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Loading speed and intensity in eccentric calf training impact acute changes in Achilles tendon thickness and stiffness : a randomized crossover trial

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Abstract
Purpose Eccentric calf training for Achilles tendinopathy shows variable success in athletes. Recent insights suggest a role for tendon fluid flow (exudation or redistribution) during exercise, which explains post-exercise reductions in thickness and increases in stiffness of the tendon. This fluid flow is thought to be beneficial as it may promote tendon remodeling, reduce intratendinous pressure, and alleviate pain. In this perspective, slow, high-load exercises are promoted as they theoretically facilitate tendon fluid flow. However, evidence supporting this assumption is lacking. Therefore, this study aimed to investigate whether loading speed and intensity during eccentric calf training impact acute changes in midportion Achilles tendon thickness and stiffness, reflecting alterations in local tendon fluid content. Methods A randomized, assessor-blinded, crossover trial was conducted with 34 healthy athletes (17 men, 17 women, age: 23.7 ± 6 years). Participants underwent 3 single-leg eccentric heel-drop interventions with 20% additional bodyweight, varying in loading speed (fast: 1 s, slow: 3 s) and loading intensity (low: to plantigrade, high: to maximal dorsiflexion). Achilles tendon anteroposterior diameter (APD), cross-sectional area (CSA), and shear-wave velocity (SWV) were assessed in the midportion region using ultrasonography and shear-wave elastography pre-and immediately post-intervention. Results The slow, high-load intervention produced greater immediate reductions in tendon APD and CSA (8.7% and 10.1%), compared to the slow, low-load (4.0% and 4.7%) and fast, high-load (2.9% and 3.4%) interventions (p < 0.001). Moreover, only the slow, high-load intervention increased tendon SWV (52.4%, p < 0.001). Conclusions These findings provide the first evidence that both loading speed and intensity during eccentric calf training impact acute changes in Achilles tendon thickness and stiffness, likely mediated by changes in fluid flow, which could be relevant for tendinopathy rehabilitation.
Keywords
ACHILLES TENDINOPATHY, ACHILLES TENDON FLUID, ACHILLES TENDON STIFFNESS, ACHILLES TENDON THICKNESS, ECCENTRIC TRAINING, SHEAR WAVE ELASTOGRAPHY, HYDRATION STATE, IN-VIVO, TENDINOPATHY, EXERCISE, MUSCLE, STRAIN, VOLUME, PAIN, TENDINOSIS, DIFFUSION

