Athletic PerformanceNCT07556315
Unilateral vs Bilateral Isometric Training in Youth Soccer Players
A study testing Unilateral Isometric Training, Bilateral Isometric Training and Complex Strength Training in people with Athletic Performance and Soccer, run by The Jerzy Kukuczka Academy of Physical Education in Katowice at 1 site in Poland.
Trial summary
This randomized controlled trial investigates the effects of unilateral and bilateral isometric strength training integrated into an 8-week complex training program on neuromuscular performance in elite youth soccer players. Read more about this study
- Who is it for?
- Ages 14 to 19 years, men onlyHealthy volunteers can take part
- Conditions the study is for
- Athletic Performance, Soccer, Resistance Training
- What is being tested?
- Unilateral Isometric Training, Bilateral Isometric Training and Complex Strength Training
- Type of treatment
- Lifestyle or therapy programme
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 41 participants
- Where
- 1 sitePoland
- Study dates
- 30 Sep 2025to 11 Dec 2025
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 14 to 19 years
- Men only
- Healthy volunteers accepted
- Child, Adult
Who may be able to join
- Male youth soccer players competing at the national level.
- Age between 15 and 19 years.
- Minimum of one year of resistance training experience.
- Regular participation in organized soccer training and strength training.
Who cannot join
- Current neuromuscular or musculoskeletal injury or disorder.
- Injury occurring during the intervention period preventing participation in training or testing.
- Failure to complete the prescribed training program or attend at least 80% of training sessions.
- Participation in additional resistance training programs outside the study protocol during the intervention period.
Trial locations and contacts
1 site in 1 country.
Poland1 site
Academy of Physical Education in Katowice
Katowice, Silesian Voivodeship, 40-065
About this study
Official title: Effects of Unilateral and Bilateral Isometric Strength Training Integrated Into an 8-Week Complex Training Program on Neuromuscular Performance in Youth Soccer Players
This randomized controlled trial investigates the effects of unilateral and bilateral isometric strength training integrated into an 8-week complex training program on neuromuscular performance in elite youth soccer players. Forty-one male players competing at the national level will be randomly assigned to one of three groups: unilateral isometric training (UNI), bilateral isometric training (BI), or a control group performing the same training program without additional isometric exercises.
All participants will complete a structured complex strength training program once per week for eight weeks during the competitive season. Neuromuscular performance will be assessed before and after the intervention using countermovement jump height, broad jump distance, maximal isometric squat peak force and 30-m sprint time. The aim of the study is to determine whether the mode of isometric training (unilateral vs bilateral) influences adaptations in strength, power and sprint performance in youth soccer players.
An additional objective of the study is to determine whether the type of isometric training intervention influences inter-limb asymmetries in neuromuscular performance. Selected tests will therefore be performed both bilaterally and unilaterally to assess potential differences between dominant and non-dominant limbs.
Read the detailed description
This study is a randomized, parallel-group intervention designed to examine the effects of unilateral and bilateral isometric strength training integrated into an 8-week complex strength training program on neuromuscular performance in elite youth soccer players.
Participants will be recruited from youth teams competing at the national level and randomly assigned to one of three groups: unilateral isometric training (UNI), bilateral isometric training (BI), or a control group (CRL). All groups will perform the same structured complex strength training program once per week for eight weeks during the competitive season. The UNI and BI groups will perform additional isometric exercises at the beginning of each session, whereas the control group will complete the same training program without the isometric component.
The isometric protocol will include three multi-joint exercises: isometric plantar flexion, isometric squat, and isometric hip extension performed against an immovable barbell in a power rack. In the BI group exercises will be performed bilaterally, whereas in the UNI group each limb will be trained separately.
The complex training program will consist of paired resistance and ballistic exercises including squats, jumps, bench press, medicine ball throws, rows, and Romanian deadlifts. Training intensity and volume will progress across two phases during the eight-week intervention.
Neuromuscular performance will be assessed before and after the intervention using countermovement jump height measured with a force plate system, standing broad jump distance, maximal isometric squat peak force measured during an isometric squat test and 30-meter sprint time measured with electronic timing gates.
In addition, selected performance tests (countermovement jump, standing broad jump, and isometric squat test) will be performed both bilaterally and unilaterally in order to assess potential inter-limb asymmetries. Participants will first perform the tests bilaterally, followed by unilateral trials with the dominant limb and then the non-dominant limb. Sprint performance will be assessed only bilaterally.
