Rationale: During exercise protein breakdown in muscles is larger than protein synthesis. This negative muscle protein balance leads to increased muscle damage and thereby to a reduced muscle tissue recovery. To achieve a positive muscle protein balance and reduce muscle damage, many athletes use proteins. In professional soccer players, considerable stress is placed on the musculoskeletal system. Recovery time is often too short for these players to restore homeostasis, which results in catabolic processes. This increases playing errors and will lead to lapses in concentration. Therefore, it is of great importance for a professional soccer team to be in optimal condition and a fast recovery after exercise is desirable to accomplish maximum performance. Supplementation with whey proteins is thought to support this.