How Eccentric Closed Chain Training Affects Knee Strength and Muscle Properties in Soccer Players

University of Americas24 enrolled

Overview

The goal of this study is to learn whether a 6-week lower-body training program using closed kinetic chain (CKC) exercises with slow, controlled movements (called "eccentric time under tension") can improve leg muscle strength and muscle-tendon viscoelastic properties in male university soccer players. The Main Questions Are: 1. Does this type of training improve knee strength? 2. Does it change the way muscles and tendons respond to movement or pressure? What Will Participants Do? 1. Join one of two groups: one does the CKC training program, the other continues regular soccer training 2. Train twice a week for 6 weeks 3. Have their leg strength tested using special equipment 4. Have their muscle and tendon properties measured with a handheld device

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.

Interventions

Field-based closed kinetic chain exercise with progressively increased time under tensionOTHER

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.

Regular soccer training routinesOTHER

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.

Outcomes

Primary Outcomes

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.