The primary objective of the study is to evaluate the effects of unilateral versus bilateral isometric strength training on changes in jump performance, sprint performance and maximal isometric strength. A secondary objective of the study is to assess whether the type of training intervention influences inter-limb asymmetry in neuromuscular performance.
- Conditions
- Athletic Performance, Soccer, Resistance Training
- Being tested
- Unilateral Isometric Training, Bilateral Isometric Training, Complex Strength Training
- Keywords
- Resistance training, Jump performance, Sprint, Maximal voluntary isometric contraction
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Unilateral Isometric TrainingBehavioural
Isometric strength exercises performed unilaterally including plantar flexion, squat, and hip extension against an immovable barbell.
Bilateral Isometric TrainingBehavioural
Isometric strength exercises performed bilaterally including plantar flexion, squat, and hip extension against an immovable barbell.
Complex Strength TrainingBehavioural
A structured complex training program consisting of paired resistance and ballistic exercises performed once per week for eight weeks.
| Study group | Role | What they receive |
|---|---|---|
| Unilateral Isometric Training | Experimental | Participants perform unilateral isometric strength training integrated into an 8-week complex strength training program. Receives: Behavioral: Unilateral Isometric Training |
| Bilateral Isometric Training | Experimental | Participants perform bilateral isometric strength training integrated into an 8-week complex strength training program. Receives: Behavioral: Bilateral Isometric Training |
| Complex Strength Training | Active comparator | Participants perform the same complex strength training program without additional isometric exercises. Receives: Behavioral: Complex Strength Training |
What is being measured
The primary outcome is the main question the study is designed to answer.
Countermovement Jump Height
Change in countermovement jump (CMJ) height measured using a dual force plate system. Jump height will be calculated using the impulse-momentum method and expressed in centimeters (cm).
Measured: Baseline (Week 0) and Week 9
30-Meter Sprint Time
Change in linear sprint performance measured during a 30-meter sprint test using electronic timing gates. Sprint time will be recorded in seconds (s) using electronic timing gates positioned at positioned at 0 m, 5 m, and 30 m.
Measured: Baseline (Week 0) and Week 9
Maximal Isometric Squat Peak Force
Change in maximal isometric squat peak force measured during an isometric squat test performed on a dual force plate system. Peak force will be expressed in Newtons (N).
Measured: Baseline (Week 0) and Week 9
Secondary outcomes (3)
Reactive Strength Index Modified (RSI-mod)
Change in reactive strength index modified (RSI-mod) obtained during the countermovement jump test and calculated as jump height divided by contraction time.
Measured: Baseline (Week 0) and Week 9
Standing Broad Jump Distance
Change in horizontal jump performance measured using the standing broad jump test. Jump distance will be recorded in centimeters (cm).
Measured: Baseline (Week 0) and Week 9
Inter-Limb Asymmetry Index
Inter-limb asymmetry calculated for unilateral performance tests including countermovement jump, standing broad jump, and isometric squat peak force. The asymmetry index (AI) will be calculated using the formula: (DL - NDL) / ((DL + NDL) / 2) × 100, where DL represents the dominant limb and NDL represents the non-dominant limb.
Measured: Baseline (Week 0) and Week 9
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted29 Apr 2026
- Study start30 Sep 2025
- Primary completion11 Dec 2025
- Study completion11 Dec 2025
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (4)Papers the sponsor has linked to this study.
- Other trials for Athletic PerformanceStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Participants will be randomly assigned to one of three parallel groups: unilateral isometric training, bilateral isometric training or a control group performing the same complex training program without additional isometric exercises.
- Masking
- None (open label)
- Enrolment
- 41 participants (actual)
Sponsor and investigators
- Lead sponsor
- The Jerzy Kukuczka Academy of Physical Education in Katowice
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07556315
- Sponsor's protocol ID
- 2-X/2025/001
- Status last verified
- Apr 2026
- First submitted
- 10 Apr 2026
- Last updated
- 29 Apr 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided: De-identified individual participant data may be shared upon reasonable request after publication of the study results.
Publications
Oranchuk DJ, Storey AG, Nelson AR, Cronin JB. Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review. Scand J Med Sci Sports. 2019 Apr;29(4):484-503. doi: 10.1111/sms.13375. Epub 2019 Jan 13.
PubMed 30580468Bishop C, Read P, Lake J, Loturco I, Dawes J, Madruga M, Romero-Rodrigues D, Chavda S, Turner A. Unilateral Isometric Squat: Test Reliability, Interlimb Asymmetries, and Relationships With Limb Dominance. J Strength Cond Res. 2021 Feb 1;35(Suppl 1):S144-S151. doi: 10.1519/JSC.0000000000003079.
