STEROIDS DO NOT IMPROVE ENDURANCE AND ONLY IMPROVE STRENGTH IF THE DOSE IS LARGE ENOUGH
Bhasin, S., Woodhouse, L., & Storer, T W. (2001). Proof of the effect of testosterone on skeletal muscle. Journal of Endocrinology, 170, 27-38.
"In spite of the widespread abuse of androgenic steroids by athletes and recreational body-builders, the effects of these agents on athletic performance and physical function remain poorly understood. Experimentally induced androgen deficiency is associated with a loss of fat-free mass; conversely, physiologic testosterone replacement of healthy, androgen-deficient men increases fat-free mass and muscle protein synthesis. Testosterone supplementation of HIV-infected men with low testosterone levels and of older men with normally low testosterone concentrations also increases muscle mass. However, we do not know whether physiologic testosterone replacement can improve physical function and health-related quality of life, and reduce the risk of falls and disability in older men or those with chronic illness. Testosterone increases maximal voluntary strength in a dose-dependent manner and thus might improve performance in power-lifting events. However, testosterone has not been shown to improve performance in endurance events. The mechanisms by which testosterone increases muscle mass are not known, but probably involve alterations in the expression of multiple muscle growth regulators".
Implication. Not all individuals will increase in strength using androgenic steroid drugs. The dose will determine that effect. [Others have said the dose needs to be 10-40 times the therapeutic level.] Tesosterone and testosterone-derivative drugs do not increase endurance performance.