Asymmetric running is associated with pain during outdoor running

Key points

1. 01Greater ground contact time on the contralateral (less symptomatic) leg corresponded to more pain in the injured tendon, and this relationship strengthened with each consecutive run day (b=-0.028, p<0.001).
2. 02The total number of running bouts over two weeks was not associated with change in symptom severity (p=0.672), suggesting continued running was not detrimental in the short term.
3. 03Ground contact time explained less than 5% of the variance in tendon pain, so other factors (running speed, ground incline, surface stiffness) likely matter too.
4. 04Runners who off-load their injured leg may benefit from the clinically recommended 2 to 3 recovery days between runs.
5. 05This was a small, two-week observational snapshot of a recovery process that can last 3 to 6 months or longer, so conclusions are preliminary.

How it was conducted

Design

Prospective observational study

Setting

Biomechanics laboratory and outdoor running

Participants

17 recreational runners with Achilles tendinopathy in the return-to-sport phase

Measures

Symptom severity via VISA-A questionnaire; worst tendon pain via 0 to 10 numeric pain rating in daily logs; ground contact time via shoe-mounted wearable sensors (MilestonePod)

Analysis

Linear mixed model for pain vs ground contact time symmetry moderated by consecutive run days; multiple regression for number of runs vs VISA-A change, adjusted for run distance

What they found

• Greater ground contact time on the contralateral leg corresponded to increased ipsilateral tendon pain for each consecutive run day (b=-0.028, p<0.001).
• Number of running bouts was not associated with 2-week changes in VISA-A scores (p=0.672).
• Ground contact time accounted for less than 5% of the variance in tendon pain during outdoor running.
• Baseline symptom severity was low, with an average VISA-A score of 78 out of 100 in the most symptomatic leg.
• The wearable sensor detected gait parameters with comparable accuracy to lab-based motion capture (less than 12% percentage error).

Limitations

• Small sample size (17 runners) over a short 2-week window of a recovery process that can last 3 to 6 months or longer.
• Observational design cannot establish that off-loading causes pain; the relationship may run either direction.
• Low baseline symptom severity (average VISA-A 78/100) may create a floor effect, so a larger sample may be needed to detect meaningful change in symptoms.
• The heterogeneous sample and unknown duration in the return-to-sport phase, plus unmeasured factors like running speed, incline, and surface, limit how far results generalize.

Why it matters

For patients

If you are returning to running with Achilles pain, favoring your other leg may be tied to more pain, so building in 2 to 3 rest days between runs is reasonable, but continuing to run did not appear harmful over two weeks.

For clinicians

Monitoring loading symmetry (for example ground contact time) during real-world running may help identify return-to-sport patients who off-load the injured leg and could benefit from recovery days, though the metric alone explains little of the pain variance.

For readers

Wearable sensors can track running gait outdoors well enough to study tendon loading patterns, opening a path to monitor rehabilitation outside the clinic.