Fatiguing intermittent isometric exertions of trunk extensor muscles will be performed.

Participants will perform three sets of intermittent isometric efforts between 50 and 60 percents of their maximal isometric strength. A padded force sensor will be placed approximately at the level of the 7th thoracic vertebrae. The first two sets will last six minutes each, while the third set will last three minutes. Between each set participants will rest for two minutes.

Muscle stiffness will be measured at rest and during standardised sub-maximal exertions in prone lying position. Muscle stiffness will be expressed as the shear modulus value in kilopascals.

Muscle activation of trunk extensors will be measured using superficial electromyography at rest and during two standardised sub-maximal exertions in prone lying position (single arm raise and upper body raise). Mean amplitude in six to eight second time frames will be calculated.

Lumbar range of motion will be evaluated using Modified modified Schober test.