For optimal jumping performance an adequate interaction of muscles and tendons is required. A parameter in the functional evaluation of both structures is their stiffness (resistance of the tissue against deformation by external forces). It is unclear so far if higher stiffness values of tendon or muscle or a specific stiffness relation of both tissues is the cause of better jumping performance. The present study examines this based on the Achilles tendon and the calf muscles or the patellar tendon and the hamstrings by three different forms of jumps (squat jump, counter-Movement Jump, Drop-Jump).

The plan is to include young healthy volunteers aged 18 to 40 years. In a cross-sectional study, the jump height of the participants will be measured for each jump form: squat jump (jump from a squatting position), Counter-Movement Jump (jump with backswing by going into the knees) or drop jump (jump from small box with direct re-jump). The order of the jump form is determined randomly. The measurements are carried out within one day. Furthermore the international physical activity questionnaire will be used in order to assess the level of physical activity.

As primary outcome the stiffness of the calf muscles, achilles tendon, hamstring and patellar tendon will be detected. The measurement is carried out before the jumps (there are three jumps after one sample jump performed). The measurement is executed non-invasively and completely painless using Indentometers and MyotonPro. With both devices, minimal pressure on the examined tissue will be exerted and measured how much of this can be compressed.

Inclusion Criteria:

• Healthy

Exclusion Criteria:

• Drug intake in the past 48 hours
• Pregnancy
• Muscle soreness