Insulin administration in uncontrolled keto-acidosis reverses lipolysis, proteolysis, ketogenesis, and gluconeogenesis. It is protein anabolic in the insulin-resistance of renal failure when administered with amino-acids (Lim et al., 2003). The “intelligent” athlete wants to inhibit proteolysis hoping to enhance performance and because it is undetectable by urinalysis (Holt and Sonksen, 2008). Administration establishes an in-vivo hyper-insulinaemic clamp, increasing muscle glycogen, before and in the recovery stages of strenuous exercise, believed to increase power, strength and stamina and assist recovery (Sonksen, 2001). This study investigated the effects of 30 days of insulin administration (0.12 IU.kg-1.day-1) combined with weight training on anthropometry, psychological profile, cardiovascular and respiratory variables and exercise performance on 12 weight lifters (I), aged between 23 and 46 years, compared to 12 non-drug using age matched exercise controls (EC) and 12 non-drug using age matched sedentary controls (SC), who were examined twice, one month apart. Anthropometry, respiratory muscle-function, endurance exercise and arterial pulse wave velocity were investigated. Biochemical analysis included; haemoglobin, packed cell volume (PCV), glucose and lipid profile. All data was analysed using parametric analysis of variance (ANOVA) and because of small sample sizes, re-analysed by the non-parametric analogue of the ANOVA (Kruskal-Wallis test). Body mass index (BMI) significantly increased within the I-group (30.8 ± 3.2 vs. 31.2 ± 3.2, kg.m-2, P<0.05). PCV significantly increased within the I-group (0.45 ± 0.01 vs. 0.47 ± 0.02, ratio; P<0.05) and was significantly increased compared with EC on-insulin administration (month 2; 0.47 ± 0.02 vs. 0.44 ± 0.01, ratio; P<0.05). Triglycerides significantly increased within the I-group (1.78 ± 0.5 vs. 1.94 ± 0.5, mmol/L; P<0.05). Maximum inspiratory pressure (MIP) significantly increased within the I-group (MIP: 117 ± 32 vs. 122 ± 28, cm.H2O; P<0.05). Exogenous insulin increases glucose metabolism in athletes determined by euglycaemic insulin-clamp technique (Sato et al., (1986). Physiological hyper-insulinaemia stimulates the activity of amino acid transport and synthesis in human skeletal muscle (Bonadonna et al., 1993). Insulin administration is still prevalent in sport and may be catastrophic. It’s short term use may increase performance, but may also predispose individuals to increased cardiovascular risk, similar to sedentary controls. Further research in this area is required to educate sportspersons that bigger is not necessarily better. However, there may be an application for its medical use in cachectic disease states, or even in the ageing musculoskeletal system.