How Eccentric Closed Chain Training Affects Knee Strength... | NCT06987344

NCT06987344

Protocol Section

Identification Module

Results Section

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Annotation Section

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Document Section

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Derived Section

Miscellaneous Info Module

Status Module

Description Module

Detailed Description

This randomized controlled trial investigated the effects of a 6-week, field-based closed kinetic chain (CKC) exercise program with progressively increased eccentric time under tension (TUT) on isokinetic knee performance and lower limb muscle-tendon viscoelastic properties in male university soccer players.

A total of 24 healthy participants were randomly assigned (1:1) to either an intervention group performing supervised CKC exercises or an active control group that maintained routine soccer training. The CKC training was performed twice per week and included progressive increases in eccentric phase duration and external loading. Training volume was quantified using both mechanical load and eccentric TUT. Each session lasted approximately 35 minutes and included a variety of multi-joint, bilateral and unilateral exercises performed on a soccer field.

Baseline and post-intervention assessments were conducted using:

Isokinetic dynamometry (Biodex System 3 Pro) to measure concentric peak torque, mean power, and agonist/antagonist ratio at 60°/s.

MyotonPRO handheld myotonometer to assess oscillation frequency and stiffness of specific lower limb muscles (VM, VL, ST, GM) and tendons (Achilles, patellar).

Muscle and tendon assessments were performed following standardized anatomical landmarks. To ensure data reliability, repeated trials were used and measurements with high variability were repeated. Pre-testing familiarization was implemented to reduce learning effects.

The statistical approach included a two-way repeated measures ANOVA to compare group (CKC vs. control) and time (pre vs. post) effects. Holm-Sidak post hoc tests were applied when appropriate, and effect sizes were interpreted using eta squared (η²). All data analyses were conducted using JASP software (v0.18.3).

The protocol was reviewed and approved by an institutional ethics committee , and written informed consent was obtained from all participants. No serious adverse events were reported, and dropout was minimal (n = 4). No dietary interventions were applied; however, participants were instructed to maintain consistent routines throughout.

Arms/Interventions Module

Arm Groups

Label	Type	Description	Intervention Names
Active Control Group	Active Comparator	Maintained their customary daily activities and regular soccer training routines: Trained three times a week, two days were dedicated to functional and tactical on-field training, while the third day was reserved for a two-hour gym session focused on flexibility, muscular strength, and endurance development.	Other: Regular soccer training routines
Closed Kinetic Chain Group	Experimental	In addition to the same activities as the active cotrol group, participants performed five to seven different closed kinetic chain drills during the two days of field-based training, completing two to three sets per drill and eight to fourteen repetitions per set. The training volume underwent gradual increments over the course of every week. The total training volume for externally loaded CKC exercises was calculated by summing sets × repetitions × load (kg), yielding a cumulative volume of approximately 10,863 kg over 12 sessions. For exercises involving bodyweight or elastic resistance, training volume was estimated using time under tension (TUT), computed as the product of repetitions and eccentric phase duration. The cumulative TUT throughout the 6-week protocol amounted to 9,300 seconds (155 minutes) of eccentric loading.	Other: Field-based closed kinetic chain exercise with progressively increased time under tension Other: Regular soccer training routines

Interventions

Name	Type	Description	Arm Group Labels	Other Names
Field-based closed kinetic chain exercise with progressively increased time under tension	Other	This intervention is uniquely characterized by the integration of field-based closed kinetic chain (CKC) exercises with a systematically increased eccentric time under tension (TUT), specifically tailored for university-level soccer players. Unlike conventional strength training protocols, which are often gym-based and rely on traditional resistance machines or free weights, this program emphasizes functional, sport-specific movement patterns performed on the field, enhancing ecological validity and transfer to soccer performance.

Outcomes Module

Primary Outcomes

Measure	Description	Time Frame
Change from baseline in the rotational peak torque relative to body mass at 6 weeks	Assessed using a Biodex® System 3 Pro isokinetic dynamometer (Shirley, NY, USA), with a validated accuracy of ±1%. Testing was performed at 60°/s angular velocity, a standard velocity for evaluating maximal voluntary muscle contraction. Participants were seated with their hips and knees at approximately 90° flexion. The dominant leg was tested and stabilized using straps at the trunk, thigh, and lower leg. Gravity correction was applied prior to testing. Following a 5-minute warm-up and 3 submaximal practice repetitions, each participant performed 3 maximal concentric repetitions of knee extension and flexion. The dominant leg was defined as the preferred leg for kicking, confirmed via observation of a standardized ball-kicking task.	From enrollment to the end of closed kinetic chain training protocol at 6 weeks
Change from baseline in the rotational mean power at 6 weeks	Assessed using a Biodex® System 3 Pro isokinetic dynamometer (Shirley, NY, USA), with a validated accuracy of ±1%. Testing was performed at 60°/s angular velocity, a standard velocity for evaluating maximal voluntary muscle contraction. Participants were seated with their hips and knees at approximately 90° flexion. The dominant leg was tested and stabilized using straps at the trunk, thigh, and lower leg. Gravity correction was applied prior to testing. Following a 5-minute warm-up and 3 submaximal practice repetitions, each participant performed 3 maximal concentric repetitions of knee extension and flexion. The dominant leg was defined as the preferred leg for kicking, confirmed via observation of a standardized ball-kicking task.	From enrollment to the end of closed kinetic chain training protocol at 6 weeks

Secondary Outcomes

Measure	Description	Time Frame
Change from baseline in the agonist/antagonist strength ratio at 6 weeks	Assessed using a Biodex® System 3 Pro isokinetic dynamometer (Shirley, NY, USA), with a validated accuracy of ±1%. Was calculated as the percentage of knee flexor peak torque relative to knee extensor peak torque. Testing was performed at 60°/s angular velocity, a standard velocity for evaluating maximal voluntary muscle contraction. Participants were seated with their hips and knees at approximately 90° flexion. The dominant leg was tested and stabilized using straps at the trunk, thigh, and lower leg. Gravity correction was applied prior to testing. Following a 5-minute warm-up and 3 submaximal practice repetitions, each participant performed 3 maximal concentric repetitions of knee extension and flexion. The dominant leg was defined as the preferred leg for kicking, confirmed via observation of a standardized ball-kicking task.

Eligibility Module