Gene expression theory.  Steroid hormones have a small molecular weight and are lipid-soluble. They can enter target cells by diffusion or carrier transport. After entering cells, steroid hormones bind to receptors in the cytosol to form hormone-receptor complexes, which can undergo allosteric translocation through the nuclear membrane under appropriate temperature and Ca2+ participation.  

After entering the nucleus, the hormone binds to the receptor in the nucleus to form a complex.  This complex binds to specific sites in chromatin that are not histones, initiates or inhibits the DNA transcription process at this site, and then promotes or inhibits the formation of mRNA. As a result, it induces or reduces the synthesis of certain proteins (mainly enzymes) to achieve its biological effects.  A single hormone molecule can generate thousands of protein molecules, thus achieving the amplified function of the hormone.  

Hormone Response During muscle activity, the levels of various hormones, especially those that mobilize energy supply, change to varying degrees and affect the metabolic level of the body and the functional level of various organs.  Measuring the levels of certain hormones during and after exercise and comparing them with the quiet values is called the hormonal response to exercise.  

Fast-response HORMONES, SUCH AS EPINEPHRINE, NOrepINEPHRINE, CORTISOL, and ADRENOCORTICOTROPIN, ARE SIGNIFICANTLY ELEVATED IN plasma IMMEDIATELY AFTER EXERCISE and peak within a short time.  

Intermediate reactive hormones, such as aldosterone, thyroxine, and pressor, rise slowly and steadily in plasma after the onset of exercise, reaching a peak within minutes.  

Slow response hormones, such as growth hormone, glucagon, calcitonin and insulin, do not change immediately after the start of exercise, but slowly increase after 30 to 40min of exercise and reach a peak at a later time.