Effect of isokinetic eccentric training on the human shoulder strength, flexibility, and muscle architecture in physically active men: A preliminary study

  1. Sebastian Vetter
  2. Pierre Hepp
  3. Axel Schleichardt
  4. Stefan Schleifenbaum
  5. Maren Witt
  6. Christian Roth
  7. Hans-Peter Köhler

Reviewed by

Read the full article See related articles

Discuss this preprint

Start a discussion What are Sciety discussions?

Listed in

Log in to save this article

Abstract

Strengthening the rotator cuff muscles is important for injury prevention and rehabilitation. Since muscle fascicle length improves motor performance and is suggested to reduce the risk of injury for the hamstring, it may be an important variable to promote multidirectional changes in the function and macroscopic structure for the shoulder. Recent literature reviews overwhelmingly suggest that eccentric exercises improve fascicle length and functional measures for the lower limb. However, there is a research gap for the shoulder. Since ultrasound imaging is the most commonly used imaging technique to quantify muscle structure, but has yielded heterogeneous results in different studies, there is another issue and a research gap for the imaging method. Based on the research gaps, the purpose of this study was to evaluate the effects of standardized eccentric strength training on the function and structure of the external rotator cuff muscles using an isokinetic dynamometer and MRI. Therefore, a preliminary pre-post intervention study was conducted and 16 physically active men were recruited in October 2021. For the right shoulder, an eccentric isokinetic training was performed twice a week for almost six weeks. The primary outcome measures (external rotators) were active and passive range of motion, eccentric and concentric torque at 30, 60, and 180°/s isokinetic speed, and fascicle length and fascicle volume for the supraspinatus and infraspinatus muscles. The findings show a training effect for the absolute mean values of eccentric strength (+24%, p = .008). The torque-angle relationship increased, especially in the final phase of range of motion, although a 4% ( p = .002) decrease in passive range of motion was found in the stretch test. Positive changes in muscle structure were shown for the supraspinatus muscle fascicle length (+16%, p = .003) and fascicle volume (+19%, p = .002). Based on the study results, we can conclude that eccentric isokinetic training has a significant positive effect on the shoulder. To our knowledge, this is the first eccentric training study using both isokinetic dynamometer and muscle diffusion tensor imaging to access functional and structural changes in the human shoulder rotator cuff muscles. The methods were shown to be applicable for interventional studies. Based on these results, populations such as high-performance handball players with highly trained shoulders should be included in future studies.

Article activity feed

  1. PREreview

    This Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/19169855.

    Main Findings Summary This preliminary study demonstrated that 6 weeks of highly standardized isokinetic eccentric training significantly enhanced eccentric strength of the shoulder external rotators (+24% at 30°/s, p=0.008; peak torque +16.82%, p=0.031), with torque-angle improvements particularly in the outer range of motion. Concentric strength gains were smaller and non-significant. Unexpectedly, internal rotation flexibility decreased (active ROM -6.66%, p=0.018; passive ROM -3.66%, p=0.002), with higher passive torque in stretched positions. Muscle architecture adapted positively in the infraspinatus (fascicle length +16.1%, p=0.003; fascicle volume +19.12%, p=0.002), with non-significant trends in supraspinatus; no changes in fractional anisotropy or internal rotators.

    Advancement of the Field This work moved the field forward by providing the first evidence (to the authors' knowledge) combining isokinetic dynamometry with muscle diffusion tensor imaging (DTI) to assess both functional and structural adaptations in the human shoulder rotator cuff following eccentric training. It extends lower-limb findings to the upper extremity, showing eccentric training induces meaningful macroscopic muscle changes (e.g., longer fascicles, increased volume) in healthy, physically active men—supporting its potential for injury prevention/rehabilitation protocols. The study also demonstrated the feasibility of DTI for shoulder muscles in interventional designs.

    Major Issues

    • No control group, limiting causal attribution (changes could stem from testing, seasonal factors, or ongoing activities).

    • Small sample size (n=16 total; n=11 for MRI), reducing statistical power and generalizability.

    • Lack of specificity: training used isokinetic mode, while participants' sports vary; unclear transfer to real-world performance or overhead athletes.

    • Decreased flexibility contradicts some eccentric training benefits (e.g., improved ROM in other studies); may indicate over-stretching risk or measurement artifact.

    Minor Issues

    • Some non-significant results (e.g., supraspinatus architecture) could benefit from clearer effect size reporting for interpretation.

    • Limited discussion of practical implications (e.g., training volume/load progression details for replication).

    • DTI methodological challenges (e.g., field-of-view limits, interpolation) noted but could use more explicit caution in results interpretation.

    • Flow could improve with consistent terminology (e.g., "external rotators" vs. specific muscles) and more visual aids for torque-angle/SPM1d curves.

    Competing interests

    The author declares that they have no competing interests.

    Use of Artificial Intelligence (AI)

    The author declares that they did not use generative AI to come up with new ideas for their review.

  2. Version published to 10.1371/journal.pone.0293439
  3. Version published to 10.1101/2023.10.15.23296999 on medRxiv