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Two-week cumulative tendon load estimated from insole sensor contact forces is associated with plantar flexor function in Achilles tendinopathy
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  • Published: 18 February 2026

Two-week cumulative tendon load estimated from insole sensor contact forces is associated with plantar flexor function in Achilles tendinopathy

  • Ke Song1,
  • Michelle P. Kwon1,
  • Andy K. Smith2,
  • Ryan T. Pohlig3,
  • Karin Grävare Silbernagel2 &
  • …
  • Josh R. Baxter1 

Scientific Reports , Article number:  (2026) Cite this article

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We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.

Subjects

  • Biomarkers
  • Lifestyle modification
  • Mechanical engineering
  • Orthopaedics
  • Rehabilitation
  • Translational research

Abstract

Tendon loading dictates rehabilitation outcomes in Achilles tendinopathy but is difficult to track in the real world. In this study, we used instrumented insole sensors to monitor Achilles tendon load for two weeks in fifteen individuals with Achilles tendinopathy, who also completed assessments of their plantar flexor strength, dynamic function, and survey-based outcomes. We used insole data to estimate two types of cumulative Achilles tendon load: overall (≥ 0.3×body weight) and high-level load (≥ 3×body weight). We determined Pearson correlations between (1) overall and high-level tendon loads, (2) plantar flexor moment, power, work, (3) heel raise height, repetitions, countermovement jump height, and (4) self-reported symptoms and activity. Overall cumulative tendon load moderately correlated to isometric plantar flexor moment (r = 0.543) and weakly to isokinetic and dynamic functions (0.128–0.413). Cumulative high-level tendon load strongly correlated to heel raise height (0.687) and fast isokinetic moment (0.625), and moderately to other functional measures (0.470–0.592). Symptoms weakly correlated to overall (0.392) and moderately to high-level load (0.436). Self-reported activity weakly correlated to overall (0.297) and strongly to high-level load (0.617). Stronger associations with the high-level Achilles tendon load than the overall load suggest that clinical function assessments provide insight into the real-world performance of high-loading activities. In contrast, the disconnect between overall tendon loading and plantar flexor function may explain the variability in recovery outcomes. Self-reported activity and standard heel raises represent high-level tendon load well, yet they do not always suggest functional deficit. Sensor-monitored tendon load shows promise as a new biomarker for real-world plantar flexor function in Achilles tendinopathy.

Data availability

The insole sensor data, dynamometer testing data, motion capture data, deidentified survey data, and data analysis code that we generated and/or analyzed during the current study are openly and freely available in a public Zenodo repository 52, https://doi.org/10.5281/zenodo.14947735, which we shared in accordance with study participant protection standards.

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Acknowledgements

The authors thank Devyn P. Russo for assistance with data collection.

Funding

This study was funded by the National Institutes of Health – National Institute of Arthritis and Musculoskeletal and Skin Diseases (grant numbers: R01AR078898 and P50AR080581). The funder played no role in study design, data collection, analysis and interpretation of data, or the writing of this manuscript.

Author information

Authors and Affiliations

  1. Department of Orthopaedic Surgery, University of Pennsylvania, 3737 Market Street, 6th Floor, Philadelphia, PA, 19104, USA

    Ke Song, Michelle P. Kwon & Josh R. Baxter

  2. Department of Physical Therapy, University of Delaware, Newark, DE, USA

    Andy K. Smith & Karin Grävare Silbernagel

  3. Biostatistics Core Facility, University of Delaware, Newark, DE, USA

    Ryan T. Pohlig

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  2. Michelle P. Kwon
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Contributions

K.S., K.G.S. and J.R.B. conceptualized the study. J.R.B. acquired funding and resources for the study and supervised project administration. K.S., R.T.P., K.G.S. and J.R.B. developed the methodology. K.S., M.P.K. and A.K.S. curated experimental data. K.S. and M.P.K. performed hardware and software validation and formal analysis of the data. K.S. developed the original draft of the manuscript, including visualization of the analyzed data. All authors reviewed and edited the manuscript and approved the final version submitted to the journal.

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Correspondence to Ke Song.

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Song, K., Kwon, M.P., Smith, A.K. et al. Two-week cumulative tendon load estimated from insole sensor contact forces is associated with plantar flexor function in Achilles tendinopathy. Sci Rep (2026). https://doi.org/10.1038/s41598-026-40438-1

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  • Received: 11 April 2025

  • Accepted: 12 February 2026

  • Published: 18 February 2026

  • DOI: https://doi.org/10.1038/s41598-026-40438-1

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Keywords

  • Ankle
  • Biomechanics
  • Foot
  • Physical therapy
  • Rehabilitation
  • Wearable sensors
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