How different types of strength training affect ankle muscles and tendons
| ISRCTN | ISRCTN35199955 |
|---|---|
| DOI | https://doi.org/10.1186/ISRCTN35199955 |
| ClinicalTrials.gov (NCT) | Nil known |
| Clinical Trials Information System (CTIS) | Nil known |
| Protocol serial number | EQI_Train3 (internal protocol ID, University of Primorska) |
| Sponsor | University of Primorska, Faculty of Health Sciences |
| Funder | Slovenian Research and Innovation Agency (ARIS) |
- Submission date
- 29/10/2025
- Registration date
- 13/11/2025
- Last edited
- 13/11/2025
- Recruitment status
- Recruiting
- Overall study status
- Ongoing
- Condition category
- Other
Plain English summary of protocol
Background and study aims
This study aims to explore how different strength training methods affect the muscles and tendons in the lower leg. We are comparing eccentric quasi-isometric (EQI) training — a method that combines slow and static muscle actions — with traditional eccentric training, which involves controlled lowering movements. Understanding how these methods influence muscle and tendon properties may help improve exercise and rehabilitation programs.
Who can participate?
Healthy men and women aged 18 to 30 years who regularly participate in resistance training (at least two to three sessions per week) can take part. Participants must have no lower-limb injuries in the past year and no other health conditions that limit physical activity.
What does the study involve?
After initial testing, participants will be randomly assigned to one of three groups: EQI training, traditional eccentric training, or a control group. The training groups will complete two supervised sessions per week for six weeks. Measurements of muscle and tendon properties, strength, and ankle flexibility will be taken before and after the training period.
What are the possible benefits and risks of participating?
The exercises may help improve muscle strength and tendon resilience. Risks are minimal and limited to temporary muscle soreness similar to that experienced after intense exercise.
Where is the study run from?
The study is coordinated by the University of Primorska, Faculty of Health Sciences, in Izola, Slovenia.
When is the study starting and how long is it expected to run for?
Recruitment begins in October 2025, and the intervention phase will last six weeks. The study is expected to finish in January 2026.
Who is funding the study?
The study is funded by the Slovenian Research and Innovation Agency (ARIS), within the postdoctoral research project EQI-TRAIN (Z5-50181).
Who is the main contact?
Dr Žiga Kozinc, ziga.kozinc@fvz.upr.si
Contact information
Public, Scientific, Principal investigator
Bernetičeva 8
Koper
6000
Slovenia
 ORCID ID |
0000-0003-3555-8680 |
|---|---|
| Phone | +38640161503 |
| ziga.kozinc@fvz.upr.si |
Study information
| Primary study design | Interventional |
|---|---|
| Study design | Randomized controlled interventional study with three parallel groups |
| Secondary study design | Randomised parallel trial |
| Participant information sheet | 48306 PIS.pdf |
| Scientific title | Effects of eccentric quasi-isometric and eccentric training on mechanical and architectural properties of the ankle plantar flexors: a randomized controlled trial |
| Study acronym | EKI-TRAIN3 |
| Study objectives | The primary objective of this study is to compare the effects of eccentric quasi-isometric (EQI) training and traditional eccentric resistance training on the mechanical and architectural properties of the ankle plantar flexor muscles and the Achilles tendon in healthy adults. Secondary objectives are to evaluate changes in: 1. Isometric, concentric, and eccentric strength of the plantar flexors, 2. Ankle range of motion 3. Perceived muscle soreness and session difficulty following both training interventions. The findings will provide insight into how distinct eccentric loading strategies influence muscle–tendon adaptation and may contribute to optimizing training and rehabilitation protocols targeting the ankle plantar flexor complex. |
| Ethics approval(s) |
Approved 15/09/2025, Komisija Republike Slovenije za medicinsko etiko (Republic of Slovenia's National Medical Ethics Committee) (Štefanova ulica 5, Ljubljana, 1000, Slovenia; +386 1 478 60 00; kme.mz@gov.si), ref: 0120-489/2024-2711-5 |
