Saturated fatty acids chains can exist in many conformations resulting from free rotation around the C-C bonds of the acyl chains. A quick review of the conformations of n-butane shows that the energetically most favorable conformation is one in which the two CH3 groups attached to the 2 methylene C’s (C2 and C3) are trans to each other, which results in decreased steric strain. Looking at a Neuman projection of n-butane shows the dihedral or torsional angle of this trans conformation to be 180 degrees. When the dihedral angle is 0 degrees, the two terminal CH3 groups are syn to each other, which is the conformation of highest energy. When the angle is 60 (gauche+) or 300 (gauche-) degrees, a higher, local minimum is observed in the energy profile. At a given temperature and moment, a population of molecules of butane would consist of some in the g+ and g- state, with most in the t state. The same applies to fatty acids. To increase the number of chains with g+tg- conformations, for example, the temperature of the system can be increased.
The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine .