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Sports Medicine · 9 min · September 28, 2026
From the course: Achilles Tendinopathy in Runners: Biomechanical Risk and Protective Factors From a Prospective Cohort · 0.5 contact hours
This episode breaks down a large prospective cohort study on Achilles tendinopathy in runners and non-runners, focusing on weekly running volume, MRI findings, and baseline ankle biomechanics linked to later injury risk.
It also looks at what did not predict injury, including cadence, strike pattern, speed, and several knee and hip measures, while highlighting the study’s strengths and limitations.
Jandacka D, Skypala J, Plesek J, Urbaczka J, Golian M, Burda M, Šustek J, Zahradnik D, Elavsky S, Jandackova VK, Selbie S, Silvernail JF, Hamill J. Biomechanical insights into Achilles tendinopathy risk and protection in runners: a large prospective study 4HAIE. Br J Sports Med. 2026;60(3):186–197. https://doi.org/10.1136/bjsports-2025-110260. PMID 41672607; PMCID PMC13018850.
Which biomechanical factors predict Achilles tendinopathy in runners? In a prospective cohort published in the British Journal of Sports Medicine in 2026, Jandacka and colleagues tested the running mechanics of 911 adults in the laboratory and then followed them for a year. Participants who later developed a physician-diagnosed Achilles tendinopathy had shown less external rotation of the foot and a smaller peak ankle inversion moment during stance, and they ran more distance each week. Footfall pattern, running speed, cadence and the knee and hip measures the authors expected to matter showed no clear link to who developed the condition. The authors describe the two ankle measures as possible protective factors. Because the design was observational, the results describe associations and do not come from a test of any treatment or gait-retraining program.
The authors note that most earlier biomechanical evidence on Achilles tendinopathy came from retrospective or cross-sectional studies, or from small prospective samples, and that the findings conflicted. Those studies could not account at the same time for prior injury, age, sex and how much each person actually ran. Jandacka and colleagues designed their cohort, part of the Healthy Aging in Industrial Environment Program 4 (4HAIE) in the Czech Republic, to combine laboratory biomechanics with a year of objectively tracked activity.
The final sample was 911 adults aged 18 to 65, with a mean age of 37.7 years; 429 were female and 528 were classified as runners. Runners had to meet the World Health Organization physical activity recommendation and cover at least 10 km per week, or 6 km for those older than 60. Non-runners were able to run but did not meet the activity recommendation. The authors included them because Achilles tendinopathy is not limited to runners.
At baseline, each participant had MRI of the right Achilles tendon and completed eight overground runs at a self-selected pace, recorded with a 10-camera motion system and three force plates. A musculoskeletal radiologist scored tendon structure with the Vienna Morphological Achilles Tendon Score, and participants rated symptoms on the VISA-A questionnaire.
For the next year, participants wore a wrist activity tracker and answered a weekly injury survey through a mobile app. Of 48 participants who reported symptoms suggesting Achilles tendinopathy, an orthopedic specialist confirmed 30, and the analysis used the 23 confirmed cases with no prior Achilles injury. Participants with lower-leg symptoms but no formal diagnosis were left out of both groups, so the comparison group had no lower-leg complaints.
The analyses controlled for age, sex and running distance, and the same pattern appeared in the full cohort and again in runners alone.
| Baseline factor | Direction of the association | What the authors reported |
|---|---|---|
| Peak ankle external rotation angle during stance | Less rotation, higher odds | Framed as a possible protective factor |
| Peak ankle inversion moment during stance | Larger moment, lower odds | The strongest protective signal in the data |
| Weekly running distance, measured by activity tracker | More distance, higher odds | Held in every model the authors tested |
| Footfall pattern, strike index, running speed and cadence | No clear link | Rearfoot, midfoot and forefoot landings were similar in both groups |
| Knee and hip measures, including peak hip adduction | No clear link | The authors had expected altered knee mechanics and greater hip adduction to raise risk |
| Age and sex | No reliable link after adjustment | Cases tended to be older, and men showed somewhat higher odds, but neither estimate held up |
The raw case counts point the same way on running exposure: 20 of 528 runners (3.8%) developed the condition, compared with 3 of 383 non-runners (0.8%). Baseline MRI also separated the groups. Participants who later developed tendinopathy had a lower median tendon score than those who stayed injury-free, a gap the authors treated as more than chance would explain.
The authors offer two mechanisms for later testing. They propose that energy absorbed through natural eversion and a strong inversion moment in the frontal plane spares the tendon from taking the whole load in the sagittal plane, where Achilles strain is greatest. They also hypothesize that greater external foot rotation shifts force transmission away from the lateral gastrocnemius subtendon.
In this cohort, footfall pattern was not associated with a higher risk of Achilles tendinopathy, and Jandacka and colleagues write that their data challenge common advice to change footfall to protect the tendon. They point to earlier retrospective work with previously injured runners in which midfoot striking was reported as a risk factor. Because they excluded anyone with a prior Achilles injury and measured mechanics before onset, the authors argue that a midfoot landing or greater eversion seen in injured runners may be an adaptation to a compromised tendon rather than its cause.
The small number of cases matters when reading these null results. The full-cohort biomechanical models rested on 14 right-sided cases, and the runners-only models on 12. With so few events, a null result means the authors did not detect a link, and a link has not been ruled out.
The authors conclude that sufficient external foot rotation and a sufficient ankle inversion moment during stance may protect against Achilles tendinopathy, and that higher weekly mileage raises risk. They describe the two ankle measures as modifiable parameters that could be built into gait assessment and individualized training plans, paired with monitoring of running volume rather than either approach on its own. They advise caution when increasing volume at older ages and in both sexes.
In the 4HAIE cohort, Jandacka and colleagues found that greater weekly running distance went with higher odds of a new physician-diagnosed Achilles tendinopathy over one year. Two ankle measures during stance pointed the other way: more external rotation of the foot and a larger peak inversion moment went with lower odds.
The authors report that rearfoot, midfoot and forefoot landings were not linked to higher risk, and they state that their prospective data do not support advice to change footfall pattern to protect the tendon. They did not test a gait-retraining program.
In this cohort, more weekly distance, measured by activity tracker, went with higher odds of onset in every model the authors tested. They recommend monitoring training volume, particularly in high-mileage runners.
Jandacka D, Skypala J, Plesek J, et al. Biomechanical insights into Achilles tendinopathy risk and protection in runners: a large prospective study 4HAIE. Br J Sports Med. 2026;60(3):186-197. doi:10.1136/bjsports-2025-110260
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