacity to tolerate these forces depends on the quantity, organisation, and cross-linking of its collagen fibres — all properties that progressive loading drives through tenocyte mechanosensing. Both midsubstance and insertional tendinopathy are treated with loading, but with important positional differences: midsubstance responds to full-range eccentric and isotonic loading; insertional requires avoiding end-range dorsiflexion (which compresses the insertion against the calcaneus).

Exercise Progression

Isometric holds (phase 1, high irritability): Single-leg calf raise isometric hold: rise to 70% of maximal height, hold 45 seconds, 5 repetitions. Perform 3–4× daily during the initial reactive phase. Pain should reduce within 5 minutes of loading (characteristic of tendon pain) — if it does not, reduce the effort level.

Heavy slow resistance (phase 2): Single-leg heel raise on a step (for midsubstance) or on a flat surface only (for insertional — no dorsiflexion below neutral): 3-second concentric rise, 3-second eccentric lower, 3 sets of 8–12 repetitions, load with a backpack when bodyweight becomes easy. 3× weekly, 48-hour recovery. This is the most evidence-supported Achilles loading protocol.

Progressed loading (phase 3): Straight-leg heel raise (knee straight — emphasises gastrocnemius) alternating with bent-knee heel raise (knee soft — emphasises soleus). Progressing both muscles is necessary for complete Achilles tendon loading since both heads contribute to the tendon. Add load progressively over 12–16 weeks before introducing plyometric work.

Morning stiffness as a loading guide: The severity of morning stiffness (stiffness in the Achilles on the first few steps out of bed, resolving within 10 minutes) provides a reliable indicator of the previous day's loading level. More stiffness the next morning = previous session was at or slightly above current capacity. Consistent absence of morning stiffness = load can be increased. Stiffness persisting beyond 20 minutes = load exceeded current capacity and should be reduced. This patient-reported measure allows daily self-calibration without clinic visits.

Programming Guidelines

Train 3× weekly with 48-hour recovery between sessions. Begin at the level where movement quality is excellent and symptoms are 0–2/10. Progress load, range, or complexity only when the current level is performed without compensation across three consecutive sessions. Allow 8–12 weeks for functional strength to meaningfully improve in a rehabilitation context.

References & Further Reading

  1. Alfredson H, et al. Heavy-load eccentric calf muscle training for the treatment of chronic Achilles tendinosis. Am J Sports Med. 1998;26(3):360–366.
  2. Beyer R, et al. Heavy slow resistance versus eccentric training for Achilles tendinopathy. Am J Sports Med. 2015;43(7):1704–1711.
  3. Cook JL, Purdam CR. Is compressive load a factor in the development of tendinopathy? Br J Sports Med. 2012;46(3):163–168.