Exercise progression to incrementally load the Achilles tendon

Key points

1. 01Peak Achilles tendon load ranged from 0.5 bodyweights (seated heel raise) to 7.3 bodyweights (single-leg forward hopping), a 12-fold difference across 30 exercises.
2. 02Exercises were ranked into four tiers using a composite loading index based on peak load, loading impulse, and loading rate, allowing systematic progression.
3. 03Two parallel progressions were identified: one using isolated ankle movements and one using multijoint movements, offering flexibility in rehabilitation design.
4. 04Asymmetric movements (lunges, step ups, step downs) load the trailing limb more than the leading limb, enabling side-specific tendon loading prescription.
5. 05Walking and running serve as clinical milestones, and exercises with similar loading indices can be substituted safely once a milestone is reached.

How it was conducted

Design

Cross-sectional biomechanical laboratory study

Participants

8 healthy recreationally active adults (6 male, 2 female; mean age 30 +/- 4 years; BMI 24.1 +/- 3.2 kg/m2); no history of Achilles tendon injury

Exercises tested

30 exercises including seated and standing heel raises, squats, lunges, step ups and downs, hopping, drop jumps, counter movement jumps, walking, and running

Measurement approach

3D motion capture (12-camera, 100 Hz) and ground reaction forces (1000 Hz); Achilles tendon load estimated as plantarflexion moment divided by a 5 cm moment arm, normalized to bodyweight

Loading index

Composite score weighting peak load (50%), loading impulse (30%), and loading rate (20%), normalized to the maximum observed value for each parameter

What they found

• Seated double-leg heel raise: loading index 0.100, peak load 0.5 +/- 0.2 bodyweights, impulse 0.6 +/- 0.2 bodyweight-seconds, rate 2.7 +/- 1.0 bodyweights/s.
• Standing single-leg heel raise: loading index 0.493, peak load 3.0 +/- 0.3 bodyweights, impulse 2.5 +/- 0.6 bodyweight-seconds, rate 13.1 +/- 3.4 bodyweights/s.
• Walking (stance): loading index 0.359, peak load 3.3 +/- 0.3 bodyweights, impulse 0.8 +/- 0.1 bodyweight-seconds, rate 18.7 +/- 2.7 bodyweights/s.
• Running (stance): loading index 0.600, peak load 5.2 +/- 0.9 bodyweights, impulse 0.7 +/- 0.1 bodyweight-seconds, rate 58.1 +/- 12.7 bodyweights/s.
• Single-leg forward hopping: loading index 0.924, peak load 7.3 +/- 1.9 bodyweights, impulse 2.3 +/- 0.3 bodyweight-seconds, rate 67.1 +/- 18.5 bodyweights/s.
• During a lunge, the trailing Achilles tendon loading index was 52% higher than the leading limb (0.435 vs 0.285), primarily due to increased time under load.
• Single-leg drop jump loading index was 0.852; double-leg drop jump was 0.519, despite similar peak loads (5.5 +/- 0.8 vs 3.6 +/- 0.6 bodyweights).
• Sensitivity analysis removing one participant did not change loading parameters or exercise rankings.

Limitations

• Small, healthy cohort of 8 participants; patients with tendon pathology may move differently, and inter-individual variability at higher exercise intensities was considerable.
• Achilles tendon load was estimated indirectly from inverse dynamics using a fixed 5 cm moment arm, not measured directly with tendon buckles or ultrasound.
• The weighting of peak load (50%), impulse (30%), and rate (20%) in the loading index was based on clinical intuition, not empirical evidence, and could alter exercise rankings if changed.
• Only healthy young adults were tested; findings may not directly generalize to older patients, those with different training backgrounds, or injured populations.

Why it matters

For patients

Patients recovering from Achilles tendon rupture or tendinopathy can use this four-tier progression to safely build up tendon load step by step, starting from seated heel raises and working toward hopping only when ready.

For clinicians

The loading index table provides a biomechanically ordered menu of 30 exercises across four tiers, enabling evidence-guided prescription of tendon load magnitude, impulse, and rate for each stage of rehabilitation.

For readers

This study offers the most comprehensive biomechanical dataset for Achilles tendon rehabilitation exercises to date, providing a quantitative foundation for designing or comparing loading protocols in research.