Context: In physiotherapy, there are several ways to check the serratus anterior muscle with respect to its strength. In this study, three common muscle function tests are compared and related to three alleged synergists descriptively. Design: Observational study, carried out as a laboratory experiment. Participants: 10 male subjects between 20 and 29 years. Intervention: Three muscle function test with an evaluation of the muscle strength of four muscles measured by electromyography. Outcome measures: The measurement results for the serratus ant. muscle yielded: Flexionstest x̄ = 0.686 mV, Abduktionstest x̄ = 0.676 mV, Protraktionstest x̄ = 0.437 mV; synergists for the flexion test: M. deltoideus PC x̄ = 127% MVC, M. latissimus dorsi x̄ = 40% MVC; synergists for Abduktionstest: M. deltoideus PC x̄ = 112% MVC, M. lat. dorsi x̄ = 39% MVC; synergists for Protraktionstest: M. pectoralis major x̄ = 32% MVC. Main results: Flexions-, and Abduktionstest are more selective than the Protraktionstest, since the latter is strongly supported by the M. pectoralis major. In the first two tests, there is no correlation between the high value of the M. deltoideus PC and the M. serratus ant. Conclusion: Fexions-, and Abduktionstest are more selective because of the additional pulse to the scapula.