In recreational athletes, supraphysiological GH doses are often used either alone or in combination with other doping substances (140), and studies have shown that GH improves anaerobic sprint capacity, but not strength and endurance (141), and increases GH, IGF-I and fasting insulin levels (142, 143) mimicking those seen in acromegaly patients (Table 1). Here, IGF1 is linked to acromegaly.