The purpose of this randomized controlled trial is to compare the effects of unilateral flywheel resistance training and unilateral traditional resistance training on change-of-direction performance in elite male soccer players.

A total of 22 elite soccer players will be randomly assigned to either a flywheel resistance training group or a traditional resistance training group. Both groups will perform supervised training twice per week for 8 weeks in addition to their regular soccer training.

Performance outcomes will include linear sprint tests (10 m and 30 m), pre-planned change-of-direction tests (Pro-agility, T-test, Arrowhead test), and agility tests under no-ball and with-ball conditions (AFL agility test).

The primary outcome is change-of-direction performance assessed by the T-test. Secondary outcomes include direction-specific change-of-direction ability and agility performance.

It is hypothesized that unilateral flywheel resistance training will produce greater improvements in change-of-direction performance compared with traditional resistance training, particularly in tasks involving braking and re-acceleration.

This study is an exploratory randomized controlled trial designed to investigate the effects of unilateral flywheel resistance training (FRT) compared with unilateral traditional resistance training (TRT) on change-of-direction (COD) performance in elite male soccer players.

Participants are highly trained soccer athletes with at least 8 years of training experience and no recent lower-limb injuries. Following baseline testing, participants are randomly allocated in a 1:1 ratio to either the FRT group or the TRT group.

Both groups perform an 8-week training intervention consisting of two supervised sessions per week. The training exercise is the unilateral Bulgarian split squat, performed with either flywheel inertial resistance (FRT) or barbell loading (TRT). Training volume, frequency, and movement pattern are matched between groups. Load prescription is standardized using mean concentric velocity matching.

Outcome measures are assessed before and after the intervention and include:

• Linear sprint performance (10 m and 30 m)
• Pre-planned change-of-direction performance (Pro-agility test, T-test)
• Direction-specific COD performance (Arrowhead test left and right)
• Agility performance under no-ball and ball conditions (AFL agility test) The primary outcome is T-test performance. Secondary outcomes include Pro-agility, Arrowhead, and AFL agility tests. Exploratory outcomes include linear sprint performance and ball-constrained agility.

The study aims to determine whether eccentric overload provided by flywheel training leads to superior improvements in COD performance compared with traditional resistance training under matched movement conditions.

Inclusion Criteria:

• Male elite or sub-elite soccer players aged 18-25 years
• Minimum of 3 years of structured soccer training experience
• Currently participating in regular team training (≥3 sessions per week)
• Free from musculoskeletal injury within the past 3 months
• No prior experience with flywheel resistance training
• Provided written informed consent to participate

Exclusion Criteria:

• History of lower-limb surgery within the past 6 months
• Current musculoskeletal pain or injury affecting performance
• Neurological or cardiovascular conditions contraindicating high-intensity exercise
• Participation in additional strength or conditioning programs outside the study
• Inability to complete the full intervention protocol

Individual participant data (IPD) will not be shared due to privacy concerns and the limited sample size. Aggregated data will be reported in peer-reviewed publications.

Outcome assessors were blinded to group allocation during performance testing and data collection.