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

Field-based Closed Kinetic Chain Training With Progressive Eccentric Time Under Tension: Effects on Knee Strength and Lower Limb Viscoelasticity in Soccer Players: a Randomized Controlled Trial

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.

Inclusion Criteria:

• Absence of any medical conditions that could compromise their ability to participate.
• Active membership in their university's soccer team for a minimum of one year.

Exclusion Criteria:

• Musculoskeletal injuries reported in the two months prior to the start of the study.
• Surgical interventions involving the lower limbs within the past year.