Unilateral vs Bilateral Isometric Training in Youth Soccer Players

NCT07556315 | Completed

• 1 other identifier: 2-X/2025/001
• Study Type: interventional
• Target: 41
• Locations: 1 country
• Sites: 1

Brief 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. 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.

Conditions

Resistance Training; Athletic Performance; Soccer

Keywords

Resistance training; Jump performance; Sprint; Maximal voluntary isometric contraction

Outcome Measures

Primary Outcomes (3)

• 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).

  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.

  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).

  Baseline (Week 0) and Week 9

Secondary Outcomes (3)

• Reactive Strength Index Modified (RSI-mod)

  Baseline (Week 0) and Week 9

• Standing Broad Jump Distance

  Baseline (Week 0) and Week 9

• Inter-Limb Asymmetry Index

  Baseline (Week 0) and Week 9

Study Arms (3)

Unilateral Isometric Training

EXPERIMENTAL

Participants perform unilateral isometric strength training integrated into an 8-week complex strength training program.

Behavioral: Unilateral Isometric Training

Bilateral Isometric Training

EXPERIMENTAL

Participants perform bilateral isometric strength training integrated into an 8-week complex strength training program.

Behavioral: Bilateral Isometric Training

Complex Strength Training

ACTIVE COMPARATOR

Participants perform the same complex strength training program without additional isometric exercises.

Behavioral: Complex Strength Training

Interventions

Unilateral Isometric Training BEHAVIORAL

Isometric strength exercises performed unilaterally including plantar flexion, squat, and hip extension against an immovable barbell.

Unilateral Isometric Training

Bilateral Isometric Training BEHAVIORAL

Isometric strength exercises performed bilaterally including plantar flexion, squat, and hip extension against an immovable barbell.

Bilateral Isometric Training

Complex Strength Training BEHAVIORAL

A structured complex training program consisting of paired resistance and ballistic exercises performed once per week for eight weeks.

Complex Strength Training

Eligibility Criteria

• Age: 14 Years - 19 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Child (0-17), Adult (18-64)

You may qualify if:

• 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.

You may not qualify if:

• 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.

Sponsors & Collaborators

• The Jerzy Kukuczka Academy of Physical Education in Katowice: lead

Study Sites (1)

Academy of Physical Education in Katowice

Katowice, Silesian Voivodeship, 40-065, Poland

Location

Related Publications (4)

• 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.

  PMID: 30580468 BACKGROUND

• Bishop 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.

  PMID: 30741869 BACKGROUND

• Helbin 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.

  PMID: 40981042 BACKGROUND

• Lum 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.

  PMID: 30943568 BACKGROUND

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: NONE
• Purpose: BASIC SCIENCE
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR

Model Details: 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.

Study Record Dates

• First Submitted: April 10, 2026
• First Posted: April 29, 2026
• Study Start: September 30, 2025
• Primary Completion: December 11, 2025
• Study Completion: December 11, 2025
• Last Updated: April 29, 2026

Record last verified: 2026-04

Locations

PL (1)