Running-related Achilles tendon injury: a prospective biomechanical study in recreational runners

Key points

1. 0125% of runners (26 of 103) developed a right-limb Achilles tendon running-related injury over 1 year
2. 02More flexed knee at initial contact (OR 1.146, p=.034) and midstance (OR 1.143, p=.037) were independent predictors after controlling for speed and physical activity
3. 03Runners with Achilles tendon injury also showed greater maximal ankle dorsiflexion during stance, but this did not reach significance in the multivariable model
4. 04Foot strike pattern (rearfoot vs non-rearfoot) was not a significant predictor in this prospective sample
5. 05The proposed mechanism is reduced effective mechanical advantage at the knee and ankle, forcing the gastrocnemius-Achilles complex to generate greater force

How it was conducted

Design

1-year prospective cohort study

Participants

103 recreational healthy runners (31-46 male/female split in no-injury group; 15 males and 11 females in injury group), mean age 35 years, running up to 51 km per week

Baseline measurement

3D motion capture (10-camera Qualisys system at 240 Hz) and force plate (Kistler at 2160 Hz) during overground running at self-selected pace in standardized neutral shoes

Injury surveillance

Weekly online questionnaire for 1 year; AT injury defined as AT-region pain causing stoppage or limitation of running for at least 7 days or 3 consecutive sessions

Primary analysis

Multivariable logistic regression of biomechanical variables (knee and ankle kinematics, foot strike index, running speed) controlled for vigorous physical activity

What they found

• 25% of the 103 participants (15 males and 11 females) reported an AT running-related injury on the right lower limb over 1 year; 30% reported AT injury on either limb
• Runners with AT injury had significantly greater knee flexion at initial contact (10.28 vs 7.91 degrees, p=.010, ES=0.630) and greater maximal knee flexion at midstance (41.17 vs 39.15 degrees, p=.034, ES=0.497)
• Runners with AT injury had significantly greater maximal ankle dorsiflexion during stance (89.50 vs 88.15 degrees, p=.036, ES=0.399)
• Multivariable logistic regression: knee angle at initial contact OR=1.146 (95% CI 1.010-1.301, p=.034); maximal knee flexion at midstance OR=1.143 (95% CI 1.008-1.295, p=.037)
• Each 1-degree increase in knee flexion at initial contact or midstance was associated with approximately 15% increased risk of AT injury
• Self-selected running speed (OR=2.391, p=.141) and foot strike index (OR=0.997, p=.807) were not significant predictors
• Runners who developed AT injury had significantly less body fat (19.82% vs 23.27%, p=.041, ES=0.491) and more vigorous physical activity (234 vs 158 min per week, p=.022) at baseline

Limitations

• AT injuries were not clinically diagnosed in most cases; classification relied on a self-report weekly questionnaire (only 2 participants received a formal clinical diagnosis)
• Running exposure (total volume accumulated during the year) was not measured, so the dose-response relationship between training load and injury timing could not be assessed
• Only right lower limb biomechanics were analyzed; left-limb injuries were not included in the biomechanical risk factor model
• Running biomechanics were measured once at baseline in standardized lab shoes; changes in mechanics over the year and differences from participants' own footwear were not captured

Why it matters

For patients

Recreational runners who tend to run with a noticeably bent knee may be at higher risk for Achilles tendon pain and should discuss gait assessment with a physiotherapist.

For clinicians

Knee flexion angle at initial contact and midstance, not foot strike pattern, emerged as the key modifiable biomechanical predictor; gait retraining aimed at reducing excessive knee flexion may be a rational injury-prevention target.

For readers

This is one of very few well-designed prospective biomechanical studies on Achilles tendon injury in runners and provides preliminary evidence that knee mechanics, rather than foot strike, drive injury risk.