PubMed 30741869Helbin J, Gawel D, Terbalyan A, Wilk M, Krzysztofik M, Lum D, Jarosz J. Acute Effects of Isometric Contraction Distribution on Jump Performance in Volleyball Players. J Funct Morphol Kinesiol. 2025 Sep 9;10(3):343. doi: 10.3390/jfmk10030343.
PubMed 40981042Lum D, Barbosa TM. Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance. Int J Sports Med. 2019 May;40(6):363-375. doi: 10.1055/a-0863-4539. Epub 2019 Apr 3.
PubMed 30943568
Study at a glance
From the registry record, last updated by the sponsor on 29 Apr 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Effects of Unilateral and Bilateral Isometric Strength Training Integrated Into an 8-Week Complex Training Program on Neuromuscular Performance in Youth Soccer Players
- ClinicalTrials.gov ID
- NCT07556315
- Acronym / sponsor ID
- 2-X/2025/001
- Conditions
- Athletic Performance, Soccer, Resistance Training
- Keywords
- Resistance training, Jump performance, Sprint, Maximal voluntary isometric contraction
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 41 participants (actual)
- Lead sponsor
- The Jerzy Kukuczka Academy of Physical Education in KatowiceUniversity, hospital or other
- Study start
- 30 Sep 2025 (actual)
- Primary completion
- 11 Dec 2025 (actual)
- Study completion
- 11 Dec 2025 (actual)
- First posted
- 29 Apr 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
This randomized controlled trial investigates the effects of unilateral and bilateral isometric strength training integrated into an 8-week complex training program on neuromuscular performance in elite youth soccer players. Forty-one male players competing at the national level will be randomly assigned to one of three groups: unilateral isometric training (UNI), bilateral isometric training (BI), or a control group performing the same training program without additional isometric exercises.
All participants will complete a structured complex strength training program once per week for eight weeks during the competitive season. Neuromuscular performance will be assessed before and after the intervention using countermovement jump height, broad jump distance, maximal isometric squat peak force and 30-m sprint time. The aim of the study is to determine whether the mode of isometric training (unilateral vs bilateral) influences adaptations in strength, power and sprint performance in youth soccer players.
An additional objective of the study is to determine whether the type of isometric training intervention influences inter-limb asymmetries in neuromuscular performance. Selected tests will therefore be performed both bilaterally and unilaterally to assess potential differences between dominant and non-dominant limbs.
Detailed description
This study is a randomized, parallel-group intervention designed to examine the effects of unilateral and bilateral isometric strength training integrated into an 8-week complex strength training program on neuromuscular performance in elite youth soccer players.
Participants will be recruited from youth teams competing at the national level and randomly assigned to one of three groups: unilateral isometric training (UNI), bilateral isometric training (BI), or a control group (CRL). All groups will perform the same structured complex strength training program once per week for eight weeks during the competitive season. The UNI and BI groups will perform additional isometric exercises at the beginning of each session, whereas the control group will complete the same training program without the isometric component.
The isometric protocol will include three multi-joint exercises: isometric plantar flexion, isometric squat, and isometric hip extension performed against an immovable barbell in a power rack. In the BI group exercises will be performed bilaterally, whereas in the UNI group each limb will be trained separately.
The complex training program will consist of paired resistance and ballistic exercises including squats, jumps, bench press, medicine ball throws, rows, and Romanian deadlifts. Training intensity and volume will progress across two phases during the eight-week intervention.
Neuromuscular performance will be assessed before and after the intervention using countermovement jump height measured with a force plate system, standing broad jump distance, maximal isometric squat peak force measured during an isometric squat test and 30-meter sprint time measured with electronic timing gates.
In addition, selected performance tests (countermovement jump, standing broad jump, and isometric squat test) will be performed both bilaterally and unilaterally in order to assess potential inter-limb asymmetries. Participants will first perform the tests bilaterally, followed by unilateral trials with the dominant limb and then the non-dominant limb. Sprint performance will be assessed only bilaterally.
The primary objective of the study is to evaluate the effects of unilateral versus bilateral isometric strength training on changes in jump performance, sprint performance and maximal isometric strength. A secondary objective of the study is to assess whether the type of training intervention influences inter-limb asymmetry in neuromuscular performance.
