The aim of this study was to investigate the effects of different concentric and eccentric muscle fatigue protocols on the knee joint position sense of healthy individuals.

A randomized controlled crossover trial will be conducted at a biomechanics laboratory with healthy males. All participants will perform with a washout period of 1 week: a control condition (5-minute rest) and 4 local muscle fatigue protocols (concentric of quadriceps; concentric of hamstrings; eccentric of quadriceps; eccentric of hamstrings) in an isokinetic dynamometer at 30º/s. Three maximum voluntary isometric contractions (MVIC) of quadriceps and hamstrings will also be assessed in the beginning of all conditions.

Knee joint position sense will be assessed before and immediately after the fatigue protocols/control condition, through active concentric and eccentric positionings/repositionings, in sitting and prone positions, to a target range of 45º of knee flexion in an isokinetic dynamometer. Surface electromyography electrodes will also be placed on the vastus lateralis and biceps femoris during all procedures.

Inclusion Criteria:

• males aged between 18 and 30 years;
• without current or previous knee pathology or surgery;
• with a low or moderate physical activity level, according to the International Physical Activity Questionnaire;
• normal Body Mass Index (under 24.9 kg/m2), according to the World Health Organization.

Exclusion Criteria:

• those with cardiorespiratory, neurological or vestibular pathologies;
• with positive knee integrity tests (anterior drawer, Lachman's test, posterior drawer; valgus and varus stress testes); and
• those taking any medication that can affect motor control (sedatives, anxiolytics, antibiotics, analgesics, NSAIDs or myorelaxants).