Inclusion Criteria:  male and female persons aged 18-65 years performing at least 1x / week a training including jumping elements familiar with counter movement jumps good knowledge of German understand verbal and written instructions signed informed consent  Exclusion Criteria:  known pregnancy known or suspected non-compliance with the protocol drug or alcohol abuse inability of the individual to follow the testing procedures, e.g., due to language problems, mental illness, dementia, etc. injuries of the lower extremity in the past year concomitant diseases of the foot, knee or hip tiring activity of the lower extremity the day before the test vigorous activity of the lower extremity one hour before the test