Study design
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 3
- Model description
- Participants will be randomly assigned to one of three parallel groups: unilateral isometric training, bilateral isometric training or a control group performing the same complex training program without additional isometric exercises.
| Arm | Type | Receives |
|---|---|---|
| Unilateral Isometric Training | Experimental | Behavioral: Unilateral Isometric TrainingParticipants perform unilateral isometric strength training integrated into an 8-week complex strength training program. |
| Bilateral Isometric Training | Experimental | Behavioral: Bilateral Isometric TrainingParticipants perform bilateral isometric strength training integrated into an 8-week complex strength training program. |
| Complex Strength Training | Active comparator | Behavioral: Complex Strength TrainingParticipants perform the same complex strength training program without additional isometric exercises. |
Who may qualify
- Ages
- 14 to 19 years
- Sex
- Male only
- Healthy volunteers
- Accepted
- Age groups
- Child, Adult
Key inclusion criteria (4 listed)
- Male youth soccer players competing at the national level.
- Age between 15 and 19 years.
- Minimum of one year of resistance training experience.
- Regular participation in organized soccer training and strength training.
Key exclusion criteria (4 listed)
- Current neuromuscular or musculoskeletal injury or disorder.
- Injury occurring during the intervention period preventing participation in training or testing.
- Failure to complete the prescribed training program or attend at least 80% of training sessions.
- Participation in additional resistance training programs outside the study protocol during the intervention period.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Unilateral Isometric TrainingIsometric strength exercises performed unilaterally including plantar flexion, squat, and hip extension against an immovable barbell. | Behavioural | Unilateral Isometric Training |
| Bilateral Isometric TrainingIsometric strength exercises performed bilaterally including plantar flexion, squat, and hip extension against an immovable barbell. | Behavioural | Bilateral Isometric Training |
| Complex Strength TrainingA structured complex training program consisting of paired resistance and ballistic exercises performed once per week for eight weeks. | Behavioural | Complex Strength Training |
Primary outcome
Countermovement Jump Height
Time frame: Baseline (Week 0) and Week 9
Change in countermovement jump (CMJ) height measured using a dual force plate system. Jump height will be calculated using the impulse-momentum method and expressed in centimeters (cm).
30-Meter Sprint Time
Time frame: Baseline (Week 0) and Week 9
Change in linear sprint performance measured during a 30-meter sprint test using electronic timing gates. Sprint time will be recorded in seconds (s) using electronic timing gates positioned at positioned at 0 m, 5 m, and 30 m.
Maximal Isometric Squat Peak Force
Time frame: Baseline (Week 0) and Week 9
Change in maximal isometric squat peak force measured during an isometric squat test performed on a dual force plate system. Peak force will be expressed in Newtons (N).
3 secondary outcomes
Reactive Strength Index Modified (RSI-mod)
Time frame: Baseline (Week 0) and Week 9
Standing Broad Jump Distance
Time frame: Baseline (Week 0) and Week 9
Inter-Limb Asymmetry Index
Time frame: Baseline (Week 0) and Week 9
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 29 Apr 2026.
- Background: PubMed 30580468Oranchuk DJ, Storey AG, Nelson AR, Cronin JB. Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review. Scand J Med Sci Sports. 2019 Apr;29(4):484-503. doi: 10.1111/sms.13375. Epub 2019 Jan 13.
- Background: PubMed 30741869Bishop C, Read P, Lake J, Loturco I, Dawes J, Madruga M, Romero-Rodrigues D, Chavda S, Turner A. Unilateral Isometric Squat: Test Reliability, Interlimb Asymmetries, and Relationships With Limb Dominance. J Strength Cond Res. 2021 Feb 1;35(Suppl 1):S144-S151. doi: 10.1519/JSC.0000000000003079.
- Background: PubMed 40981042Helbin J, Gawel D, Terbalyan A, Wilk M, Krzysztofik M, Lum D, Jarosz J. Acute Effects of Isometric Contraction Distribution on Jump Performance in Volleyball Players. J Funct Morphol Kinesiol. 2025 Sep 9;10(3):343. doi: 10.3390/jfmk10030343.
- Background: PubMed 30943568Lum D, Barbosa TM. Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance. Int J Sports Med. 2019 May;40(6):363-375. doi: 10.1055/a-0863-4539. Epub 2019 Apr 3.
- Individual participant dataSharing planned: Undecided. De-identified individual participant data may be shared upon reasonable request after publication of the study results.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Unilateral Isometric Training, Bilateral Isometric Training and Complex Strength Training in people with Athletic Performance and Soccer, run by The Jerzy Kukuczka Academy of Physical Education in Katowice at 1 site in Poland.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 4 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 29 Apr 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Poland. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Countermovement Jump Height (time frame: Baseline (Week 0) and Week 9). The study lists 3 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07556315, which also lists 4 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 29 Apr 2026.