| Health condition(s) or problem(s) studied | This study focuses on muscle–tendon adaptation and function in healthy adults. It does not involve patients with pathological conditions. The research investigates how different eccentric loading strategies affect the mechanical and architectural properties of the ankle plantar flexor muscles and Achilles tendon. |
| Intervention | Participants will be randomly assigned to one of three groups: Eccentric quasi-isometric (EQI) training: Participants will complete a 6-week EQI training program targeting the right ankle plantar flexors, performed twice weekly. Each session includes a standardized warm-up and repeated quasi-isometric contractions under load, alternating with eccentric muscle actions until fatigue. The load corresponds to 100% of one-repetition maximum (1RM), re-evaluated at weeks 1, 3, and 5. Traditional eccentric training: Participants will perform a 6-week unilateral eccentric heel-drop program using an Olympic barbell load equal to 100% of 1RM (reassessed at weeks 1, 3, and 5). The program progresses from 2 × 15 repetitions in week 1 to 4 × 15 from week 4 onward, with a 3-second eccentric phase and 2-minute rest between sets. Control group: Participants will maintain their normal physical activity routines but will refrain from any targeted strengthening or proprioceptive training involving the ankle plantar flexors. Participants will be randomly assigned to one of the three groups (1:1:1 ratio) using sealed opaque envelopes. The envelopes will contain pre-prepared group assignments and will be shuffled prior to the start of the study. Each participant will draw one envelope after completing baseline testing to determine group allocation. The envelope method ensures allocation concealment, as neither participants nor assessors will know the assignment until the envelope is opened. |
| Intervention type | Behavioural |
| Primary outcome measure(s) |
1. Muscle fascicle length is measured using panoramic B-mode ultrasound imaging of the medial and lateral gastrocnemius at baseline and 1 week after completion of the 6-week intervention |
| Key secondary outcome measure(s) |
1. Isometric peak torque of the ankle plantar flexors is measured using an isokinetic dynamometer (HumacNorm, USA) under isometric conditions at baseline and 1 week after completion of the 6-week intervention |
| Completion date | 30/01/2026 |
Eligibility
| Participant type(s) | Healthy volunteer |
|---|---|
| Age group | Adult |
| Lower age limit | 18 Years |
| Upper age limit | 30 Years |
| Sex | All |
| Target sample size at registration | 45 |
| Key inclusion criteria | 1. Healthy adults (male and female) aged 18–30 years. 2. No musculoskeletal injuries in the past 3 months. 3. No ankle injuries in the past 12 months. 4. Regular participation in resistance training (≥2–3 sessions per week during the past 6 months). 5. Ability and willingness to participate in all testing and training sessions. 6. Agreement to maintain usual daily physical activity and to refrain from any additional resistance or proprioceptive training targeting the ankle plantar flexors during the study period. |
| Key exclusion criteria | 1. Presence of chronic infectious or metabolic disease. 2. Cardiovascular or respiratory disorder that limits physical activity. 3. Diagnosed neurological condition (e.g., multiple sclerosis, Parkinson’s disease). 4. Current or recent musculoskeletal injury not meeting inclusion criteria. 5. Use of medications that may influence physical performance or neuromuscular function. 6. Pregnancy. |
| Date of first enrolment | 06/11/2025 |
| Date of final enrolment | 20/11/2025 |
Locations
Countries of recruitment
- Slovenia
Study participating centre
Izola
6310
Slovenia
Results and Publications
| Individual participant data (IPD) Intention to share | No |
|---|---|
| IPD sharing plan summary | Not expected to be made available |
| IPD sharing plan |
Study outputs
| Output type | Details | Date created | Date added | Peer reviewed? | Patient-facing? |
|---|---|---|---|---|---|
| Participant information sheet | 30/10/2025 | No | Yes | ||
| Participant information sheet | Participant information sheet | 11/11/2025 | 11/11/2025 | No | Yes |
Additional files
- 48306 PIS.pdf
- Participant information sheet
Editorial Notes
30/10/2025: Trial's existence confirmed by Komisija Republike Slovenije za medicinsko etiko (Republic of Slovenia's National Medical Ethics Committee).
