The study aims to evaluate the accuracy and consistency of assessing trunk muscle strength using an isometric device (Pegasus, Leipzig, Germany). Thirty healthy volunteers will undergo maximal isometric strength testing with the device, repeated one week later to assess repeatability. Surface electrodes will measure muscle activation, while MRI scans will assess structural condition.

The aim of the study is to assess the validity and repeatability of trunk muscle strength evaluation using an isometric device (Pegasus, Leipzig, Germany) and to investigate it. Thirty healthy volunteer participants will undergo testing of maximal isometric (non-moving) strength using this device. The same strength measurement procedure will be repeated one week later for all participants to determine if the measurements are repeatable, i.e., if the device is capable of providing similar strength data in two closely timed measurements. To assess whether the device actually provides reliable strength data for the trunk muscles, surface electrodes will be additionally placed on the involved muscles to understand the extent of neural activation of these muscles during the test. Additionally, an MRI examination will be conducted for all study participants to assess the structural condition of the trunk muscles.

Inclusion Criteria:

• both male and female subjects
• age between 18 and 59 years
• BMI < 30 kg/m2
• cognitively intact (self-reported)
• autonomous walking

Exclusion Criteria:

• age under 18 years or over 60 years
• any prior spinal surgery or other musculoskeletal surgery having an impact on movement
• acute or chronic back pain in the last 6 months(self-reported)
• pregnancy (self-reported)
• inability to perform the planned set of activities included in the study (e.g. maximal voluntary contraction torque test)
• inability to give consent

The study is open to both males and females (biologically); 15 for each group