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

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.