The Influence of Passive Local Muscle Vibration on Mechanical Power Output and Neuromuscular Activity During Counterbalanced RPE-clamped Cycling: A Randomized Controlled Trial

The purpose of this study is to find out if applying mild mechanical vibration (100 Hz) to the the Achilles and patellar tendons before and during exercise can make cycling feel easier and help athletes generate more power. The researchers also want to test if a new, lightweight wearable sleeve called "Tendo" is just as effective at doing this as a stationary laboratory machine. The study will involve 40 healthy, active student-athletes aged 18 to 26. Each participant will attend three separate testing sessions in a laboratory, with at least 48 hours of rest between sessions. During each 85-minute session, participants will: Complete baseline resting measurements of their muscles and tendons. Ride a stationary exercise bicycle with a covered screen, adjusting their speed and pedaling based only on how hard they feel they are working, using a 0-100 effort scale called Borg CR100. Receive a 10-minute resting tendon vibration. Repeat the cycling test with a short "booster" vibration to see how their performance changes. To understand how the vibration works, the researchers will use harmless skin sensors to measure muscle activity (sEMG), a gentle tapping device to check tendon stiffness (MyotonPRO), and ultrasound imaging to look at tendon structure. Stationary Vibration: High-frequency (100 Hz) vibration from a fixed laboratory machine. Wearable Vibration: High-frequency (100 Hz) vibration from the portable Tendo sleeve. Sham Vibration: A low-frequency (15 Hz) vibration that does not trigger a physiological response, serving as a control to make sure the results are not just due to a placebo effect.

Inclusion Criteria: * Age between 18 and 26 years * Active student or doctoral student status at a higher education institution * Active participation in sports training (endurance or mixed disciplines, e.g., cycling, running, triathlon, team sports) with a minimum frequency of 3 times per week, verified by a recruitment questionnaire. * Good general health, with no medical contraindications to performing intense exercise testing on a cycle ergometer. * Normal anatomical condition of the Achilles tendon and patellar ligament during baseline screening - no history of acute inflammation or ruptures. * Provision of voluntary, written informed consent to participate in the study and for medical data processing. Exclusion Criteria: * Orthopedic and structural contraindications: Recent injuries in less than 6 months, joint ruptures, or surgical interventions in the lower limbs; chronic or acute inflammation of the Achilles tendon or patellar ligament; presence of metal implants or joint replacements in the stimulated limbs. * Neurological contraindications: Diagnosed epilepsy or susceptibility to seizures, superficial or deep sensory impairment such as neuropathy, radiculopathy, that could impair stimulus evaluation or risk tissue damage. * Cardiovascular contraindications: Diagnosed heart defects, unstable arterial hypertension, cardiac arrhythmias; presence of a pacemaker or implantable cardioverter-defibrillator, active thromboembolic diseases, deep vein thrombosis, or severe varicose veins of the lower limbs. * General medical contraindications: Pregnancy; active oncological diseases; active infections or fever on the day of testing; dermatological changes, open wounds, or skin ulcers at the planned application sites of sEMG electrodes or Tendo vibration sleeves. * Other: Regular intake of medications or substances that affect the threshold of pain or fatigue perception (e.g., strong analgesics, steroids, or pre-workout supplements containing high amounts of stimulants taken directly before the test).