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MLA
Pringels, Lauren, et al. “Loading Speed and Intensity in Eccentric Calf Training Impact Acute Changes in Achilles Tendon Thickness and Stiffness : A Randomized Crossover Trial.” MEDICINE & SCIENCE IN SPORTS & EXERCISE, vol. 57, no. 5, 2025, pp. 895–903, doi:10.1249/mss.0000000000003638.
APA
Pringels, L., Pieters, D., Van Den Berghe, S., Witvrouw, E., Burssens, A., Vanden Bossche, L., & Wezenbeek, E. (2025). Loading speed and intensity in eccentric calf training impact acute changes in Achilles tendon thickness and stiffness : a randomized crossover trial. MEDICINE & SCIENCE IN SPORTS & EXERCISE, 57(5), 895–903. https://doi.org/10.1249/mss.0000000000003638
Chicago author-date
Pringels, Lauren, Dries Pieters, Sarah Van Den Berghe, Erik Witvrouw, Arne Burssens, Luc Vanden Bossche, and Evi Wezenbeek. 2025. “Loading Speed and Intensity in Eccentric Calf Training Impact Acute Changes in Achilles Tendon Thickness and Stiffness : A Randomized Crossover Trial.” MEDICINE & SCIENCE IN SPORTS & EXERCISE 57 (5): 895–903. https://doi.org/10.1249/mss.0000000000003638.
Chicago author-date (all authors)
Pringels, Lauren, Dries Pieters, Sarah Van Den Berghe, Erik Witvrouw, Arne Burssens, Luc Vanden Bossche, and Evi Wezenbeek. 2025. “Loading Speed and Intensity in Eccentric Calf Training Impact Acute Changes in Achilles Tendon Thickness and Stiffness : A Randomized Crossover Trial.” MEDICINE & SCIENCE IN SPORTS & EXERCISE 57 (5): 895–903. doi:10.1249/mss.0000000000003638.
Vancouver
1.
Pringels L, Pieters D, Van Den Berghe S, Witvrouw E, Burssens A, Vanden Bossche L, et al. Loading speed and intensity in eccentric calf training impact acute changes in Achilles tendon thickness and stiffness : a randomized crossover trial. MEDICINE & SCIENCE IN SPORTS & EXERCISE. 2025;57(5):895–903.
IEEE
[1]
L. Pringels et al., “Loading speed and intensity in eccentric calf training impact acute changes in Achilles tendon thickness and stiffness : a randomized crossover trial,” MEDICINE & SCIENCE IN SPORTS & EXERCISE, vol. 57, no. 5, pp. 895–903, 2025.
@article{01JJ6P9NKWNH6Q1RPT0ETVKHJ5,
  abstract     = {{Purpose 
Eccentric calf training for Achilles tendinopathy shows variable success in athletes. Recent insights suggest a role for tendon fluid flow (exudation or redistribution) during exercise, which explains post-exercise reductions in thickness and increases in stiffness of the tendon. This fluid flow is thought to be beneficial as it may promote tendon remodeling, reduce intratendinous pressure, and alleviate pain. In this perspective, slow, high-load exercises are promoted as they theoretically facilitate tendon fluid flow. However, evidence supporting this assumption is lacking. Therefore, this study aimed to investigate whether loading speed and intensity during eccentric calf training impact acute changes in midportion Achilles tendon thickness and stiffness, reflecting alterations in local tendon fluid content.

Methods 
A randomized, assessor-blinded, crossover trial was conducted with 34 healthy athletes (17 men, 17 women, age: 23.7 ± 6 years). Participants underwent 3 single-leg eccentric heel-drop interventions with 20% additional bodyweight, varying in loading speed (fast: 1 s, slow: 3 s) and loading intensity (low: to plantigrade, high: to maximal dorsiflexion). Achilles tendon anteroposterior diameter (APD), cross-sectional area (CSA), and shear-wave velocity (SWV) were assessed in the midportion region using ultrasonography and shear-wave elastography pre-and immediately post-intervention.

Results 
The slow, high-load intervention produced greater immediate reductions in tendon APD and CSA (8.7% and 10.1%), compared to the slow, low-load (4.0% and 4.7%) and fast, high-load (2.9% and 3.4%) interventions (p < 0.001). Moreover, only the slow, high-load intervention increased tendon SWV (52.4%, p < 0.001).

Conclusions 
These findings provide the first evidence that both loading speed and intensity during eccentric calf training impact acute changes in Achilles tendon thickness and stiffness, likely mediated by changes in fluid flow, which could be relevant for tendinopathy rehabilitation.}},
  author       = {{Pringels, Lauren and Pieters, Dries and Van Den Berghe, Sarah and Witvrouw, Erik and Burssens, Arne and Vanden Bossche, Luc and Wezenbeek, Evi}},
  issn         = {{0195-9131}},
  journal      = {{MEDICINE & SCIENCE IN SPORTS & EXERCISE}},
  keywords     = {{ACHILLES TENDINOPATHY,ACHILLES TENDON FLUID,ACHILLES TENDON STIFFNESS,ACHILLES TENDON THICKNESS,ECCENTRIC TRAINING,SHEAR WAVE ELASTOGRAPHY,HYDRATION STATE,IN-VIVO,TENDINOPATHY,EXERCISE,MUSCLE,STRAIN,VOLUME,PAIN,TENDINOSIS,DIFFUSION}},
  language     = {{eng}},
  number       = {{5}},
  pages        = {{895--903}},
  title        = {{Loading speed and intensity in eccentric calf training impact acute changes in Achilles tendon thickness and stiffness : a randomized crossover trial}},
  url          = {{http://doi.org/10.1249/mss.0000000000003638}},
  volume       = {{57}},
  year         = {{2025}},
}

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