PREreview of A 6-week randomized-controlled field study: Effect of isokinetic eccentric resistance training on strength, flexibility and muscle structure for the shoulder external rotator in male junior handball players

Short Summary of Main Findings In this 6-week randomized controlled trial (preprint Dec 2023; now fully published in Frontiers in Physiology 2024), 29 male junior handball players (intervention n=14, control n=13) performed twice-weekly eccentric isokinetic training of the shoulder external rotators versus conventional preventive exercises. The eccentric group achieved a significant +15% increase in eccentric strength, along with lengthening of muscle fascicles (+13% supraspinatus, +8% infraspinatus) and increases in fractional anisotropy on diffusion tensor imaging (+9% supraspinatus, +6% infraspinatus). These structural and strength gains were superior to the active control group. No significant changes occurred in range of motion/flexibility.

How This Work Has Moved the Field Forward It provides one of the first randomized, controlled demonstrations in overhead athletes that short-term eccentric isokinetic training can simultaneously improve functional strength and induce positive macroscopic changes in shoulder rotator muscle architecture (fascicle length and fiber organization via advanced DTI-MRI). This bridges the well-established lower-limb eccentric training literature to the upper extremity and introduces DTI as a sensitive tool for monitoring shoulder muscle adaptations, supporting its potential role in injury-prevention programs for handball and similar throwing sports.

Major Issues

• Small sample size (n=27 analyzed) limits statistical power and generalizability beyond junior male handball players.

• Training required specialized isokinetic dynamometer equipment, making it difficult to translate directly to most field or clinical settings.

• Short intervention (6 weeks) with no long-term follow-up; sustainability of gains and injury-prevention effects remain unknown.

• Although now peer-reviewed, the original preprint version lacked full journal scrutiny at posting.

Minor Issues

• Title is lengthy and slightly cumbersome.

• Flexibility (ROM) showed no improvement and a minor shift toward internal rotation that could have been discussed more.

• Some effect sizes and clinical relevance interpretations are only modestly detailed.

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.